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Rehabilitation And Advances In Surgical Reconstruction For Anterior Cruciate Ligament Insufficiency: What Has Changed Since The 1960s? - State Of The Art

Open AccessPublished:November 18, 2022DOI:https://doi.org/10.1016/j.jisako.2022.10.001

      Abstract

      Anterior cruciate ligament (ACL) insufficiency can be disabling, given the physical and sports activity constraints that negatively impact the quality of life. Consequently, surgery is the main approach for most active patients. Nonetheless, ACL reconstruction cannot be successful without adequate pre- and postoperative rehabilitation. Since the 1960s, post-ACL reconstruction rehabilitation has evolved, mainly from advances in surgery, coupled with a better understanding of the biological concepts of graft revascularization, maturation and integration, which have impacted ACL postoperative rehabilitation protocols. However, new technologies do involve a definite learning curve which could affect rehabilitation programs and produce inconsistent results. The development of rehabilitation protocols cannot be defined without an accurate diagnosis of ACL injury and considering the patient's main physical demands and expectations. This article discusses how postoperative rehabilitation following ACL reconstruction has changed from the 1960s to now, focussing on surgical technique (type of tendon graft, fixation devices, and graft tensioning), biological concepts (graft maturation and integration), rehabilitation protocols (prevention of ACL injuries, preoperative rehabilitation, postoperative rehabilitation), criteria to return to sports, patient's reported outcomes (PROM), and outcome. Although rehabilitation plays an essential role in managing ACL injuries, it cannot be fully standardized pre- or postoperatively. Pre- and postoperative rehabilitation should be based on an accurate clinical diagnosis, patients' understanding of their injury, graft tissue biology and biomechanics, surgical technique, the patient's physical demands and expectations, geographical differences in ACL rehabilitation, and future perspectives.

      Keywords

      Introduction

      Anterior cruciate ligament (ACL) insufficiency can be disabling, given the physical and sports activity constraints which it imposes and impact negatively on quality of life [
      • Bisciotti G.N.
      • Chamari K.
      • Cena E.
      • Bisciotti A.
      • Bisciotti A.
      • Corsini A.
      • Volpi
      Anterior cruciate ligament injury risk factors in football.
      ]. The importance of the anterior cruciate ligament (ACL) on knee stability was first reported in the period 460-370 BC, but only in the mid-19th century was the clinical description of ACL deficiency actually recorded.[

      V. Chouliaras and H. H. Passler, "The history of the anterior cruciate ligament from Galen to double-bundle ACL reconstruction, Acta Orthop Traumatol Hellenica. ;12:127-131.

      ,
      • Schindler O.S.
      Surgery for anterior cruciate ligament deficiency: a historical perspective.
      ] The clinical tests for the diagnosis of ACL injury started to be developed in the 1960s [
      • Chambat P.
      • Guier C.
      • Sonnery-Cottet B.
      • Fayard J.M.
      • THaunat M.
      The evolution of ACL reconstruction over the last fifty years.
      ], when surgical treatment for ACL insufficiency focused on extra-articular techniques [
      • O'Donoghue D.H.
      Reconstruction for medial instability of the knee.
      ,
      • Nicholas J.A.
      The five-one reconstruction for anteromedial instability of the knee. Indications, technique, and the results in fifty-two patients.
      ,
      • Hughston J.C.
      • Eilers A.F.
      The role of the posterior oblique ligament in repairs of acute medial (collateral) ligament tears of the knee.
      ]
      The pivot shift and Lachman tests, more accurate and specific clinical tests, were gradually introduced to evaluate the anatomical functional integrity of the ACL [
      • Galway H.R.
      • Beaupre A.
      • MacIntosh D.L.
      Pivot shift: a clinical sign of symptomatic anterior cruciate deficiency.
      ,
      • Torg J.S.
      • Conrad W.
      • Kalen V.
      Clinical diagnosis of anterior cruciate ligament instability in the Athlete.
      ].
      The initial satisfactory results of extra-articular reconstruction techniques were found to gradually deteriorated, and intra-articular techniques started to be employed. [
      • Galway H.R.
      • Beaupre A.
      • MacIntosh D.L.
      Pivot shift: a clinical sign of symptomatic anterior cruciate deficiency.
      ,
      • Torg J.S.
      • Conrad W.
      • Kalen V.
      Clinical diagnosis of anterior cruciate ligament instability in the Athlete.
      ] With the continuous development of new devices for graft fixation, a better understanding of different tendon graft biomechanical behavior, ACL anatomy and biomechanics, surgical reconstruction of the ACL has become a much more predictable procedure [
      • Siegel L.
      • Vandernakker-Albanese C.
      • Siegel D.
      Anterior cruciate ligament injuries: anatomy, physiology, biomechanics, and management.
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      • Markatos K.
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      • Lallos S.N.
      • Korres D.S.
      • Efstahopoulos N.
      The anatomy of the ACL and its importance in ACL reconstruction.
      ].
      Nevertheless, surgery cannot be successful without adequate postoperative rehabilitation. The advances in surgery, coupled with better understanding of the biological concepts of graft revascularization, maturation and integration, have impacted on ACL postoperative rehabilitation protocols [
      • Claes S.
      • Verdonk P.
      • Forsyth R.
      • Bellemans J.
      The "ligamentization" process in anterior cruciate ligament reconstruction: what happens to the human graft? A systematic review of the literature.
      ,
      • Malempati C.
      • Jurjans J.
      • Noehren B.
      • Ireland M.L.
      • Johnson D.L.
      Current Rehabilitation Concepts for Anterior Cruciate Ligament Surgery in Athletes.
      ].
      This article discusses how postoperative rehabilitation following ACL reconstruction has changed from the 1960s to the present day, focussing on surgical technique (type of tendon graft, fixation devices, and graft tensioning), biological concepts (graft maturation and integration), rehabilitation protocols (prevention of ACL injuries, preoperative rehabilitation, postoperative rehabilitation), criteria to return to sports, patient's reported outcomes (PROM), and outcome.

      ACL reconstruction surgical techniques

      Several authors proposed extra-articular reconstructions, including anterolateral tenodesis, using the fascia lata combined with a posteromedial imbrication[
      • Bosworth D.M.
      • Bosworth B.M.
      Use of fascia lata to stabilize the knee in case of ruptured crucial ligament.
      , 15].[14, 15]. The procedure was followed by immobilization of the knee in a cast for 6 to 8 weeks, an obvious obstacle to early postoperative rehabilitation [
      • Chambat P.
      • Guier C.
      • Sonnery-Cottet B.
      • Fayard J.M.
      • THaunat M.
      The evolution of ACL reconstruction over the last fifty years.
      ,
      • Dodds A.L.
      • Gupte C.M.
      • Neyret P.
      • Williams A.M.
      • Amis A.A.
      Extra articular techniques in anterior cruciate ligament reconstruction.
      ]. As peripheral reconstructions did not afford long term knee stability, the focus of surgery shifted to intra-articular reconstructions [
      • Chambat P.
      • Guier C.
      • Sonnery-Cottet B.
      • Fayard J.M.
      • THaunat M.
      The evolution of ACL reconstruction over the last fifty years.
      ,
      • Dodds A.L.
      • Gupte C.M.
      • Neyret P.
      • Williams A.M.
      • Amis A.A.
      Extra articular techniques in anterior cruciate ligament reconstruction.
      ].
      In the early 1960s, Jones described a technique of intra-articular reconstruction of the ACL using an ipsilateral patellar-tendon bone graft, keeping the distal end of the patellar tendon attached to the tibial tubercle [
      • Chambat P.
      • Guier C.
      • Sonnery-Cottet B.
      • Fayard J.M.
      • THaunat M.
      The evolution of ACL reconstruction over the last fifty years.
      ,
      • Dodds A.L.
      • Gupte C.M.
      • Neyret P.
      • Williams A.M.
      • Amis A.A.
      Extra articular techniques in anterior cruciate ligament reconstruction.
      ]. This technique resulted in a graft shorter than desired, and the position of the femoral tunnel was therefore forcedly non-anatomical. These potential problems stimulated new surgical approaches and grafts, such as the over-the-top technique using fascia lata [18, 19] A free patellar-tendon bone graft allowed to harvest a graft of adequate length, thus allowing to drill appropriate tibial and femoral tunnels, and gained worldwide popularity [
      • Erikson E.
      Reconstruction of the anterior cruciate ligament.
      ,
      • Clancy W.G.
      • Nelson D.A.
      • Reider B.
      • Narechania R.G.
      Anterior cruciate ligament reconstruction using one third of the patellarligament augmented by extra articular tendon transfers.
      ,
      • Dejour H.
      • Dejour D.
      • Aït Si Selmi T.
      Laxité chronique du genou traité par une greffe de tendon rotulien libre et une plastie extra articulaire antérolatérale. 10 ans de recul. 148 cas.
      ].
      Later, novel surgical procedures were proposed, including double-bundle reconstruction, ACL reconstruction associated with anterolateral ligament reconstruction, and the use of different grafts, with no surgical techniques manifestly superior to the others [
      • DePhillipo N.N.
      • Cinque M.E.
      • Chahla J.
      • Geesslin A.G.
      • LaPrade R.F.
      Anterolateral Ligament Reconstruction Techniques, Biomechanics, and Clinical Outcomes.
      ,
      • Lin M.K.
      • Boyle C.
      • Niv Marom
      • Marx R.G.
      Graft Selection in Anterior Cruciate Ligament Reconstruction Sports.
      ]. FIGURE 1 summarizes the process of ACL rehabilitation since the 1960's.
      Figure 1
      Figure 1Summary of ACL postoperative rehabilitation evolution during the advances of clinical diagnosis, graft fixation devices, and surgical techniques.

