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Paediatric reference anatomy for ACL reconstruction and secondary anterolateral ligament or lateral extra-articular tenodesis procedures

Open AccessPublished:May 16, 2022DOI:https://doi.org/10.1016/j.jisako.2022.04.008

      Abstract

      Objectives

      For iliotibial band (ITB) lateral extra-articular tenodesis or anterolateral ligamentous/capsular reconstruction with anterior cruciate ligament reconstruction, a clear understanding of the referenced anterolateral knee anatomy is critical—especially given the risk of injury to the physis or key anterolateral structures in the paediatric population, which is at high-risk for primary and secondary anterior cruciate ligament injury. The purpose of this study was to quantitatively assess the anatomy of the knee physes, paediatric lateral collateral ligament (LCL) origin, popliteus origin and ITB tibial insertion.

      Methods

      Nine paediatric cadaveric knee specimens with average age 4.2 years (range 2 months–10 years) underwent dissection to identify the LCL's and popliteus’ femoral origins and the ITB's tibial insertion. Metallic marking pins demarcated precise anatomic attachment sites, and subsequent computerised tomography scans enabled quantified measurements among them.

      Results

      LCL & Popliteus: On the femur, the popliteus origin lay consistently deep to the LCL and inserted both distally and anteriorly to the LCL, a mean distance of 4.6 mm (range 1.9–7.6; standard deviation 2.0). From the joint line, the LCL lay a mean distance of 12.5 mm proximally while the popliteus measured a mean of 8.2 mm. Both were consistently distal to the physis. The LCL was a mean distance of 4.4 mm (range 1.0–9.5) and the popliteus was a mean distance of 8.2 (range 1.7–12.5) from the physis. ITB insertion: The ITB insertion at Gerdy's tubercle had an average footprint measuring 28.2 mm2 (range 10.3–58.4) and the ITB centre lay proximal to the physis in 6 specimens (mean age 4.2 years, median 2.5 years) and distal in 3 specimens (mean age 1.5 years, median 4 months). Mean distance from the footprint centre to the physis was 1.6 mm proximal (range 7.1 proximal – 2.2 distal).

      Conclusion

      This study describes relative and quantitative positions of the femoral LCL and popliteus origins and tibial ITB attachment and their respective physeal relationships. Knowledge of paediatric anterolateral knee anatomy will help guide essential future research and procedures providing extra-articular anterolateral rotatory stabilisation and may help reduce iatrogenic physeal injury risk.

      Level of evidence

      N/A (descriptive anatomic study).

      Keywords

      What is already known?

      • Paediatric athletes are at high-risk for re-tear after anterior cruciate ligament (ACL) reconstruction, causing surgeons to consider combining ACL reconstructions with extra-articular stabilising techniques like lateral extra-articular tenodesis (LET) or anterolateral ligamentous/capsular (ALL) reconstruction.
      • In adults, these extra-articular stabilising techniques reference the anterolateral knee anatomy, specifically the lateral collateral ligament (LCL), popliteus tendon and ITB insertion at Gerdy's tubercle; however, data are sparse regarding the location of these structures for the paediatric population.
      • Knowledge of these structures’ anatomic relationships is essential to address the specific concerns in paediatric ligament reconstruction of iatrogenic physeal damage, growth arrest and deformity and to implement techniques for physeal-sparing tunnel placement.

      What are the new findings?

      • The popliteus attachment on the femur was found consistently anterior and distal to the LCL origin, which may help with the identification of appropriate femoral socket position.
      • The attachment of the popliteus and the LCL origin were consistently distal to the distal femoral physis, suggesting the placement of tunnels or sockets should be in the epiphysis. The femoral origin of this reconstructed tissue can be placed below the physis and above the joint line to avoid physeal injury.
      • The ITB insertion at Gerdy's tubercle possessed an inconsistent relationship to the physis—proximal to the physis in 6 specimens and distal in 3 specimens—that may promote surgeon preference to leave the ITB insertion intact and minimise additional tibial fixation.

