Introduction
After the ‘rediscovery’ of the anterolateral ligament (ALL) by Claes et al. in 2013, there was considerable controversy regarding whether this structure even existed. Several authors reported that they were unable to identify its presence in a proportion of dissection specimens, or even at all. This confusion arose because of the complex anatomy of structures around the lateral epicondyle, inconsistent application of the nomenclature used in the literature and the use of incorrect dissection protocols. However, a wealth of subsequent anatomical and biomechanical studies have allowed the scientific community to bypass this early confusion. There is now widespread agreement regarding key anatomical parameters and international consensus that the ALL has an important role as a stabiliser of coupled anterior translation and internal rotation near extension. Furthermore, clinical studies from multiple groups have demonstrated that combined anterior cruciate ligament (ACL) and ALL reconstruction offers significant advantages over isolated ACL reconstruction with respect to graft rupture rates, knee laxity parameters, meniscal repair protection and functional outcome measures, including return to sport. This chapter provides an overview of the relevant anatomy and biomechanics, surgical technique and clinical outcomes.
Anatomy
Much of the controversy related to the ALL has arisen because of early confusion regarding the anatomy, which then led to flawed biomechanical studies. The nomenclature used to describe the structures of the anterolateral complex has also added confusion because it has been inconsistently and interchangeably applied. It is suggested that the terms middle third capsular ligament, anterolateral femorotibial ligament, capsulo-osseous layer iliotibial band (ITB), anterolateral ligament, short lateral ligament, lateral capsular ligament and ligamentum tractotibiale have all been used to describe the same structure. However, the original anatomical descriptions do not precisely match, and ambiguity remains regarding whether the authors really were describing the same structures. In 2017 the international ALC consensus group agreed that the structures of the anterolateral complex were the superficial iliotibial band and iliopatellar band, the deep ITB (Kaplan fibres, retrograde condylar attachment continuous with the capsulo-osseous layer) and the anterolateral ligament. However, an anatomical study and reanalysis of the nomenclature of the ALC has called for abandonment of the term capsulo-osseous layer . The authors highlighted that most previous dissection studies have used an anterior approach, but that using a posterior approach gives a completely different perspective and allows a more precise understanding of the anatomy. By using both approaches the authors were able to clearly define the anatomy and reported that no structure matching the original description of the capsulo-osseous layer could be identified. Specifically, and like Claes, they reported that there was no connection between the deep surface of the ITB and the ALL. The authors recommended abandonment of the term capsulo-osseous layer not simply because a structure matching the description could not be identified but also because the terms anterolateral ligament and condylar attachment of the distal ITB clarify the anatomically discrete nature of these structures ( Fig. 10.1 ).
Another major source of confusion in understanding the anatomy has been the fact that some authors simply could not find any structure resembling an anterolateral ligament and even suggested that it could be fictitious. Helito et al. in a systematic review demonstrated that the failure to identify the ALL was significantly correlated to the use of embalmed specimens. It was reported that when the authors of included studies had used fresh specimens, they typically reported identification in all or at least a large proportion of specimens, but if embalmed specimens had been used, then failure to identify the ALL was common. Despite this early confusion, there is now a wealth of anatomical and imaging studies clearly demonstrating the anatomy of this structure and widespread consensus that it exists as a capsular ligament in Seebacher layer III of the lateral aspect of the knee. ,
The fact that the use of embalmed specimens has made identification of the ALL difficult also explains why there has been confusion regarding the precise location of the femoral origin. In 2013 Claes et al. described a femoral origin anterior to the lateral collateral ligament (LCL) in embalmed specimens. Although some subsequent authors also agreed with this finding, the majority described a position proximal and posterior to the lateral epicondyle ( Fig. 10.2 ). , Helito et al. demonstrated in a systematic review that since 2012 there had been an increasing trend to report a proximoposterior position and in 2017 no anatomical studies published in the English language reported an alternative location. There is now international consensus that this is the correct location. Ariel de Lima et al. summarised some of the key parameters of the ALL reported in the literature:
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length typically 33 to 42 mm (range 30 to 59 mm)
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width 4 to 7 mm
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thickness 1 to 2 mm
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anteroinferior trajectory (with an attachment to meniscus) attaches midway between Gerdy tubercle and fibular head
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4 to 7 mm below joint line
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mean load to failure approximately 180 N
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mean stiffness 31 N/mm
Histology
Several authors have reported that the ALL contains strictly organised dense collagen bundles. , , In contrast, the adjacent capsule has a disorganised structure. Smeets et al. reported that the ALL has structural characteristics similar to another capsular ligament, the inferior glenohumeral ligament. They also demonstrated that the mechanical properties (elastic modulus, ultimate stress, ultimate strain at failure and strain energy density) of the ALL were significantly different than the adjacent capsule and consistent with those of the inferior glenohumeral ligament (IGHL), thus confirming its true ligamentous nature from a histological and mechanical perspective.
Biomechanics
The proximoposterior location of the femoral attachment of the ALL results in a structure that is anisometric. When the knee is flexed at 90 degrees, the ALL is lax, allowing physiological internal rotation. However, when the knee is close to extension, the ALL is taut and resists internal rotation. Sectioning studies of the ALL and ITB demonstrate that both structures are important secondary restraints to the pivot shift and that they work in conjunction with the ACL to confer knee stability. , The important role of the ALL in controlling the pivot shift was further confirmed by Monaco et al., who demonstrated that isolated cutting of the ACL typically does not result in high-grade pivot shift. However, if the anterolateral structures are also cut, the occurrence of high-grade pivot shift is almost universal. The important role of the anterolateral structures in the control of knee stability in vivo is highlighted by the abolishment of the pivot shift by repair of an anterolateral injury, before ACL reconstruction. Furthermore, Inderhaug et al. demonstrated that when a combined ACL and anterolateral ligament injury is created in the laboratory, isolated ACL reconstruction fails to restore normal kinematics with respect to internal rotation and anteroposterior laxity control. However, if an ALL reconstruction is added, normal kinematics can be restored.
Diagnosis
Clinical Diagnosis
There is no specific physical examination test that has been demonstrated to reliably identify an injury to the anterolateral structures of the knee. However, as mentioned previously, isolated ACL sectioning in the laboratory does not produce high-grade pivot. In keeping with this finding, several authors have reported clinical studies that demonstrate a significant association between a high-grade pivot shift and ALL injury in ACL-injured knees.
Diagnostic Imaging Procedures
Researchers have reported that 1.5T magnetic resonance imaging (MRI) is highly accurate in the diagnosis of ALL injury. It demonstrates a high-percentage agreement with intraoperative exploration of the anterolateral structures in acute ACL-injured knees. Several authors have reported that in this scenario, MRI is able to detect a rate of injury to the ALL of between 80% to 90%. In addition, three-dimensional (3D) MRI has also been used to evaluate the ALL and arguably has better spatial resolution ( Fig. 10.3 ). Using this modality, a similar rate of injury in acute ACL-injured knees is reported, and in chronic ACL-injured knees the rate is closer to 60%, suggesting that some injuries may heal. Simple radiographs may also be useful in identifying ALL injuries in some patients because they can detect Segond fractures (bony avulsions of the tibial ALL insertion; Fig. 10.4 ).
