Anatomic alignment of the patellar groove.

The variability in alignment of the natural patellar groove was determined about various anatomic axes of the femur, using 3 plane radiographs and electronic digitization. After the patellar groove was identified and marked on 15 anatomic specimen femurs, radiographs were taken in the coronal, sagittal, and transverse planes so that principal anatomic axes could be outlined. Through electronic digitization, a 3-dimensional representation of the patellar groove was constructed about the distal anatomic axis, mechanical axis, transepicondylar axes, and transcondylar axes. Regarding these 4 principal anatomic axes, the variability in orientation of the patellar groove was profound in both coronal and transverse planes, typically involving a range of 11 degrees to 16 degrees about the mean. The average orientation most closely approximated the perpendicular to the transepicondylar axis in the coronal plane; however, the range varied extensively. None of the anatomic axes tested proved reliable as a reference axis for proper position of the patellar groove, and this study shows that the orientation of the natural patellar groove is more variable than previously suspected. The failure of femoral components to accommodate this variability may explain many complications associated with the patellar component in total knee arthroplasty.