Intercondylar Notch Width as a Risk Factor for Medial Femoral Condyle Osteochondritis Dissecans in Skeletally Immature Patients.

BACKGROUND Juvenile osteochondritis dissecans (OCD) of the medial femoral condyle (MFC) is one of the most common causes of knee pain in adolescents. Wilson sign reproduces knee pain with internal rotation of the tibia during extension of the knee from 90 to 30 degrees due to impingement of the tibial eminence on the MFC. This impingement may result in microtrauma and contribute to lesion formation. The purpose of this study was to evaluate anatomic factors that may increase the likelihood of impingement by using magnetic resonance imaging scans of patients with MFC OCD lesions to measure tibial eminence height and femoral notch width. METHODS A retrospective, case-control study was performed using the radiology database at our institution between July 2009 and February 2014. Magnetic resonance imagings of patients with MFC OCD lesions and matched controls were identified. For each patient, tibial eminence height and femoral notch width were measured and then normalized for patient size [creating the tibial eminence height normalized, and the notch width index (NWI), respectively]. Values for OCD and control knees were compared using Student t test. Interrater and intrarater reliability were calculated using intraclass correlation coefficients. RESULTS Thirty-five MFC OCD patients and matched controls were identified. Comparison of the groups showed a significantly smaller NWI in MFC OCD knees than in the matched controls (0.2620±0.0248 vs. 0.2886 ±0.0323, P=0.0003). There was no difference in tibial eminence height normalized between groups (0.1387±0.0161 vs. 0.1428±0.0108, P=0.21). Interrater and intrarater reliability of all measurements was good to excellent (0.81 to 1.00) when measurements were made using bony margins. CONCLUSIONS Knees with MFC OCD lesions have significantly smaller NWIs than matched controls. This anatomic factor may increase the likelihood of tibial eminence impingement and contribute to OCD lesion formation. LEVEL OF EVIDENCE Level III-case-control study.