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Anterior cruciate ligament reconstruction

      Anterior cruciate ligament (ACL) reconstruction is a common procedure performed by orthopaedic surgeons, particularly in association with sports-related injuries. Over the past 10 years, a renewed interest in the native anatomy of the ACL has facilitated a progression from non-anatomic to more anatomic reconstruction techniques. The anatomic and individualised ACL reconstruction concept attempts to closely reproduce the patient's individual anatomy with the goal of reproducing the native ACL characteristics and improving patient outcomes. Measurements of the patient's anatomy help determine graft choice and whether anatomic reconstruction should be performed with an single-bundle or double-bundle technique. The bony landmarks and insertions of the ACL are preserved to assist with anatomic placement of both tibial and femoral tunnels. Long-term outcomes for anatomic ACL reconstruction are unknown and future research, considering biomechanics and clinical outcomes, should be focused on this area. Future studies may yield important information with regard to the potential progression to osteoarthritis after ACL reconstruction, including factors affecting or preventing it. In this State of the art review, we have attempted to summarise the best available evidence addressing ACL injury diagnostics, treatment, surgical techniques, complications, tips, pitfalls and geographical differences, following our primary goal of improving medical care and outcomes for patients who suffer an ACL injury.
      What this paper adds
      • The gold standard of ACL reconstruction is known as the anatomic and individualised ACL reconstruction concept.
      • Following this concept, anatomic SB or DB reconstruction is performed with the goal of reproducing the patient's individual knee anatomy and restore its normal kinematics, focused on protecting long-term knee health.
      • Future research, considering biomechanics and clinical outcomes, should be focused on this area.

      Anterior cruciate ligament injury: prevalence and societal impact

      Anterior cruciate ligament (ACL) injury is one of the most frequent sports injuries, with an incidence of 35/100 000 people per year,
      • Gianotti SM
      • Marshall SW
      • Hume PA
      • et al.
      Incidence of anterior cruciate ligament injury and other knee ligament injuries: a national population-based study.
      This injury, without appropriate treatment, results in increased joint laxity, instability of the knee, reduced physical activity and decreased sports participation.
      • Meuffels DE
      • Favejee MM
      • Vissers MM
      • et al.
      Ten year follow-up study comparing conservative versus operative treatment of anterior cruciate ligament ruptures. A matched-pair analysis of high level athletes.
      This is particularly important in physically active patients, allowing them to return to daily activities, including sports, and reducing their risk of developing degenerative knee changes at 10 years.
      • Ajuied A
      • Wong F
      • Smith C
      • et al.
      Anterior cruciate ligament injury and radiologic progression of knee osteoarthritis: a systematic review and meta-analysis.
      In this review, a critical assessment of the evidence for diagnosis and treatment of the primary ACL rupture in adults is provided, including detailed descriptions of surgical techniques, patient management strategies and clinical outcomes.

      Historical perspective of ACL reconstruction

      The first ACL repair is attributed to the English surgeon Arthur William Mayo Robson in 1895. In 1934, the Italian surgeon Riccardo Galeazzi described a technique for ACL reconstruction using the semitendinosus tendon, and in 1935, Willis Campbell, from the USA, described the first use of a patellar tendon graft and fixation through tunnels in the femur and tibia. In the 1970s, extra-articular ACL reconstruction techniques came into favour, even though primary ACL repair was commonly performed. In the 1980s, intra-articular ACL reconstruction developed. John Insall is often given credit for the early intra-articular reconstructions using a band of fascia lata. A free patellar tendon graft came shortly thereafter with Clancy establishing the first step of the current standard of practice: using a free tendon graft through tunnels in the tibia and femur along the course of the native ACL.
      Since the development of the arthroscopically assisted reconstruction that was initially performed by Dandy in 1980, arthroscopic techniques for ACL reconstruction became increasingly popular. The transtibial (TT) single-bundle (SB) technique, in which the femoral tunnel is drilled inside-out through the tibial tunnel was, and probably still is, the most common ACL reconstruction technique.
      As early as 1836, ACL anatomy has been described in detail as two functional bundles (anteromedial, AM, and posterolateral, PL, according to the tibial insertion site position). In spite of this, reconstruction techniques initially restored only one bundle. It was not until 1982 that the an open method of double-bundle (DB) ACL reconstruction was described and published by Mott, and not until 1994, when Rosenberg described the arthroscopic method later popularised in Japan. Modifications of this technique have been described by a number of authors, and research into this area continues.
      Nowadays, the gold standard of ACL reconstruction is known as the anatomic ACL reconstruction concept. This concept is rooted in anatomy, aiming to restore the native ACL according to each patient's characteristics, and is described in detail in this review.
      • Fu FH
      • van Eck CF
      • Tashman S
      • et al.
      Anatomic anterior cruciate ligament reconstruction: a changing paradigm.
      Knowledge of the evolution of ACL reconstruction is invaluable to those who continue to try to improve the outcomes of the procedure and to keep progressing in this area.

      ACL reconstruction main articles: reviews, state of the art and current concepts

      In the past 10 years, almost 250 systematic reviews and more than 60 meta-analyses have been published about the ACL. The most recent evidence-based clinical practice guideline on the management of ACL was published according to a systematic review that considered the most important topics about this injury.
      • Shea KG
      • Carey JL
      • Richmond J
      • et al.
      The American Academy of Orthopaedic Surgeons evidence-based guideline on management of anterior cruciate ligament injuries.
      The highest quality studies, related to diagnosis, treatment, rehabilitation and return to sports (RTS), were reviewed and most of them were included in this article.
      Historically, the most cited papers related to ACL reconstruction focus on biomechanics and outcomes evaluation, which have been the basis of all clinical studies. The 10 most cited papers about ACL reconstruction are summarised in table 1.
      Table 1Ten most cited papers about anterior cruciate ligament (ACL) reconstruction
      RankAuthor/Journal/YearArticleCitations*Reference
      1Tegner et al

      Clin Orthop Relat Res

      1985
      Rating systems in the evaluation of knee ligament injuries1459
      • Tegner Y
      • Lysholm J
      Rating systems in the evaluation of knee ligament injuries.
      2Lysholm et al

      Am J Sports Med

      1982
      Evaluation of knee ligament surgery results with special emphasis on use of a scoring scale1279
      • Lysholm J
      • Gillquist J
      Evaluation of knee ligament surgery results with special emphasis on use of a scoring scale.
      3Noyes et al

      J Bone Joint Surg Am

      1984
      Biomechanical analysis of human ligament grafts used in knee-ligament repairs and reconstructions716
      • Noyes FR
      • Butler DL
      • Grood ES
      • et al.
      Biomechanical analysis of human ligament grafts used in knee-ligament repairs and reconstructions.
      4Hewett et al

      Am J Sports Med

      2005
      Biomechanical measures of neuromuscular control and valgus loading of the knee predict anterior cruciate ligament injury risk in female athletes701
      • Hewett TE
      • Myer GD
      • Ford KR
      • et al.
      Biomechanical measures of neuromuscular control and valgus loading of the knee predict anterior cruciate ligament injury risk in female athletes: a prospective study.
      5Daniel et al

      Am J Sports Med

      1994
      Fate of the ACL-injured patient: a prospective outcome study653
      • Daniel DM
      • Stone ML
      • Dobson BE
      • et al.
      Fate of the ACL-injured patient. A prospective outcome study.
      6Rodeo et al

      J Bone Joint Surg Am

      1993
      Tendon healing in a bone tunnel. A biomechanical and histological study in the dog634
      • Rodeo SA
      • Arnoczky SP
      • Torzilli PA
      • et al.
      Tendon-healing in a bone tunnel. A biomechanical and histological study in the dog.
      7Hewett et al

      Am J Sports Med

      1999
      The effect of neuromuscular training on the incidence of knee injury in female athletes—a prospective study632
      • Hewett TE
      • Lindenfeld TN
      • Riccobene JV
      • et al.
      The effect of neuromuscular training on the incidence of knee injury in female athletes. A prospective study.
      8Butler et al

      J Bone Joint Surg Am

      1980
      Ligamentous restraints to anteroposterior drawer in the human knee—biomechanical study618
      • Butler DL
      • Noyes FR
      • Grood ES
      Ligamentous restraints to anterior-posterior drawer in the human knee. A biomechanical study.
      9Shelbourne et al

      Am J Sports Med

      1990
      Accelerated rehabilitation after anterior cruciate ligament reconstruction577
      • Shelbourne KD
      • Nitz P
      Accelerated rehabilitation after anterior cruciate ligament reconstruction.
      10Girgis et al

      Clin Orthop Relat Res

      1985
      Cruciate ligaments of knee joint—anatomical, functional and experimental analysis562
      • Girgis FG
      • Marshall JL
      • Monajem A
      The cruciate ligaments of the knee joint. Anatomical, functional and experimental analysis.
      *August 2015.
      During the past 10 years, more than 15 ‘current concepts’ reviews and two ‘state of the art’ reviews have been published.
      • Murawski CD
      • Wolf MR
      • Araki D
      • et al.
      Anatomic anterior cruciate ligament reconstruction: current concepts and future perspective.
      ,
      • Voigt C
      • Schönaich M
      • Lill H
      Anterior cruciate ligament reconstruction: state of the art.
      ,
      • Fu FH
      • Schulte KR
      Anterior cruciate ligament surgery 1996. State of the art?.
      This article is the first ‘state of the art’ review on ACL reconstruction that discusses the diagnostics, treatment, surgical techniques, complications, pitfalls, regional or geographical differences, and future directions, based on the best available evidence.

