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° 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° (17° internal rotation [IR] to 11° ER); (2) PCL, 27° (13° IR to 14° ER); (3) WSL, 32° (17° IR to 15° ER); (4) GAP, 26° (14° IR to 12° ER). If an error of more than 5° 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.