[Rotational landmarks and total knee arthroplasty in osteoarthritic knees]

To investigate the rotational mismatch of total knee replacement with medial 1/3 of tibial tuberosity as bony landmark in osteoarthritic patients with varus or valgus deformity.

Axial images on computed tomography of 62 knees (including 55 varus deformities and 7 valgus deformities) in 32 Chinese osteoarthritic patients who had total knee arthroplasty were analyzed, compared with that of 10 healthy knees. On images of the distal femur, the angle between the lines of surgical epicondylar axis (SEA) and posterior condylar axis was measured as posterior condylar angle (PCA), and on images of the proximal tibia, a baseline for the anteriorposterior axis of each component was drawn based on the SEA for the femur and the medial 1/3 of the tibial tuberosity for the tibia. The angle between these lines (Angle a) was defined as the rotational mismatch between the components when they were aligned to the anatomic landmarks of each bone.

The sulcus of medial epicondyle of femur could be identified on CT images of over 80% osteoarthritic knees; the median value of PCA was +2.36 degrees, with an individual variation of 0 degree to +7.5 degrees. Angle a was +6.45 +/- 3.68 degrees (range, 0 degree to +11.8 degrees) in 10 healthy knees, which increased significantly to +10.85 +/- 10.47 degrees (range, 0 degree to +28.1 degrees) in 55 varus knees (P < 0.05), which also increased significantly to +11.6 +/- 7.3 degrees (range, -6.5 degrees to +26.8 degrees) in 7 valgus knees (P < 0.05).

With the medial 1/3 of the tibial tuberosity as the rotational landmark for the tibial component, there was a tendency to align the tibial component in external rotational position relative to the femoral component in knees with normal alignment, the rotational mismatch increased in Chinese osteoarthritic knees with varus and valgus deformity.