Current Concepts of the Anterolateral Ligament of the Knee
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Clinical Sports Medicine Update Current Concepts of the Anterolateral Ligament of the Knee Anatomy, Biomechanics, and Reconstruction Matthew J. Kraeutler,*y MD, K. Linnea Welton,y MD, Jorge Chahla,z MD, PhD, Robert F. LaPrade,z§ MD, PhD, and Eric C. McCarty,y MD Investigation performed at CU Sports Medicine and Performance Center, University of Colorado School of Medicine, Department of Orthopedics, Boulder, Colorado, USA In 1879, Paul Segond described an avulsion fracture (now known as a Segond fracture) at the anterolateral proximal tibia with the presence of a fibrous band at the location of this fracture. Although references to this ligament were occasionally made in the anat- omy literature after Segond’s discovery, it was not until 2012 that Vincent et al named this ligament what we know it as today, the anterolateral ligament (ALL) of the knee. The ALL originates near the lateral epicondyle of the distal femur and inserts on the proximal tibia near Gerdy’s tubercle. The ALL exists as a ligamentous structure that comes under tension during internal rotation at 30°.Inthe majority of specimens, the ALL can be visualized as a ligamentous structure, whereas in some cases it may only be palpated as bundles of more tense capsular tissue when internal rotation is applied. Biomechanical studies have shown that the ALL functions as a secondary stabilizer to the anterior cruciate ligament (ACL) in resisting anterior tibial translation and internal tibial rotation. These biomechanical studies indicate that concurrent reconstruction of the ACL and ALL results in significantly reduced internal rotation and axial plane tibial translation compared with isolated ACL reconstruction (ACLR) in the presence of ALL deficiency. Clinically, a variety of techniques are available for ALL reconstruction (ALLR). Current graft options include the iliotibial (IT) band, gracilis ten- don autograft or allograft, and semitendinosus tendon autograft or allograft. Fixation angle also varies between studies from full knee extension to 60° to 90° of flexion. To date, only 1 modern study has described the clinical outcomes of concomitant ALLR and ACLR: a case series of 92 patients with a minimum 2-year follow-up. Further studies are necessary to define the ideal graft type, location of fixation, and fixation angle for ALLR. Future studies also must be designed in a prospective comparative manner to com- pare the clinical outcomes of patients undergoing ACLR with ALL reconstruction versus without ALL reconstruction. By discovering the true effect of the ALL, investigators can elucidate the importance of ALLR in the setting of an ACL tear. Keywords: anterolateral ligament; anterior cruciate ligament reconstruction; allograft; autograft; biomechanics In 1879, Paul Segond described an avulsion fracture (now internal rotation (of the knee).’’13 Although references to known as a Segond fracture) at the anterolateral proximal this ligament were occasionally made in the anatomy liter- tibia.13 At the location of this fracture, Segond noted the ature after Segond’s discovery,10 it was not until 2012 that presence of a ‘‘pearly, resistant, fibrous band which invari- Vincent et al65 named this ligament what we know it as ably showed extreme amounts of tension during forced today, the anterolateral ligament (ALL). Interestingly, most credit for the ‘‘rediscovery’’ of the ALL has been given to Claes et al,13 who in 2013 published a detailed anatomic *Address correspondence to Matthew J. Kraeutler, MD, CU Sports description of the ALL as found in a series of cadaveric Medicine and Performance Center, 2150 Stadium Drive, 2nd Floor, Boul- knees. Since this time, many authors have tested the biome- der, CO 80309, USA (email: [email protected]). yUniversity of Colorado School of Medicine, Department of Orthope- chanics of the ALL in an effort to determine the anatomic dics, Aurora, Colorado, USA. function of the ALL, the effect of ALL rupture on knee kine- zSteadman Philippon Research Institute, Vail, Colorado, USA. matics, and the effect of ALL reconstruction using various § The Steadman Clinic, Vail, Colorado, USA. graft sources. The purpose of this Current Concepts review One or more of the authors has declared the following potential con- flict of interest or source of funding: R.F.L. receives IP royalties from is to highlight the findings of the current literature on the Arthrex, Ossur, and Smith & Nephew; receives research support from native anatomy of the ALL, the function and biomechanics Arthrex, Linvatec, Ossur, and Smith & Nephew; and is a paid consultant of the ALL, and techniques for ALL reconstruction. for Arthrex, Ossur, and Smith & Nephew. E.C.M. receives IP royalties from Biomet; receives research support from Biomet, Mitek, Smith & Nephew, and Stryker; and