      ACL reconstruction: current state of the art

      Diagnostics

      A detailed medical history, physical examination and imaging are vital in the diagnosis of an ACL injury, and can also provide useful information regarding the adequate treatment options. Strong evidence supports the use of the history and physical examination as effective diagnostic tools for ACL injury.
      • Shea KG
      • Carey JL
      • Richmond J
      • et al.
      The American Academy of Orthopaedic Surgeons evidence-based guideline on management of anterior cruciate ligament injuries.
      The history gives an idea of the patient's activity level and mechanism of injury, and the physical examination has been shown to be as sensitive and specific as imaging modalities.
      • Benjaminse A
      • Gokeler A
      • van der Schans CP
      Clinical diagnosis of an anterior cruciate ligament rupture: a meta-analysis.
      Physical examination should include range of motion (ROM), the Lachman test, the pivot shift test, and evaluation of concomitant ligamentous, meniscal and neurovascular injuries.
      • Shea KG
      • Carey JL
      • Richmond J
      • et al.
      The American Academy of Orthopaedic Surgeons evidence-based guideline on management of anterior cruciate ligament injuries.
      According to the most recent meta-analysis of ACL tear diagnosis, the Lachman and the pivot shift tests have a sensitivity of 0.77 and 0.28, respectively, and a specificity of 0.53 and 0.81, respectively, without anaesthesia (positive likelihood ratio (LR) 4.50 and 5.5, negative LR 0.22 and 0.84, respectively).
      • Shea KG
      • Carey JL
      • Richmond J
      • et al.
      The American Academy of Orthopaedic Surgeons evidence-based guideline on management of anterior cruciate ligament injuries.
      • van Eck CF
      • van den Bekerom MPJ
      • Fu FH
      • et al.
      Methods to diagnose acute anterior cruciate ligament rupture: a meta-analysis of physical examinations with and without anaesthesia.
      The pivot shift test should be standardised to avoid interindividual and intraindividual variability and improve measurement accuracy.
      • Hoshino Y
      • Araujo P
      • Ahldén M
      • et al.
      Standardized pivot shift test improves measurement accuracy.
      Additionally, instrumented measurements (KT-arthrometer) can objectively evaluate the anteroposterior (AP) tibial translation, and allows the evaluation of the postoperative results.
      • van Eck CF
      • Loopik M
      • van den Bekerom MP
      • et al.
      Methods to diagnose acute anterior cruciate ligament rupture: a meta-analysis of instrumented knee laxity tests.
      A complete X-ray series of the knee can give information about any fractures or subtle signs of a rotational injury, such as the Segond or reverse Segond capsular lesion. In addition, the status of the physes or any arthritic changes should be noted and compared with the contralateral side. Long cassette films should be obtained for any patient with knee malalignment on examination, or if any arthritic changes are noted on the knee series.
      MRI can confirm the diagnosis of the ACL injury. A recent meta-analysis showed that MRI has a sensitivity of 0.92 and a specificity of 0.96 for ACL injury (LR+ 23.8; LR− 0.08).
      • Shea KG
      • Carey JL
      • Richmond J
      • et al.
      The American Academy of Orthopaedic Surgeons evidence-based guideline on management of anterior cruciate ligament injuries.
      More importantly, it allows the surgeon to also examine the rupture pattern, measure the native ACL insertion site, evaluate for other ligamentous or bony injuries, and assess the meniscus and cartilage status. It can also provide information about potential autograft options, such as the quadriceps and patellar tendons. With access to special MRI cuts, such as the coronal oblique and sagittal oblique, the ACL bundles can be evaluated with higher sensitivity.

      ACL reconstruction indications and contraindications

      Several studies indicate that ACL reconstruction decreases pathological knee laxity and the incidence of subsequent injuries, including meniscal tears and degenerative changes.
      • Ajuied A
      • Wong F
      • Smith C
      • et al.
      Anterior cruciate ligament injury and radiologic progression of knee osteoarthritis: a systematic review and meta-analysis.
      • Shea KG
      • Carey JL
      • Richmond J
      • et al.
      The American Academy of Orthopaedic Surgeons evidence-based guideline on management of anterior cruciate ligament injuries.
      • Frobell RB
      • Roos EM
      • Roos HP
      • et al.
      A randomized trial of treatment for acute anterior cruciate ligament tears.
      • Laxdal G
      • Kartus J
      • Ejerhed L
      • et al.
      Outcome and risk factors after anterior cruciate ligament reconstruction: a follow-up study of 948 patients.
      These findings have defined ACL reconstruction surgery as the standard treatment for ACL injuries.
      The ideal patient for ACL reconstruction is a young patient (<40 years) with an active lifestyle and an acute ACL injury.
      • Shea KG
      • Carey JL
      • Richmond J
      • et al.
      The American Academy of Orthopaedic Surgeons evidence-based guideline on management of anterior cruciate ligament injuries.
      Knee instability is the main indication for surgical treatment and it should be evaluated subjectively (history, symptoms) and objectively (physical examination and instrumented side-to-side differences).
      ACL reconstruction is contraindicated in patients with partial tears, minimal instability and no joint laxity on examination. It is also contraindicated in elderly, low-demand patients with minimal instability, patients with knee malalignment and associated comorbidities that make surgical intervention unsafe (eg, active infection). Relative contraindications, which should be evaluated case by case, include patients with open physes (Tanner stage ≤3, males ≤16 years, or females ≤14 years), radiographic evidence of degenerative joint disease (Kellgren-Lawrence grade ≥3), a sedentary or inactive lifestyle, and an unwillingness or inability to comply with the required postoperative rehabilitation protocol.

      Non-operative treatment

      Considering contraindications to surgical treatment and a patient's preferences, there are some patients for whom non-operative treatment is indicated. Some studies have shown that non-operative treatment does provide satisfactory results.
      • Moksnes H
      • Risberg MA
      Performance-based functional evaluation of non-operative and operative treatment after anterior cruciate ligament injury.
      • Grindem H
      • Eitzen I
      • Engebretsen L
      • et al.
      Nonsurgical or surgical treatment of ACL injuries: knee function, sports participation, and knee reinjury: the Delaware-Oslo ACL cohort study.
      In a Norwegian study,
      • Moksnes H
      • Risberg MA
      Performance-based functional evaluation of non-operative and operative treatment after anterior cruciate ligament injury.
      the treatment between non-operative and ACL reconstruction was chosen by the patients. At a 1-year or 2-year follow-up examination, no differences were detected between the two groups with regard to the ability to resume preinjury activity level, muscle strength or functional performance.
      Another Norwegian study
      • Grindem H
      • Eitzen I
      • Engebretsen L
      • et al.
      Nonsurgical or surgical treatment of ACL injuries: knee function, sports participation, and knee reinjury: the Delaware-Oslo ACL cohort study.
      reported that there were few differences between the clinical courses following non-surgical and surgical treatment of ACL injury, highlighting the potential for good outcomes with non-operative care following ACL injury. Roughly a third of the entire study population experienced good function and low reinjury rates with non-operative treatment. However, one-third of the patients of the non-surgical group crossed over to the surgical group, presumably because of reinjury, unacceptable function or limitations imposed by the treatment protocol. Additionally, good outcomes of this study were most likely due to careful screening, followed by a personalised rehabilitation programme, and close follow-up monitoring for at least 2 years.
      Similarly, a randomised study reported that an ACL reconstruction could be avoided in 61% of the patients, without compromising the results evaluated at 2 years after injury, by initially providing a structured rehabilitation followed by an optional delayed ACL reconstruction, instead of directly performing an early reconstruction.
      • Frobell RB
      • Roos EM
      • Roos HP
      • et al.
      A randomized trial of treatment for acute anterior cruciate ligament tears.
      Nevertheless, the frequency of meniscal resections was greater in the delayed surgery group than in the early surgery group (70% vs 48%, respectively). These data might demonstrate that menisci may be saved by an early surgical reconstruction.
      Different methods have been described trying to define the individualised requirements of treatment after the ACL injury. Hurd et al
      • Hurd WJ
      • Axe MJ
      • Snyder-Mackler L
      A 10-year prospective trial of a patient management algorithm and screening examination for highly active individuals with anterior cruciate ligament injury: part 1, outcomes.
      classified highly active patients (International Knee Documentation Committee, IKDC, level I or II) with good dynamic knee stability early after ACL rupture, using simple hop tests and validated knee outcome surveys (KOS–ADLS: Knee Outcome Survey–Activities of Daily Living Scale). These so-called potential copers, which represented 42% of the initial population of ACL-injured patients in this study, had good potential to be conservatively treated with physical therapy over a 2-week to 5-week protocol. However, after the rehabilitation programme, 59% of the ‘potential copers’ required ACL reconstruction. The other ACL-deficient patients who did not require surgery could return to preinjury sports activities and were very satisfied with this choice at the latest follow-up (range 1–10 years). Nevertheless, another study showed that ACL-deficient patients with residual instability can present by giving way during sports activities six times more frequently than ACL reconstruction patients (18% and 3%, respectively).
      • Daniel DM
      • Stone ML
      • Dobson BE
      • et al.
      Fate of the ACL-injured patient. A prospective outcome study.
      The most recent systematic review reported that there is limited evidence to support non-surgical management, even in less active patients with less laxity.
      • Shea KG
      • Carey JL
      • Richmond J
      • et al.
      The American Academy of Orthopaedic Surgeons evidence-based guideline on management of anterior cruciate ligament injuries.
      In fact, 25% of the low-risk patients with ACL-deficient knees ultimately require surgery, including ACL reconstruction or meniscal surgery.
      • Shea KG
      • Carey JL
      • Richmond J
      • et al.
      The American Academy of Orthopaedic Surgeons evidence-based guideline on management of anterior cruciate ligament injuries.

      Operative treatment

      Timing for surgery

      Once the decision to proceed with the operative treatment of an ACL rupture is made, timing of the procedure becomes an important variable to consider. Preoperative ROM, swelling and quadriceps strength have been investigated as factors that can affect the ultimate success of ACL reconstruction.
      • Mayr HO
      • Weig TG
      • Plitz W
      Arthrofibrosis following ACL reconstruction—reasons and outcome.
      • Eitzen I
      • Holm I
      • Risberg MA
      Preoperative quadriceps strength is a significant predictor of knee function two years after anterior cruciate ligament reconstruction.
      Preoperative limited ROM and swelling have been related to the development of arthrofibrosis after surgery.
      • Mayr HO
      • Weig TG
      • Plitz W
      Arthrofibrosis following ACL reconstruction—reasons and outcome.
      Preoperative quadriceps strength deficits of >20% have been shown to significantly affect the 2-year functional outcomes of ACL reconstruction with bone-patellar tendon-bone autograft.
      • Eitzen I
      • Holm I
      • Risberg MA
      Preoperative quadriceps strength is a significant predictor of knee function two years after anterior cruciate ligament reconstruction.
      Surgical intervention is recommended to be delayed until any postinjury knee effusion has resolved, full knee ROM has been regained, quadriceps control is achieved, and personal and professional issues permit that the patient is physically and psychologically prepared for surgery and a full postoperative physical therapy programme.
      Although some studies have not reported significant differences in objective and subjective clinical outcomes between early (<2 weeks) versus late ACL reconstruction (>4–12 weeks),
      • Raviraj A
      • Anand A
      • Kodikal G
      • et al.
      A comparison of early and delayed arthroscopically-assisted reconstruction of the anterior cruciate ligament using hamstring autograft.
      most recent recommendations, based on moderate quality evidence, support surgery timing at 3 weeks to 5 months after injury.
      • Shea KG
      • Carey JL
      • Richmond J
      • et al.
      The American Academy of Orthopaedic Surgeons evidence-based guideline on management of anterior cruciate ligament injuries.
      Surgery within this period is associated with improved objective knee stability, higher activity level and better knee function when compared with reconstruction after 5 months.
      • Daniel DM
      • Stone ML
      • Dobson BE
      • et al.
      Fate of the ACL-injured patient. A prospective outcome study.
      • Frobell RB
      • Roos EM
      • Roos HP
      • et al.
      A randomized trial of treatment for acute anterior cruciate ligament tears.
      • Park S-J
      • Jung YB
      • Jung H-J
      • et al.
      Outcome of arthroscopic single-bundle versus double-bundle reconstruction of the anterior cruciate ligament: a preliminary 2-year prospective study.
      After 5 months, surgery can increase the incidence of meniscus tears from 37% to 62% and subsequent meniscectomy from 8% to 44%.
      • Anderson AF
      • Snyder RB
      • Lipscomb AB
      Anterior cruciate ligament reconstruction. A prospective randomized study of three surgical methods.

