How precise is the determination of rotational alignment of the femoral prosthesis in total knee arthroplasty: an in vivo study.

Correct rotation of the femoral component is critical in avoiding patellar instability in total knee arthroplasty. This study attempted to compare the precision of 4 commonly used methods (transepicondylar axis [TEA], 3 degrees external rotation [ER] from posterior condylar line [PCL], perpendicular cut to Leo Whiteside line [WSL], and balanced flexion gap [GAP]) in determining the rotational alignment of the femoral prosthesis in an in vivo setting. The ranges of error were as follows: (1) TEA, 28 degrees (17 degrees internal rotation [IR] to 11 degrees ER); (2) PCL, 27 degrees (13 degrees IR to 14 degrees ER); (3) WSL, 32 degrees (17 degrees IR to 15 degrees ER); (4) GAP, 26 degrees (14 degrees IR to 12 degrees ER). If an error of more than 5 degrees from neutral alignment is defined as an outlier, 56% in TEA, 72% in PCL, 60% in WSL, and 20% in GAP methods would fall in the outlier zone.