Musculoskeletal Ultrasound Imaging of the Recently Described Anterolateral Ligament of the Knee

The anterolateral ligament (ALL) was recently found to be present in 97% (40/41) of human cadaveric knees by Claes et al.1 They hypothesized that it is important to control internal tibial rotation and prevent pivot shift. Its existence was suspected as far back as 1879 when Dr Segond described a “pearly, fibrous band” while describing avulsion fractures at the anterolateral proximal tibia above and behind the Gerdy tubercle (Segond fracture).2 The term anterolateral ligament was first introduced by Vierira et al.3 The ALL shares an origin from the lateral femoral condyle with the lateral collateral ligament. It runs obliquely parallel but deep to the iliotibial band (ITB). It inserts on the midportion of the proximal tibia halfway between the Gerdy tubercle and the fibular head. The close proximity to the ITB for much of its course until its terminus 2 cm posterior to ITB insertion1 may have contributed to difficulty identifying it until now. This visual vignette describes the identification of the ALL with diagnostic ultrasound. The lateral knee of a 52-yr-old healthy male subject was examined with a GE P6 musculoskeletal ultrasound machine. Initially, the ligament was difficult to discern from surrounding structures with the knee in full extension. The knee was then flexed to approximately 90 degrees to enhance visualization. The ligament was seen in long axis passing over the lateral meniscus and emerging from underneath the ITB as it traveled in an oblique parallel orientation to the ITB (Fig. 1). The terminus of the ligament was identified inferior to the proximal lateral edge of the tibia, posterior and proximal to the Gerdy tubercle on the lateral tibial recess (Fig. 1). Short-axis views of the ligament are represented at the tibial insertion (Fig. 2).FIGURE 1: Long-axis view of the ALL and the lateral knee joint (proximal is to the left and distal is to the right [R]). LFC = lateral femoral condyle; ALL= Anterior lateral ligament; PT = popliteus tendon; LM = lateral meniscus; LIGA= lateral inferior geniculate artery; Tib= tibia; ITB =iliotibial band.FIGURE 2: Insertion of the ALL at the proximal tibia (anterior is to the left and posterior is to the right). ITB =iliotibial band; ALL= Anterior lateral ligament; LCL=lateral collateral ligament; T= Tibia; F= Fibula; SAX, short axis.Using the descriptions of the ALL in the article by Claes et al.1, the authors found that the ligament was easiest to identify when the knee was in 90-degree flexion and slight internal rotation, resulting in the ligament being taut. The ability to visualize this ligament may prove to be useful to clinicians on the field of play when an anterior cruciate ligament injury is suspected. Identifying it with ultrasound would be a distinct advantage to the clinician. The authors intend to present follow-up reports correlating cadaveric ultrasound images before and after dissection of the knee to elaborate further on the sonographic appearance of the ALL.