      Portals

      A three-portal approach has been shown to provide the best intraoperative visualisation of the ACL native insertion sites, which is crucial for anatomic reconstruction.
      • Araujo PH
      • van Eck CF
      • Macalena JA
      • et al.
      Advances in the three-portal technique for anatomical single- or double-bundle ACL reconstruction.
      The use of an accessory medial portal (AMP) aids in visualisation of the femoral insertion site and allows an anatomical placement of the femoral tunnel.
      A ‘high’ anterolateral portal (AL) is recommended to be positioned above Hoffa's fat pad. The AM and AMP are then created under direct vision through the AL using a spinal needle. The final position of the AM and AMP varies according to the orientation of the intercondylar notch. Through the AM, the spinal needle should be close to the central portion of the notch in the coronal plane and in the lower third of the notch in the proximal to distal direction. The AMP is ideally located superior to the medial joint line, approximately 2 cm medial to the medial border of the patellar tendon. In establishing the AMP, careful attention should be paid to the medial femoral condyle, to avoid iatrogenic damage during femoral tunnel drilling.
      • Araujo PH
      • van Eck CF
      • Macalena JA
      • et al.
      Advances in the three-portal technique for anatomical single- or double-bundle ACL reconstruction.

      Partial tears and augmentation

      Diagnostic arthroscopy is performed first to assess for concomitant injuries and to confirm the ACL rupture pattern (figure 1). If a partial one-bundle rupture is evident, augmentation surgery can be considered.
      • Yagi M
      • Wong EK
      • Kanamori A
      • et al.
      Biomechanical analysis of an anatomic anterior cruciate ligament reconstruction.
      Partial ACL ruptures have been reported to occur in approximately 5–35% of patients,
      • Shen W
      • Forsythe B
      • Ingham SM
      • et al.
      Application of the anatomic double-bundle reconstruction concept to revision and augmentation anterior cruciate ligament surgeries.
      • Borbon CA
      • Mouzopoulos G
      • Siebold R
      Why perform an ACL augmentation?.
      and performing a one-bundle augmentation surgery carries the theoretical advantages of maintaining proprioceptive fibres, biomechanical strength and biological healing potential.
      • Shen W
      • Forsythe B
      • Ingham SM
      • et al.
      Application of the anatomic double-bundle reconstruction concept to revision and augmentation anterior cruciate ligament surgeries.
      • Borbon CA
      • Mouzopoulos G
      • Siebold R
      Why perform an ACL augmentation?.
      However, a recent systematic review evaluated the best evidence on the surgical management of partial tears of the ACL, and reported that no study had a sample large enough to establish guidelines about ACL augmentation.
      • Papalia R
      • Franceschi F
      • Zampogna B
      • et al.
      Surgical management of partial tears of the anterior cruciate ligament.
      Figure thumbnail gr1
      Figure 1Arthroscopic picture showing an isolated posterolateral (PL) bundle tear, while the anteromedial (AM) bundle appears to be intact.

      Anatomic ACL reconstruction concept

      Presently, the majority of surgeons who perform ACL reconstructions do so using an SB technique. Regardless, it is important to understand the two-bundle anatomy of the ACL so that surgeons can follow the anatomic ACL reconstruction concept, in spite of their choice to perform SB or DB reconstruction.
      The concept of anatomic ACL reconstruction is based on four fundamental principles: (1) restore the two functional bundles of the ACL; (2) restore the native insertion sites of the ACL by placing the tunnels in the true anatomic positions; (3) correctly tension each bundle; (4) individualise surgery for each patient so that the tunnel diameter and graft size are dictated by native insertion sites.
      The approach to ACL reconstruction surgery is governed by this principle and the restoration of normal anatomy is necessary to restore normal function of the knee.
      • Fu FH
      • van Eck CF
      • Tashman S
      • et al.
      Anatomic anterior cruciate ligament reconstruction: a changing paradigm.
      This concept applies to SB and DB reconstruction. For example, if SB reconstruction is indicated, the graft should be positioned anatomically on both the tibia and the femur (‘PL to PL’ and ‘AM to AM‘), so that the graft will acquire the functional properties of the native two-bundle ligament.
      Table 2 summarises the key concepts in ACL reconstruction surgical techniques.
      Table 2Key concepts in ACL reconstruction
      SB ACL reconstructionSurgical technique that restores the ACL using a single graft in the form of an SB
      DB ACL reconstructionSurgical technique that restores the ACL using two separate grafts to restore each bundle individually
      Transtibial ACL reconstructionSurgical technique in which the femoral tunnel is drilled through the tibial tunnel. It can be used for SB or DB ACL reconstruction
      Anteromedial portal ACL reconstructionSurgical technique in which the femoral tunnel is drilled inside-out through an accessory anteromedial portal, allowing less restricted access to the femoral insertion site compared with the transtibial technique. It can be used for SB or DB ACL reconstruction
      Two-incision ACL reconstructionSurgical technique in which the femoral tunnel is drilled outside-in through a mini-open incision on the lateral side of the distal femur, also allowing better access to the femoral insertion site compared to the transtibial procedure. It can be used for SB or DB ACL reconstruction
      Anatomic ACL reconstruction conceptRestoration of the ACL to its native dimensions, collagen orientation and insertion sites. It is a concept that can be applied to different surgical techniques including SB reconstruction, DB reconstruction, augmentation and ACL revision surgery
      Individualised ACL reconstructionPart of the anatomic ACL reconstruction concept in which the surgical technique (SB or DB) and graft size are chosen depending on preoperative (MRI) and intraoperative measurements of the patient's native ACL and bony anatomy
      ACL, anterior cruciate ligament; DB, double-bundle; SB, single-bundle.

      SB versus DB ACL reconstruction

      The decision to perform SB or DB reconstruction is based on several criteria. A comprehensive flow chart to assist surgeons in this decision has been described previously
      • van Eck CF
      • Lesniak BP
      • Schreiber VM
      • et al.
      Anatomic single- and double-bundle anterior cruciate ligament reconstruction flowchart.
      (figure 2). The variation in size of the tibial insertion site is one element to consider
      • Kopf S
      • Pombo MW
      • Szczodry M
      • et al.
      Size variability of the human anterior cruciate ligament insertion sites.
      (figure 3). A tibial insertion site <14 mm in length, measured arthroscopically, makes it difficult to perform a DB reconstruction without obtaining non-anatomic tunnels or damaging the meniscal roots.
      • van Eck CF
      • Lesniak BP
      • Schreiber VM
      • et al.
      Anatomic single- and double-bundle anterior cruciate ligament reconstruction flowchart.
      Other variables that support an SB reconstruction technique are concomitant arthritic changes (Kellgren-Lawrence grade ≥3), multiligament injury, severe bone bruising, open physes, and a narrow and/or shallow intercondylar notch (<14 mm each).
      • Shen W
      • Forsythe B
      • Ingham SM
      • et al.
      Application of the anatomic double-bundle reconstruction concept to revision and augmentation anterior cruciate ligament surgeries.
      • van Eck CF
      • Lesniak BP
      • Schreiber VM
      • et al.
      Anatomic single- and double-bundle anterior cruciate ligament reconstruction flowchart.
      Figure thumbnail gr2
      Figure 2Anatomic and individualised single-bundle (SB) and double-bundle (DB) ACL reconstruction flow chart. Reprinted with permission from van Eck et al.
      • van Eck CF
      • Lesniak BP
      • Schreiber VM
      • et al.
      Anatomic single- and double-bundle anterior cruciate ligament reconstruction flowchart.
      ACL, anterior cruciate ligament; AM, anteromedial; pre-op, preoperatively; AP, anteroposterior; PCL, posterior cruciate ligament; PL, posterolateral; post-op, postoperatively; 3D, 3-dimensional.
      Figure thumbnail gr3
      Figure 3Anatomical variability of the ACL tibial insertion site and intercondylar notch. ACL, anterior cruciate ligament; AM, anteromedial; PL, posterolateral.
      Biomechanical studies have shown that DB reconstruction restores knee kinematics better than TT SB reconstruction, leading to less rotational laxity, increased tibiofemoral contact area and lower contact pressures.
      • Yagi M
      • Wong EK
      • Kanamori A
      • et al.
      Biomechanical analysis of an anatomic anterior cruciate ligament reconstruction.
      • Morimoto Y
      • Ferretti M
      • Ekdahl M
      • et al.
      Tibiofemoral joint contact area and pressure after single- and double-bundle anterior cruciate ligament reconstruction.
      • Zelle BA
      • Vidal AF
      • Brucker PU
      • et al.
      Double-bundle reconstruction of the anterior cruciate ligament: anatomic and biomechanical rationale.
      Also, several prospective level I or II clinical studies have reported superior clinical results of anatomic DB reconstruction compared with SB reconstruction.
      • Aglietti P
      • Giron F
      • Losco M
      • et al.
      Comparison between single-and double-bundle anterior cruciate ligament reconstruction: a prospective, randomized, single-blinded clinical trial.
      ,
      • Ibrahim SAR
      • Hamido F
      • Al Misfer AK
      • et al.
      Anterior cruciate ligament reconstruction using autologous hamstring double bundle graft compared with single bundle procedures.
      ,
      • Järvelä T
      • Moisala A-S
      • Sihvonen R
      • et al.
      Double-bundle anterior cruciate ligament reconstruction using hamstring autografts and bioabsorbable interference screw fixation: prospective, randomized, clinical study with 2-year results.
      ,
      • Kondo E
      • Yasuda K
      • Azuma H
      • et al.
      Prospective clinical comparisons of anatomic double-bundle versus single-bundle anterior cruciate ligament reconstruction procedures in 328 consecutive patients.
      Conversely, other studies have shown no difference between DB and SB reconstruction in terms of improvement in laxity or function.
      • Park S-J
      • Jung YB
      • Jung H-J
      • et al.
      Outcome of arthroscopic single-bundle versus double-bundle reconstruction of the anterior cruciate ligament: a preliminary 2-year prospective study.
      • Adachi N
      • Ochi M
      • Uchio Y
      • et al.
      Reconstruction of the anterior cruciate ligament. Single- versus double-bundle multistranded hamstring tendons.
      • Streich NA
      • Friedrich K
      • Gotterbarm T
      • et al.
      Reconstruction of the ACL with a semitendinosus tendon graft: a prospective randomized single blinded comparison of double-bundle versus single-bundle technique in male athletes.
      However, for several of the aforementioned studies, it remains unclear whether both the SB and DB reconstructions performed in these studies were anatomic or not.
      On the basis of the evolution of clinical studies comparing both techniques, multiple authors have conducted systematic reviews and meta-analyses comparing SB and DB reconstruction.
      • Mascarenhas R
      • Cvetanovich GL
      • Sayegh ET
      • et al.
      Does double-bundle anterior cruciate ligament reconstruction improve postoperative knee stability compared with single-bundle techniques? A systematic review of overlapping meta-analyses.
      • Tiamklang T
      • Sumanont S
      • Foocharoen T
      • et al.
      Double-bundle versus single-bundle reconstruction for anterior cruciate ligament rupture in adults.
      Recently, nine available overlapping meta-analyses about this topic were evaluated, in an attempt to reconcile conclusions from both techniques.
      • Mascarenhas R
      • Cvetanovich GL
      • Sayegh ET
      • et al.
      Does double-bundle anterior cruciate ligament reconstruction improve postoperative knee stability compared with single-bundle techniques? A systematic review of overlapping meta-analyses.
      The current highest level of evidence suggests that DB reconstruction provides improved postoperative knee laxity compared with SB reconstruction. This was evaluated using the KT-arthrometer, the Lachman and anterior drawer tests for AP translation, and the pivot shift test for rotational laxity. Nevertheless, this difference between SB and DB clinical results should be interpreted cautiously. For example, the significant difference in the KT-arthrometer may have questionable clinical significance because its magnitude ranged from 0.56 to 0.74 mm. Also, the differences for the clinical tests (Lachman, anterior drawer and pivot-shift tests) were heterogeneous between studies. This can be explained by the subjectivity in grading, interexaminer variability and dependence on patient cooperation for these tests. The other clinical outcomes and risk of graft failure were not found to be significantly different between SB and DB in this systematic review.
      • Mascarenhas R
      • Cvetanovich GL
      • Sayegh ET
      • et al.
      Does double-bundle anterior cruciate ligament reconstruction improve postoperative knee stability compared with single-bundle techniques? A systematic review of overlapping meta-analyses.
      The most recent clinical practice guidelines have shown similar clinical outcomes between SB and DB techniques.
      • Shea KG
      • Carey JL
      • Richmond J
      • et al.
      The American Academy of Orthopaedic Surgeons evidence-based guideline on management of anterior cruciate ligament injuries.
      Considering high-quality studies with consistent findings, these guidelines strongly recommend that in patients undergoing ACL reconstruction, the surgeon should use either the SB or DB technique, because the measured clinical outcomes are similar.
      • Shea KG
      • Carey JL
      • Richmond J
      • et al.
      The American Academy of Orthopaedic Surgeons evidence-based guideline on management of anterior cruciate ligament injuries.

