Accuracy of femoral rotational alignment in total knee arthroplasty using computer assisted navigation

Proper rotational alignment of components is crucial for the success of total knee arthroplasty (TKA). The traditional reference guides for assessment of femoral rotation include the posterior condylar axis, the anteroposterior axis, also known as Whiteside's line, and the transepicondylar axis (TEA). The fixed-angle posterior referencing system recommends that the rotational femoral cut be made at 3 degrees of external rotation. In a consecutive series of 100 patients undergoing TKA at our institution, the accuracy of these reference guides in determining the rotation of the femoral component was compared with that of a computerized navigation system. Although differences between the three reference methods were not statistically significant, the possibility of finding an outlier leading to excessive external or internal rotation of the femoral component when using a fixed posterior condyle reference guide mandates the use of other referencing methods to avoid this error. Using fixed posterior referencing, up to 17% of femoral components would have differed by more than 5 degrees from the anatomic reference landmarks (TEA, Whiteside's line). This degree of rotational malalignment could lead to knee instability and early failure.