      Graft fixation

      A critical variable for the success of ACL reconstruction is the method of fixation of the graft. Originally, tendon grafts were sutured to the surrounding periosteum. This remained the main option until the early 1940s, when nails, buttons, staples, and the concept of press-fit fixation of the bone-end of the bone-patellar tendon-bone graft were introduced.[
      • Lemaire M.
      Instabilité chronique du genou. Techniques et résultat des plasties ligamentaires en traumatologie sportive.
      ,
      • Jones K.G.
      Reconstruction of the anterior cruciate ligament.
      ,
      • Campbell C.
      Repair of the ligaments of the knee. Report of a new operation for the repair of the anterior cruciate ligament.
      ,
      • Macey H.B.
      A new operative procedure for repair of ruptured cruciate ligament of the knee joint.
      ] In the 1980's, with the advent of arthroscopy, screw with washer fixation became widely used. Around that time, Lambert described intra-tunnel fixation with a cortical screw [
      • Boszotta H.
      Arthroscopic anterior cruciate ligament reconstruction using a patella tendon graft in press-fit technique: surgical technique and follow-up.
      ,
      • Lambert K.L.
      Vascularized patellar tendon graft with rigid internal fixation for anterior cruciate ligament insufficiency.
      ].
      In the mid-1980's, Kurosaka et al. developed the interference screw.[
      • Boszotta H.
      Arthroscopic anterior cruciate ligament reconstruction using a patella tendon graft in press-fit technique: surgical technique and follow-up.
      ,
      • Lambert K.L.
      Vascularized patellar tendon graft with rigid internal fixation for anterior cruciate ligament insufficiency.
      ] This system allowed rigid fixation, rapid graft integration into the bone tunnels, and positively sped up rehabilitation following ACL reconstruction [
      • Boszotta H.
      Arthroscopic anterior cruciate ligament reconstruction using a patella tendon graft in press-fit technique: surgical technique and follow-up.
      ,
      • Lambert K.L.
      Vascularized patellar tendon graft with rigid internal fixation for anterior cruciate ligament insufficiency.
      ]. Interference screws were initially conceived to fix the bone portion of the graft in the femoral and tibial tunnels. In the late 1980s, Pinczewski [
      • Boszotta H.
      Arthroscopic anterior cruciate ligament reconstruction using a patella tendon graft in press-fit technique: surgical technique and follow-up.
      ,
      • Lambert K.L.
      Vascularized patellar tendon graft with rigid internal fixation for anterior cruciate ligament insufficiency.
      ] reported good ACL postoperative outcomes using interference screw fixation with soft tissue grafts.
      Cortical screws and washers evolved, and serrated washers were developed to prevent graft slipping into the bone tunnel. In the 1990's, the interference screws became rounded and less sharp, minimizing their potential damage to the hamstring tendon during tunnel fixation. Other new devices were the endobotton, cross-pin ("rider" fixation), and BoneMulch (transverse screw). All these devices are now available in metallic and bioabsorbable materials [
      • Rosenberg T.D.
      Technique for Endoscopic Method of ACL Reconstruction.
      ,
      • Clark R.
      • Olsen R.E.
      • Larson B.J.
      • et al.
      Cross-pin femoral fixation: a new technique for hamstring anterior cruciate ligament reconstruction of the knee.
      ,
      • Howell S.
      • Gottilieb J.
      Endoscopic fixation of a double-looped semi- tendinosus and gracilis ACL graft using Bone Mulch screw.
      ].

      The use of biologics

      Being an intra-articular ligament with a thin synovial membrane, the ACL has a low potential for spontaneous healing [35]. The management of partial and incomplete tears of the ACL remains controversial [
      • Papalia R.
      • Franceschi F.
      • Zampogna B.
      • Tecame A.
      • Maffulli N.
      • Denaro V.
      Surgical management of partial tears of the anterior cruciate ligament.
      ]. To avoid surgical reconstruction in patients with partial ruptures, biologicals, such PRP, MSCs, GFs, have been used to favour healing of partial ACL tears, and biologicals have been employed to accelerate tendon graft integration to the bone tunnel following surgical reconstruction [
      • Andriolo L.
      • Di Matteo B.
      • Kon E.
      • Filardo G.
      • Veniero G.
      • Marcacci M.
      PRP Augmentation for ACL Reconstruction.
      ,
      • Figueroa D.
      • Figueroa F.
      • Calvo R.
      • Vaisman A.
      • Ahumada X.
      Arellano Platelet-rich plasma use in anterior cruciate ligament surgery: systematic review of the literature..
      ].
      Some authors reported an increase in ACL cell density and neovascularization with better collagen fibers maturation and biomechanical properties following the use of orthobiologicals. Although these findings seem impressive, the use of biologicals did not result in clinically relevant improvement compared to the patients who underwent ACL surgery without them [
      • Di Matteo B.
      • Loibl M.
      • Andriolo L.
      • Filardo G.
      • Zellner J.
      • Koch M.
      • Angele P.
      Biologic agents for anterior cruciate ligament healing: A systematic review.
      ,
      • Murray M.M.
      • Martin S.D.
      • Martin T.L.
      • Spector M.
      Histological changes in the human anterior cruciate ligament after rupture.
      ].

      Graft tensioning

      Graft tensioning plays a critical role in surgical outcomes, as it affects the mechanical behaviour of the tendon graft. Postoperatively, the ACL tendon graft may elongate because of its viscoelastic characteristics [
      • Di Matteo B.
      • Loibl M.
      • Andriolo L.
      • Filardo G.
      • Zellner J.
      • Koch M.
      • Angele P.
      Biologic agents for anterior cruciate ligament healing: A systematic review.
      ,
      • Murray M.M.
      • Martin S.D.
      • Martin T.L.
      • Spector M.
      Histological changes in the human anterior cruciate ligament after rupture.
      ]. This biomechanical phenomenon, stress relaxation, may be a critical factor for graft failure and post-reconstruction outcomes [
      • Yoshiya S.
      • Kurosaka M.
      • Ouchi K.
      • Kuroda R.
      • Mizuno K.
      Graft tension and knee stability after anterior cruciate ligament reconstruction.
      ,
      • Nicholas S.J.
      • D'Amato M.J.
      • Mullaney M.J.
      • Tyler T.F.
      • Kolstad K.
      • McHugh M.P.
      A prospectively randomized double-blind study on the effect of initial graft tension on knee stability after anterior cruciate ligament reconstruction.
      ] Graft tensioning before implantation prevents excessive graft elongation postoperatively. Most graft tensioning protocols apply tension to the graft in a cyclic or static mode [
      • Noyes F.R.
      • Huser L.E.
      • Ashman B.
      • Palmer M.
      Anterior Cruciate Ligament Graft Conditioning Required to Prevent an Abnormal Lachman and Pivot Shift After ACL Reconstruction: A Robotic Study of 3 ACL Graft Constructs.
      ,
      • Heis F.T.
      • Paulos L.E.
      Tensioning of the anterior cruciate ligament graft.
      ]. However, in clinical practice, the forces applied to the graft may vary from each surgeon, and the various protocols do not take into account the graft used, and whether two different tendons are coupled together. Also, the type of fixation and the surgeon's experience are not taken into account [
      • Noyes F.R.
      • Huser L.E.
      • Ashman B.
      • Palmer M.
      Anterior Cruciate Ligament Graft Conditioning Required to Prevent an Abnormal Lachman and Pivot Shift After ACL Reconstruction: A Robotic Study of 3 ACL Graft Constructs.
      ,
      • Heis F.T.
      • Paulos L.E.
      Tensioning of the anterior cruciate ligament graft.
      ].