      Graft choice

      Typical graft options for ACL reconstruction include hamstring tendon autograft, bone-patellar tendon-bone autograft, quadriceps tendon autograft and allograft. The advantages and disadvantages of each of them are summarised in table 3.
      • Steiner ME
      • Hecker AT
      • Brown CH
      • et al.
      Anterior cruciate ligament graft fixation. Comparison of hamstring and patellar tendon grafts.
      ,
      • Beynnon BD
      • Johnson RJ
      • Fleming BC
      • et al.
      Anterior cruciate ligament replacement: comparison of bone-patellar tendon-bone grafts with two-strand hamstring grafts. A prospective, randomized study.
      ,
      • Adam F
      • Pape D
      • Schiel K
      • et al.
      Biomechanical properties of patellar and hamstring graft tibial fixation techniques in anterior cruciate ligament reconstruction: experimental study with roentgen stereometric analysis.
      Table 3Graft options for ACL reconstruction
      • Steiner ME
      • Hecker AT
      • Brown CH
      • et al.
      Anterior cruciate ligament graft fixation. Comparison of hamstring and patellar tendon grafts.
      ,
      • Beynnon BD
      • Johnson RJ
      • Fleming BC
      • et al.
      Anterior cruciate ligament replacement: comparison of bone-patellar tendon-bone grafts with two-strand hamstring grafts. A prospective, randomized study.
      ,
      • Adam F
      • Pape D
      • Schiel K
      • et al.
      Biomechanical properties of patellar and hamstring graft tibial fixation techniques in anterior cruciate ligament reconstruction: experimental study with roentgen stereometric analysis.
      GraftAdvantagesDisadvantages
      Bone-patellar tendon-bone
      • Bone-to-bone healing in both tunnels
      • Comparable stiffness to native ACL
      • Not suitable for DB reconstruction
      • Risk of anterior kneeling pain
      • Invasive, large incision
      • Risk of patellar fracture
      • Fixed length
      • - Weaker than native ACL
      Hamstring
      • Ease of harvest
      • Cosmesis
      • Minimal donor site morbidity
      • Comparable strength to native ACL
      • Soft tissue healing
      • Graft size can be unpredictable
      • Not suitable for certain athletes who rely heavily on their hamstring muscles
      • Less stiffness than native ACL
      Quadriceps tendon
      • Large graft
      • Can be used for SB or DB reconstruction
      • Option of a one-sided bone block
      • Invasive, large incision
      • Risk of patellar fracture
      Allograft
      • No donor site morbidity
      • Available in various types and sizes
      • Shortens operative time
      • Theoretical risk of disease transmission
      • Longer healing time
      • Increased risk of re-rupture, especially in younger patients, and irradiated grafts
      • Cost
      ACL, anterior cruciate ligament; DB, double-bundle; SB, single-bundle.
      Magnussen et al
      • Magnussen RA
      • Lawrence JTR
      • West RL
      • et al.
      Graft size and patient age are predictors of early revision after anterior cruciate ligament reconstruction with hamstring autograft.
      found that a hamstring autograft size of ≤8 mm in diameter was associated with a higher rate of early revision than were those of >8 mm. For the purposes of preoperative planning, studies have evaluated the use of MRI in predicting hamstring graft size and have found that cross-sectional area measurements on MRI correlate positively with intraoperative graft size.
      • Beyzadeoglu T
      • Akgun U
      • Tasdelen N
      • et al.
      Prediction of semitendinosus and gracilis autograft sizes for ACL reconstruction.
      However, measurements of graft diameter on the MRI do not correlate with intraoperative graft size.
      • Beyzadeoglu T
      • Akgun U
      • Tasdelen N
      • et al.
      Prediction of semitendinosus and gracilis autograft sizes for ACL reconstruction.
      For patellar and quadriceps tendons preoperative measurements, the sagittal thickness measured on the MRI can provide the surgeon with an idea of the potential graft size.
      • Araujo P
      • van Eck CF
      • Torabi M
      • et al.
      How to optimize the use of MRI in anatomic ACL reconstruction.

      Hamstrings versus bone-patellar tendon-bone grafts

      Most of the recent systematic reviews and meta-analyses, based on high-quality studies, have reported that there is no significant difference between hamstrings and bone-patellar tendon-bone autografts considering stability testing, patient satisfaction, IKDC score and graft failure.
      • Shea KG
      • Carey JL
      • Richmond J
      • et al.
      The American Academy of Orthopaedic Surgeons evidence-based guideline on management of anterior cruciate ligament injuries.
      However, postoperative kneeling pain was more frequently present in the patellar tendon group (48–65% vs 30–35% at ≥2-year follow-up).
      • Sajovic M
      • Strahovnik A
      • Dernovsek MZ
      • et al.
      Quality of life and clinical outcome comparison of semitendinosus and gracilis tendon versus patellar tendon autografts for anterior cruciate ligament reconstruction: an 11-year follow-up of a randomized controlled trial.
      • Leys T
      • Salmon L
      • Waller A
      • et al.
      Clinical results and risk factors for reinjury 15 years after anterior cruciate ligament reconstruction: a prospective study of hamstring and patellar tendon grafts.
      Consequently, sports activities and patient lifestyle should influence graft choice for ACL reconstruction.

      Autograft versus allograft

      In patients having primary reconstruction, an allograft may be considered when there are concerns of donor site morbidity or cosmesis. Some studies report that an appropriately processed allograft has similar clinical outcomes than an autograft.
      • Lawhorn KW
      • Howell SM
      • Traina SM
      • et al.
      The effect of graft tissue on anterior cruciate ligament outcomes: a multicenter, prospective, randomized controlled trial comparing autograft hamstrings with fresh-frozen anterior tibialis allograft.
      ,
      • Sun K
      • Zhang J
      • Wang Y
      • et al.
      Arthroscopic anterior cruciate ligament reconstruction with at least 2.5 years' follow-up comparing hamstring tendon autograft and irradiated allograft.
      ,
      • Kaeding CC
      • Aros B
      • Pedroza A
      • et al.
      Allograft versus autograft anterior cruciate ligament reconstruction: predictors of failure from a MOON prospective longitudinal cohort.
      However, these results may not be generalisable to all patients (eg, young and active patients) or all allografts (eg, irradiated allografts).
      • Shea KG
      • Carey JL
      • Richmond J
      • et al.
      The American Academy of Orthopaedic Surgeons evidence-based guideline on management of anterior cruciate ligament injuries.
      For example, several studies have reported a higher failure rate of allograft in younger patients,
      • Kaeding CC
      • Aros B
      • Pedroza A
      • et al.
      Allograft versus autograft anterior cruciate ligament reconstruction: predictors of failure from a MOON prospective longitudinal cohort.
      • Mascarenhas R
      • Erickson BJ
      • Sayegh ET
      • et al.
      Is there a higher failure rate of allografts compared with autografts in anterior cruciate ligament reconstruction: a systematic review of overlapping meta-analyses.
      and the most recent clinical practice guidelines recommend against allografts for young and highly active patients.
      • Shea KG
      • Carey JL
      • Richmond J
      • et al.
      The American Academy of Orthopaedic Surgeons evidence-based guideline on management of anterior cruciate ligament injuries.
      Comparing autograft and allograft data, studies have reported 6% failure rate with autograft, 9% failure rate with non-irradiated allograft, and 34% failure rate with irradiated allograft (2.5 Mrad).
      • Sun K
      • Zhang J
      • Wang Y
      • et al.
      Arthroscopic anterior cruciate ligament reconstruction with at least 2.5 years' follow-up comparing hamstring tendon autograft and irradiated allograft.
      The difference between autograft and non-irradiated allograft was not statistically significant, in contrast with the difference between failures in the autograft group and the irradiated allograft group.
      • Sun K
      • Zhang J
      • Wang Y
      • et al.
      Arthroscopic anterior cruciate ligament reconstruction with at least 2.5 years' follow-up comparing hamstring tendon autograft and irradiated allograft.

      ACL remnant preservation

      Preserving the ACL remnants during surgery can facilitate determination of the appropriate tunnel location and potentially improve the graft maturation process. The remaining functional fibres biomechanically protect the graft, contribute to proprioception and vascularisation, and may prevent the synovial fluid leakage to the tunnel, which can prevent future tunnel enlargement.
      • Zhang Q
      • Zhang S
      • Cao X
      • et al.
      The effect of remnant preservation on tibial tunnel enlargement in ACL reconstruction with hamstring autograft: a prospective randomized controlled trial.
      A staged approach is recommended for the assessment of the remaining ACL tissue during the surgery. This approach involves the evaluation of the morphology and remaining functionality of the ACL tissue.

