Natural history of shelf gap and paleo-acetabular depth after shelf acetabuloplasty for Perthes disease.

The purpose of this study was to evaluate the morphologic evolution of the shelf gap, acetabulum and femoral head after shelf acetabuloplasty in patients affected by Perthes disease. 54 patients operated for Perthes disease with shelf acetabuloplasty were retrospectively reviewed regarding the radiographic results. Three pelvic antero-posterior radiographs have been studied for each patient, one at 2 postoperative months, one at 1 postoperative year and one at the latest clinical follow up (mean 76 postoperative months). The shelf gap decreased from 108% at 2 months to 104% at the last follow-up (p<0.001). There was an increase of the total acetabular depth to 168% by the presence of the shelf graft (p<0.001). The acetabular index of the operated side related to the contralateral side was 68% at 2 months due to the effect of the graft (p<0.001). The migration index of the shelf side was in mean -24% at 2 months and -3% at last follow- up (p<0.001). According to the Stulberg classification, there were 9 type 1 (17%), 20 type 2 (37%), 19 type 3 (35%), 5 type 4 (9%) and 1 type 5 (2%). A progressive remodeling with shelf gap reduction was occurring during the following months after the surgery. An increase of the total acetabular depth and a decrease of the migration index without a lateral overgrowth of the paleo-acetabulum was observed. Shelf acetabuloplasty is a good procedure to prevent early osteoarthritis by a better femoral head coverage.