      Strategies of ACL injury rehabilitation

      Nearly three decades ago, Shelbourne reported that the patients who ignored a restrictive rehabilitation program and challenged themselves early actually did better following ACL reconstruction [
      • Shelbourne K.D.
      • Nitz P.
      Accelerated rehabilitation after anterior cruciate ligament reconstruction.
      ,
      • Shelbourne K.D.
      • Wilckens J.H.
      Current concepts in anterior cruciate ligament rehabilitation.
      ]. Nevertheless, supervised rehabilitation remains an integral part of management of patients with anterior cruciate ligament injuries.[
      • Shelbourne K.D.
      • Patel D.V.
      • Martini D.J.
      Classification and management of arthrofibrosis of the knee after anterior cruciate ligament reconstruction.
      ,
      • Shaarani S.R.
      • Moyna N.
      • Moran R.
      • O'Byrne J.M.
      Rehabilitation: the void in the management of anterior cruciate ligament injuries- a clinical review.
      ].
      An ACL injury impacts on several fields, causing motor dysfunction, deficits of neuromotor interaction compromising muscle balance, and psychological distress. All these points reinforce the importance of a comprehensive rehabilitation program approach, both pre-and postoperatively. [
      • Keays S.L.
      • Bullock-Saxton J.
      • Keays A.C.
      Strength and function before and after anterior cruciate ligament reconstruction.
      ,
      • te Wierike S.C.M.
      • van der Sluis A.
      • van den Akker-Scheek I.
      • Elferink-Gemser M.T.
      • Visscher C.
      Psychosocial factors influencing the recovery of athletes with anterior cruciate ligament injury: a systematic review.
      ,
      • Flosadottir V.
      • Frobell R.
      • Roos E.M.
      • Ageberg E.
      Impact of treatment strategy and physical performance on future knee-related self-efficacy in individuals with ACL injury.
      ].

      Preoperative Rehabilitation

      Preoperative rehabilitation following ACL reconstruction aims to achieve better quadriceps motor control and range of motion (ROM), establishing favourable clinical conditions to prevent anterior knee pain and quadriceps inhibition in the early postoperative phase. [
      • Shelbourne K.D.
      • Nitz P.
      Accelerated rehabilitation after anterior cruciate ligament reconstruction.
      ,
      • Giesche F.
      • Niederer D.
      • Banzer W.
      • Vogt L.
      Evidence for the effects of prehabilitation before ACL-reconstruction on return to sport-related and self-reported knee function: A systematic review.
      ] In addition, preoperative rehabilitation may also contribute to reduce the occurrence of new injuries and decrease the risk of knee osteoarthritis. Moreover, patients should be informed on the pro and cons of conservative and operative management of ACL injury before deciding on the best treatment.[
      • Shelbourne K.D.
      • Gray T.
      Minimum 10-year results after anterior cruciate ligament reconstruction: how the loss of normal knee motion compounds other factorsrelated to the development of osteoarthritis after surgery.
      ] This preoperative intervention may increase the patient's awareness and better understanding of their injury and the importance of rehabilitation, improving the functional and psychological recovery, and positively reflecting on postoperative outcomes. Table 1 presents the main goals of the preoperative strategy of ACL reconstruction.
      Table 1Main Goals Of Preoperative Rehabilitation Of Acl Injury (3-24 Weeks).
      MAIN GOALS OF PREOPERATIVE REHABILITATION OF ACL INJURY (3-24 weeks)
      control and diminish pain, swelling and inflammation
      restore normal knee range of motion, especially extension
      identify and approach psychological hurdles involved in return sports practicefear or lack of trust in the knee

      discussing pros and cons of treatment options quadriceps and hamstring
      muscles strengthening and stretching exercisesquadriceps and hamstring
      hip strength and stability

      closed kinetic chain exercises
      open kinetic chain exercises
      balance and coordination training
      Balance and proprioceptionSingle leg standing, BAPS board and BOSU ball exercises
      neuromuscular trainingcore strengthening and balance, plyometrics, resistance and speed training (drop and jump exercises)
      improve quality of life
      In 1996, Shelbourne et al. [
      • Shelbourne K.D.
      • Patel D.V.
      • Martini D.J.
      Classification and management of arthrofibrosis of the knee after anterior cruciate ligament reconstruction.
      ] demonstrated, in retrospective studies, that intensive rehabilitation protocols initiated before surgery may have a beneficial impact on functional outcome after surgery. After more than 25 years, systematic reviews have validated these programs and their positive effects on postoperative functional outcomes [
      • Giesche F.
      • Niederer D.
      • Banzer W.
      • Vogt L.
      Evidence for the effects of prehabilitation before ACL-reconstruction on return to sport-related and self-reported knee function: A systematic review.
      ].
      Preoperative rehabilitation of ACL injury focuses on regaining knee range of motion, quadriceps and hamstring strengthening and muscle balance, knee proprioception, plyometrics, and specific functional rehabilitation.[
      • Filbay S.R.
      • Grindem H.
      Evidence-based recommendations for the management of anterior cruciate ligament (ACL) rupture.
      ] However, when analyzing the effectiveness of this preoperative rehabilitation process on postoperative physical and psychological outcomes, a recent review identified a lack of consensus on the optimal preoperative program regarding the content, frequency, and length. Therefore, even though preoperative rehabilitation of patients with ACL insufficiency is recommended as a valuable tool for postoperative outcomes, more research should be performed. [
      • Carter H.M.
      • Webster K.E.
      • Smith B.E.
      Current preoperative physiotherapy management strategies for patients awaiting Anterior Cruciate Ligament Reconstruction (ACLR): A worldwide survey of physiotherapy practice.
      ].
      Table 1 shows the main goals of preoperative Rehabilitation of ACL injury.

      Postoperative Rehabilitation

      ACL postoperative rehabilitation aims to minimize knee pain, swelling, and inflammation following surgical trauma, reestablish full knee range of motion and neuromuscular control, enhance recovery, and return to pre-injury physical or sports activities level. The better understanding of graft biomechanics, biology, advances in surgical technique, and improvements in graft fixation devices have guided the development of postoperative rehabilitation protocols.
      At the beginning of the 1980s, the graft was protected during the first several postoperative weeks. At that time, the rehabilitation protocol following a modified Jones patellar tendon-bone graft involved knee immobilization and no weight-bearing for 6 to 8 weeks [
      • Shelbourne K.D.
      • Nitz P.
      Accelerated rehabilitation after anterior cruciate ligament reconstruction.
      ]. Rehabilitation transitioned from rigid knee immobilization to immediate, continuous passive motion in 1983. [
      • Paulos L.
      • Noyes F.R.
      • Grood E.
      • Butler D.L.
      Knee rehabilitation after anterior cruciate ligament reconstruction and repair.
      ,
      • Noyes F.R.
      • Mangine R.E.
      • Barber S.
      Early knee motion after open and arthroscopic anterior cruciate ligament reconstruction.
      ].
      At that time, Shelbourne and Nitz [
      • Shelbourne K.D.
      • Nitz P.
      Accelerated rehabilitation after anterior cruciate ligament reconstruction.
      ] collected subjective and objective data from two populations that differed in terms of whether they had followed the recommended cautious approach or had voluntarily strayed away from it and accelerated their weight-bearing mobilization and physical activities. Surprisingly, non-compliant patients experienced better outcomes than compliant ones, returning to their normal function sooner, with no adverse effects.
      The development of new reliable fixation devices such as the interference screw (Kurosaka's screw) contributed to change the early rehabilitation protocol, allowing early knee mobilization and weight-bearing [29, 30, 58]. Figure 1 shows the changes in ACL postoperative rehabilitation with the advances in clinical diagnosis, graft fixation devices, and surgical techniques.

      Postoperative rehabilitation protocols

      The rehabilitation protocols have evolved, in line with new knowledge on how tendon grafts behave under mechanical stresses in the early postoperative stages [
      • Perriman A.
      • Leahy E.
      • Semciw A.I.
      The Effect of Open- Versus Closed-Kinetic-Chain Exercises on Anterior Tibial Laxity, Strength, and Function Following Anterior Cruciate Ligament Reconstruction: A Systematic Review and Meta-analysis.
      ,
      • Nyland J.
      • Mattocks A.
      • Kibbe S.
      • Kalloub A.
      • Greene J.W.
      • Caborn D.N.
      Anterior cruciate ligament reconstruction, rehabilitation, and return to play: 2015 update.
      ]. A suitable rehabilitation protocol should maintain the integrity of the graft during the various phases of maturation to avoid breakdowns and functional instability. The most recent international clinical consensus [
      • Noyes F.R.
      • Huser L.E.
      • Ashman B.
      • Palmer M.
      Anterior Cruciate Ligament Graft Conditioning Required to Prevent an Abnormal Lachman and Pivot Shift After ACL Reconstruction: A Robotic Study of 3 ACL Graft Constructs.
      ,
      • Heis F.T.
      • Paulos L.E.
      Tensioning of the anterior cruciate ligament graft.
      ] agrees that the ideal physiotherapy protocol should include early mobilization, cryotherapy, functional quadriceps electrical stimulation and weight unloading during the first three weeks postoperatively, in addition to incorporating both closed and open kinetic chain exercises and neuromuscular control. Functional braces and continuous passive motion are not recommended, and rehabilitation can be undertaken under supervision by a rehabilitation specialist or, in selected patients, at home. Both closed and open kinetic chain exercises can be introduced before the third postoperative months, restricting only the angle of execution of the quadriceps strengthening in open-kinetic chain mode between 45 and 90 degrees [
      • Noyes F.R.
      • Huser L.E.
      • Ashman B.
      • Palmer M.
      Anterior Cruciate Ligament Graft Conditioning Required to Prevent an Abnormal Lachman and Pivot Shift After ACL Reconstruction: A Robotic Study of 3 ACL Graft Constructs.
      ,
      • Heis F.T.
      • Paulos L.E.
      Tensioning of the anterior cruciate ligament graft.
      ]. Furthermore, there is currently no evidence of superiority of closed over open kinetic chain exercises in terms of return to sport, ligament laxity, functional questionnaires, or reported physical function, regardless of the graft or surgical techniques [59].