      Tunnel placement for ACL reconstruction

      Proper tunnel placement is critical to restore the native ACL insertion site. Non-anatomic tunnel placement can result in abnormal knee kinematics, limited ROM and, ultimately, graft failure.
      • Kopf S
      • Forsythe B
      • Wong AK
      • et al.
      Nonanatomic tunnel position in traditional transtibial single-bundle anterior cruciate ligament reconstruction evaluated by three-dimensional computed tomography.
      ,
      • Steiner ME
      • Battaglia TC
      • Heming JF
      • et al.
      Independent drilling outperforms conventional transtibial drilling in anterior cruciate ligament reconstruction.
      ,
      • Zantop T
      • Diermann N
      • Schumacher T
      • et al.
      Anatomical and nonanatomical double-bundle anterior cruciate ligament reconstruction: importance of femoral tunnel location on knee kinematics.
      ,
      • Tashman S
      • Collon D
      • Anderson K
      • et al.
      Abnormal rotational knee motion during running after anterior cruciate ligament reconstruction.
      Soft tissue remnants, along with bony landmarks, are essential in determining the anatomic tunnel positions during ACL reconstruction surgery.
      • Ferretti M
      • Ekdahl M
      • Shen W
      • et al.
      Osseous landmarks of the femoral attachment of the anterior cruciate ligament: an anatomic study.
      • Lu W
      • Wang D
      • Zhu W
      • et al.
      Placement of double tunnels in ACL reconstruction using bony landmarks versus existing footprint remnant: a prospective clinical study with 2-year follow-up.
      A deficient interobserver agreement between surgeons can be present if these structures are not considered for anatomic tunnel placement.
      • McConkey MO
      • Amendola A
      • Ramme AJ
      • et al.
      Arthroscopic agreement among surgeons on anterior cruciate ligament tunnel placement.
      The ACL tibial insertion site has a fanned-out shape, with an insertion length of 17 mm average in the sagittal plane (range 12–22 mm) and 11 mm width average in the coronal plane.
      • Hara K
      • Mochizuki T
      • Sekiya I
      • et al.
      Anatomy of normal human anterior cruciate ligament attachments evaluated by divided small bundles.
      • Harner CD
      • Baek GH
      • Vogrin TM
      • et al.
      Quantitative analysis of human cruciate ligament insertions.
      The insertion site is aligned with the anterior horn of the lateral meniscus, and has a close relationship with the medial and lateral tibial spine
      • Hara K
      • Mochizuki T
      • Sekiya I
      • et al.
      Anatomy of normal human anterior cruciate ligament attachments evaluated by divided small bundles.
      • Harner CD
      • Baek GH
      • Vogrin TM
      • et al.
      Quantitative analysis of human cruciate ligament insertions.
      (Figure 4, Figure 5, Figure 6).
      Figure thumbnail gr4
      Figure 4ACL tibial insertion site showing its close relation with the anterior horn of the lateral meniscus. Preservation of native landmarks can be accomplished with careful debridement with a thermal device. ACL, anterior cruciate ligament; AM, anteromedial; PL, posterolateral; MFC, medial femoral condyle.
      Figure thumbnail gr5
      Figure 5Anterior view of a cadaveric knee showing both ACL bundles. ACL, anterior cruciate ligament; AM, anteromedial; PL, posterolateral; PCL, posterior cruciate ligament.
      Figure thumbnail gr6
      Figure 6Femoral (left) and tibial (right) ACL insertion sites. Black line demarcates the position of the lateral intercondylar ridge (‘resident's ridge‘). Dotted line demarcates the position of the lateral bifurcate ridge. Asterisk: approximate centre of the AM and PL insertion sites. ACL, anterior cruciate ligament; AM, anteromedial; PL, posterolateral.
      The ACL femoral insertion site is oval shaped,
      • Hara K
      • Mochizuki T
      • Sekiya I
      • et al.
      Anatomy of normal human anterior cruciate ligament attachments evaluated by divided small bundles.
      • Harner CD
      • Baek GH
      • Vogrin TM
      • et al.
      Quantitative analysis of human cruciate ligament insertions.
      normally smaller than the tibial insertion site, posterior to the lateral intercondylar ridge, or so-called resident's ridge.
      • Ferretti M
      • Ekdahl M
      • Shen W
      • et al.
      Osseous landmarks of the femoral attachment of the anterior cruciate ligament: an anatomic study.
      The AM bundle originates from the proximal portion of the lateral notch wall, while the PL bundle lies more distally near the anterior articular cartilage surface of the lateral femoral condyle.
      • Ferretti M
      • Ekdahl M
      • Shen W
      • et al.
      Osseous landmarks of the femoral attachment of the anterior cruciate ligament: an anatomic study.
      The lateral bifurcate ridge runs perpendicular to the lateral intercondylar ridge, between the femoral insertion sites of the AM and PL bundles
      • Ferretti M
      • Ekdahl M
      • Shen W
      • et al.
      Osseous landmarks of the femoral attachment of the anterior cruciate ligament: an anatomic study.
      (Figure 5, Figure 6).
      For SB reconstruction, a single femoral and tibial tunnel is positioned midway between the centre of the AM and PL insertion sites, using the AMP for the femoral side. The tibial guide is recommended to be set to 55° for tunnel drilling, and is important to consider this drill-guide angle because it can affect the tibial tunnel aperture size and orientation.
      • Kopf S
      • Forsythe B
      • Wong AK
      • et al.
      Nonanatomic tunnel position in traditional transtibial single-bundle anterior cruciate ligament reconstruction evaluated by three-dimensional computed tomography.
      For DB reconstruction, the femoral PL tunnel is created first, through the AMP, followed by the tibial AM and PL tunnels. A tibial guide is recommended to be set to 45° for the PL bundle and 55° for the AM bundle, and the tunnel entrance should be 2 cm apart on the tibial extra-articular cortex. Then the femoral AM tunnel is drilled normally using the AMP.

      TT versus tibial independent approach for femoral tunnel drilling

      Various techniques for ACL femoral tunnel drilling exist, including four primary techniques: arthroscopic TT technique, AMP technique, outside-in (OI) technique, and OI retrograde drilling (RD) technique.
      Discrepancy between the tunnel position and the native ACL insertion site is common when the femoral tunnel is drilled using the TT technique. The popularity of ‘tibial independent’ femoral tunnel techniques (AMP, OI, RD) has increased because these techniques are designed for more accurate and anatomic ACL femoral placement. Each of these techniques has its own risks and benefits. A recent systematic review summarised the advantages and disadvantages of each of them (table 4).
      • Robin BN
      • Jani SS
      • Marvil SC
      • et al.
      Advantages and disadvantages of transtibial, anteromedial portal, and outside-in femoral tunnel drilling in single-bundle anterior cruciate ligament reconstruction: a systematic review.
      Table 4Advantages and disadvantages of femoral tunnel drilling techniques in SB ACL reconstruction
      • Robin BN
      • Jani SS
      • Marvil SC
      • et al.
      Advantages and disadvantages of transtibial, anteromedial portal, and outside-in femoral tunnel drilling in single-bundle anterior cruciate ligament reconstruction: a systematic review.
      TechniqueAdvantagesDisadvantages
      Transtibial
      • Requires a single incision and is less invasive than a two-incision technique
      • Results in a stable Lachman test in most patients
      • The graft's vertical position may minimise impingement
      • The tibial tunnel dictates the femoral tunnel
      • Results in vertical and anterior graft placement
      • Vertical grafts result in excessive femoral external (tibial internal) rotation at mid stance
      • Interference screw-tunnel divergence
      • Notchplasty required for visualisation of femoral footprint
      Anteromedial portal
      • Femoral tunnel and tibial tunnel are made independently
      • Allows anatomic placement of femoral tunnel
      • Parallel placement of interference screw
      • Restores AP stability in swing phase and external rotation at mid stance
      • Useful for augmentation when preserving remaining fibres
      • Allows for all-inside technique
      • Faster return to activity compared with TT
      • Better short-term ROM compared with TT
      • Useful for revision ACL reconstruction
      • No special instruments or guides necessary
      • Difficulty visualising in hyperflexion possibly leading to iatrogenic chondral injury
      • Posterior wall blowout
      • Technically demanding
      • Short or bicortical sockets, which may limit fixation options
      • Higher revision rate
      • Increased risk of injury to common peroneal nerve
      • Extension loss during stance phase
      • Hyperflexion requires an assistant
      Outside-in
      • Predictable anatomic placement
      • Eliminates posterior wall blowout
      • Useful in revision ACL reconstruction
      • Less risk of bone tunnel divergence compared with TT
      • Decreased bone absorption at bone–graft interface
      • Second incision and increased surgical morbidity
      • Lateral femoral dissection
      • Increased operative time
      • Worse cosmesis
      Outside-in retrograde drilling
      • Allows for independent anatomic tunnel placement
      • Allows for anatomic placement
      • Does not require hyperflexion
      • Longer socket compared with the anteromedial portal
      • Small cosmetic accessory incision
      • Higher IKDC subjective scores related to knee joint stability and pivot-shift grade compared with TT
      • Increased operative time
      • Increased cost
      • Horizontal tunnel creates a steep angle that may increase graft wear
      ACL, anterior cruciate ligament; AP, anteroposterior; IKDC, International Knee Documentation Committee; ROM, range of motion; SB, single-bundle; TT, transtibial.
      Even though the AMP technique has many advantages related to the anatomic ACL reconstruction, some studies have shown a higher graft failure with this technique. The Danish Knee Ligament Reconstruction Register reported a revision rate of 5.16% (95% CI 3.61% to 7.34%) for the AMP technique versus 3.20% (95% CI 2.51% to 4.08%) for the TT technique.
      • Rahr-Wagner L
      • Thillemann TM
      • Pedersen AB
      • et al.
      Increased risk of revision after anteromedial compared with transtibial drilling of the femoral tunnel during primary anterior cruciate ligament reconstruction: results from the Danish Knee Ligament Reconstruction Register.
      One explanation for this is that in the TT technique, since the graft is not anatomically positioned, it is submitted to less stress and thus presents with less graft failure.
      • Yasuda K
      • van Eck CF
      • Hoshino Y
      • et al.
      Anatomic single- and double-bundle anterior cruciate ligament reconstruction, part 1: basic science.
      The most recent systematic review and clinical practice guidelines state that moderate evidence supports the use of either the tibial independent or TT technique, because measured outcomes are similar.
      • Shea KG
      • Carey JL
      • Richmond J
      • et al.
      The American Academy of Orthopaedic Surgeons evidence-based guideline on management of anterior cruciate ligament injuries.
      Only long-term prospective studies and randomised studies will be able to demonstrate that the independent femoral drilling techniques will be able to prevent joint degeneration and osteoarthritis.
      Finally, the choice of the femoral tunnel technique should be based on a combination of variables, including surgeon experience, available equipment, cost, efficiency, patient age, patient activity level, graft choice and cosmesis.

