The Coronal Angulation of the Femur in Thai Osteoarthritic Knee Patients with Varus Deformity

Abstract

Objective: To determine the angulation of the distal femoral axis - femoral mechanical axis and the coronal femoral bowing in varus OA knees. This information is necessar, because the routine distal femoral valgus cut can potentially lead to error in post-operative alignment. Methods: Hip to ankle standing radiographs were ordered in 160 varus OA patients (200 limbs). The mean age of the patients was 63.8 years. In addition, 50 limbs of young volunteers with an average age of 28.8 years, were also studied for comparison. The distal femoral axis-femoral mechanical axis angle, femoral bow, and other angles were determined and compared between two groups. Results: Mean distal femoral axis-mechanical axis angle was 7.0o ± 1.5o and mean femoral bow was 2.4o ± 2.6o in patients compared to 5.7o ± 0.5o and 0.3o ± 0.5o respectively, in controls. The varus deformity significantly correlated with femoral bowing. Thirty-five (17.5 percent) of OA limbs showed a distal femoral axis-mechanical axis angle of more than 9o and there were 42 OA limbs (21%) that had significant (> 3o) femoral bowing. Conclusion: These findings have implications in deciding the optimum valgus angle at which to perform distal femoral resection during TKA in varus OA knee.

Keywords

• Distal femoral axis-femoral mechanical axis angle; femoral bow; varus deformity