Abstract
Introduction
Total hip arthroplasty (THA) is the only successful treatment for patients in whom the hip joint is destroyed by inflammatory arthritis. Due to the effects of both the disease and its treatment elevated rates of complications and of aseptic loosening have been described. Whether with modern uncemented hip prostheses the results can be improved is not fully known. Therefore, we decided to carry out a prospective study.
Material and methods
At the introduction of a new press-fit acetabular component a prospective study on the results of uncemented THA was started. From 1995 to 1999 85 primary THAs were carried out in 72 patients (57 women, 15 men) suffering from inflammatory arthritis. Diagnosis: RA 76, adult-onset Still 4, JIA 3, miscellaneous 2. Mean age at operation was 60 years (SD 15. 9). Clinically, the Harris Hip Score was used for evaluation. Radiographically, the Larsen classification was used and at follow-up radiolucencies and signs of migration were registered.
The implants used in this study were the EPF-PLUS® acetabular component and the SL-PLUS® femoral component (PLUS Endoprothetik AG, Rotkreuz-CH). The EPF-PLUS® acetabular component is a novel modular press-fit cup. Its shell has a triple radius profile on cross-section, thereby creating a gradual lowering of the polar part of the cup. This produces a small gap of about 2 mm. between the acetabulum and the pole of the cup. Therefore, forces are mainly transmitted to the peripheral part of the acetabulum, leading to an enhanced primary stability. Originally, the shell had a gritblasted surface for osseointegration. Since 1996, the outer surface of the cup has been coated with a ground layer of pure titanium and a superficial layer of a crystalline hydroxyapatite (Ti-HA). The gritblasted version was used in 14 hips (1995–1996), the Ti-HA coated version in 71 hips. In 68 hips the cup was implanted by press-fit fixation, in 17 screws were added.
Results
Larsen classification was as follows: 0-1: 6; 3: 17; 4: 60; 5: 2. At follow-up, 5 patients (6 THAs) were deceased. Deep infection required revision in one hip. Another revision was carried out for recurrent dislocations. One grit-blasted cup developed late subsidence and was revised almost 4 years postoperatively. One Ti-HA coated cup failed early due to severe acetabular bone loss. Finally, one femoral component developed a varus tilt and became symptomatic 2 years after implantation, requiring revision. In all 62 patients with 74 THAs in follow-up cup and stem are functioning well, both clinically and radiographically. Harris Hip Score increased from 36. 6 (SD 17. 7) to 87. 9 (SD 11. 8).
Discussion
The medium-term results of the EPF®-PLUS cup show that its primary stability is good and that, as the polar gap rapidly disappears, osseointegration is secure. Only severe acetabular deficiency appears to be a contra-indication for this implant. Also, the SL-PLUS® stem performs well in inflammatory arthritis.