      Current evidence-based postoperative ACL rehabilitation

      Continued advances in ACL reconstruction techniques and a better understanding of the biological healing time frames of ACL grafts support the adoption of more aggressive rehabilitation involving early mobilization, and strength and endurance conditioning. However, some linear or non-linear periodic model of changes and adjustments on variable intensity, volume, and frequency are performed to avoid muscle and neuromuscular overloading and consequently fatigue. In this context, periodization of ACL rehabilitation seems to be an attractive strategy to optimize adaptation of the neuromuscular system and increase muscle performance. In clinical practice, periodization programs of ACL rehabilitation may change according to the number and exercise order, rest periods, training frequency, among others. [
      • Kakavas G.
      • Malliaropoulos N.
      • Bikos G.
      • Pruna R.
      • Valle X.
      • Tsaklis P.
      • Maffulli N.
      Periodization in Anterior Cruciate Ligament Rehabilitation: A Novel Framework.
      ].
      Most of the recent ACL postoperative rehabilitation protocols include initial (phases 1 and 2) and late phases (phase 3 and 4). [
      • Brunetti O.
      • Filippi G.M.
      • Lorenzini M.
      • Liti A.
      • Panichi R.
      • Roscini M.
      • Pettorossi V.E.
      • Cerulli G.
      Improvement of posture stability by vibratory stimulation following anterior cruciate ligament reconstruction.
      ,
      • Brunetti O.
      • Filippi G.M.
      • Lorenzini M.
      • Liti A.
      • Panichi R.
      • Roscini M.
      • Pettorossi V.E.
      • Cerulli G.
      Improvement of posture stability by vibratory stimulation following anterior cruciate ligament reconstruction.
      ,
      • Peultier-Celli L.
      • Mainard D.
      • Wein F.
      • Paris N.
      • Boisseau P.
      • Ferry A.
      • Gueguen R.
      • Chary-Valckenaere I.
      • Paysant J.
      • Perrin P.
      Comparison of an Innovative Rehabilitation, Combining Reduced Conventional Rehabilitation with Balneotherapy, and a Conventional Rehabilitation after Anterior Cruciate Ligament Reconstruction in Athletes.
      ,
      • Hohmann E.
      • Tetsworth K.
      • Bryant A.
      Physiotherapy-guided versus home-based, unsupervised rehabilitation in isolated anterior cruciate injuries following surgical reconstruction.
      ] The first phase of the initial rehabilitation program spans between 2 and 5 weeks, and phase 2 covers 2 to 12 weeks. In phase 1, isometric exercises of the quadriceps and hamstrings muscle complexes, active and passive mobilization to gain knee ROM, and cryotherapy are the most commonly reported components of the program. Transcutaneous (TENS) and neuromuscular (NMES) electrical nerve stimulation, hip abduction and adduction exercises, knee and patella mobilization, gait training and ankle exercises are commonly adopted. In phase 2, rehabilitation concentrates on neuromuscular training and proprioception exercises, aiming to regain full active and passive ROM of the knee. Progressive resistance training, including leg press, calf and step-ups, and exercise bike, stepping on the stepping machine or a stair stepper, elliptical training or walking on a treadmill can also be introduced in this phase.
      Phase 3 takes 2 to 24 weeks, and phase 4 ranges from 2 to 12 weeks. In phase 3, proprioceptive training and balance exercises, running, plyometric exercises and jump training are introduced. In phase 4, resistance training, sport-specific exercises for neuromuscular control and proprioception training are started. Moreover, agility exercises, sprinting, cutting drills, and plyometrics can also be added to the rehabilitation protocol in this phase. Gradual return to sports practice starts in this phase. The effectiveness of different strategies and approaches in ACL postoperative rehabilitation directly impacts on the outcomes of the reconstruction. In a recent systematic review, Nelson et. al. (2021) [
      • Noyes F.R.
      • Huser L.E.
      • Ashman B.
      • Palmer M.
      Anterior Cruciate Ligament Graft Conditioning Required to Prevent an Abnormal Lachman and Pivot Shift After ACL Reconstruction: A Robotic Study of 3 ACL Graft Constructs.
      ,
      • Heis F.T.
      • Paulos L.E.
      Tensioning of the anterior cruciate ligament graft.
      ] reported that vibration training has been described as an exciting approach to the process of neuroplasticity involved in ACL reconstruction, improving strength, neuromuscular control and knee stability. Moreover, the short- and long-term clinical benefits of accelerated rehabilitation are not so consistent compared to traditional ones and need further investigation. Open kinetic chain exercises in the initial phases of rehabilitation remain controversial, while closed kinetic chain exercises are commonly recommended in the initial postoperative phase. In relation to neuromuscular stimulation and water exercises, the authors found moderate benefits in the early rehabilitation stages. Table 2 presents the main goals of the postoperative strategy of ACL reconstruction and implemented phases.
      TABLE 2MAIN GOALS IN POSTOPERATIVE REHABILITATION OF ACL RECONSTRUCTION.
      MAIN GOALS IN POSTOPERATIVE REHABILITATION OF ACL RECONSTRUCTION
      PHASE 1 (until 5-week postoperative)
       pain relief, diminish swelling, and inflammatory response to surgery
       restore normal knee range of motionpassive and active exercises
       isometric exercises of quadriceps and hamstrings
       Cryotherapy
      additional measurestranscutaneous (TENS) and neuromuscular (NMES) electrical nerve stimulation, hip abduction and adduction exercises, knee and patella mobilization, gait training and ankle exercises
      PHASE 2 (until 12-week postoperative)
       restore full active and passive range of motion of the knee
       proprioception exercises
       neuromuscular training
      PHASE 3 (until 24-week postoperative)
       proprioceptive and balance exercises,
       plyometric exercises
       jump training
       Running
      PHASE 4 (until 24-week postoperative)
       resistance training
       neuromuscular control and proprioception
       sport-specific exercise (sprinting, cutting drills, and plyometrics)
      Tabled 1
      KEY ARTICLES
      1. Galway HR, Beaupre A, MacIntosh DL. Pivot shift: a clinical sign of symptomatica anterior cruciate ligament deficiency. J Bone Joint Surg Br. 1972;54:763-4
      2. Jones KG (1963) Reconstruction of the anterior cruciate ligament. J Bone Joint Surg Br 45-A:925–932
      3. Kurosaka M, Yoshiya S, Andrish JT. A biomechanical comparison of different surgical techniques of graft fixation in anterior cruciate ligament reconstruction. Am J Sports Med. 1987;15:225–229.
      4. Shelbourne KD, Nitz P. Accelerated rehabilitation after anterior cruciate ligament reconstruction. JOrthop Sport Phys Ther. 1992;15(6):256-64.
      5. Giesche F, Niederer D, Banzer W, Vogt L. Evidence fir the effects of prehabilitation before ACL-reconstruction on return to sport-related and self-reported knee fucnstion: A systematic review. PLoS One. 2020 Oct 28;15(10):e0240192.
      6. Nelson C, Rajan L, Day J, Hinton R, Bodendorfer BM. Postoperative rehabilitation of anterior cruciate ligament reconstruction: a systematic review. Sports Med Arthrosc Rev 2021 Jun 1;29(2):63-80.
      7. Fukuda TY, Fingerhut D, Moreira VC, Camarini PM, Scodeller NF, Duarte A Jr, Martinelli M, Bryk FF. Open kinetic chain exercises in a restricted range of motion after anterior cruciate ligament reconstruction: a randomized controlled trail. Am J Sports Med. 2013 apr;41(4):788-94.
      8. Ashigbi EYK, Banzer W, Niederer D. Return to sport tests’ prognostic value for reinjury risk after anterior cruciate ligament reconstruction: a systematic review. Med Sci Sports Exerc. 2020 Jun;52(6):1263-1271.
      9. Della Villa F, Hägglund M, Della Villa S, Ekstrand J, Waldén M. High rate of second ACL injury following ACL reconstruction in male professional footballers: an updated longitudinal analysis from 118 players in the UEFA Elite Club Injury Study. Br J Sports Med. 2021 Apr 12:bjsports-2020-103555. https://doi.org/10.1136/bjsports-2020-103555. Epub ahead of print. PMID: 33846157.
      10. Andrade R, Pereira R, van Cingel R, Staal JB, Espregueira-Mendes J. How should clinicians rehabilitate patients after ACL reconstruction? A systematic review of clinical practice guidelines (CPGs) with focus on a quality apprasail (AGREE II). Br J Sports Med. 2020 May;54:512-9