      Graft fixation

      Secure graft fixation for ACL reconstruction is an important goal. The graft fixation should be secure, allow normal tendon healing and provide the graft construct with biomechanical properties close to that of the native ligament. Over the past 10 years, significant advances in fixation have led to the development of many different fixation devices for bony and soft tissue graft fixation.
      For femoral tunnel fixation with a bone plug, metal or bio-interference screws are the most commonly used devices. Metal interference screws have been used as the standard fixation with a bone-patellar tendon-bone autograft. However, with the increasing use of hamstring soft tissue grafts, bioabsorbable interference screws (poly-l-lactic acid, PLLA, polyglyconate) and biocompatible, non-resorbable screws (polyetheretherketone, PEEK) are becoming more popular. While the bioabsorbable screw has some advantages, such as less screw thread-induced laceration of the graft, incorporation into the surrounding tissue and less interference with MRI, it seems to provide similar clinical results to metal screws according to a systematic review.
      • Mascarenhas R
      • Saltzman BM
      • Sayegh ET
      • et al.
      Bioabsorbable versus metallic interference screws in anterior cruciate ligament reconstruction: a systematic review of overlapping meta-analyses.
      However, bioabsorbable screws showed more frequent and prolonged knee effusion, most likely secondary to foreign body reaction, and more screw breakage than metallic screws (relative risk 2.57–2.81 and 12.81, respectively).
      • Mascarenhas R
      • Saltzman BM
      • Sayegh ET
      • et al.
      Bioabsorbable versus metallic interference screws in anterior cruciate ligament reconstruction: a systematic review of overlapping meta-analyses.
      For femoral tunnel fixation with soft tissue graft, the suspensory devices are the ones most commonly used. The benefit of this fixation is that it has a higher failure load and less stiffness than interference screws, and avoids disruption of the insertion site, which can occur with the screws. However, an increased risk of tunnel enlargement has been reported in some studies, according to a potential ‘bungee effect’ (or pistoning) and ‘windshield effect’.
      • Baumfeld JA
      • Diduch DR
      • Rubino LJ
      • et al.
      Tunnel widening following anterior cruciate ligament reconstruction using hamstring autograft: a comparison between double cross-pin and suspensory graft fixation.
      Nevertheless, a meta-analysis and high-quality studies have reported no clinically significant differences in knee AP stability or functional outcomes comparing interference screw and suspensory fixation for soft tissue grafts.
      • Colvin A
      • Sharma C
      • Parides M
      • et al.
      What is the best femoral fixation of hamstring autografts in anterior cruciate ligament reconstruction? A meta-analysis.
      • Ibrahim SAR
      • Abdul Ghafar S
      • Marwan Y
      • et al.
      Intratunnel versus extratunnel autologous hamstring double-bundle graft for anterior cruciate ligament reconstruction: a comparison of 2 femoral fixation procedures.
      Biomechanical studies have compared different types of cortical suspensory devices and have found some mechanical differences between them under different loads
      • Johnson JS
      • Smith SD
      • LaPrade CM
      • et al.
      A biomechanical comparison of femoral cortical suspension devices for soft tissue anterior cruciate ligament reconstruction under high loads.
      (Table 5, Table 6).
      Table 5Mechanical properties of cortical suspension devices for femoral side fixation
      • Johnson JS
      • Smith SD
      • LaPrade CM
      • et al.
      A biomechanical comparison of femoral cortical suspension devices for soft tissue anterior cruciate ligament reconstruction under high loads.
      DeviceFirmStiffness, N/mmUltimate strength, N
      ENDOBUTTONSmith and Nephew927±151530±180
      RIGIDLOOPDePuy Mitek1628±451976±229
      TightRopeArthrex1354±35784±45
      TightRope retensionedArthrex1353±601020±421
      ToggleLocBiomet1480±1031995±217
      ToggleLoc retensionedBiomet1538±572231±511
      XO ButtonConmed Linvatec1747±582218±114
      Table 6Mechanical properties of interference screws and combination screw and sheath devices for soft tissue tibial side fixation
      • Aga C
      • Rasmussen MT
      • Smith SD
      • et al.
      Biomechanical comparison of interference screws and combination screw and sheath devices for soft tissue anterior cruciate ligament reconstruction on the tibial side.
      DeviceFirmLength (mm)Diameter (mm)Tunnel diameter (mm)MaterialPullout stiffness (N/mm)Ultimate failure (N)
      Bio-Interference Screw (S)Arthrex28.09.09.0PLDLA343.0±46.43973.3±95.82
      BIOSURE PK (S)Smith and Nephew30.09.09.0PEEK352.3±42.73990.8±182.1
      RCI Screw (S)Smith and Nephew25.09.09.0Titanium384.3±105.2817.7±114.0
      AperFix II (SS)Cayenne30.011.010.0PEEK366.4±40.761122±182.9
      BIOSURE SYNC (SS)Smith and Nephew32.511.09.0PEEK326.9±74.51829.5±172.4
      ExoShape (SS)MedShape30.09.09.0PEEK342.3±51.47814.7±178.8
      GraftBolt (SS)Arthrex30.010.09.0PEEK402.3±58.891136±115.6
      Intrafix (SS)DePuy Mitek30.010.59.0polyethylene (sheath) and acetal (screw)372.5±50.021127±155.0
      PEEK, polyetheretherketone; PLDLA, bioabsorbable poly-ld-lactic; S, screw device; SS, combination device (screw and sheath).
      Cross biodegradable or metal pins can be also used for femoral side fixation. A systematic review compared transfemoral fixation versus cortical button fixation, and showed no differences in clinical outcomes and tunnel widening.
      • Saccomanno MF
      • Shin JJ
      • Mascarenhas R
      • et al.
      Clinical and functional outcomes after anterior cruciate ligament reconstruction using cortical button fixation versus transfemoral suspensory fixation: a systematic review of randomized controlled trials.
      For tibial side fixation, the interference screw is the most commonly used device for bone plug and soft tissue grafts. It has several advantages including ease of insertion, aperture fixation, which creates a stiffer graft construct, and minimal slippage during cyclic loading.
      • Caborn DNM
      • Nyland J
      • Selby J
      • et al.
      Biomechanical testing of hamstring graft tibial tunnel fixation with bioabsorbable interference screws.
      As aforementioned, bioabsorbable and metallic interference screws have reported similar clinical and functional outcomes, except for the more frequent knee effusion and screw breakage with the bioabsorbable devices.
      • Mascarenhas R
      • Saltzman BM
      • Sayegh ET
      • et al.
      Bioabsorbable versus metallic interference screws in anterior cruciate ligament reconstruction: a systematic review of overlapping meta-analyses.
      Other options for tibial or femoral fixation can be extracortical fixations such as staples and suture posts. Thus, these types of fixation are recommended only as a backup or hybrid fixation.
      • Scheffler SU
      • Südkamp NP
      • Göckenjan A
      • et al.
      Biomechanical comparison of hamstring and patellar tendon graft anterior cruciate ligament reconstruction techniques: the impact of fixation level and fixation method under cyclic loading.
      Several studies have shown that the initial tension of the graft is mechanically relevant in the fixation. However, there is a lack of consensus regarding pretensioning and preconditioning protocols for the ACL reconstruction graft.
      • Jisa KA
      • Williams BT
      • Jaglowski JR
      • et al.
      Lack of consensus regarding pretensioning and preconditioning protocols for soft tissue graft reconstruction of the anterior cruciate ligament.
      Also, the precise amount of tension that should be applied to the graft when it is fixed has yet to be defined.
      • Arneja S
      • McConkey MO
      • Mulpuri K
      • et al.
      Graft tensioning in anterior cruciate ligament reconstruction: a systematic review of randomized controlled trials.
      Lastly, the knee flexion angle for graft fixation should be determined according to biomechanical studies that have evaluated the ACL native tension pattern.
      • Gabriel MT
      • Wong EK
      • Woo SLY
      • et al.
      Distribution of in situ forces in the anterior cruciate ligament in response to rotatory loads.
      Fixation is recommended at 15–20° of flexion for SB reconstruction, and differentiated angles are recommended for DB reconstruction according to each bundle: full extension for the PL bundle and 45° of flexion for the AM bundle.
      • Austin JC
      • Phornphutkul C
      • Wojtys EM
      Loss of knee extension after anterior cruciate ligament reconstruction: effects of knee position and graft tensioning.
      All these technical precisions intend to replicate accurately the native ACL biomechanical properties.

      Common pitfalls and tips for successful ACL reconstruction

      Table 7, Table 8 show the common pitfalls and tips for successful ACL reconstruction.
      Table 7Common pitfalls in ACL reconstruction surgery
      • Colvin AC
      • Shen W
      • Musahl V
      • et al.
      Avoiding pitfalls in anatomic ACL reconstruction.
      PitfallSolution
      Femoral tunnel misplacementImproper visualisation of the complete femoral insertion siteA high lateral portal is ideal for observing the tibial insertion site, and the medial portal should be used to visualise the femoral insertion site. The accessory anteromedial portal avoids the use of notchplasty for visualisation and tunnel drilling (see Portals section)
      Non-anatomical position of the femoral tunnel secondary to the use of the ‘clock face’ methodThe ‘clock face’ method should not be used as a reference for femoral tunnel positioning. Definitions of the clock face differ among surgeons and its relation with anatomical structures depends on the degree of knee flexion, arthroscopic view and the anteroposterior axis. A two-dimensional reference cannot be used as a reference for a three-dimensional structure such as the intercondylar notch. Anatomical structures of the joint, ACL remnant, bony landmarks and/or radiographic references should be used (see Tunnel placement section)
      Non-anatomical position of femoral tunnel secondary to the use of transtibial techniqueThe transtibial technique typically results in the graft being placed in a high anteromedial position for the femoral tunnel. The use of the accessory medial portal allows the femoral tunnel to be placed independent of the tibial tunnel in a more anatomical position (see Tunnel placement section)
      Graft impingementNon-anatomic tunnel placementUsually secondary to an anterior placement of the tibial tunnel. For anatomic tibial placement, anatomical structures of the joint, ACL remnant and/or radiographic references should be used (see Tunnel placement section)
      Non-individualised graft sizeA mismatch between the native ACL diameter and the graft diameter can lead to graft impingement, despite the anatomic tunnel placement. Using the anatomic and individualised ACL reconstruction concept, the graft size is chosen according to preoperative and intraoperative measurements of the native ACL insertion sites (see Anatomic ACL reconstruction section)
      Inadequate graft tensionOver-tensioning or insufficient tensioning of the graftAppropriate graft tensioning is achieved by an adequate initial tension and stable fixation, using specific knee flexion angles according to SB or DB reconstruction techniques (see Graft fixation section)
      ACL, anterior cruciate ligament; DB, double-bundle; SB, single-bundle.
      Table 8Tips for successful ACL reconstruction
      Diagnostics
      • A detailed medical history and physical examination are vital in the diagnosis of an ACL injury (see Diagnostics section)
      • X-rays and MRI are recommended as complementary exams to evaluate concomitant injuries, confirm the diagnosis of ACL injury and assist in the surgical planning (see Diagnostics section)
      Surgical treatment
      • ACL reconstruction is recommended to be delayed until the knee effusion has resolved, full knee ROM has been regained, quadriceps control is achieved, and the patient is prepared for surgery and rehabilitation (see Timing for surgery section)
      • ACL reconstruction should be performed following the anatomic and individualised concept, which is focused on the restoration of the ACL to its native dimensions, collagen orientation and insertion sites. This concept can be applied to SB and DB ACL reconstruction (see Anatomic ACL reconstruction concept' section)
      • Proper patient selection is essential to decide between SB and DB reconstruction (see SB versus DB ACL reconstruction section)
      • Correct portal placement is critical in ACL reconstruction. Care and needle localisation should be used to create the anteromedial and accessory medial portals as they are in close proximity to the medial meniscus and medial femoral condyle (see Portals section)
      • The key to obtain a reproducible anatomic ACL reconstruction is to have a satisfactory visualisation of the notch, soft tissue remnants and bony landmarks of native ACL for adequate tunnel placement. A three-portal approach has been shown to provide the best intraoperative visualisation for ACL reconstruction (see Tunnel placement for ACL reconstruction section)
      • Preservation of native landmarks can be accomplished with careful debridement with a thermal device (see ACL remnant preservation' section)
      • Careful measurement of notch and ACL insertion dimensions allows for individualised reconstruction (see Anatomic ACL reconstruction concept section)
      • Avoid using the ‘clock face’ method to create the femoral ACL tunnels. Native ACL insertion sites and bony landmarks should be used for an accurate tunnel(s) placement (see Tunnel placement for ACL reconstruction section)
      • Graft fixation has many critical points, including the specific technique of the fixation device, the adequate knee flexion and tension of the graft (see Graft fixation section)
      Rehabilitation
      • A proper rehabilitation protocol must be followed which focuses on functional tests rather than time points to advance through phases (see Postoperative care and rehabilitation section)
      • Return to sports should be based on individual patient rehabilitation progression instead of a specific time from surgery (see Return to sports after ACL reconstruction section)
      ACL, anterior cruciate ligament; DB, double-bundle; ROM, range of motion; SB, single-bundle.