      Introduction

      The anterolateral knee provides stability for both anterior translation and anterolateral rotation of the knee. Following ACL reconstruction, such stability is crucial to maximise the performance of outcome measures and minimise the risk of re-tear. Surgical techniques for optimal knee stabilisation continue to evolve for intra- and extra-articular techniques [
      • Monaco E.
      • Labianca L.
      • Conteduca F.
      • De Carli A.
      • Ferretti A.
      Double bundle or single bundle plus extraarticular tenodesis in ACL reconstruction? A CAOS study.
      ,
      • Hewison C.E.
      • Tran M.N.
      • Kaniki N.
      • Remtulla A.
      • Bryant D.
      • Getgood A.M.
      Lateral extra-articular tenodesis reduces rotational laxity when combined with anterior cruciate ligament reconstruction: a systematic review of the literature.
      ,
      • Getgood A.
      • Bryant D.
      • Firth A.
      • et al.
      Stability Group
      The Stability study: a protocol for a multicenter randomized clinical trial comparing anterior cruciate ligament reconstruction with and without Lateral Extra-articular Tenodesis in individuals who are at high risk of graft failure.
      ,
      • Getgood A.M.J.
      • Bryant D.M.
      • Litchfield R.
      • Heard M.
      • McCormack R.G.
      • Rezansoff A.
      • et al.
      Lateral extra-articular tenodesis reduces failure of hamstring tendon autograft anterior cruciate ligament reconstruction: 2-year outcomes from the STABILITY study randomized clinical trial.
      ]. Combined ACL reconstruction with LET or ALL reconstruction procedures continue to advance [
      • Getgood A.
      • Bryant D.
      • Firth A.
      • et al.
      Stability Group
      The Stability study: a protocol for a multicenter randomized clinical trial comparing anterior cruciate ligament reconstruction with and without Lateral Extra-articular Tenodesis in individuals who are at high risk of graft failure.
      ,
      • Getgood A.M.J.
      • Bryant D.M.
      • Litchfield R.
      • Heard M.
      • McCormack R.G.
      • Rezansoff A.
      • et al.
      Lateral extra-articular tenodesis reduces failure of hamstring tendon autograft anterior cruciate ligament reconstruction: 2-year outcomes from the STABILITY study randomized clinical trial.
      ,
      • Lemaire M.
      Rupture ancienne du ligament croisé antérieur du genou.
      ,
      • Macintosh D.
      • Darby T.
      Lateral substitution reconstruction.
      ] reflecting a growing body of evidence regarding the role of anterolateral structures as secondary stabilisers and the biomechanical impact of anterolateral injury and repair on tibial internal rotation [
      • Kittl C.
      • Inderhaug E.
      • Williams A.
      • Amis A.A.
      Biomechanics of the anterolateral structures of the knee.
      ,
      • Thein R.
      • Boorman-Padgett J.
      • Stone K.
      • Wickiewicz T.L.
      • Imhauser C.W.
      • Pearle A.D.
      Biomechanical assessment of the anterolateral ligament of the knee: a secondary restraint in simulated tests of the pivot shift and of anterior stability.
      ,
      • Noyes F.R.
      • Huser L.E.
      • Levy M.S.
      Rotational knee instability in ACL-deficient knees: role of the anterolateral ligament and iliotibial band as defined by tibiofemoral compartment translations and rotations.
      ]. These procedures may involve anatomic reconstruction of the anterolateral capsule and/or non-anatomic stabilising procedures of the anterolateral tissues either by free graft harvest or iliotibial band (ITB). In adults, studies have shown reduction in rotational laxity in ACL reconstruction combined with LET compared to those receiving ACL reconstruction alone [
      • Hewison C.E.
      • Tran M.N.
      • Kaniki N.
      • Remtulla A.
      • Bryant D.
      • Getgood A.M.
      Lateral extra-articular tenodesis reduces rotational laxity when combined with anterior cruciate ligament reconstruction: a systematic review of the literature.
      ], and studies on two-year complication rates and functional outcome scores for combined ACL and ALL reconstruction have shown promising results [
      • Sonnery-Cottet B.
      • Thaunat M.
      • Freychet B.
      • Pupim B.H.
      • Murphy C.G.
      • Claes S.
      Outcome of a combined anterior cruciate ligament and anterolateral ligament reconstruction technique with a minimum 2-year follow-up.
      ].
      ACL reconstruction procedures combined with extra-articular stabilising techniques are gaining interest and being evaluated for high-risk patient populations—especially paediatric athletes in which re-tear rates have been reported up to 29% of patients younger than 20 years of age [
      • Webster K.E.
      • Feller J.A.
      Exploring the high reinjury rate in younger patients undergoing anterior cruciate ligament reconstruction.
      ]. Physeal-sparing ACL reconstruction as described by Micheli and Kocher [
      • Kocher M.S.
      • Garg S.
      • Micheli L.J.
      Physeal sparing reconstruction of the anterior cruciate ligament in skeletally immature prepubescent children and adolescents. Surgical technique.
      ] utilises a harvested ITB to create a combined extra-articular tenodesis as well as intra-articular ACL reconstruction without drilling osseous tunnels and has shown excellent short-term [
      • Kocher M.S.
      • Garg S.
      • Micheli L.J.
      Physeal sparing reconstruction of the anterior cruciate ligament in skeletally immature prepubescent children and adolescents.
      ] and long-term [
      • Kocher M.S.
      • Heyworth B.E.
      • Fabricant P.D.
      • Tepolt F.A.
      • Micheli L.J.
      Outcomes of physeal-sparing ACL reconstruction with iliotibial band autograft in skeletally immature prepubescent children.
      ] outcomes. In a paediatric population, Wilson and Ellis [
      • Wilson P.L.
