Purpose: Impacted piecemeal allografts for nonce-mented hemispheric cups raises a problem of primary stability in the case of extensive bone defects. The high centre of rotation of the oversized cup further increases bone loss, requiring an extralong neck. The purpose of this study was to describe the use of impacted piecemeal grafts associated with a pressfit supporting ring with reposition of the centre of rotation.

Material and methods: The piecemeal grafts were impacted into the acetabulum to fill the defect. The hydroxyapatite coated ring was pressfit for primary stability then stabilised with axial screws in the upper paste. A distal hook on the obturator foramen repositioned the centre of rotation. The study group included 103 cases of acetabular reconstruction, including 34 for aseptic loosening and type 2 and 3 acetabular substance loss. Clinical and radiographic assessment was performed at 5 and 12 years.

Results: Mean patient age was 58 years, mean weight was 64kg. The Harris score improved from 53 points preoperatively to 88 points at last follow-up. Radiographically, there were no cases of cup migration according to the Massin classification, and the centre of rotation (Pierchon) was anatomic in 66% horizontally and in 44% vertically. There were two lucent lines in zone 2 and mean polyethylene wear was 0.015 mm per year. Graft integration (Conn) was identical to the host in 84% with disappearance of the interface in 67%. There were three dislocations treated without changing the implant and two revisions for infection.

Discussion: Several theoretical and clinical studies have shown that the high centre of rotation increases stress on the implants and decreased abductor force. The results obtained in this study with a maximum 12 year follow-up show that indications for this pressfit technique associating reposition of the centre of rotation, fixation for stability, and restoration of bone stock can be widened. Limitations are bone destructions with rupture of the pelvic girdle.