      Prevention of ACL injuries in Athletes

      Tabled 1
      TIPS AND TRICKS
      PREOPERATIVE REHABILITATION OF ACL REHABILITATION ACHIEVEMENT
      • ⁃minimize knee pain, swelling, and inflammation following injury
      • ⁃better quadriceps motor control
      • ⁃reestablish full knee range of motion (ROM)
      • ⁃prevent anterior knee pain and quadriceps inhibition in the early postoperative phase
      • ⁃reduce the occurrence of episodes of knee instability and consequence of new injuries
      • ⁃opportunity to inform and discuss with the patient the pro and cons of conservative and operative management of ACL injury
      • ⁃minimize knee pain, swelling, and inflammation following surgical trauma
      POSTOPERATIVE ACL REHABILITATION
      • ⁃early mobilization
      • ⁃reestablish and improve neuromuscular control
      • ⁃reestablish full knee range of motion
      • ⁃knee proprioception, plyometrics
      • ⁃gradual return to pre-injury physical or sports activities level
      PREVENTING COMPLICATIONS IN ACL POSTOPERATIVE REHABILITATION
      • ⁃respect the biological time frames of the graft
      • ⁃attention to patient's emotional status during rehabilitation
      • ⁃reestablish quadriceps motor control and range of motion
      • ⁃manage patients’s expectations based on their ACL injury pattern

      Criteria for returning to sport

      Patients with ACL injuries wish to return to the same pre-injury level after surgery or conservative treatment. Graft maturity post-reconstruction may play a role in failure rate when athletes return to play too quickly; various modern explanations include inadequate graft maturation, decreased psychologic readiness and confidence, poor core control, inadequate rehabilitation of coordination, and fitness. There are remarkable differences between professional athletes compared to recreational athletes. For example, professional soccer players exhibit return rates at the same pre-injury level of 83% (6), while recreational athletes have significantly lower rates at 55% [
      • Ardern C.L.
      • Taylor N.F.
      • Feller J.A.
      • Webster K.E.
      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.
      ].
      After analyzing ACL biomechanical risk factors in football players, Dauokas et al. [69] identified that players who sustained a lower-limb injury within the previous 12 months showed an increased maximum knee valgus angle and decreased minimum knee flexion angle at initial landing contact compared to players with no history of lower limb injuries within the previous 12 months, and concluded that ACL rehabilitation and return to sport should focus on restoring knee kinematics.
      In addition, the graft rupture rate has been between 20-23% in the same knee or contralateral knee in a young population [
      • Wiggins A.J.
      • Grandhi R.K.
      • Schneider D.K.
      • Stanfield D.
      • Webster K.E.
      • Myer G.D.
      Risk of Secondary Injury in Younger Athletes After Anterior Cruciate Ligament Reconstruction: A Systematic Review and Meta-analysis.
      ]. To decrease the rates of graft re-rupture and increase the rates of return to sport at the same pre-injury level, rehabilitation specialists have focused on elaborating intensive rehabilitation and test battery protocols for return to sport to be performed 6 to 10 months after surgery [
      • Ashigbi E.Y.K.
      • Banzer W.
      • Niederer D.
      Return to Sport Tests' Prognostic Value for Reinjury Risk after Anterior Cruciate Ligament Reconstruction: A Systematic Review.
      ]. These test batteries should include functional questionnaires, kinesiophobia questionnaires, limb strength and symmetry tests, arthrometry ligament laxity tests, different unipodal jump tests, and agility tests. Recent systematic reviews and meta-analyses give conflicting results, as only 23% of patients can pass all test batteries. In addition, as a predictive value, the return to sport tests shows a 60% reduction in the risk of reinjury to the operated knee, but a 235% increase in the risk of injury to the contralateral knee [
      • Ashigbi E.Y.K.
      • Banzer W.
      • Niederer D.
      Return to Sport Tests' Prognostic Value for Reinjury Risk after Anterior Cruciate Ligament Reconstruction: A Systematic Review.
      ]. These findings are based on a few high-quality studies which cannot be fully generalized yet to produce widely accepted strategies to optimize return to sport at the pre-injury level.

      Analyzing the postoperative outcomes - Patient's voice (PROM)

      Tabled 1
      VALIDATED OUTCOME MEASURES AND CLASSIFICATIONS
      CLINICAL ESCORES
      IKDC
      MARX ACTIVITY RATING SCALE
      LYSHOLM SCORE
      TEGNER ACTIVITY SCALE
      4-DOMAIN Sports PROM
      FUNCTIONAL EVALUATION
      HOP TEST
      ISOKINETIC EVALUATION