      Postoperative imaging evaluation

      Postoperatively, AP and lateral radiographs can be used to evaluate tunnel angle and implant position. Postoperative MRI measurements of the insertion site, inclination angle and length of the ACL can also be compared with those made preoperatively. Some authors consider evaluation on MRI to assess graft healing.
      • Miyawaki M
      • Hensler D
      • Illingworth KD
      • et al.
      Signal intensity on magnetic resonance imaging after allograft double-bundle anterior cruciate ligament reconstruction.
      A three-dimensional CT (3D-CT) scan is presently considered the gold standard for postoperative evaluation of tunnel placement. Moreover, a 3D-CT scan can be particularly useful in planning for knees in which revision surgery is required (Figure 7, Figure 8).
      • Kopf S
      • Forsythe B
      • Wong AK
      • et al.
      Nonanatomic tunnel position in traditional transtibial single-bundle anterior cruciate ligament reconstruction evaluated by three-dimensional computed tomography.
      • Forsythe B
      • Kopf S
      • Wong AK
      • et al.
      The location of femoral and tibial tunnels in anatomic double-bundle anterior cruciate ligament reconstruction analyzed by three-dimensional computed tomography models.
      Figure thumbnail gr7
      Figure 7SB (left) and DB ACL reconstructions (right). Arthroscopic pictures of the grafts (top) and postoperative three-dimensional CT showing the femoral tunnel(s) (middle) and tibial tunnel(s) (bottom). ACL, anterior cruciate ligament; AM, anteromedial; PL, posterolateral; DB, double-bundle; SB, single-bundle.
      Figure thumbnail gr8
      Figure 8Three-dimensional CT evaluation of the femoral and tibial tunnel location. Anatomical anteromedial tunnel position: blue; anatomical posterolateral tunnel position: green. Adapted with permission from Forsythe et al
      • Forsythe B
      • Kopf S
      • Wong AK
      • et al.
      The location of femoral and tibial tunnels in anatomic double-bundle anterior cruciate ligament reconstruction analyzed by three-dimensional computed tomography models.
      and Kopf et al.
      • Kopf S
      • Forsythe B
      • Wong AK
      • et al.
      Nonanatomic tunnel position in traditional transtibial single-bundle anterior cruciate ligament reconstruction evaluated by three-dimensional computed tomography.
      (A) Quadrant method (for femoral side): the locations of the femoral tunnels are established within a 4×4 grid, which is oriented along the most anterior edge of the notch roof, parallel (t) and perpendicular (h) to the Blumensaat line. (B and C) Anatomical coordinate axes method (for the femoral and tibial sides): the locations of the tunnels are determined in the axial and sagittal planes, aligned with the respective bone anatomical axes. Lines: F1—posterior border of the medial wall of the lateral condyle; F2—most anterior point of the notch; F3—proximal border of the notch; F4—distal point of the notch roof; T1—anterior border of the tibial plateau; T2—most posterior border of the tibial plateau; T3—medial border of the tibial plateau; T4—lateral border of the tibial plateau. Axes: Femoral side— posterior-to-anterior (PA)=F1 to F2; proximal-to-distal (Pr-D)=F3 to F4. Tibial side: anterior-to-posterior (AP)=T1 to T2; medial-to-lateral (ML)=T3 to T4.
      Tabled 1
      Measurement methodAnatomical anteromedial tunnel position
      • Forsythe B
      • Kopf S
      • Wong AK
      • et al.
      The location of femoral and tibial tunnels in anatomic double-bundle anterior cruciate ligament reconstruction analyzed by three-dimensional computed tomography models.
      Anatomical posterolateral tunnel position
      • Forsythe B
      • Kopf S
      • Wong AK
      • et al.
      The location of femoral and tibial tunnels in anatomic double-bundle anterior cruciate ligament reconstruction analyzed by three-dimensional computed tomography models.
      Femoral sideQuadrant methodt=21.7%±2.5% h=33.2%±5.6%t=35.1%±3.5% h=55.3%±5.3%
      Anatomical coordinate axes methodPA=23.1%±6.1% Pr-D=28.2%±5.4%PA=15.3%±4.8% Pr-D=58.1±7.1%
      Tibial sideAnatomical coordinate axes methodAP=25%±2.8% ML=50.5%±4.2%AP=46.4%±3.7% ML=52.4%±2.5%

      Postoperative care and rehabilitation

      Immediately after surgery, the knee is immobilised with a brace. The patient can be discharged with adequate pain medication and a cooling device the same day.
      During the first week(s), focus should be placed on reducing pain and swelling, and restoring full ROM and quadriceps muscle strength. On the day after surgery, patients begin to perform ankle pumps, straight leg raise, quadriceps sets, gastrocnemius stretch and heel slides. At the end of the first week, continuous passive motion is initiated with progression to full extension.
      Depending on the progress made, crutches and brace are typically weaned after 6 weeks. Once quadriceps muscle strength returns, straight line walking can be initiated at 6 weeks, with progression to jogging in a straight line and a stationary bike around 3 months.
      Pivoting and cutting exercises are not initiated until at least 6 months and return to sport is generally no sooner than 9 months postoperatively. A functional ACL brace for sports is recommended until the patient is 2 years after surgery from the reconstruction. However, there is insufficient evidence to support its routine use.
      Patient progression through the rehabilitation phases is dependent on the patient's readiness according to the periodic evaluation of the physical therapist and surgeon.
      To standardise the management of ACL reconstruction rehabilitation, an evidence-based rehabilitation guideline was developed by the Multicenter Orthopaedic Outcomes Network (MOON).
      • Wright RW
      • Haas AK
      • Anderson J
      • et al.
      Anterior cruciate ligament reconstruction rehabilitation: MOON guidelines.
      This guideline is focused on progression phases, which are based on achieving functional criteria, rather than the time elapsed since surgery.
      • Wright RW
      • Haas AK
      • Anderson J
      • et al.
      Anterior cruciate ligament reconstruction rehabilitation: MOON guidelines.
      The most recent systematic review, based on moderate quality evidence, shows no difference in clinical outcomes between accelerated and non-accelerated rehabilitation protocols.
      • Shea KG
      • Carey JL
      • Richmond J
      • et al.
      The American Academy of Orthopaedic Surgeons evidence-based guideline on management of anterior cruciate ligament injuries.
      The benefit of early accelerated rehabilitation is that patients may be able to return to full, unrestricted activity sooner. However, the impact on long-term outcomes (eg, progression of osteoarthritis) of the timing and intensity of rehabilitation programmes is currently unknown.
      • Shea KG
      • Carey JL
      • Richmond J
      • et al.
      The American Academy of Orthopaedic Surgeons evidence-based guideline on management of anterior cruciate ligament injuries.

