Posterior Displacement of Meniscal Ramp Lesion Is Observed on Flexed Knee Magnetic Resonance Imaging of Anterior Cruciate Ligament-Deficient Knees

Purpose: To confirm whether posterior displacement of the detached meniscocapsular structure in ramp lesions could be observed on magnetic resonance imaging (MRI) in the flexed knee position and to clarify whether this displacement on MRI is related to greater anterior knee laxity. Methods: This retrospective comparative trial study included 50 patients with anterior cruciate ligament injuries in whom attendant ramp lesions were observed on preoperative MRI. All patients underwent 3-T MRI at 120 degrees of knee flexion preoperatively. The gap distance of the ramp lesion on sagittal slices was measured, and a distance greater than 1 mm was classified as gap positive. Additionally, joint effusion in the posteromedial recess was quantitatively evaluated by measuring the surface area of joint fluid. Prior to surgery, the side-to-side difference in anterior tibial translation (ATT) on stress radiographs at 20 degrees of knee flexion was measured to evaluate anterior knee laxity. During anterior cruciate ligament reconstruction, the length of the ramp lesion was measured by a scale from the posteromedial portal. Results: Of the 50 knees, 29 had ramp lesion gaps greater than 1 mm on MRI at knee flexion. The gap-positive group had a significantly greater side-to-side difference in ATT (9.6 + 3.6 mm vs 5.0 + 2.7 mm, P < .001) and significantly larger ramp lesion length (15.7 + 4.9 mm vs 11.7 + 3.9 mm, P = .002) than the gap-negative group. The gappositive group also had a significantly greater amount of joint effusion than the gap-negative group (P < .001). Conclusions: Posterior displacement of the detached meniscocapsular structure in ramp lesions can be observed on MRI at knee flexion and is related to greater anterior knee laxity, lesion size, and joint effusion. Level of Evidence: Level III, retrospective comparative trial.