Femoral mechanical-anatomical angle of osteoarthritic knees.

BACKGROUND To perform total knee arthroplasty, some surgeons prefer to use a fixed valgus angle, for example 5° or 6°, for the distal femoral cut with every patient. This angle may be appropriate for some patients, but may not be for all. OBJECTIVE To determine the proper angle of the distal femoral cut during total knee arthroplasty (TKA) in Thai patients with osteoarthritis of the knee. MATERIAL AND METHOD A cross-sectional study was conducted of 80 osteoarthritic knees of 50 Thai patients with a mean age of 69 years (range 52-82, SD 7.64) who had received total knee arthroplasty at Chiang Mai University Hospital between January 2011 and March 2013. The femoral mechanical-anatomical (FMA) angle, femorotibial (FT) angle, mechanical femorotibial (MFT) angle, femoral bowing angle, femoral length, hip offset, gender, and age of the patients were analysed using multivariate regression analysis. RESULTS Average FMA angle was 6.46° (range 4°-10°, SD 1.26°). The FMA angle was 6.85° and 5.28° in patients with varus and valgus deformity, respectively. Fifteen percent of all patients showed a FMA angle either less than 5° or greater than 7°. CONCLUSION The average FMA angle of patients with gonarthrosis was 6.46°. If it is not possible to measure the FMA angle in Thai patients, 7° valgus cut angle is recommended for patients with varus deformity. Variation in this angle was high. Pre-operative measurement of FMA angle is beneficial for precise TKA.