      Return to sports after ACL reconstruction

      RTS is a primary goal of ACL reconstruction, but the timing of the return is multifactorial, considering preoperative, intraoperative and postoperative factors (table 9).
      Table 9Factors affecting return to play in athletes following anterior cruciate ligament reconstruction
      • Ellman MB
      • Sherman SL
      • Forsythe B
      • et al.
      Return to play following anterior cruciate ligament reconstruction.
      PreoperativeIntraoperativePostoperative
      • Age
      • Preoperative rehabilitation
      • Full knee extension
      • Neuromuscular control
      • Graft choice
      • Autograft vs allograft
      • Hamstring vs bone-patellar tendon-bone
      • Rehabilitation protocol
      • Psychological factors
      Preoperative factors that can affect return to play are age, preoperative rehabilitation, full knee extension and neuromuscular control.
      • Ellman MB
      • Sherman SL
      • Forsythe B
      • et al.
      Return to play following anterior cruciate ligament reconstruction.
      The most important intraoperative factor is graft choice. The advantages of a bone-patellar tendon-bone autograft, considering RTS, include good graft strength/stiffness and stable interference screw fixation, allowing for bone-to-bone healing within the ACL tunnels.
      • Kaeding CC
      • Aros B
      • Pedroza A
      • et al.
      Allograft versus autograft anterior cruciate ligament reconstruction: predictors of failure from a MOON prospective longitudinal cohort.
      Whereas incorporation of the graft does not equate to maturation, earlier graft incorporation may allow for more aggressive rehabilitation protocols and a more rapid RTS.
      Considering postoperative factors, several authors have reported that RTS is more dependent on the rehabilitation than on the technique or the graft choice used intraoperatively. This is directly related to the rehabilitation protocol, functional assessment according to specific sports, and psychological factors of the patient.
      • Ellman MB
      • Sherman SL
      • Forsythe B
      • et al.
      Return to play following anterior cruciate ligament reconstruction.
      In a systematic review and meta-analysis,
      • Ardern CL
      • Taylor NF
      • Feller JA
      • et al.
      Fifty-five per cent return to competitive sport following anterior cruciate ligament reconstruction surgery: an updated systematic review and meta-analysis including aspects of physical functioning and contextual factors.
      with a mean follow-up of 40 months after ACL reconstruction, 81% of patients returned to sport, 65% returned to their preinjury level of sport and 55% returned to competitive level sport after surgery. Factors that favoured returning to the preinjury level sport were younger age (mean difference −0.3), male gender (OR 1.4), playing elite sport (OR 2.5), symmetrical hopping performance and having a positive psychological response (mean difference 0.3). In fact, one of the leading reasons given for not returning to sporting activity is fear of reinjury.
      • Ardern CL
      • Taylor NF
      • Feller JA
      • et al.
      Fifty-five per cent return to competitive sport following anterior cruciate ligament reconstruction surgery: an updated systematic review and meta-analysis including aspects of physical functioning and contextual factors.
      The same review compared ACL reconstruction grafts, showing that a hamstring autograft favoured returning to competitive level sport (OR 2.4), whereas a bone-patellar tendon-bone autograft favoured returning to the preinjury level sport (OR 1.2).
      • Ardern CL
      • Taylor NF
      • Feller JA
      • et al.
      Fifty-five per cent return to competitive sport following anterior cruciate ligament reconstruction surgery: an updated systematic review and meta-analysis including aspects of physical functioning and contextual factors.
      According to the most recent systematic review, there is no high level evidence that can support a specific time for RTS.
      • Shea KG
      • Carey JL
      • Richmond J
      • et al.
      The American Academy of Orthopaedic Surgeons evidence-based guideline on management of anterior cruciate ligament injuries.
      Although an expeditious return can be an achievable and realistic goal, the factors that most influence safe, timely and successful return to play remain unknown. Further research is warranted to validate reliable consensus guidelines with objective criteria to facilitate the return to play process.
      • Ellman MB
      • Sherman SL
      • Forsythe B
      • et al.
      Return to play following anterior cruciate ligament reconstruction.
      Validated outcome measures commonly used after ACL reconstruction are shown in table 10.
      Table 10Validated outcomes measures for ACL reconstruction
      OutcomeDescriptionReference
      IKDC
      • Evaluates variety of knee conditions: ACL, PCL, meniscus, cartilage patellofemoral problems
      • Scoring: 0–100 (100 best)
      • Test–retest reliability (>0.7)=0.87–0.98
      • Minimal clinically important difference=3.19–16.7
      http://www.sportsmed.org/components/layouts/Standard.aspx?pageid=523&id=810&terms=ikdc
      Lysholm
      • Initially designed for ACL. Subsequently used for a variety of other knee conditions
      • Scoring: 0–100 (100 best)
      • Test–retest reliability (>0.7)=0.68–0.97
      • Minimal clinically important difference=10.1
      • Lysholm J
      • Gillquist J
      Evaluation of knee ligament surgery results with special emphasis on use of a scoring scale.
      Tegner
      • Evaluates activity level—competitive sports, recreational sports, work and activities of daily living
      • Scoring: 0–10 (10 best)
      • Test–retest reliability (>0.7)=0.82–0.92
      • Minimal clinically important difference=not reported
      • Barber-Westin SD
      • Noyes FR
      • McCloskey JW
      Rigorous statistical reliability, validity, and responsiveness testing of the Cincinnati knee rating system in 350 subjects with uninjured, injured, or anterior cruciate ligament-reconstructed knees.
      Cincinnati
      • Evaluates variety of knee conditions: ACL, PCL, MCL, lateral/posterolateral knee ligaments, meniscal repairs and allografts, high tibial osteotomy
      • Scoring: 0–100 (100 best) various calculations possible
      • Test–retest reliability (>0.7)=0.80–0.98
      • Minimal clinically important difference=14.0–26.0
      • Noyes FR
      • Barber SD
      • Mooar LA
      A rationale for assessing sports activity levels and limitations in knee disorders.
      KOOS
      • Evaluates post-traumatic OA; eg, ACL, meniscus, chondral injuries
      • Scoring: 0–100 (100 best)
      • Test–retest reliability (>0.7)=0.45–0.95
      • Minimal clinically important difference=not reported
      http://www.koos.nu/
      ACL, anterior cruciate ligament; IKDC, International Knee Documentation Committee; KOOS, Knee Injury and Osteoarthritis Outcome Score; OA, osteoarthritis; MCL, medial collateral ligament; PCL, posterior cruciate ligament.

      Complications

      ACL reconstruction, as with surgical intervention, can have associated morbidity. Some studies reported 23–28% of reintervention after ACL reconstruction during a 32–89 months of follow-up.
      • Laxdal G
      • Kartus J
      • Ejerhed L
      • et al.
      Outcome and risk factors after anterior cruciate ligament reconstruction: a follow-up study of 948 patients.
      The most frequent morbidities were meniscal injury (6.9%) and ROM deficits (6.3%).
      • Laxdal G
      • Kartus J
      • Ejerhed L
      • et al.
      Outcome and risk factors after anterior cruciate ligament reconstruction: a follow-up study of 948 patients.
      Infection was reported in 0.6% of the cases.
      • Laxdal G
      • Kartus J
      • Ejerhed L
      • et al.
      Outcome and risk factors after anterior cruciate ligament reconstruction: a follow-up study of 948 patients.
      The most frequent intraoperative complications are technical errors, which have been described in 9.6% of the cases during graft harvesting, tunnel placement or graft fixation. These complications might not have an effect on the final outcome if the surgeon has the expertise required to solve these incidents during the surgery.
      The most serious complications after ACL reconstruction are neurological or vascular injuries, arthrofibrosis and infections. The incidence of the most severe complications, not readily published, is probably underestimated because of publication bias.
      One of the most serious postoperative complications is graft rupture. The incidence increases with time after surgery: 3%, 6%, 9% and 12% at 2-year, 5-year, 8-year and 13-year follow-up, respectively.
      • Wright RW
      • Dunn WR
      • Amendola A
      • et al.
      Risk of tearing the intact anterior cruciate ligament in the contralateral knee and rupturing the anterior cruciate ligament graft during the first 2 years after anterior cruciate ligament reconstruction: a prospective MOON cohort study.
      ,
      • Drogset JO
      • Grøntvedt T
      Anterior cruciate ligament reconstruction with and without a ligament augmentation device: results at 8-Year follow-up.
      ,
      • Salmon L
      • Russell V
      • Musgrove T
      • et al.
      Incidence and risk factors for graft rupture and contralateral rupture after anterior cruciate ligament reconstruction.
      A contralateral ACL rupture has been reported to occur in 3–24% of the surgically treated patients, depending on the length of the follow-up.
      • Wright RW
      • Dunn WR
      • Amendola A
      • et al.
      Risk of tearing the intact anterior cruciate ligament in the contralateral knee and rupturing the anterior cruciate ligament graft during the first 2 years after anterior cruciate ligament reconstruction: a prospective MOON cohort study.
      ,
      • Drogset JO
      • Grøntvedt T
      Anterior cruciate ligament reconstruction with and without a ligament augmentation device: results at 8-Year follow-up.
      ,
      • Salmon L
      • Russell V
      • Musgrove T
      • et al.
      Incidence and risk factors for graft rupture and contralateral rupture after anterior cruciate ligament reconstruction.
      It is not known if this incidence is higher than in a normal active population or in participants who were conservatively treated after an ACL injury. However, the high percentage (34%) reported of subsequent ACL injury, graft rupture or contralateral ACL rupture might be greater than that seen in the normal population.
      • Salmon LJ
      • Russell VJ
      • Refshauge K
      • et al.
      Long-term outcome of endoscopic anterior cruciate ligament reconstruction with patellar tendon autograft: minimum 13-year review.
      It is suggested that specific motor-retraining programmes should be added to the rehabilitation to reduce this risk. Finally, the increase in ACL revision reconstruction publications gives evidence that ACL reconstruction is not a 100% guaranteed successful treatment.
      All these unexpected events could explain why return to the same level of sport activities, which is the primary goal of ACL reconstruction, has generally been reported as 65% of the patients.
      • Laxdal G
      • Kartus J
      • Ejerhed L
      • et al.
      Outcome and risk factors after anterior cruciate ligament reconstruction: a follow-up study of 948 patients.
      • Ardern CL
      • Taylor NF
      • Feller JA
      • et al.
      Fifty-five per cent return to competitive sport following anterior cruciate ligament reconstruction surgery: an updated systematic review and meta-analysis including aspects of physical functioning and contextual factors.
      This suggests that there remains considerable room for improvement in ACL reconstruction surgery.

      Geographical differences

      Registries and multicentre prospective cohort studies are progressively contributing to our knowledge regarding ACL reconstruction. They can also give evidence about the geographical differences in ACL injury treatment and prognosis. The most important prospective cohorts in this area are ongoing in the USA, Norway, Denmark and Sweden (MOON; Multicenter ACL Revision Study, MARS; Norwegian National Knee Ligament Registry, NKLR; Danish National ACL Registry and Swedish National ACL Registry).
      Significant diversity in patients, injury and surgical factors exists among large prospective cohorts collected in different locations. For example, a comparison between the MOON and NKLR registries has shown some significant differences related to ACL injury between the USA and Norway, respectively.
      • Magnussen RA
      • Granan L-P
      • Dunn WR
      • et al.
      Cross-cultural comparison of patients undergoing ACL reconstruction in the United States and Norway.
      In the MOON cohort, there was a lower percentage of males (52% vs 57%) with younger age (23 vs 27 years). Sports associated with injury in the MOON cohort were basketball (20%), soccer (17%) and American football (14%), while soccer (42%), handball (26%) and downhill skiing (10%) were most common in the NKLR cohort. Median time to reconstruction was shorter in MOON (2.4 vs 7.9 months). Concomitant injuries such as meniscal tears and articular cartilage defects were more common in the MOON cohort than in the NKLR cohort (65% and 46% vs 48% and 26%, respectively). Hamstring autografts and patellar tendon autografts were commonly utilised in both cohorts (MOON 44% and 42% vs NKLR 63% and 37%, respectively). Allografts were much more frequently utilised in the MOON cohort (13% vs 0.04%).
      Important geographical differences have been also reported in the same continent and country.
      • Magnussen RA
      • Granan L-P
      • Dunn WR
      • et al.
      Cross-cultural comparison of patients undergoing ACL reconstruction in the United States and Norway.
      Considering the geographical differences, surgeons should analyse the characteristics of the regional cohorts when applying knowledge gleaned from these groups to their own patient populations.

      Future perspectives

      Although traditional reconstruction techniques used an SB graft that was typically placed in a non-anatomic position, a renewed interest in anatomy has facilitated the understanding of anatomic and individualised reconstruction. This concept is based on each patient's native anatomical characteristics (eg, ACL insertion site size and notch size), thereby dictating the ultimate procedure of choice. An anatomic SB or DB reconstruction is performed with a goal of reproducing the characteristics of the native ACL.
      Long-term outcomes for anatomic ACL reconstruction are unknown and the future research, considering biomechanics and clinical outcomes, should be focused on this area. These future studies may yield important information with regard to the progression to osteoarthritis after ACL reconstruction, including factors affecting or preventing it. It is imperative that these studies be adequately powered and use patient-relevant and sensitive outcome measures, keeping our primary goal of improving medical care for individuals who suffer an ACL injury.

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