      Considerations In Acl Rehabilitation

      Postoperative rehabilitation following ACL reconstruction is still relatively heterogeneous. It has gone through several phases, including the most conservative protocol by Paulos et al.[
      • Noyes F.R.
      • Huser L.E.
      • Ashman B.
      • Palmer M.
      Anterior Cruciate Ligament Graft Conditioning Required to Prevent an Abnormal Lachman and Pivot Shift After ACL Reconstruction: A Robotic Study of 3 ACL Graft Constructs.
      ,
      • Heis F.T.
      • Paulos L.E.
      Tensioning of the anterior cruciate ligament graft.
      ], in the early 1980s, whose discharge criteria was a 9 to 12-month postoperative period, and the accelerated protocol by Shelbourne et al., in the early 1990s. Evidence-based practice points to the fact that rehabilitation after ACL reconstruction (ACLR) should be carried out progressively, respecting the physiological process of biological maturation of the graft. The rehabilitatiove goals should not just be time-based [
      • Noyes F.R.
      • Huser L.E.
      • Ashman B.
      • Palmer M.
      Anterior Cruciate Ligament Graft Conditioning Required to Prevent an Abnormal Lachman and Pivot Shift After ACL Reconstruction: A Robotic Study of 3 ACL Graft Constructs.
      ,
      • Heis F.T.
      • Paulos L.E.
      Tensioning of the anterior cruciate ligament graft.
      ], and include objective functional parameters [
      • Noyes F.R.
      • Huser L.E.
      • Ashman B.
      • Palmer M.
      Anterior Cruciate Ligament Graft Conditioning Required to Prevent an Abnormal Lachman and Pivot Shift After ACL Reconstruction: A Robotic Study of 3 ACL Graft Constructs.
      ,
      • Heis F.T.
      • Paulos L.E.
      Tensioning of the anterior cruciate ligament graft.
      ] and psychosocial aspects.
      Over time, new approaches have improved rehabilitation, accelerating knee function recovery pre- and postoperatively. Since then, the advances in knee joint biomechanics, kinetics, biology, and new technologies (surgical instruments, fixation devices) have guided the development of rehabilitation. The current foundations for ACL rehabilitation have five main fields, with the final goals to correct undesirable knee kinematics adaptations following ACL injury either in the preoperative or perioperative condition [
      • Noyes F.R.
      • Huser L.E.
      • Ashman B.
      • Palmer M.
      Anterior Cruciate Ligament Graft Conditioning Required to Prevent an Abnormal Lachman and Pivot Shift After ACL Reconstruction: A Robotic Study of 3 ACL Graft Constructs.
      ,
      • Heis F.T.
      • Paulos L.E.
      Tensioning of the anterior cruciate ligament graft.
      ], such as restoring passive and active knee range of motion, quadriceps activation and strengthening, training of neuromuscular control, and return to sports practice (discharge criteria).
      An ACL-deficient knee is more vulnerable to repeated episodes of uncomfortable and painful joint instability, tested using the pivot shift and reported by ACL deficient patients as knee "giving-way", a phenomenon that occurs when an extended ACL-deficient knee is charged by valgus stress and moves to slight flexion. The pivot shift sign involves knee joint movements in more than one plane and is more pronounced when the knee is under weight-bearing conditions, clinically manifested by rotatory instability. In a laboratory in vivo study, Ferrer et al. [
      • Ferrer A.
      • Twycross-Lewis R.
      • MAFFULLI N.
      Anterior cruciate ligament deficiency: rotational instability in the transverse plane. A preliminary laboratory in vivo study.
      ] reported lower torque values of internal rotation at the beginning and mid-stance time intervals and higher values in the crossover task toward the end of the stance phase, and also an avoidance pattern when performing a pivoting-jump task comparing ACL-deficient knees with a control group.
      As knee instability is recurrent, patients unconsciously adopt a slight flexion of the knee to avoid the pivot shift phenomenon. However, this strategy will increase the shear forces on the knee joint, predisposing to new or additional meniscus and osteochondral injuries.
      A knee extension deficit is undesirable, and is reported in 4% to 35% of patients with ACL deficiency [
      • Noyes F.R.
      • Huser L.E.
      • Ashman B.
      • Palmer M.
      Anterior Cruciate Ligament Graft Conditioning Required to Prevent an Abnormal Lachman and Pivot Shift After ACL Reconstruction: A Robotic Study of 3 ACL Graft Constructs.
      ,
      • Heis F.T.
      • Paulos L.E.
      Tensioning of the anterior cruciate ligament graft.
      ]. A lower knee extension range could be harmful to the patient's daily living activities, such as walking, climbing and descending stairs, sitting and standing, as well as running. A deficit of only 5° of the knee extension could result in an abnormal gait from increased joint load, patellofemoral pain, and quadriceps weakness, and lower muscle torque at the extremes of knee extension [
      • Noyes F.R.
      • Huser L.E.
      • Ashman B.
      • Palmer M.
      Anterior Cruciate Ligament Graft Conditioning Required to Prevent an Abnormal Lachman and Pivot Shift After ACL Reconstruction: A Robotic Study of 3 ACL Graft Constructs.
      ,
      • Heis F.T.
      • Paulos L.E.
      Tensioning of the anterior cruciate ligament graft.
      ], and increase the risk of knee osteoarthritis [
      • Noyes F.R.
      • Huser L.E.
      • Ashman B.
      • Palmer M.
      Anterior Cruciate Ligament Graft Conditioning Required to Prevent an Abnormal Lachman and Pivot Shift After ACL Reconstruction: A Robotic Study of 3 ACL Graft Constructs.
      ,
      • Heis F.T.
      • Paulos L.E.
      Tensioning of the anterior cruciate ligament graft.
      ]. Moreover, in the postoperative period, a knee extension deficit may also predispose to graft failure [
      • Noyes F.R.
      • Huser L.E.
      • Ashman B.
      • Palmer M.
      Anterior Cruciate Ligament Graft Conditioning Required to Prevent an Abnormal Lachman and Pivot Shift After ACL Reconstruction: A Robotic Study of 3 ACL Graft Constructs.
      ,
      • Heis F.T.
      • Paulos L.E.
      Tensioning of the anterior cruciate ligament graft.
      ], given its greater vulnerability to mechanical stress and shearing forces resulting from such deficit.
      A retrospective cohort study showed that failure to achieve full knee extension in the early postoperative period was a significant risk factor in developing the "cyclops" syndrome – a nodule of fibrovascular tissue formed in the anterior portion of the ACL graft [
      • Noyes F.R.
      • Huser L.E.
      • Ashman B.
      • Palmer M.
      Anterior Cruciate Ligament Graft Conditioning Required to Prevent an Abnormal Lachman and Pivot Shift After ACL Reconstruction: A Robotic Study of 3 ACL Graft Constructs.
      ,
      • Heis F.T.
      • Paulos L.E.
      Tensioning of the anterior cruciate ligament graft.
      ]. The symptomatic knee extension deficit results from the impact of the "cyclops" lesion against the intercondylar space.
      These clinical findings reinforce the importance of starting physiotherapy as soon as the diagnosis of ACL injury is confirmed. Consequently, one of the primary goals in rehabilitation is to reach full knee extension, comparable to that of the non-injured knee as quickly as possible, and physiological quadriceps muscle activation [
      • van Melick N.
      • van Cingel R.E.
      • Brooijmans F.
      • Neeter C.
      • van Tienen T.
      • Hullegie W.
      • Nijhuis-van der Sanden M.W.
      Evidence-based clinical practice update: practice guidelines for anterior cruciate ligament rehabilitation based on a systematic review and multidisciplinary consensus.
      ,
      • Hanada M.
      • Yoshikura T.
      • Matsuyama Y.
      Muscle recovery at 1 year after the anterior cruciate ligament reconstruction surgery is associated with preoperative and early postoperative muscular strength of the knee extension.
      ]. Moreover, even starting up to 6 weeks preoperatively, physiotherapy produces positive results, leading to a faster return to sport [
      • van Melick N.
      • van Cingel R.E.
      • Brooijmans F.
      • Neeter C.
      • van Tienen T.
      • Hullegie W.
      • Nijhuis-van der Sanden M.W.
      Evidence-based clinical practice update: practice guidelines for anterior cruciate ligament rehabilitation based on a systematic review and multidisciplinary consensus.
      ,
      • Hanada M.
      • Yoshikura T.
      • Matsuyama Y.
      Muscle recovery at 1 year after the anterior cruciate ligament reconstruction surgery is associated with preoperative and early postoperative muscular strength of the knee extension.
      ].
      Therefore, restoring full knee extension after ACLR is of paramount importance, and should be an early goal of rehabilitation. In a cross-sectional study with 74 individuals after ACLR, Noll et al. [
      • van Melick N.
      • van Cingel R.E.
      • Brooijmans F.
      • Neeter C.
      • van Tienen T.
      • Hullegie W.
      • Nijhuis-van der Sanden M.W.
      Evidence-based clinical practice update: practice guidelines for anterior cruciate ligament rehabilitation based on a systematic review and multidisciplinary consensus.
      ,
      • Hanada M.
      • Yoshikura T.
      • Matsuyama Y.
      Muscle recovery at 1 year after the anterior cruciate ligament reconstruction surgery is associated with preoperative and early postoperative muscular strength of the knee extension.
      ] demonstrated that the pattern of knee extension ROM achieved at four weeks postoperatively has a strong correlation with the knee ROM at 12 weeks.
      Biggs et al. [
      • van Melick N.
      • van Cingel R.E.
      • Brooijmans F.
      • Neeter C.
      • van Tienen T.
      • Hullegie W.
      • Nijhuis-van der Sanden M.W.
      Evidence-based clinical practice update: practice guidelines for anterior cruciate ligament rehabilitation based on a systematic review and multidisciplinary consensus.
      ,
      • Hanada M.
      • Yoshikura T.
      • Matsuyama Y.
      Muscle recovery at 1 year after the anterior cruciate ligament reconstruction surgery is associated with preoperative and early postoperative muscular strength of the knee extension.
      ] reported complete knee extension in 100% of participants using a specific protocol focused on ROM recovery started immediately after the surgery. Isberg et al. [
      • van Melick N.
      • van Cingel R.E.
      • Brooijmans F.
      • Neeter C.
      • van Tienen T.
      • Hullegie W.
      • Nijhuis-van der Sanden M.W.
      Evidence-based clinical practice update: practice guidelines for anterior cruciate ligament rehabilitation based on a systematic review and multidisciplinary consensus.
      ,
      • Hanada M.
      • Yoshikura T.
      • Matsuyama Y.
      Muscle recovery at 1 year after the anterior cruciate ligament reconstruction surgery is associated with preoperative and early postoperative muscular strength of the knee extension.
      ] demonstrated no functional impairment or graft laxity after ACLR when knee extension was introduced immediately in the early postoperative phase.
      In a randomized controlled study, Yazdi et al. [
      • van Melick N.
      • van Cingel R.E.
      • Brooijmans F.
      • Neeter C.
      • van Tienen T.
      • Hullegie W.
      • Nijhuis-van der Sanden M.W.
      Evidence-based clinical practice update: practice guidelines for anterior cruciate ligament rehabilitation based on a systematic review and multidisciplinary consensus.
      ,
      • Hanada M.
      • Yoshikura T.
      • Matsuyama Y.
      Muscle recovery at 1 year after the anterior cruciate ligament reconstruction surgery is associated with preoperative and early postoperative muscular strength of the knee extension.
      ] reported improving knee extension in two weeks when manoeuvres of knee extension were performed during ACL reconstruction. However, there was no difference at 6, 12 or 24 weeks compared to participants who did not receive this intervention.
      Wilk and Arrigo [
      • van Melick N.
      • van Cingel R.E.
      • Brooijmans F.
      • Neeter C.
      • van Tienen T.
      • Hullegie W.
      • Nijhuis-van der Sanden M.W.
      Evidence-based clinical practice update: practice guidelines for anterior cruciate ligament rehabilitation based on a systematic review and multidisciplinary consensus.
      ,
      • Hanada M.
      • Yoshikura T.
      • Matsuyama Y.
      Muscle recovery at 1 year after the anterior cruciate ligament reconstruction surgery is associated with preoperative and early postoperative muscular strength of the knee extension.
      ] applied clinical physiotherapeutic techniques to restore knee extension such as hamstring stretching in the operated lower limb, thigh and calf, maintaining knee extension with a rolled up towel under the ankle for 10-15 minutes, four times a day, totaling 60 minutes. Biggs et al. [
