PurposeThe presence of anterolateral ligament of the knee is still controversial, and some physicians prefer to call this structure anterolateral complex (ALC) to infer plural nature of structures involved. The purpose of this study was to describe the scanning techniques and to classify various sonographic appearances of the tibial-side ALC of the knee in subjects with anterior cruciate ligament (ACL) injury. It was hypothesized that sonographic abnormity of the ALC would be associated with ACL injury history.MethodsPatients with a history of unilateral ACL injury were prospectively recruited, and the ALC was sonographically evaluated. During the evaluation, the lateral femoral epicondyle was visualized in anatomic transverse view first. At this location, the ALC was typically most conspicuous between the short head of the biceps femoris muscle and the posterior and deep aspect of the iliotibial band superficial to the origin of the lateral collateral ligament. The ALC was followed distally to the broad insertion centralizing to the area posterior to Gerdy’s tubercle. The appearance of the distal insertion of the ALC was classified based both on echogenicity and on the presence of a Segond fracture as follows: Grade 0: isoechoic to the rest of the ALC, Grade 1: hypoechoic, Grade 2: anechoic, and Grade 3: Segond fracture. The uninjured side was similarly scanned for comparison.ResultsA total of 28 patients (13 men; mean age 22.1 ± 8.1 years old with range: 12–44; mean body mass index 25.0 with range: 18.9–39.2) were included in this study. The average time from injury to sonograhpic evaluation was 4 months (range: 2 days to 1 year). Of 28 ACL-deficient knees, 19 were (68%) graded as Grade 0 in the distal insertion of the ALC, 7 (25%) as Grade 1, 1 (3.5%) as Grade 2, and 1 (3.5%) as Grade 3. Contralateral knees showed 25 knees (89%) with Grade 0 and 3 knees (11%) with Grade 1.ConclusionACL injury history was associated with a higher incidence of sonographic abnormalities within the distal insertion of the anterolateral complex.Level of evidenceIII.