The lateral femoral notch sign following ACL injury: frequency, morphology and relation to meniscal injury and sports activity.

Purpose: The purpose of this study was to determine the incidence of the "lateral femoral notch sign" in acute anterior cruciate ligament (ACL) tears and its correlation with lateral meniscal tears.
Methods: Lateral plain radiographs and sagittal magnetic resonance images (each performed within 1 month following injury) of 500 patients with acute and arthroscopically confirmed ACL tears were retrospectively evaluated for depth, length and position of the "lateral femoral notch sign". The accompanying bone bruise was measured, as well. The correlation of the lateral femoral notch sign with high-risk and low-risk pivoting activities as well as with a lateral meniscus tear was evaluated.
Results: A total of 26.4 % of the patients had a lateral femoral notch sign deeper than 2.0 mm with a mean depth of 2.8 ± 0.8 mm SD. All lateral femoral notches were situated near or slightly posterior to Blumensaat's line. ACL injuries sustained during high-risk pivoting sports were more prone to a lateral femoral notch sign than ACL injuries in low-risk pivoting sports (r = 0.107 vs r = -0.107). Of all patients with a lateral femoral notch sign, 40.2 % also had lateral meniscus tears. The correlation between the presence of the lateral femoral notch sign and lateral meniscus tears was statistically significant (p = 0.004).
Conclusion: In more than one-quarter of patients, plain radiographs may help to establish the diagnosis of an ACL tear. Further, a lateral femoral notch sign greater than 2.0 mm also correlates with lateral meniscus tears. Hence, the lateral femoral notch sign is a useful diagnostic tool in daily clinical practice.
Level of Evidence: IV.