MRI of Incidental Osteochondral Lesions of the Anterior Femoral Condyle: Are they caused by Repetitive Patellar Impaction?

Objective: Osteochondral lesions of the anterior femoral condyle are frequent incidental findings. However, little is known about these lesions. The purpose of this investigation was to determine the location, prevalence and pattern of these lesions. Materials and Methods: 322 consecutive knee MRI's were retrospectively reviewed on PACS by a fellowship trained musculoskeletal radiologist for presence, location, and grade of the osteochondral lesions in anterior femoral condyle. Other data included suprapatellar or infrapatellar fat pad edema, patellar or patellar tendon lateralization. Results: 13% of cases demonstrated osteochondral lesions in the anterior femoral condyle. All 44 positive cases demonstrated lesions at the level of inferior margin of the patella (57%) or within 1 cm below the level of the patella (43%). In 29% of cases, the lesions were located in the trochlear groove, 38% in medial aspect of the lateral femoral condyle and 32% in the lateral aspect of the medial femoral condyle. 40% of cases showed suprapatellar fat pad edema, 11% infrapatellar fat pad edema, 22% lateralization of patella or patellar tendon. Conclusion: Incidental finding of osteochondral lesions in the anterior femoral condyle had a prevalence of 13% in our study. All of the lesions were located at or within 1 cm below the level of the inferior margin of the patella. Based on the location of the lesions, we propose that the mechanism of injury is from repetitive chronic impaction of the inferior margin of patella against the femur during hyperextension or hyperflexion of the knee.