      • van Melick N.
      • van Cingel R.E.
      • Brooijmans F.
      • Neeter C.
      • van Tienen T.
      • Hullegie W.
      • Nijhuis-van der Sanden M.W.
      Evidence-based clinical practice update: practice guidelines for anterior cruciate ligament rehabilitation based on a systematic review and multidisciplinary consensus.
      ,
      • Hanada M.
      • Yoshikura T.
      • Matsuyama Y.
      Muscle recovery at 1 year after the anterior cruciate ligament reconstruction surgery is associated with preoperative and early postoperative muscular strength of the knee extension.
      ] proposed knee extension performed by the patient in a sitting position pulling a towel tied to the foot while stabilizing the proximal portion of the knee.
      Patellar mobility is a vital point to be assessed during postoperative ACL rehabilitation. Restricted or absent patella motion may cause knee pain and discomfort in the operated knee. This complication may result from the scar tissue adhering to the patellar retinaculum and its fat pad, causing patellar tendon retraction and reduction of overall knee ROM comprising the complete knee extension and patellar movements. It reinforces the importance of starting patellar mobilizations (lateromedial and superior-inferior), anti-inflammatory measures, reducing oedema, which also play an essential role in restoring knee extension postoperatively.[
      • van Melick N.
      • van Cingel R.E.
      • Brooijmans F.
      • Neeter C.
      • van Tienen T.
      • Hullegie W.
      • Nijhuis-van der Sanden M.W.
      Evidence-based clinical practice update: practice guidelines for anterior cruciate ligament rehabilitation based on a systematic review and multidisciplinary consensus.
      ,
      • Hanada M.
      • Yoshikura T.
      • Matsuyama Y.
      Muscle recovery at 1 year after the anterior cruciate ligament reconstruction surgery is associated with preoperative and early postoperative muscular strength of the knee extension.
      ].
      Quadriceps muscle deficit is a common barrier to the restoration of knee function. The leading cause is still arthrogenic muscle inhibition (AMI), where the quadriceps muscle contraction fails as a consequence of neural inhibition. These mechanisms can come from changes in the resting motor threshold, changes in the triggering of joint sensory receptors, spinal reflex and abnormal cortical activity [
      • van Melick N.
      • van Cingel R.E.
      • Brooijmans F.
      • Neeter C.
      • van Tienen T.
      • Hullegie W.
      • Nijhuis-van der Sanden M.W.
      Evidence-based clinical practice update: practice guidelines for anterior cruciate ligament rehabilitation based on a systematic review and multidisciplinary consensus.
      ,
      • Hanada M.
      • Yoshikura T.
      • Matsuyama Y.
      Muscle recovery at 1 year after the anterior cruciate ligament reconstruction surgery is associated with preoperative and early postoperative muscular strength of the knee extension.
      ]. Therefore, quadriceps activation and strengthening are imperative, acting as turning points of ACL rehabilitation.
      A review of the level of evidence of the main interventions against arthrogenic muscle inhibition (AMI) showed that cryotherapy and exercises for quadriceps and hamstrings muscles are adequate measures, with moderate evidence against arthrogenic muscle inhibition (AMI).[
      • van Melick N.
      • van Cingel R.E.
      • Brooijmans F.
      • Neeter C.
      • van Tienen T.
      • Hullegie W.
      • Nijhuis-van der Sanden M.W.
      Evidence-based clinical practice update: practice guidelines for anterior cruciate ligament rehabilitation based on a systematic review and multidisciplinary consensus.
      ,
      • Hanada M.
      • Yoshikura T.
      • Matsuyama Y.
      Muscle recovery at 1 year after the anterior cruciate ligament reconstruction surgery is associated with preoperative and early postoperative muscular strength of the knee extension.
      ].
      In addition, the quadriceps muscles activation should start in the first few days after the ACL R with open-kinetic chain exercises (i.e. exercises performed with the foot free, not fixed to on object or ground), isometric exercises or elevation (straight leg raise - SLR) without long-term functional impairment [
      • Isberg J.
      • Faxén E.
      • Brandsson S.
      • Eriksson B.I.
      • Kärrholm J.
      • Karlsson J.
      Early active extension after anterior cruciate ligament reconstruction does not result in increased laxity of the knee.
      ,
      • Shaw T.
      • Williams M.T.
      • Chipchase L.S.
      Do early quadriceps exercises affect the outcome of ACL reconstruction? A randomized controlled trial.
      ].
      Fukuda et al. (2013) [
      • Isberg J.
      • Faxén E.
      • Brandsson S.
      • Eriksson B.I.
      • Kärrholm J.
      • Karlsson J.
      Early active extension after anterior cruciate ligament reconstruction does not result in increased laxity of the knee.
      ,
      • Shaw T.
      • Williams M.T.
      • Chipchase L.S.
      Do early quadriceps exercises affect the outcome of ACL reconstruction? A randomized controlled trial.
      ] used a protocol for quadriceps muscles training performed in a controlled angle extension chair (90°-45°) in patients with hamstring grafts, comparing early training initiation (4 weeks) to late training (12 weeks), and found no difference in functional variables or graft laxity at a 17-month follow-up.
      Closed-kinetic chain (CKC) exercises have been related to less pain and lower risk of graft loosening.
      After the third week, and depending on the patient's tolerance, eccentric exercises performed within limited ROM can be started because they produce better strength development than concentric ones [
      • van Melick N.
      • van Cingel R.E.
      • Brooijmans F.
      • Neeter C.
      • van Tienen T.
      • Hullegie W.
      • Nijhuis-van der Sanden M.W.
      Evidence-based clinical practice update: practice guidelines for anterior cruciate ligament rehabilitation based on a systematic review and multidisciplinary consensus.
      ,
      • Wright R.W.
      • Haas A.K.
      • Anderson J.
      • Calabrese G.
      • Cavanaugh J.
      • Hewett T.E.
      • Lorring D.
      • McKenzie C.
      • Preston E.
      • Williams G.
      MOON Group
      Anterior Cruciate Ligament Reconstruction Rehabilitation: MOON Guidelines.
      ] give some preference to CKC exercises, starting the modalities in OKC exercises (except SLR and isometrics) after six weeks, again within limited ROM.
      CKC and OKC exercises play an essential role in quadriceps muscle activation and strengthening. Furthermore, when neuromuscular electrical stimulation (NMES) is associated, it is more effective in strengthening the quadriceps muscle group than rehabilitation alone. [
      • van Melick N.
      • van Cingel R.E.
      • Brooijmans F.
      • Neeter C.
      • van Tienen T.
      • Hullegie W.
      • Nijhuis-van der Sanden M.W.
      Evidence-based clinical practice update: practice guidelines for anterior cruciate ligament rehabilitation based on a systematic review and multidisciplinary consensus.
      ,
      • Wright R.W.
      • Haas A.K.
      • Anderson J.
      • Calabrese G.
      • Cavanaugh J.
      • Hewett T.E.
      • Lorring D.
      • McKenzie C.
      • Preston E.
      • Williams G.
      MOON Group
      Anterior Cruciate Ligament Reconstruction Rehabilitation: MOON Guidelines.
      ].
      Recently, Toth et al. (2020) [
      • van Melick N.
      • van Cingel R.E.
      • Brooijmans F.
      • Neeter C.
      • van Tienen T.
      • Hullegie W.
      • Nijhuis-van der Sanden M.W.
      Evidence-based clinical practice update: practice guidelines for anterior cruciate ligament rehabilitation based on a systematic review and multidisciplinary consensus.
      ,
      • Wright R.W.
      • Haas A.K.
      • Anderson J.
      • Calabrese G.
      • Cavanaugh J.
      • Hewett T.E.
      • Lorring D.
      • McKenzie C.
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      MOON Group
      Anterior Cruciate Ligament Reconstruction Rehabilitation: MOON Guidelines.
      ] randomized 25 individuals with ACL injury, comparing the use of NMES and placebo NMES. In this study, all patients used placebo NMES or NMES for three weeks, preoperatively, and for three weeks, postoperatively, starting 72 hours after surgery, for 60 minutes, five days a week. The results demonstrate decreased atrophy in type II muscle fibers and preservation of contractility in type I muscle fibers.
      Therefore, strengthening or initial activation of quadriceps muscles must be carried out promptly and progressed according to tolerance to biological responses of the graft and the patient.
      Neuromuscular control is a critical aim to achieve the success of ACL rehabilitation. In addition to quadriceps strengthening, other strategies allow to improve the limb's motor control, aiming to develop dynamic unconscious joint motor control. Ghaderi et al. (2020) [
      • van Melick N.
      • van Cingel R.E.
      • Brooijmans F.
      • Neeter C.
      • van Tienen T.
      • Hullegie W.
      • Nijhuis-van der Sanden M.W.
      Evidence-based clinical practice update: practice guidelines for anterior cruciate ligament rehabilitation based on a systematic review and multidisciplinary consensus.
      ,
      • Wright R.W.
      • Haas A.K.
      • Anderson J.
      • Calabrese G.
      • Cavanaugh J.
      • Hewett T.E.
      • Lorring D.
      • McKenzie C.
      • Preston E.
      • Williams G.
      MOON Group
      Anterior Cruciate Ligament Reconstruction Rehabilitation: MOON Guidelines.
      ] demonstrated that neuro-training control could be beneficial even after rehabilitation. On the other hand, recent systematic reviews [
      • Andrade R.
      • Pereira R.
      • van Cingel R.
      • Staal J.B.
      • Espregueira-Mendes J.
      How should clinicians rehabilitate patients after ACL reconstruction? A systematic review of clinical practice guidelines (CPGs) with a focus on quality appraisal (AGREE II).
      ,
      • van Melick N.
      • van Cingel R.E.
      • Brooijmans F.
      • Neeter C.
      • van Tienen T.
      • Hullegie W.
      • Nijhuis-van der Sanden M.W.
      Evidence-based clinical practice update: practice guidelines for anterior cruciate ligament rehabilitation based on a systematic review and multidisciplinary consensus.
      ] recommend the use of neuromuscular control training (NCT) in rehabilitation protocols, although there is no specific NCT intervention[
      • Ardern C.L.
      • Taylor N.F.
      • Feller J.A.
      • Webster K.E.
      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.
      ,
      • van Melick N.
      • van Cingel R.E.
      • Brooijmans F.
      • Neeter C.
      • van Tienen T.
      • Hullegie W.
      • Nijhuis-van der Sanden M.W.
      Evidence-based clinical practice update: practice guidelines for anterior cruciate ligament rehabilitation based on a systematic review and multidisciplinary consensus.
      ].
      Returning to sports practice is the main focus of the ACLR. However, preventing new injury and re-rupturing after the ACLR is also a concern for both the medical team and the Athlete as it can reach 5% in the ipsilateral limb and 10% in the contralateral limb for the ACLR. [
      • Waldén M.
      • Hägglund M.
      • Magnusson H.
      • Ekstrand J.
      ACL injuries in men's professional football: a 15-year prospective study on time trends and return-to-play rates reveals only 65% of players still play at the top level 3 years after ACL rupture.
      ] The actual rate of return to the pre-injury sports level does not exceed 65%, while the rate of athletes who return to their desired at a competitive level longer than two years drops to 38%. [
      • van Melick N.
      • van Cingel R.E.
      • Brooijmans F.
      • Neeter C.
      • van Tienen T.
      • Hullegie W.
      • Nijhuis-van der Sanden M.W.
      Evidence-based clinical practice update: practice guidelines for anterior cruciate ligament rehabilitation based on a systematic review and multidisciplinary consensus.
      ].
      Vila et al. [95] followed elite soccer athletes who suffered ACL injuries for up to 19 years: most reinjuries occurred within two years after returning to the sport, both on ipsilateral to the ACLR and contralaterally. At the end of the follow-up, almost 20% of the athletes had suffered an ACL re-rupture.
      Tabled 1
      MAJOR PITFALLS OF ACL REHABILITATION
      • ⁃delay and inaccurate diagnosis of associated ligament injuries
      • neglecting the biological time frames of the graft
      • absence of a careful evaluation of patients' response during rehabilitation
      • ⁃inadequate management of patient's expectations

