The effect of distal femur bony morphology on in vivo knee translational and rotational kinematics.

PURPOSE: Tibio-femoral kinematics are clearly influenced by the bony morphology of the femur. Previous morphological studies have not directly evaluated relationships between morphology and knee kinematics. Therefore, the purpose of this study was to examine the relationship between distal femur bony morphology and in vivo knee kinematics during running. It was hypothesized that the posterior offset of the transcondylar axis would be related to the magnitude of anterior/posterior tibio-femoral translation and that the rotational angle of the transcondylar axis would be related to the magnitude of internal/external knee rotation. METHODS: Seventeen contralateral (uninjured) knees of ACL-reconstructed patients were used. Distal femoral geometry was analyzed from 3D-CT data by determining the anteroposterior location (condyle offset ratio--COR) and rotational angle (condylar twist angle--CTA) of the femoral transcondylar axis. Six degree-of-freedom knee kinematics were obtained during running using a dynamic stereo radiograph system. Knee kinematics were correlated with the femoral morphologic measures (COR and CTA) to investigate the influence of femoral geometry on dynamic knee function. RESULTS: Significant correlations were identified between distal femur morphology and knee kinematics. Anterior tibial translation was positively correlated with the condyle offset ratio (R(2) = 0.41, P < 0.01). Internal tibial rotation was positively correlated with the condylar twist angle (R(2) = 0.48, P < 0.01). CONCLUSIONS: Correlations between knee kinematics and morphologic measures describing the position and orientation of the femoral transcondylar axis suggest that these specific measures are valuable for characterizing the influence of femur shape on dynamic knee function. LEVEL OF EVIDENCE: III.