      • Wyatt C.W.
      • Wagner K.J.
      • Boes N.
      • Sabatino M.J.
      • Ellis Jr., H.B.
      Combined transphyseal and lateral extra-articular pediatric anterior cruciate ligament reconstruction: a novel technique to reduce ACL reinjury while allowing for growth.
      ] showed only a 5.3% reinjury rate with the combined transphyseal hamstring autograft and ITB LET procedure. Most recently, the multicentre, randomised control trial STABILITY [
      • Getgood A.
      • Bryant D.
      • Firth A.
      • et al.
      Stability Group
      The Stability study: a protocol for a multicenter randomized clinical trial comparing anterior cruciate ligament reconstruction with and without Lateral Extra-articular Tenodesis in individuals who are at high risk of graft failure.
      ] of young athletes with a high-risk of failure has shown that hamstring graft ACL reconstruction with ITB LET led to a statistically and clinically significant reduction in graft rupture and rotatory laxity at 24 months postoperatively [
      • Getgood A.M.J.
      • Bryant D.M.
      • Litchfield R.
      • Heard M.
      • McCormack R.G.
      • Rezansoff A.
      • et al.
      Lateral extra-articular tenodesis reduces failure of hamstring tendon autograft anterior cruciate ligament reconstruction: 2-year outcomes from the STABILITY study randomized clinical trial.
      ]. Furthermore, to evaluate the reported increased pain and possible lateral compartment over-constraint with added ITB LET, STABILITY also monitored functional outcomes and found them to be unaffected and not inferior to ACL reconstruction alone [
      • Getgood A.
      • Hewison C.
      • Bryant D.
      • Litchfield R.
      • Heard M.
      • Buchko G.
      • et al.
      Stability Study Group
      No difference in functional outcomes when lateral extra-articular tenodesis is added to anterior cruciate ligament reconstruction in young active patients: the stability study.
      ].
      The basis for any surgical reconstruction is precise knowledge of anatomy and biomechanics. Adult reconstructive techniques for ALL reconstruction and LET procedures reference the anterolateral knee anatomy, specifically the LCL, popliteus tendon and ITB insertion at Gerdy's tubercle. However, data have been sparse regarding the locations of these structures in the paediatric population, to say nothing of the controversy regarding the ALL as a discrete ligamentous structure (histological analysis of the purported ALL structure is highlighted recently by Iseki et al. [
      • Iseki T.
      • Rothrauff B.B.
      • Kihara S.
      • Novaretti J.V.
      • Shea K.G.
      • Tuan R.S.
      • et al.
      Paediatric knee anterolateral capsule does not contain a distinct ligament: analysis of histology, immunohistochemistry and gene expression.
      ]) or its several patterns of femoral attachment in adult and paediatric contexts [
      • Shea K.G.
      • Milewski M.D.
      • Cannamela P.C.
      • Ganley T.J.
      • Fabricant P.D.
      • Terhune E.B.
      • et al.
      Anterolateral ligament of the knee shows variable anatomy in pediatric specimens.
      ]. Specific to the paediatric population are concerns of iatrogenic physeal damage, growth arrest and deformity associated with ligament reconstruction procedures [
      • Shea K.G.
      • Apel P.J.
      • Pfeiffer R.P.
      • Traughber P.D.
      The anatomy of the proximal tibia in pediatric and adolescent patients: implications for ACL reconstruction and prevention of physeal arrest.
      ,
      • Shea K.G.
      • Belzer J.
      • Apel P.J.
      • Nilsson K.
      • Grimm N.L.
      • Pfeiffer R.P.
      Volumetric injury of the physis during single-bundle anterior cruciate ligament reconstruction in children: a 3-dimensional study using magnetic resonance imaging.
      ,
      • Shea K.G.
      • Grimm N.L.
      • Belzer J.S.
      Volumetric injury of the distal femoral physis during double-bundle ACL reconstruction in children: a three-dimensional study with use of magnetic resonance imaging.
      ]. The risks of growth disturbance and secondary deformity may be higher with peripheral physis or peri-chondral ring injury, which are closely associated with LET procedures [
      • Arkader A.
      • Skaggs D.L.
      Physeal injuries.
      ,
      • Shea K.G.
      • Grimm N.L.
      • Nichols F.R.
      • Jacobs Jr., J.C.
      Volumetric damage to the femoral physis during double-bundle posterior cruciate ligament reconstruction: a magnetic resonance imaging computer modeling study.
      ]. Furthermore, physeal-sparing ACL reconstruction techniques such as femoral all-epiphyseal tunnel drilling [
      • Shea K.G.
      • Cannamela P.C.
      • Fabricant P.D.
      • Terhune E.B.
      • Polousky J.D.
      • Milewski M.D.
      • et al.
      All-epiphyseal anterior cruciate ligament femoral tunnel drilling: avoiding injury to the physis, lateral collateral ligament, anterolateral ligament, and popliteus—a 3-dimensional computed tomography study.
      ,
      • Shea K.G.
      • Cannamela P.C.
      • Fabricant P.D.
      • Terhune E.B.
      • Polousky J.D.
      • Milewski M.D.
      • et al.
      Lateral radiographic landmarks for ACL and LCL footprint origins during all-epiphyseal femoral drilling in skeletally immature knees.
      ] have been established in the past studies to risk anterolateral ligamentous and tendinous knee structures. Understanding this specific anatomy may both maximise the surgical efficiency and clinical outcome, as well as minimise iatrogenic physeal injury to the growing knee.
      Thus, the purpose of this study was to quantitatively assess the anatomy of the paediatric LCL origin, the popliteus origin and the tibial insertion of the ITB, their relationships to physeal structures and ultimately how this anatomic information may influence surgical techniques for lateral extra-articular procedures.

