To describe a method of femoral derotational osteotomy using an external fixator.

A retrospective review was conducted of 6 patients with 12 femora treated by derotational osteotomy with a semicircular modified Ilizarov external fixator and Schanz screws. The mean follow-up period was 17 months (in the range 12-28 months). There were two boys and four girls of mean age 11 years (in the range 10 to 13 years). The deformities were all idiopathic and there was no combined disease. Mean preoperative femoral anteversion was 38 ° (in the range 31-50 °) and mean internal and external hip rotation were 76 ° (in the range 70-85 °) and 23 ° (in the range 20-30 °), respectively.

After operation, the mean internal rotation at the hip diminished to 47 ° (in the range 40-50 °) and the mean external rotation increased to 52 ° (in the range 45-55 °). In all cases, the mean varus angle 6 ° (3-9 °) was made with conical washers on the osteotomy site to correct combined genu valgum. Mean clutch ambulation was started at 5 days postoperatively. The Ilizarov external fixator was removed at a mean 9 weeks after the operation and there was no refracture. No significant complication occured in any cases excepting 3 cases of superficial pin tract infection.

Femoral derotational osteotomy using a semicircular modified Ilizarov external fixator with Schanz screws has the advantages of simplicity, an exact correction of deformity, early ambulation, and the freedom to alter the alignment postoperatively.