Distal torsion of the femur in osteoarthritic knees: a computed tomographystudy

Purpose of the study We used computed tomography (CT) to measure external torsion of the distal femur preoperatively in patients with osteoarthritic knees presenting genu varum in order to assess the correlation between femoral distal external to rsion (FDET) and radiological or epidemiological data obtained during the g eneral preoperative work-up. Material and methods Seventy-five knees were studied in 38 patients. Mean age was 70.4 years; th ere were 13 men and 25 women, The degree of external torsion of the distal femur was defined as the angle measured on the CT-scan between a line drawn tangent to the most posterior part of the condyles and the epidondylar lin e drawn from the lateral epicondyle to the most prominent point of the medi a[ epicondyle, This angle was compared with the angle of the epiphyseal tib ial varum. measured on the anteroposterior radiograph and the overall devia tion of the lower limb (HKA), and with the angle between the mechanical axi s and the femoral shaft axis (HKS). We assessed the effect of gender and se x and looked for correlations between the FDET angle and measurements made on standard radiographs. Student's t test was used compare the FDET angle b y sex and side. The alpha risk was set at 5%, Results The FDET angle measured a mean 5.36 +/- 1.87 degrees (0-9 degrees). We did not find any correlation between the FDET angle and tibial epiphyseal varum or HKS angles. A weak statistical correlation between the FDET and the HKA angles had no clinical value. Finally, the FDET angle was not correlated w ith sex or side. Discussion Computed tomography provides reliable and reproducible measurements. Our wo rk clearly demonstrated the wide interindividual variability of the FDET an gle. We were unable to identify any measurement on standard radiographs all owing an Indirect prediction of the FDET angle, Conclusion Our findings suggest that measuring the FDET angle on preoperative CT-scans in candidates for total hip arthroplasty can be useful for adapting the an gle of rotation for the femoral component to each patient.