      Materials and methods

      An institutional review board (IRB) deemed IRB approval was not necessary for this study, as it did not include patient identifiers, the use of genetic information or contact with patient families as per guidelines by Health and Human Services (www.hhs.gov). A tissue harvesting facility (Allosource, Centennial, CO, USA) sourced the cadaveric tissue, which possessed family consent for use in research purposes prior to conducting this study.
      Nine paediatric cadaveric knee specimens underwent dissection to identify the ligamentous femoral origin of the LCL, popliteus and tibial insertion of the ITB. The specimens possessed an age range of 2 months–10 years and were comprised of 7 males and 2 females (5 right, 4 left). Teams of three to four fellowship-trained orthopaedic surgeons conducted the dissections and placed marking pins to localise the central footprint of these structures as described below. Computed tomography (CT) scans (0.625 mm slices, GE Litespeed Scanner, Cincinnati, Ohio, USA) enabled the identification of the pin insertions onto the cortical bone as well as precise measurements among the pinned structures using the Osirix Imaging Software (v10.0.4).

      Coronal plane measurements of ITB insertion

      During the dissection, the team of surgeons placed four marking pins at the most superior, most inferior, most lateral and most medial aspects of the ITB insertion at Gerdy's (Fig. 1). On coronal CT image (Fig. 2), the location at which these pins entered the epiphysis or cortical bone formed the points defining the footprint of the ITB insertion. The relevant measurements for this structure included distances between the most superior and most inferior points and the most lateral and most medial points. Using these points, the team defined the centre of the ITB footprint at Gerdy's tubercle as the point as equidistant between these perimeter points. Lastly, the team calculated footprint size through the measurement of a best-fit ellipsoid area outlined by these perimeter points.
      Fig. 1
      Fig. 1Dissected specimen with marking pins was placed to denote studied structures. (a) Left knee of a 4-year-old specimen. On the femur, the larger-headed blue pin was placed at the popliteus’ origin, demonstrating the anterior and distal relationship to the smaller-headed blue pin placed at the LCL's origin. (b) Left proximal tibia of a 10-year-old specimen. ITB reflected inferiorly, exposing Gerdy's tubercle with green pins marking medial- and lateral-most extent and pink pins marking superior- and inferior-most points (inferior pin obscured by reflected ITB).
      Fig. 2
      Fig. 2CT images of specimens with pins marking anatomic structures. (a) Coronal CT view of proximal tibia with marker indicating most superior point of Gerdy's tubercle and its relationship to the physis and cartilaginous articular surface in this specimen. (b) Sagittal CT view of the left distal femur and proximal tibia with markers indicating key labelled structures. Compared to the LCL's origin, the popliteus’ origin is found anterior and distal. Relation to the physis and cartilaginous articular surface are clearly identified. CT, computed tomography; LCL, lateral collateral ligament.

      Sagittal plane measurements of LCL and popliteus origins

      The team also placed marking pins during the dissection at the origins of the LCL and popliteus tendon on the femur (Fig. 1). On sagittal CT, the location at which these pins entered the epiphysis or cortical bone similarly formed the reference points for the measurement of distances between these origins, as depicted in Fig. 2. The use of 3D CT renderings assisted with the identification of these locations, illustrated in Supplemental Fig. 1. Other relevant measurements surrounding these structures included their respective distances to the physis and to the joint line as well as the distance from the LCL origin to the cortex of the proximal-most aspect of the posterosuperior femoral condyle, exemplified in Fig. 2.

