Ahn et al. Knee Surgery & Related Research (2019) 31:12 Knee Surgery https://doi.org/10.1186/s43019-019-0012-4 & Related Research REVIEW ARTICLE Open Access The anterolateral ligament of the knee joint: a review of the anatomy, biomechanics, and anterolateral ligament surgery Ji Hyun Ahn1*, Nilay A. Patel2, Charles C. Lin3 and Thay Q. Lee4 Abstract Residual knee instability and low rates of return to previous sport are major concerns after anterior cruciate ligament (ACL) reconstruction. To improve outcomes, surgical methods, such as the anatomical single-bundle technique or the double-bundle technique, were developed. However, these reconstruction techniques failed to adequately overcome these problems, and, therefore, new potential answers continue to be of great interest. Based on recent anatomical and biomechanical studies emphasizing the role of the anterolateral ligament (ALL) in rotational stability, novel surgical methods including ALL reconstruction and anterolateral tenodesis have been introduced with the possibility of resolving residual instability after ACL reconstruction. However, there is still little consensus on many aspects of the ALL, including: several anatomical issues, appropriate indications for ALL surgery, and the optimal surgical method and graft choice for reconstruction surgery. Therefore, further studies are necessary to advance our knowledge of the ALL and its contribution to knee stability. Keywords: Anterior cruciate ligament, Knee instability, Anterolateral ligament, ALL reconstruction, Anterolateral tenodesis Background synergistic relationship with the ACL with respect to rota- Anterior cruciate ligament (ACL) reconstruction has im- tional knee stability [2–4]. Despite some arguments against proved significantly over the last several decades due to bet- the efficacy of extra-articular ALL reconstruction [7–10], ter understanding of anatomy and technical advancements several biomechanical studies have reported that the in surgical techniques, resulting in satisfactory results in the addition of extra-articular ALL reconstruction showed su- majority of cases. Despite these advancements, some pa- perior outcomes compared to intra-articular ACL recon- tients continue to experience unsatisfactory outcomes with struction alone, especially with regards to objective residual knee instability after conventional ACL reconstruc- postoperative knee stability [11–14]. However, there is no tion [1]. To address this issue, there has been recent focus consensus on several anatomical issues, including the bony on adding additional extra-articular augmentation to ACL origin and insertion of the ALL, and the change in ALL reconstruction, specifically with augmentation or recon- length with knee flexion [4–6, 15–19]. Due to this, the opti- struction of the anterolateral ligament (ALL) [2–6]. The mal surgical technique is still debated, with outstanding is- ALL is a ligament on the lateral aspect of the knee, anterior sues of ideal graft choice [20, 21], location of fixation, and to the fibular collateral ligament. Recent anatomical and fixation angle [11, 22–24] still unresolved. In the aspect of biomechanical studies have reported on the role of this the surgical indications, the additional ALL surgery is usually extra-articular anterolateral structure, demonstrating its recommended for the revision surgery or the ACL-deficient knee with a high-grade pivot-shift test [22, 23]. Recently, its * Correspondence: [email protected] surgical indications have been extended to chronic ACL 1Department of Orthopaedic Surgery, Dongguk University Ilsan Hospital, 814 rupture, concomitant meniscal repair, or pivoting activities Siksadong, Ilsandonggu, Goyangsi, Gyeonggido 411-773, Korea [25]. But there is still no consensus for the appropriate Full list of author information is available at the end of the article © The Author(s). 