Ultrasonographic visualization and assessment of the anterolateral ligament

Injury to the anterolateral ligament (ALL) of the knee has recently received attention as a potential risk factor for failure of anterior cruciate ligament reconstruction. However, evaluation of the anterolateral ligament is currently difficult, and radiologic data are sparse with regard to the normal appearance of this ligament. The purpose of the present study was to determine whether the ALL could be identified and visualized using ultrasonography.

Ten non-paired, fresh-frozen cadaveric knees underwent ultrasound by an experienced musculoskeletal radiologist using a Siemens S2000 Acuson Ultrasound machine with a 14-MHz linear transducer. After first identifying anatomical landmarks by palpation, a thin band of tissue originating in the vicinity of the fibular collateral ligament (FCL) origin was identified and followed up distally. The tibia was held at 30° of flexion and internally rotated to verify tightening of the structure. Under ultrasound guidance, 25-gauge hypodermic needles were placed at what were sonographically determined to be the origin and insertion points of the ligament. One-tenth of a CC of aniline blue dye was injected. The specimens were then dissected to confirm the presence and location of the ALL. If an ALL was found, distances between the epicentre of the injected dye and the actual origin and insertion points were calculated. Additionally, ligament length based on dissection images and ultrasound images was calculated.

Eight of ten specimens had an anterolateral structure that originated from the lateral femoral epicondyle just posterior and superior to the origin of the FCL and inserted on the lateral plateau approximately halfway between Gerdy's tubercle and the fibular head. The average length based on ultrasound was 3.8 cm (±.7; range 3.1-4.7) and 4.1 cm (±1.1; range 2.6-6.1) based on dissection. Length based on dissection and ultrasound had minimal agreement (ICC = .308; 95 % confidence interval .257-.382, p = .265). The average width of the structure on dissection was .8 cm (±.24; range .5-1.2). The mean distance from ultrasound-determined origin and insertion points to anatomical origin and insertion based on dissection was 10.9 mm (±2.9, range 7.0-15.8) and 12.5 mm (±5.7 range 3.2-19.3), respectively. Inter-observer reliability was excellent for all measurements based on dissection and ultrasound.

Ultrasound was unable to reliably identify the anterolateral structure from its femoral to tibial attachment sites. Distinguishing it from the posterior IT band and anterolateral capsule was challenging, and it is possible that the structure is a thickened band of fascia rather than a true ligament. As a clinical diagnostic tool, ultrasound likely offers little utility in the evaluation of the ALL for injury.

IV.