      Geographical Differences In Acl Rehabilitation

      Brazil

      Worldwide, ACL rehabilitation protocols have followed the advances in ACL surgical techniques and instruments, biomechanical studies, and a better understanding of graft healing and its integration to the bone tunnel. Firstly, a sizeable scientific production has occurred at centers in the United States, Europe and Australia. With world globalization, knowledge and experiences on ACL rehabilitation have become more available, especially with the advent of the internet, increasing this capacity exponentially, and allowing physicians and physiotherapists to access quality literature anywhere worldwide.
      In Brazil, the rehabilitation of ACL insufficiency has converged into a consensus regarding preoperative and postoperative approaches, closely connected to the literature updates. Based on large university centers, many research groups have been carrying out studies on the rehabilitation of ACL insufficiency, allowing Brazil to achieve a place in the hall of references on this subject. Moreover, since telerehabilitation has been introduced to the rehabilitation protocol, it has become popular in Brazil as a valuable alternative tool to offer information to patients and continue their rehabilitation even in pandemic times.

      Europe

      Europe is composed of many states, each with their own peculiarities. In this respect, there cannot be a Europe-wide approach. In general, the Nordic states have produced scientifically valid strong research in this field, and have shown, for example, that conservative management of ACL injuries can be feasible in selected individuals, and that structured rehabilitation produces consistently favourable results. In countries where a National Health Service is strongly radicated, and a finite expenditure health expenditure is available, research has focused on the health economics of given procedures. In this context, therefore, it is not surprising that in such countries it has been established that home rehabilitation is feasible, and can produce results similar to what achieved following formal rehabilitation in dedicated settings.
      Often, in Southern Europe research has focused on ‘the fastest return to sport’ paradigm, and it is therefore not surprising that reports have emerged of elite athletes return to first team duties in less than 100 days. Though eye catching, these reports do not necessarily stress that elite athletes are genetically gifted, are superbly trained and highly motivated: it is therefore understandable that they may be able to return to high level sport participation, but this does not imply that their feats are the norm in the weekend warriors.

      Australia

      Management of ACL injuries within Australia has largely historically paralleled practices described in this review, as Australian surgeons have often studied overseas in North America and the UK, and have also looked to literature from these regions for guidance. As such there has been a similar evolution from the era of open surgery with postoperative immobilization and very restricted rehabilitation protocols in the 1970’s and ‘80’s, to less invasive arthroscopic techniques with more accelerated rehabilitation protocols thereafter.
      Whilst traditional rehabilitation protocols have been largely time-based, with set time frames for progression through stages of the program and return to play, more recent protocols have emphasized safe return to sport, and performance-based progression through the sequential phases of rehabilitation. This has been driven by recognition of the need to minimise the high rate of reinjury, particularly in younger populations, and rehabilitation programs have therefore been developed around regular testing, using assessments that have high level evidence for predicting success of return to sport and risk of reinjury. What has also been recognized is the need to respect additional meniscal or chondral pathology that may require modification of rehabilitation time frame expectations. Well-structured preoperative injury rehabilitation, followed with individualized, performance-based postoperative rehabilitation and a graduated return to training and ultimately competition is a fundamental principle of managing these patients.
      A comprehensive postoperative testing protocol has both objective and subjective elements. Subjectively patients complete PROMS to measure performance and confidence (IKDC and ACL-RSI) and objective measures that include isokinetic strength testing, balance and agility testing, laximetry and high resolution MRI scans. In our practice high resolution MRI scans at 12 months postoperatively have proven useful in assessing the entire joint, but particularly assessing graft signal. Recent studies have demonstrated a relationship between increased graft signal and the risk of re-rupture, as well as improvements in signal in certain patients between 1 and 2 years, lending some credibility to possibly recommending a delay in return to sport in these patients [
      • Putnis S.E.
      • Oshima T.
      • Klasan A.
      • Grasso S.
      • Nery T.
      • Fritsch B.A.
      • Parker D.A.
      Magnetic resonance imaging 1 year after hamstring autograft anterior cruciate ligament reconstruction can identify those at higher risk of graft failure: An analysis of 250 cases.
      ]. Overall, we believe that once patients have completed the appropriate rehabilitation program, and successfully met the above objective and subjective criteria, their chance of successful return to sport with minimised reinjury risk has been optimized.

      Future perspectives

      Regarding the future of rehabilitation protocols for ACL insufficiency, biomechanical studies and technological advances could play an essential role in developing new approaches; however, neuromotor control, early knee mobilization, quadriceps activation should remain at the heart of rehabilitation protocols.
      Preventing an ACL injury and reinjury will remain major topics in rehabilitation. Studies addressing physical demands, potential muscle imbalances, inappropriate sports gestures, and injury risk factors related to each sports modality will contribute to develop new rehabilitation protocols and prevent their occurrence.
      The application of a PROM tailored for sports practitioners may meet the expectations in the patient's reports by offering a more detailed analysis of rehabilitation, and also helping to monitor and evaluate treatment outcomes, contributing to guide changes in ACL rehabilitation protocol.
      Return to sports after ACL reconstruction will remain a crucial rehabilitation protocol aim; the development of a comprehensive analysis of physical demands related to each modality of sport, level of sports training and competition, and assessment of athlete's biotype will continue to be the primary references to establish a customized strategy for return to sport.
      The care of the mental health of athletes should receive closer attention in a rehabilitation protocol, guiding the outcomes evaluation and helping to develop new rehabilitation strategies.
      Tabled 1
      FUTURE PERSPECTIVES IN ACL POSTOPERATIVE REHABILITATION
      • ⁃neuromotor control, early knee mobilization, quadriceps activation should remain at the heart of rehabilitation protocols
      • ⁃advances in prevention measures in ACL injury and reinjury
      • ⁃PROM tailored for sports practitioners may meet their expectations and contribute to improve rehabilitation protocols
      • ⁃new approaches to accelerate return to sports after ACL reconstruction
      • ⁃closer attention to Athlete's mental health care
      • ⁃telerehabilitation
      To sum up, the rehabilitation protocols following ACL injury have markedly changed since the 1960's. Rehabilitation plays an essential role in managing ACL injuries, but it cannot be fully standardized pre- or postoperatively. Pre- and postoperative rehabilitation should be based on an accurate clinical diagnosis, patients' understanding of their injury, graft tissue biology and biomechanics, surgical technique, and the patient's physical demands and expectations.

      Conflict of interest

      The authors declare that there is no conflict of interest for any author. We declare to be aware that failure to comply with this commitment will subject the violator to penalties and penalties provided for in the Copyright Protection Act (No. 9610, of 02/19/98).

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      Acknowledgments

      “We wish to thank Ana Karina Castro Zandona Rocha Piedade for the help given in preparing the Figure 1.”

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