Relationship Between Number of Lateral Intercondylar Ridges and Area of Denser Bone on the Lateral Intercondylar Wall

BACKGROUND: A deeper understanding of the anatomy of the intercondylar notch of the femur may help reduce technical errors during anatomic anterior cruciate ligament (ACL) reconstruction. PURPOSES: To classify the number of ridges on the lateral intercondylar wall, identify factors influencing the number of ridges, and define the relationship between the area of denser bone on the lateral intercondylar wall and the lateral intercondylar ridge. STUDY DESIGN: Descriptive laboratory study. METHODS: Included were 89 patients with computed tomography (CT) images of the knee joint. On full lateral view of the lateral femoral condyle, the authors evaluated for the presence of a lateral intercondylar ridge. The height and area of the lateral intercondylar wall (notch height and lateral notch area) and the length of Blumensaat line were calculated. Notch outlet length, axial notch area, notch width index, and transepicondylar length were also calculated using 3-dimensional CT. Maximum intensity projection was used to identify the area of denser bone on the femoral lateral intercondylar wall, and the relationship between this area and the lateral intercondylar ridge was investigated. RESULTS: The lateral intercondylar ridge exhibited 3 types of morphological variations. The invisible type (no ridge) was observed in 20 knees (22.5%); the ridge type (1 ridge), in 23 knees (25.8%); and the plateau type (2 ridges), in 46 knees (51.7%). There were significant differences in notch height, lateral notch area, Blumensaat line length, and denser bone area among the ridge types (P ≤ .031 for all). The locations of the anterior ridge of the plateau type and of all 23 ridges of the ridge type corresponded to the anterior margin line of the area of denser bone. CONCLUSION: Significant differences were seen in the 3 types of lateral intercondylar ridges. The anterior margin line of the denser bone area on the lateral intercondylar wall was found to correspond to the anterior border of the plateau type and the ridge type. CLINICAL RELEVANCE: The variations in the lateral intercondylar ridge may affect measurement accuracy during evaluation of ACL tunnel position while using the ridge as a landmark. The plateau-type ridge and the area of denser bone on the lateral intercondylar wall may provide a new way for surgeons to determine the femoral tunnel.