      Results

      ITB insertion

      The location of the centre of Gerdy's tubercle relative to the physis was proximal to the physis in 6 specimens and distal in 3 specimens. Mean distance from the footprint centre to the physis was 1.6 mm proximal (range 7.1 mm proximal to 2.2 mm distal). Fig. 3 depicts how this distance varied with respect to specimen age. Mean distance from the footprint centre to the joint line was 9.6 mm distal (range 5.4 mm proximal to 14.9 mm distal). The ITB insertion at Gerdy's tubercle had an average footprint measuring 28.2 mm2 (range 10.3–58.4). The distance from the tubercle's superior-most point to the inferior-most point was a mean 8.0 mm (4.6 & 16.1 mm). The distance from the tubercle's lateral-most point to the medial-most point found on the tubercle was a mean 4.5 mm (2.9 mm–8.3 mm). Table 1 provides per specimen measurements for these quantities, and Supplemental Fig. 2 depicts graphically how the dimensions and area of Gerdy's tubercle vary with respect to specimen age. To provide a normalised distance quantity taking into account varying specimen size, the distance from Gerdy's tubercle to the physis was also represented as a percent of the distance of Gerdy's tubercle to the joint line, provided in Table 1 and in Supplemental Fig. 3.
      Fig. 3
      Fig. 3ITB insertion distance to proximal tibial physis as a function of age, presented as clustered bar plot. ITB, iliotibial band.
      Table 1ITB insertion measurements.
      #AgeLateralityGT superior to inferiorGT lateral to medialArea of GTGT centre to physisGT centre to joint lineGT centre to physis, as % of GT centre to joint line
      I2 moL4.552.8910.32−1.18.113.6
      22 moR5.553.7316.254.17.4255.3
      32 moR5.34.418.311.425.4326.2
      44 moL4.64.817.33−1.66.0526.4
      52 yrsR5.812.9413.411.746.3227.5
      63 yrsR6.875.3929.070.5512.024.6
      74 yrsL14.134.4349.14−2.1614.914.5
      810 yrsL8.968.3158.457.0911.5561.4
      910 yrsR16.123.645.563.9414.1927.8
      # = refers to specimen number. GT = Gerdy's Tubercle. ∗ = For Gerdy's tubercle centre to physis measurements, negative values indicate Gerdy's tubercle centre being found distal to the physis. All distance units in mm unless specified.

      LCL & popliteus

      Of the 9 specimens, 7 had femurs available for CT measurements, with the LCL and popliteus tendon origins readily identified on each of these as exemplified in Fig. 2. On the femur, the popliteus was consistently found deep to the LCL and inserted both distally and anteriorly to the LCL at a mean distance of 4.6 mm (range 1.9 mm–7.6 mm). The LCL measured a mean distance of 12.5 mm (range 6.9 mm–20.4 mm) to the joint line while the popliteus measured a mean distance of 8.2 mm (range 1.3 mm–13.2) from the joint line. Both the LCL and popliteus were consistently distal to the physis for each of the 7 specimens. The LCL was a mean distance of 4.4 mm (range 1.0 mm–9.5 mm) and the popliteus was a mean distance of 8.2 (range 1.7 mm–12.5 mm), respectively. The LCL was a mean distance of 11.5 mm (range 7.7 mm–19.4 mm) from the posterosuperior femoral condyle. Table 2 provides per specimen measurements for these quantities. Fig. 4 along with Supplemental Fig. 4 depict how these distances vary with respect to specimen age. To provide a normalised distance quantity taking into account varying specimen size, the distances from LCL and popliteus to the physis were also represented as a percent of their respective distances to the joint line, provided in Table 2 and in Supplemental Fig. 3.
      Table 2LCL & popliteus femoral origin measurements.
      #AgeLateralityLCL to Pop.Pop. to joint lineLCL to joint linePop. to physis∗LCL to physis∗LCL to PSFCLCL to physis, as % of LCL to joint linePop. to physis, as % of Pop. to joint line
      12 moL1.8910.0711.2−1.73−1.018.8617.29.0
      22 moR2.735.66.92−8.58−7.069.14153.2102.0
      52 moR4.587.0611.9−7.99−3.3710.45113.228.3
      63 yrsR5.451.38.13−7.85−3.857.65603.847.4
      74 yrsL6.418.8215.03−9.58−3.2211.03108.621.4
      810 yrsL7.6213.2420.38−8.87−3.0413.6867.014.9
      910 yrsR3.7211.3914.17−12.46−9.5319.36109.467.3
      # = refers to specimen number. Pop. = popliteus. ∗ = for the popliteus and LCL measurements to the physis, negative values indicate the popliteus or LCL origin being found distal to the physis. PSFC = posterosuperior femoral condyle. All distance units in mm unless specified.
      Fig. 4
      Fig. 4LCL and popliteus origin measurements as a function of age, presented as clustered bar plot. (a) Depicts the distance of the LCL origin to the physis, (b) depicts the popliteus origin to the physis, and (c) depicts the distance between the LCL origin and the Posterosuperior Femoral Condyle (PSFC). LCL, lateral collateral ligament.

