LARGE DIAMETER FEMORAL HEADS IN REVISION HIP SURGERY

Abstract

Postoperative dislocations are known to be a big problem in revision surgery. In literature dislocation rates vary from 4.8% to 33% after previous surgery. In revision surgery, impingement of the implant components, the capsular and soft tissue release, muscular weakness and greater trochanter problems can give additional instability. The reason for revision is important, where instability, infection and tumour cases will lead to a higher percentage of dislocations. The use of big metal heads on polyethylene should be avoided because of the higher volumetric wear. With the new developments of metal-on-metal hip resurfacing and the production of big modular metal heads, the metal-on-metal bearing should guarantee a low-wear result without osteolysis.

Between November 2000 and December 2003 45 patients requiring a revision were treated with a Birmingham Hip Resurfacing cup (MMT, UK) and a big metal-on-metal modular head. All surgery was done with a posterolateral approach. Cup sizes range from 44 to 66 mm, head sizes range from 38 to 58 mm. The head sizes most often used were 58 mm, 54 mm and 50 mm. All patients were prospective followed using the Orthowave software (CRDA France).

In this series of 45 revisions (mean age 56.17) with large modular heads we encountered 2 dislocations, which give us a dislocation rate of 4.4%. One of these dislocations became recurrent and was revised to a full-constrained acetabular component.

Our own dislocation rate in revision hip surgery is 13% (21/159) in the anterolateral approach. Dislocations using the posterolateral approach increased this percentage to 14.8% (21/141). Taking in account that 31% of the causes of revision were infection and recurrent dislocation, this trial demonstrates that large diameter ball heads give beside a better range of movement also a statistically proven reduction in the dislocation rate in revision hip surgery.