Femoral Mechanical-Anatomical Angle
of Osteoarthritic Knees
Warakorn Jingjit MD*, Pakpoom Poomcharoen MD*,
Sakkadech Limmahakhun MD*, Kasisin Klunklin MD*,
Taninnit Leerapun MD*, Sattaya Rojanasthien MD*
Affiliation :
* Department of Orthopaedics, Faculty of Medicine, Chiang Mai University, Chiang Mai, Thailand
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.
Keywords : Knee arthroplasty, Osteoarthritis, Femoral mechanical-anatomical angle, Femoral valgus cut, Thai
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