is a paid consultant for Biomet. PREVALENCE The American Journal of Sports Medicine, Vol. XX, No. X DOI: 10.1177/0363546517701920 Debate exists as to the presence and prevalence of the Ó 2017 The Author(s) ALL, enough that some authors have questioned whether 1 2 Kraeutler et al The American Journal of Sports Medicine Figure 1. Anatomy of the anterolateral ligament (ALL). Note the origin of the ALL near the lateral epicondyle of the femur and inserting on the proximal tibia between the fibular head and Figure 2. Lateral meniscal insertion of the anterolateral liga- Gerdy’s tubercle. The ALL overlaps with the fibular collateral lig- ment (ALL). Thin black line represents the ALL. Black arrow ament (FCL) near its femoral origin. LM, lateral meniscus; PFL, points to collagen fibers of the ALL inserting onto the lateral popliteofibular ligament; PLT, popliteus tendon. meniscus (LM). FCL, fibular collateral ligament; LE, lateral epicondyle; PTFJ, proximal tibiofibular joint. the ALL is fact or fiction.43 Ingham et al29 performed knee dissections on 58 specimens from 24 different animal spe- and lateral collateral ligament (LCL).33,63 The length of the cies and did not find the ALL in any of the specimens. In ALL also increases with internal tibial rotation.72 studies of human specimens, the ALL has been identified The ALL originates on the femur either directly on the as a distinct anatomic structure in 12% to 100% of speci- lateral epicondyle or posterior and proximal to the lateral mens.14,23,49,58,68 Given the results of these studies, there epicondyle (Figure 1).14,16 The ligament attaches to the has been a call for a better understanding of the anterolat- femur in a fanlike shape with an average attachment eral knee anatomy,36 with some authors suggesting that area at its femoral origin of 67.7 mm2.14,31 The ligament through careful dissection with a clear knowledge of the may attach posterior and proximal or anterior and distal anatomic insertions of the ALL, this ligament can be iden- to the attachment site of the LCL.23,31,63 The ALL overlaps tified in all human cases.55 with the LCL near its femoral origin. At the femoral origin, the mean diameter of the ALL is 11.85 mm.14 ANATOMY Between the femur and tibia, dense collagen fibers of the ALL insert onto the external surface of the lateral The ALL exists as a ligamentous structure that comes under meniscus (Figure 2). The site of meniscal insertion is tension during internal rotation at 30°.31 In the majority of between the anterior horn of the lateral meniscus and specimens, the ALL can be visualized as a ligamentous struc- the lateral meniscus body, with a mean attachment length ture, whereas in some cases it may only be palpated as bun- of 5.6 mm.22 Four types of meniscal attachment may be dles of more tense capsular tissue when internal rotation is appreciated: complete, central, bipolar, or inferior-only.35 applied.60 The ligament originates on the femur and inserts At the tibia, the ALL has an average attachment area of on the tibia, with a mean length at full extension of 33 to 53.0 to 64.9 mm2 and attaches an average of 24.7 mm pos- 37.9mm,ameanwidthof7.4mm,ameanthicknessof terior to the center of Gerdy’s tubercle and 26.1 mm prox- 2.7 mm, and a mean cross-sectional area of 1.54 mm2.23,25,71 imal to the anterior margin of the fibular head.8,31 The The ALL is not an isometric ligament.25,33,63,72 The length of tibial insertion site of the ALL can be found an average the ligament increases with knee flexion, to a degree which of 9.5 mm distal to the joint line and just proximal to the depends on the relationship of the femoral origin of the ALL tibial insertion of the biceps femoris.8,31 AJSM Vol. XX, No. X, XXXX Current Concepts of the Anterolateral Ligament 3 BIOMECHANICS On the basis of magnetic resonance imaging (MRI) of 206 patients undergoing ACL reconstruction, Claes et al12 Several studies have tested the biomechanical properties of described radiological abnormalities in 78.8% of knees, with the ALL, with a mean ultimate load to failure measured the majority seen in the distal (tibial) portion of the ligament. between 50 and 205 N, a mean stiffness of 20 to 42 N/mm, In a similar study, van Dyck et al64 found ALL abnormalities and a mean ultimate strain of 36%.21,31,71 Through biome- in 46% of 90 knee MRIs of patients with an acute ACL rup- chanical testing, failure of the ALL has been shown to occur ture. Furthermore, van Dyck et al64 found that patients with by a variety of mechanisms, including ligamentous tear at an abnormal ALL on MRI were significantly more likely to the femoral or tibial insertions, intrasubstance tears, and have a lateral meniscal tear (P = .008), collateral ligament complete detachment from the tibia with an associated injury (P .05), and osseous injury (P = .0037) compared bony avulsion (Segond fracture).31 with patients with an intact ALL.