Radiographic Classification of the Femoral Intercondylar Notch Posterolateral Rim

Purpose: The purpose of this study was to determine whether posterolateral rim morphology can be delineated on plain radiographic images. Methods: We obtained 20 femora from the Cleveland Museum of Natural History (10 each with distinct and indistinct posterolateral rims). Four blinded reviewers evaluated radiographic posterolateral rim morphology on lateral radiographs. The reviewers included a musculoskeletal radiologist, a fellowship-trained sports medicine surgeon, a pediatric orthopaedic surgeon, and a junior orthopaedic resident. Interobserver and intraobserver reliability was determined. Results: Radiographically, posterolateral rim morphology was classified into 2 types. Type 1 rims have a defined transition from Blumensaat's line to the posterior femoral cortex. Type 2 rims have an indistinct transition. Interobserver reliability showed substantial agreement during the first (κ = 0.65) and second (κ = 0.70) sessions. Intraobserver reliability was nearly perfect, with κ values ranging from 0.8 to 1.0. Conclusions: It has been shown anatomically that the posterolateral rim has variable morphology. We have shown that posterolateral rim morphology can be delineated on lateral plain film images. Radiographic type 1 rims correlate with distinct posterolateral rim morphology. Radiographic type 2 rims correlate with indistinct posterolateral rim morphology. Clinical Relevance: For surgeons who reference the posterolateral rim for femoral tunnel placement during anterior cruciate ligament reconstruction, indistinct posterolateral rim morphology may result in errant tunnel placement. Improved awareness of posterolateral rim morphology preoperatively may help avoid technical errors with placement of the femoral tunnel.