      Discussion

      The findings of this study provide a quantitative description of the anatomy of paediatric anterolateral knee structures which are key to stabilisation procedures such as LET or ALL reconstruction. In addition to the provided mean dimensions and distances among the aforementioned structures, physis and joint line, several relationships appreciated during this study merit emphasis. First, the popliteus attachment on the femur consistently lay anterior and distal to the LCL origin. Second, both the attachment of the popliteus and the LCL origin were consistently distal to the distal femoral physis. Third and by contrast, the ITB insertion at Gerdy's tubercle possessed an inconsistent relationship to the physis: proximal to the physis in 6 specimens and distal in 3. These relationships may guide physeal-respecting/protecting surgical technique development around the lateral aspect of the knee.
      A few studies have described the relationships of these structures in the paediatric context. One previous study of the paediatric anterolateral ligament anatomy notably reported a similar orientation of the popliteal and LCL origins relative to each other [
      • Shea K.G.
      • Cannamela P.C.
      • Fabricant P.D.
      • Terhune E.B.
      • Polousky J.D.
      • Milewski M.D.
      • et al.
      Lateral radiographic landmarks for ACL and LCL footprint origins during all-epiphyseal femoral drilling in skeletally immature knees.
      ]. LaPrade et al. demonstrated this same relationship in adult anatomy (mean age of 63 years) [
      • LaPrade R.F.
      • Ly T.V.
      • Wentorf F.A.
      • Engebretsen L.
      The posterolateral attachments of the knee. A qualitative and quantitative morphologic analysis of the fibular collateral ligament, popliteus tendon, popliteofibular ligament, and lateral gastrocnemius tendon.
      ], suggesting these structures’ relative positioning may be conserved throughout the process of skeletal maturity. Of note, the distance between these two structures reported in LaPrade et al. study is 18 mm, in contrast to 4.6 mm in this study, suggesting that these structures move farther apart with growth.
      Previous paediatric studies have reported relationships to the physis for some of these structures. One cadaveric study [
      • Shea K.G.
      • Milewski M.D.
      • Cannamela P.C.
      • Ganley T.J.
      • Fabricant P.D.
      • Terhune E.B.
      • et al.
      Anterolateral ligament of the knee shows variable anatomy in pediatric specimens.
      ] reported a median 9 mm between the LCL origin and femoral physis longer than the median 3.4 mm (mean 4.4 mm) reported in this study. Likely, this difference in median distance reflects a difference in specimen age between the studies’ cohorts: range 7–11 years with a median age of 8 years in the study from Shea et al. vs. range 2 months–10 years with a median age of 3 years for this study. To the best of the authors’ knowledge, little to no previous data exist that reports position of the reported anatomic landmarks with respect to the joint line.
      Elucidating the positions of these anterolateral knee landmarks in the context of paediatric anatomy can hopefully guide extra-articular stabilisation procedures such as LET and ALL reconstruction. On the femoral side, appreciating the position of the LCL origin relative to the popliteus may help with the identification of appropriate femoral socket position for ALL reconstruction [
      • Smith J.O.
      • Yasen S.K.
      • Lord B.
      • Wilson A.J.
      Combined anterolateral ligament and anatomic anterior cruciate ligament reconstruction of the knee.
      ]. Furthermore, given the LCL and popliteus origins being consistently distal to the physis, the placement of tunnels or sockets should be in the epiphysis. Of note, these structures—especially the more proximal LCL origin—lie a short distance from the physis and thus warrant caution when placing tunnels or sockets near them, especially given the undulating nature of the distal femoral physis [
      • Defrancesco C.J.
      • Storey E.P.
      • Shea K.G.
      • Kocher M.S.
      • Ganley T.J.
      Challenges in the management of anterior cruciate ligament ruptures in skeletally immature patients.
      ]. Techniques that allow drilling closer to the joint line would potentially create a greater margin of safety from these key structures. From the perspective of ACL reconstruction tunnel placement, this data provide information when using an all-epiphyseal technique, as outlined in past studies [
      • Shea K.G.
      • Cannamela P.C.
      • Fabricant P.D.
      • Terhune E.B.
      • Polousky J.D.
      • Milewski M.D.
      • et al.
      All-epiphyseal anterior cruciate ligament femoral tunnel drilling: avoiding injury to the physis, lateral collateral ligament, anterolateral ligament, and popliteus—a 3-dimensional computed tomography study.
      ,
      • Xerogeanes J.W.
      • Hammond K.E.
      • Todd D.C.
      Anatomic landmarks utilized for physeal-sparing, anatomic anterior cruciate ligament reconstruction: an MRI-based study.
      ], to produce tunnels that proceed from the ACL femoral footprint to exit posterior to the LCL origin or near the popliteus tendon insertion.
      On the tibial side, the variety of extra-articular tenodesis techniques available vary based on their treatment of the ITB insertion, such as maintaining the insertion [
      • Lemaire M.
      Rupture ancienne du ligament croisé antérieur du genou.
      ], detaching its insertion [
      • Ellison A.E.
      Distal iliotibial-band transfer for anterolateral rotatory instability of the knee.
      ], looping around with subsequent reattachment to an anterolateral tibial reinsertion point [
      • Losee R.E.
      • Johnson T.R.
      • Southwick W.O.
      Anterior subluxation of the lateral tibial plateau. A diagnostic test and operative repair.
      ] or utilisation of completely independent autograft or allograft [
      • Smith J.O.
      • Yasen S.K.
      • Lord B.
      • Wilson A.J.
      Combined anterolateral ligament and anatomic anterior cruciate ligament reconstruction of the knee.
      ,
      • Helito C.P.
      • Bonadio M.B.
      • Gobbi R.G.
      • da Mota e Albuquerque R.F.
      • Pécora J.R.
      • Camanho G.L.
      • et al.
      Combined intra- and extra-articular reconstruction of the anterior cruciate ligament: the reconstruction of the knee anterolateral ligament.
