RM CUPS IN PATIENTS WITH ACETABULAR DYSPLASIA

Abstract

The Acetabular Dysplasia creates serious technical problems for the insertion of acetabular socket. In first, cup must have a good primary stable fixation in a shallow acetabulum. In second, smaller cups are usually required in dysplasia hip, but small sockets must have thick polyethylene wall. And in third, cup design must ensuring easy reconstruction of the anterolateral bone defect. In our opinion, all these problems can be achieved by using of cementless acetabular Robert Mathys (RM) cups.

Materials and Methods

In the period from 1996 to 2000 168 patients with ace-tabular dysplasia were operated with titanium powder coated RM cups. The patients age was from 18 to 75 years old (average 43,5). In 77 patients with type I dysplasia (AAOS classification) a primary stable fixation of the acetabular component in a good position without of filling bone defect was achieved. In 53 patient with type II dysplasia stable fixation was supplemented by closing of a cup by filler bone grafts in a place of bone defect. In case of type III dysplasia (38 patients) with very shallow acetabulum and extensive bone defects initial stabilization was achieved by the press-fit one or two anchoring pegs and insertion cancellous screws. In type III dysplasia the massive bone transplant was fixed by additional screws. The features of a design of a cup allowed to stop on the small socket sizes without danger of use implant with critically thin polyethylene wall. It considerably improved a covering of a cup.

Results

In 166 patients (98,8 %) a good medium-term results (2–6 years) were obtained. The radiologic controls have shown that the prostheses underwent good osteointegration. 2 patients (1,2%) needed revision. Of them one patient had a infected complication, one other had an aceptic necrosis of acetabulum and secondary cup migration. In all other patients no osteolisis was observed. The good primary fixation of the RM cup decreased the risk of aseptic loosing of the autologous bone graft. The temporal partial (not more than 1/3) bone graft resorption was find in 33,9 % at the type II and 42,1 % at the type III dysplasia. After 2 years in all cases we observed improvement of the bone stock quality at the site of bone grafting.

Conclusions

The features of a design of RM cup allow to use implants of the small size. The application for cup fixation pegs and screws allows to receive its reliable primary stability even at expressed acetabular dysplasia. The good primary stability and ease of application of bone grafts allows to achieve with RM cup of an overall objective of operation - maximal restoration of anatomy and biomechanics of the dysplastic hip joint.