Twenty six embalmed human cadaveric knees were collected from the Department of Anatomy, Amrita School of Medicine, Amrita Institute of Medical Sciences, Kochi, Kerala, India, and were dissected for the anterolateral ligament. The skin on the lateral aspect of the extended knee was reflected. The Iliotibial Band (ITB), extensor apparatus, the short head of the biceps femoris and its tendon were cleared of subcutaneous fat tissue. The ITB was then cut just above the lateral femoral condyle and reflected distally upto its tibial insertion at the GT. The Lateral Collateral Ligament (LCL) was palpated and the lamina covering the LCL was then carefully incised posteriorly and parallel to the LCL.

A distinct fibrous structure running distally from lateral femoral condyle to the proximal tibia, posterior to GT, was identified. It was clearly delineated from the capsule following which all the visible fibres of the ligamentous structure were isolated and dissected out.

Special care was taken not to damage fibers intersecting with the proximal LCL. Furthermore, the lateral meniscus, the LCL and the popliteus tendon were carefully separated to study the relationship with the ALL.

A qualitative and a quantitative characterization of the ALL was done. A digital caliper with an accuracy of 0.01 mm (Mit500196-20; Mitutoyo, Japan) was used to measure various parameters of the ALL. The measurements observed were length of ALL, width at the femoral and tibial attachments and at the midpoint, distance between the center of tibial attachment of ALL to GT and to the tip of the fibular head, distance between femoral attachment of the ALL and the tip of the lateral epicondyle.

In all the 26 cadaveric knees dissected, a distinct ligamentous structure was identified at the anterolateral aspect, connecting the femur to the tibia. It appeared as an extracapsular structure, passing obliquely over the superficial aspect of the upper part of LCL. In view of its location, appearance and orientation, it seemed appropriate to call it as the Anterolateral Ligament (ALL) [Table/Fig-1].

[Table/Fig-1]:

Lateral region of right knee. Blue markers show the ALL. (* – femoral attachment of ALL, FM- Femoral condyle, LCL-Lateral collateral ligament, P-Popliteus).

In all cases, the proximal attachment of the ALL to the femoral condyle was found to be proximal and posterior to the lateral epicondyle with a fan-like spreading of the fibres. The distal attachment was broader than the main body and passed onto the proximal tibial plateau midway between GT and head of the fibula. The measurements observed were recorded and tabulated [Table/Fig-2]

The morphometric measurements of ALL from the present study are represented in [Table/Fig-2,3].

In this study, the anterolateral ligament was identified as a distinct ligamentous structure, consistently present in all 26 cadaveric specimens, easily distinguishable from the adjacent thin joint capsule at the anterolateral aspect of the knee.

Segond P defined it as a fibrous structure whereas Terry GC et al., in defined it as a strong capsular ligament, supported superficially by the Iliotibial tract [4,6]. It was thought to play an important role in the anterolateral stability pattern of the knee. Some literatures used the term ‘mid third’ lateral capsular ligament for the same [14]. Vincent EL et al., in 2012 noticed ‘a relatively consistent structure in the lateral knee’ which he called as ALL [11]. Johnson LL performed dissections on six amputated specimens to elucidate the anatomy of what he called the “lateral capsular ligament complex” [15]. Terry GC et al., described a functional ALL formed by the deep capsulo-osseous and superficial layers of the iliotibial tract [7].

The femoral attachment of ALL showed a high degree of variablity in majority of studies whereas the tibial attachment was relatively more consistent and was approximately midway between GT and the fibular head. Claes S et al., and Vincent J et al., described the ALL to get attached anterior to the FCL [1,11], whereas Vieira EL et al., stated it deep to iliotibial tract [10]. Dodds AL et al., stated that the ALL does not attach directly onto bone, but rather blends with locally adherent fibres of the capsule, posterior to FCL [2].

According to our findings, the proximal attachement of ALL was directly to the femoral condyle, proximal and posterior to the lateral epicondyle, and the distal attachment to the tibial plateau, similar to that observed by Vincent J et al., and Helito CP et al., [11,12].

It is suggested that along with ACL reconstruction, ALL reconstruction should also be done to prevent the recurrence of rotational injury. In common knee instability patterns such as pivot shift the precise anatomical knowledge of the ALL could be of great relevance to orthopaedic surgeons. However more research is required to establish the function of ALL in providing stability for knee joint.

According to our study its proximal attachment was 7.1±3.4 mm proximal and 4±2.9 mm posterior to the lateral femoral epicondyle. At the femoral attachment the fibers of ALL were fanning out. In the present study we have also noted a close association of ALL with the upper part of lateral collateral ligament as it crosses the latter superficially which is similar to that recorded by Claes S [1].

The tibial attachment of ALL is seen midway between Gerdy’s tubercle and fibular head. It is 20.4±3.1 mm away from GT and 21.3±4.6 mm away from fibular head. It is the only structure attached to that particular area of tibial plateau; so, can be considered as the cause for Segond’s avulsion fracture as described by Stevens MA et al., [16].

The length of ALL in the present study is comparable to those of the previous studies with an exception to the observation done by Dodds AL et al., [Table/Fig-4] [1,2,11,17].

Present study confirms ALL as an independent structure on the anterolateral aspect of the knee joint but to prove its role in providing rotational stability to the knee joint, the biomechanical analysis of ALL should be studied further.

The high incidence of ALL lesions in ACL injuries and its causative relationship with high grade pivot shift yield a new insight related to the interaction between ALL and ACL and its role in providing rotational stability. Thus, including an ALL reconstruction led to a decrease in the alarming re-injury rates following an ACL reconstruction procedure. The knowledge of gross anatomy of ALL will help the orthopaedic surgeons to perform a more efficient reconstruction of ACL.