      ] in the area of the ITB. The variability of the position of the ITB attachment at Gerdy's tubercle relative to the physis should inform technique selection or implementation. For instance, due to this variability and concerns for physeal injury, a surgeon may prefer leaving the ITB insertion intact and minimising additional tibial fixation. Furthermore, the results of this study suggest that the ITB attachment at Gerdy's tubercle migrates farther away from the physis with increasing age—potentially between ages 4 and 10 in this study's data—and lies proximal to the physis at older ages closer to 10 years of age. Thus, for techniques where tibial fixation is necessary, surgeons should consider placing such fixation in older patients proximal to the physis or avoiding tibial fixation altogether by preserving the native ITB attachments on the tibia, if this tissue is used as part of an ALL/LET procedure.
      The limitations of this study include limited samples from each age, consistent with the reality that access to paediatric tissue for cadaveric/anatomic studies is severely limited. The specimens represented a wide age range, but the study was not able to determine correlation with measured quantities and age-adjusted expectations for the lateral knee structures. With inclusion of specimens less than 8 years old, the study's cohort's age range is also notably younger than that of paediatric patients most often receiving ACL reconstructions. Some studies have shown variation in knee ligament anatomy and physeal relationship with the growth and development in paediatric knees [
      • Shea K.G.
      • Martinson W.D.
      • Cannamela P.C.
      • Richmond C.G.
      • Fabricant P.D.
      • Anderson A.F.
      • et al.
      Variation in the medial patellofemoral ligament origin in the skeletally immature knee: an anatomic study.
      ,
      • Düppe K.
      • Gustavsson N.
      • Edmonds E.W.
      Developmental morphology in childhood patellar instability: age-dependent differences on magnetic resonance imaging.
      ], including younger specimens in this study still can provide clinically relevant insight for older skeletally immature patients with open physes. First, the discussed anatomic relationships that are consistent between young patients <1 year of age and adult populations highly suggest the same consistent relationship in older pre-pubescent or adolescent anatomy. Second, despite the size of knees varying considerably between infant and 10-year-old specimens, this contributes to establishing the consistency of structures’ relationship to the physis across a range of development; as discussed, this consistency can potentially guide how a surgeon might choose an LET technique for combined ACL reconstruction or place tunnels for all-epiphyseal ACL reconstruction in older skeletally immature patients with open physes. Furthermore, studies on paediatric ACL injuries or combined ACL reconstruction outcomes have been shown to include patients as young as 5.7 years of age [
      • Kocher M.S.
      • Heyworth B.E.
      • Fabricant P.D.
      • Tepolt F.A.
      • Micheli L.J.
      Outcomes of physeal-sparing ACL reconstruction with iliotibial band autograft in skeletally immature prepubescent children.
      ] and more frequently patients of 9–11 years of age and also have shown an increase of injuries in the age bracket of 5–12 and 5–14 years old [
      • Webster K.E.
      • Feller J.A.
      Exploring the high reinjury rate in younger patients undergoing anterior cruciate ligament reconstruction.
      ,
      • Stracciolini A.
      • Stein C.J.
      • Zurakowski D.
      • Meehan 3rd, W.P.
      • Myer G.D.
      • Micheli L.J.
      Anterior cruciate ligament injuries in pediatric athletes presenting to sports medicine clinic: a comparison of males and females through growth and development.
      ,
      • Shaw L.
      • Finch C.F.
      Trends in pediatric and adolescent anterior cruciate ligament injuries in Victoria, Australia 2005–2015.
      ,
      • Bloom D.A.
      • Wolfert A.J.
      • Michalowitz A.
      • Jazrawi L.M.
      • Carter C.W.
      ACL injuries aren’t just for girls: the role of age in predicting pediatric ACL injury.
      ], overlapping with the older specimens in this study. This study's cohort also consisted of more male specimens than female specimens; therefore, the extrapolation of any data may face limits due to skewed sex representation. Future studies building on this work should incorporate older paediatric specimens with more balanced sex representation if more of these exceptionally rare specimens become available. Additionally, given the findings regarding the position of the ITB attachment relative to the physis, another future direction of interest could consist of biomechanical analysis comparing LET procedures with ITB that insert proximally to the physis with those that insert distally.
      Paediatric athletes as a group are at high-risk for re-tear of their reconstructed ACL [
      • Webster K.E.
      • Feller J.A.
      Exploring the high reinjury rate in younger patients undergoing anterior cruciate ligament reconstruction.
      ], causing surgeons to consider and evaluate LET and ALL reconstruction techniques as adjuncts to ACL reconstruction with recently promising outcomes for this high-risk group [
      • Getgood A.M.J.
      • Bryant D.M.
      • Litchfield R.
      • Heard M.
      • McCormack R.G.
      • Rezansoff A.
      • et al.
      Lateral extra-articular tenodesis reduces failure of hamstring tendon autograft anterior cruciate ligament reconstruction: 2-year outcomes from the STABILITY study randomized clinical trial.
      ,
      • Wilson P.L.
      • Wyatt C.W.
      • Wagner K.J.
      • Boes N.
      • Sabatino M.J.
      • Ellis Jr., H.B.
      Combined transphyseal and lateral extra-articular pediatric anterior cruciate ligament reconstruction: a novel technique to reduce ACL reinjury while allowing for growth.
      ,
      • Getgood A.
      • Hewison C.
      • Bryant D.
      • Litchfield R.
      • Heard M.
      • Buchko G.
      • et al.
      Stability Study Group
      No difference in functional outcomes when lateral extra-articular tenodesis is added to anterior cruciate ligament reconstruction in young active patients: the stability study.
      ,
      • Defrancesco C.J.
      • Storey E.P.
      • Shea K.G.
      • Kocher M.S.
      • Ganley T.J.
      Challenges in the management of anterior cruciate ligament ruptures in skeletally immature patients.
      ]. Work to evaluate these procedures and optimise their outcomes requires an understanding of the lateral knee anatomy, including the LCL, popliteus and Gerdy's tubercle. This study provides an evaluation of such structures and their relationships unique to the paediatric population.

