REDISLOCATION AND THE COMPUTERISED TOMOGRAPHY EVALUATION OF DEVELOPMENTAL DYSPLASIA OF THE HIP

Aims The purpose of this study was to calculate the dislocation rate following open or closed reduction for developmental dysplasia of the hip (DDH) in our unit. In addition we evaluated the posterior neck line as a method of determining hip relocation and assessed the morphology of the dysplastic acetabulum on single slice CT scan. Method We retrospectively assessed all patients operated on for either open or closed reduction for DDH between August 2007 and August 2009 and evaluated their notes, CT scans and radiographs. The immediate post-operative dislocation rate was calculated, as was the subsequent re-dislocation rate and late subluxation rate. The acetabular morphology was assessed to determine whether the acetabulae were “S” shaped or “C” shaped. A novel method for confirming hip reduction was also appraised. Results Seventy-five hips were operated on during the study period. The immediate post-operative dislocation rate was 9.3%. There were no subsequent dislocations in any of the patients in whom CT scans had confirmed adequate initial reduction. Two patients went on to develop late subluxation. 98.6% of dysplastic acetabulae displayed an S shaped acetabulum and 1 hip had a virtually flat acetabulum. The posterior neck line test for dislocation had a 85.7% sensitivity and 96.9% specificity. Conclusions Immediate post-operative CT scan of the hip is a useful investigation following reduction of the hip for DDH. If it can be established that the hip is reduced on the scan it is unlikely to re-dislocate. The S shape of the acetabulum in DDH is consistently present and is a marker of the dysplastic posterior acetabular wall. The posterior neck line is a reliable measure of hip reduction.