Reference axes for optimal femoral rotational alignment in varus osteoarthritic Indian knees - A CT based study

Optimal rotational alignment of femoral component is important for longevity and success of total knee replacement. Whiteside line (WL), posterior condylar axis (PCA) and femoral transepicondylar axis are various intra-operative landmarks to guide femoral rotation. Each of these has its pros and cons. The aims of our study were to assess the relationship of posterior condylar axis and the antero-posterior axis of femur with the surgical epicondylar axis and evaluate whether degree of deformity or severity of osteoarthritis alters the rotational alignment of the femur when posterior condylar axis is taken as a reference. Are we justified in using a 3° external rotation with respect to posterior condylar axis in each knee?

The study is a single-centre, CT-based, cross-sectional, radiological study in 56 bilateral osteoarthritic varus Indian knees. The following were deduced using a uniform standardised method: Whiteside-surgical transepicondylar angle and posterior condylar angle. The study population was subdivided based on age, sex, deformity and grade of osteoarthritis.

The mean posterior condylar angle (N = 112) was 3.25 ± 1.379° (95% CI). The posterior condylar angle ranged from '0' degrees to '6' degrees with only 27.7% having an angle of 3°. The mean Whiteside-transepicondylar angle (N = 112) is 89.72 ± 3.537° (95% CI).

PCA and the WL are comparable in establishing the rotational alignment of the femoral component with respect to the surgical transepicondylar axis. A fixed, 3° external rotation with respect to the PCA is an oversimplification and rotational alignment of the knees should be individualised.