Purpose: (1) To compare the diagnostic ability of ultrasonography (US) and magnetic resonance imaging (MRI) to detect anterolateral ligament (ALL) injuries in anterior cruciate ligament (ACL)-deficient patients, and (2) to evaluate the correlation between ALL injury status (as determined by US and MRI) and the knee's rotational stability.
Methods: Thirty patients with an isolated ACL injury were included prospectively over a 3-month period. The condition of the ALL was evaluated by 2 experienced radiologists using both US and MRI. Rotational stability was evaluated by 2 surgeons with the pivot-shift test with patients under general anesthesia. It was classified as either negative (grades 0 and I) or positive (grades II and III). The radiologists were blinded to the knee's rotational stability, and the surgeons were blinded to the ALL's status based on the US images. The correlation between the ALL's injury status (US and MRI) and the pivot shift was determined with the Pearson χ2 test. To evaluate the reproducibility of the results, the agreement between observers was determined with the Cohen κ coefficient.
Results: On US, the ALL was identified and visible over its entire length in 100% of patients (30 of 30, κ = 1). The ALL was injured in 63% of patients (19 of 30, κ = 0.93). On MRI, the ALL was identified in 96% of patients (29 of 30, κ = 0.91). The ALL appeared injured in 53% of cases (16 of 30, κ = 0.93). An ALL that appeared injured on US was more often associated with a positive pivot shift than was an uninjured ALL (75% vs 39%, χ2 = 13.7, P < .05). The interobserver agreement was high for both US (κ = 0.91-1) and MRI (κ = 0.76-1).
Conclusions: US is a reproducible examination for the diagnosis of ALL injury. An ALL injury is most often associated with a high pivot-shift grade.
Level of evidence: Level II, prospective comparative study.
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