Rotational deformity in varus osteoarthritis of the knee: analysis with computed tomography.

UNLABELLED: Rotational deformities in varus osteoarthritis of the knee were evaluated with computed tomography. Preoperative computed tomography scans of 150 knees (114 patients) having total knee arthroplasty and 31 control knees (20 patients) were included. The femorotibial rotation was quantified using the clinical epicondylar axis of the femur and the tibial tuberosity (patella tendon) as the references. The knees with osteoarthritis were divided into three groups according to the femorotibial angle (Group 1, 0 degrees -9 degrees varus, n = 87; Group 2, 10 degrees -19 degrees varus, n = 51; Group 3, 20 degrees or greater varus, n = 12) and statistically analyzed. Rotational deformities (external rotation of the tibia) existed in knees with osteoarthritis and were larger in knees with increased varus deformities (mean +/- standard deviation, -2.24 degrees +/- 4.19 degrees in Group 1; 0.33 degrees +/- 4.14 degrees in Group 2; and 5.33 degrees +/- 5.71 degrees in Group 3). When the femorotibial rotation of each knee was stratified by the corresponding femorotibial angle, we found a correlation. The information should help minimize the rotational mismatch between the femoral and the tibial components in total knee arthroplasty and elucidate the pathogenesis of varus osteoarthritis of the knee. LEVEL OF EVIDENCE: Diagnostic study, Level III-1 (study of nonconsecutive patients--no consistently applied reference gold standard). See the Guidelines for Authors for a complete description of levels of evidence.