External fixation for femoral derotation osteotomy in developmental dysplasia of the hip.

We present a technique for the external fixation of femoral derotation osteotomy performed as part of the management of patients who present with developmental dysplasia of the hip. The technique was used following open (25 hips) or closed (31 hips) reduction and clinical and radiologic review was undertaken between 5 and 18 years (mean 11 years) after the procedure. Eighty-four percent of the patients (43 patients, 47 hips) were found to have a Severin clinical grading of 1 or 2 and over 70% were grade 1 or 2 radiologically. Nine hips/patients had required further surgery following the reduction (open or closed) and osteotomy. The complications of the procedure are described; whilst some of these are clearly associated with the osteotomy it is probable that others, such as avascular necrosis, are attributable to the method of reduction. The overall results are thought to stand up well to comparison with other series, suggesting that the technique has no major disadvantage, apart from being unable to control the pins and pin holes and to detect discharge and infection underneath the spica, which did not seem to be a problem in our study. It is suggested that the main advantages are: (1) a lower risk of damage to the trochanteric growth cartilage in comparison with other fixation techniques, because soft tissue dissection is less extensive and the implant is already removed after 6 weeks; (2) a greater accuracy with regard to the derotation angle; and (3) the avoidance of a further open procedure to remove the implant, which can be difficult with plates if the removal is postponed for too long.