The effect of valgus and varus femoral osteotomies on measures of anteversion in the dog

Abstract

Summary Objective: To determine whether femoral osteotomies that change frontal plane alignment without affecting torsion influence anteversion and inclination. Methods: Femurs without deformity were scanned to create three-dimensional reconstructions. The femoral head-neck axis was identified by placement of a virtual intra-medullary pin. A proximal osteotomy was simulated to create three conditions while keeping torsion constant: Normal, Coxa Valga (neck-shaft angle increased by 12°), and Coxa Vara (neck-shaft angle decreased by 12°). Femoral anteversion was measured from an axial image in all three conditions. Femoral inclination was calculated for all conditions using the neck-shaft and anteversion angles. Changes in anteversion and inclination were calculated and compared using a one-way repeated measures analysis of variance. Distal femoral osteotomies were then simulated with the native femurs, inducing 18° of distal varus with no change to torsion. Changes in anteversion and inclination for the Normal and Distal Varus conditions were calculated and compared by a paired t-test. Results: Version changed by a mean of 13.9° (± 1.5; p <0.0001) from the Coxa Valga to Coxa Vara conditions while inclination changed by a mean of 1.3° (± 0.39; p <0.01). Version changed by a mean of 6.6° (± 0.7; p <0.0001) between the Distal Varus and Normal conditions while inclination changed by a mean of –3.8° (± 0.75; p <0.001). Clinical significance: Femoral version changes with changing frontal plane alignment even when torsion is constant. This should be considered when correcting femoral deformities.