Anatomical variation of the distal femur - a CT data analysis of 24,042 knees

Abstract

Aims and Objectives: Based on a large quantity of CT data, variations in distal femoral geometry was examined and evaluated for TKA. Materials and Methods: A retrospective study was performed on 24,042 data sets generated during the process of designing individual knee implants. Following parameters were recorded for the distal femur: Femoral absolute anterior-posterior (AP) and medial-lateral (ML) extent, lateral and medial condyle and trochlea size, distal condylar offset (DCO) between lateral and medial condyle, and the difference between medial and lateral posterior condylar offset (PCO) measured in AP direction. Results: Variable patient geometry was found with analysis of the AP and ML extent. Approximately one-third of the patients would experience size conflicts of +/- 3 mm with standard arthroplasty systems. 62% of the knees had a DCO> 1 mm. 83% of the distal femur had a mediolateral difference in PCO> 2 mm, which corresponds to about 3° external rotation and does not correlate with the femoral size. Conclusion: There is a distinct variability of femoral AP and ML extent as well as offsets / asymmetries. Medial and lateral PCOs are different and do not correlate with femoral size. This first results in mismatches between size of implant and individual knee anatomy and secondly in possible softtissue release and different femoral external rotations to adapt systems with fixed distal geometry to the individual situation.