Abnormal femoral antetorsion-a subtrochanteric deformity.

Femoral rotational malalignment is associated with pain and functional disability and may be a contributing factor to hip impingement as well as to instability. In general, the deformity can be addressed surgically by rotational osteotomy. However, the anatomic location of the deformity is debated. The goal of the present study was to narrow down the anatomic site of deformity using the lesser trochanter (LT) as an additional landmark. One hundred and eight patients underwent computer tomography (CT)-based rotational analysis of their lower extremities. Femoral torsion (FT) and LT torsion (LTT) were measured. The combined angle (CoA) between FT and LTT was calculated. Statistical evaluation was done by multiple regression analysis. Ninety-seven extremities were examined for FT and LTT. Average age was 41 years (SD = 16.9) with a range of 18-85 years. Mean values were 20° for FT (SD = 12.2) and -16° for LTT (SD = 11.3). Mean CoA was 37.2 (SD = 8.7). Statistical analysis reveals a strong linear relationship between FT and LTT (y=31+0.74x) and a weaker relationship between FT and CoA (y=31+0.24x). This study identifies the LT as a reliable landmark and shows a strong linear relationship between the orientation of the LT and the overall torsion of the femur below and above the LT with about two-thirds of torsional changes occurring distal to it. These results provide a considerable indication for a subtrochanteric osteotomy to address correction of femoral rotational deformity at its anatomical origin. Level of Evidence: Level III, observational study.