Introduction: Various techniques have been described for cup position in deficient acetabuli. Medialization allows an optimal cup position in the true acetabulum affording cover of the implant in the superolateral area by the bony roof and avoiding the need for a structural graft to cover the protruding lateral edge of the cup.

Materials and Methods: During the last 5 years 51 cases of cup medialization have been done during Resurfacing Replacement or THR with hard-hard bearing surfaces (mean follow up 35.2 month). 15 cases were done with the medial acetabuloplasty technique and 36 cases were done by simple over-reaming the medial wall and morselized bone grafting. The mean followed up was 16 months.

Surgical technique: Medial Acetabuloplasty: After a cartilage removal, we drill perforations in a horizontal line to weaken the central area of the medial wall. Using an impactor the medial wall is fractured and shifted medially for a few millimeters and the cavitation so produced is filled with morselized bone graft. This technique preserves a shell of bone medially which together with the graft brings about medial bony wall preservation. In extreme acetabular deficiency, this technique is also useful by minimizing the extent of morselized bone grafting needed in the superolateral area for lateral roof bone formation.

Results: The medial wall defect was consistently reformed during the first year. In neither the over-reaming with morselized bone graft nor in the group using the medial acetabuloplasty was the stability of the cup compromised.

Conclusion: The lateral structural graft techniques are more cumbersome, take more time and the results are less certain.

In the short term there was no difference in hip scores or in the radiological assessment between medialization with or without acetabuloplasty. We suggest this technique seems to have the potential for very good long term results.