      Conclusion

      This study quantitatively describes the paediatric anterolateral knee anatomy commonly referenced in descriptions of the anterolateral ligament and techniques for lateral extra-articular reconstruction. Knowledge of the relative and quantitative positions of the LCL and popliteus origins on the femur and ITB attachment at Gerdy's tubercle on the tibia and their respective relationships to the physes will help guide extra-articular procedures that provide extra-articular anterolateral rotatory stabilisation in the paediatric patients and may help reduce the risk of iatrogenic physeal injury.

      Funding

      This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

      Declaration of competing interest

      Based on signed ICMJE disclosure forms from each author, the following authors reported the below declarations.
      Dr. Philip Wilson:
      • -
        Pylant Medical, educational support in 2018 (cadaveric supply, <3000$) and not related to this study
      Dr. Daniel Green:
      • -
        Royalties and licenses: Arthrex Inc., Pega Medical
      • -
        Consulting fees: Arthrex Inc.
      • -
        Payment or honoraria for lectures, presentations, speakers bureaus, manuscript writing or educational events: AO Trauma International, Arthrex Inc.
      Dr. Peter Fabricant:
      • -
        Participation on a Data Safety Monitoring Board or Advisory Board: On editoral and governing board for Clinical Orthopaedics and Related Research, Paediatric Orthopaedic Society of North America, Research in Osteochondritis of the Knee (ROCK)
      Dr. Theodore Ganley:
      • -
        Other from Vericel Corporation, other from Arthrex, other from AlloSource, outside the submitted work; and The American Journal of Sports Medicine -- associate editor, Paediatric Research in Sports Medicine (PRiSM) -- committee member, American Academy of Paediatrics Section on Orthopaedics -- board or committee member, International Paediatric Orthopaedic Symposium (IPOS) -- board or committee member, POSNA -- committee member, AAOS -- board or committee member.
      Dr. Henry Ellis:
      • -
        Grants from POSNA, grants from AAOS, outside the submitted work; and Texas Orthopaedic Association - Board of Directors; Paediatric Research in Sports Medicine (PRiSM) - Board of Directors.

      Acknowledgements

      The authors thank Tom CyCota, CEO, and Todd Huft of Allosource (Centennial, CO, USA) for the donation of the cadaveric specimens and non-financial research support. We are grateful to the families that made these remarkable donations to allow us to continue to improve patient care and outcomes.

      Appendix A. Supplementary data

      The following is the Supplementary data to this article:

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