2019 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Ahn et al. Knee Surgery & Related Research (2019) 31:12 Page 2 of 7 surgical indication. The purpose of this review is to highlight the findings of the current literature on the anatomy of the ALL, the function and biomechanics of the ALL, the techniques for ALL surgery, and its clinical outcomes. Anatomy Prevalence Among the various names used to refer to this ligament- ous structure, such as the “mid-third lateral capsular ligament” and the “capsulo-osseous layer of the iliotibial band (ITB),” the term “anterolateral ligament (ALL)” has been the most widely accepted. Paul Segond, a French surgeon, first reported the presence of the ALL in 1879 [26]. In 2013, Claes et al. further described the presence and characteristics of the ALL [6]. In this study, 41 Fig. 1 Photograph of dissected specimen. ALL anterolateral ligament, unpaired human cadaveric knees were examined and the LCL lateral collateral ligament, FH fibular head, GT Gerdy’s tubercle, ITB ALL was found as a well-defined ligamentous structure, iliotibial band, BF biceps femoris, LFE lateral femoral epicondyle clearly distinguishable from the anterolateral joint capsule in all but one of the cadaveric knees (97%) [6]. In another cadaveric study by Helito et al. [27], the osseous layer of the ITB. Helito et al. have even suggested ALL was found in all dissected anatomical specimens that the ALL consists of two separate layers: the superficial out of 10 specimens (eight knees from men and two layer located immediately under the ITB and another from women). Kennedy et al. also reported that they deeper layer located within the anterolateral capsule [17]. could identify the ALL as a ligamentous structure in all Magnetic resonance imaging (MRI) has been reported 15 nonpaired, fresh-frozen human cadaveric knees [4]. as a useful modality to identify the ALL injury in recent Daggett et al. reported that the ALL was present in all studies. It is suggested that MRI on injured knees pro- 52 specimens of embalmed cadaveric knees [18]. vides better visualization of the ALL than on intact However, several anatomical studies did not show 100% knees. Soft-tissue inflammation and joint effusion may prevalence of the ALL. Runer et al. defined the ALL as a provide signal intensification, leading to this observation ligamentous structure at the anterolateral side of the knee, [22, 28]. The assessment of the ALL injury varied with a bony origin at the lateral epicondylar region and an between using 1.5-T and 3.0-T MRIs. The recent MRI oblique course to a bony insertion at the anterolateral study suggested that 3.0-T MRI may provide increased proximal tibia [16]. After removing the superficial, deep visualization [29]. The insertion of the ALL into the and capsular-osseous layer of the ITB, the ALL could be proximal tibia just distal to the lateral joint line was well clearly identified only in 45.5% (n =20)ofthedissected identified in most studies [22, 25, 28–33]. The origin on knees according to their definition. Recently, Roessler the distal femur was difficult to visualize because of the et al. suggested that the ALL could be identified as an in- close proximity of other lateral structures such as the dependent ligamentous structure in front of the anterola- LCL, popliteus tendon and ITB [22]. The variability in teral joint capsule in only 60% (n =12)of thedissected identifying the ALL through the dissections in previous knee joints [15]. anatomical studies may also explain the various results These previous studies dealing with the presence and in the identification of the ALL injury in MRI studies. prevalence of the ALL [4, 6, 15, 16, 27] have generally Monaco et al. reported that MRI is highly sensitive, spe- used similar dissection protocols to access the ALL. The cific, and accurate for the detection of abnormalities of ITB was sharply detached from the intermuscular the ALL and anterolateral capsule and shows a high per- septum, and the lateral retinaculum and the fibers were centage of agreement with surgical findings [30]. They reflected up from their insertion at Gerdy’s tubercle. proved that the percentage agreement between MRI and With the knee flexed at 60° and the tibia maximally in- surgical findings was 88% for ALL and anterolateral cap- ternally rotated, the firm fibers running from the lateral sule injuries through the surgical exploration in acute epicondyle of the femur to the anterolateral portion of ACL-injured knees. In a recent systemic review, the ALL the tibia were unveiled (Fig. 1). Despite the application appeared on the MRI findings in 51–100% of all assessed of similar dissection protocols, the prevalence of the 2427 knees in a total of 24 studies [28]. This study ALL has ranged between 45.5 and 100%. These confus- suggested that high variability was found in the identifi- ing results could be due to the unclear anatomical defin- cation of normal and injured ALL in MRI, and the entire ition to distinguish between the ALL and the capsular- portion of the ligament was often not seen. 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