The effect of varus and valgus osteotomies on femoral version.

BACKGROUND

Although seldom described, varus and valgus osteotomies of the proximal femur can affect femoral version. The magnitude of the effect can be predicted with an understanding of the distinction between femoral version and femoral neck inclination. The purpose of this study was to elucidate this relationship.

METHODS

Version, inclination, apparent neck-shaft angle, and true neck-shaft angle were defined and measured in 72 preserved femora.

RESULTS

Average values were 19.8+/-11.8 degrees for version versus 14.5+/-10.1 degrees for inclination (P=0.004), giving a mean difference of 27% between version and inclination, with greater discrepancy with increasing neck-shaft angle. There were high correlations between measured inclination and inclination calculated using version and apparent neck-shaft angle (r=0.96) and true neck-shaft angle (r=0.97), validating our formulaic relationship between these variables.

CONCLUSIONS

We present and validate the concept of inclination, and its relationship with version and neck-shaft angle. This explains the mechanism for a varus osteotomy decreasing anteversion, and a valgus osteotomy increasing anteversion.

CLINICAL RELEVANCE

With an understanding of these concepts, a surgeon can incline the femoral neck axis to achieve a desired amount of version, for any given neck-shaft angle. Without this understanding, precise control of the version and neck-shaft angle is difficult.