Idiopathic increased anteversion of the femoral neck. Radiological and clinical study in non-operated and operated patients.

The development of femoral neck angles in children with idiopathic increased anteversion was investigated. The anteversion (AV) angle in 16 non-operated patients (n = 32) decreased from a mean of 45 degrees at the age of 7.3 years (median) to 31 degrees at the age of 15.7 years. The neckshaft (CCD) angle remained unchanged. A subtrochanteric derotational osteotomy was performed in 24 patients (n = 48) aged 7.7 years (median). The AV angle was corrected from 47 to 3 degrees, and the CCD angle from 134 to 124 degrees. At follow-up at the age of 16.5 years the AV and the CCD angles had increased to 14 and 135 degrees respectively. The internal rotation of the hip was increased to the same extent in the two patient groups. The degree of external rotation as well as total rotation was significantly larger in the non-operated patients compared to the patients who needed an operation. At follow-up the rotational movements of the hip and the external torsion of the leg/foot were measured and compared with the corresponding measurements for a control group of 26 healthy subjects whose median age was 16.3 years. In the non-operated patients the internal rotation was reduced at a rate corresponding to the spontaneous reduction of the femoral anteversion, while the external rotation was unchanged. In the operated patients the rotational movements were normalized, as was the anteversion of the femoral neck. No differences in external torsion of the leg/foot were found in the three groups. Based on these results we conclude that cases of idiopathic increased anteversion of the femoral neck are not corrected spontaneously as the child grows up. With a subtrochanteric derotational osteotomy slight overcorrection may be indicated, but simultaneous varus correction of the femoral neck seems to be unnecessary. The degree of external rotation of the hip determines gait symptoms in patients with increased femoral anteversion. No regular compensatory external torsion of the leg/foot develops during growth.