Long-term results of cementless primary total hip arthroplasty with a threaded cup and a tapered, rectangular titanium stem in rheumatoid arthritis and osteoarthritis

Abstract

The aim of this study was to assess the outcome of primary cementless total hip arthroplasty in rheumatoid arthritis patients and to compare the results with osteoarthritis patients. Sixty-four patients (77 hips) with rheumatoid arthritis and 120 patients (135 hips) with osteoarthritis had a conical-shaped Zweymueller threaded cup and a tapered, rectangular Zweymueller stem implanted and were assessed after an average of 12.5 years. The endpoints for survival analysis were failure of one or both components due to radiographic loosening or revision. Revision was defined as exchange of cup, stem or both. When the PE-insert or the ceramic ball head were exchanged leaving cup and stem in place, e.g. for PE-wear or dislocation, this was not considered a revision but a re-intervention. No differences were found in survival rates; however, in the rheumatoid arthritis group there was an increased rate of malposition of the cup, avulsions of the greater trochanter, and increased bone resorption in the trochanteric region. This study shows that despite altered biomechanical properties of rheumatoid bone, mechanical stability and osseous integration of cementless prosthesis are not compromised and, although a higher complication rate did occur, long-term survival is excellent.

Fig. 1

a Protrusion of the cup through the acetabular floor perforating the internal lamina of the pelvis. b A too cranial position of the cup in relation to the anatomical acetabulum. c Tilting of the cup with radiolucent lines in all three zones 2 1/2 years after implantation

Fig. 2

AP radiograph of the left hip of a 78-year-old female patient with rheumatoid arthritis 11 years after implantation of the Zweymueller prosthesis. Typical radiographic result with bone atrophy in the acetabulum in zones I and II, thin radiolucent lines around the stem in zones I and VII, and bone atrophy in the proximal femur in zones I and VII

Fig. 3

Kaplan-Meier survival analysis of the cup (a) and stem (b) with failure due to aseptic loosening as endpoint. Failure due to any cause other than aseptic loosening was regarded as a censoring event. X-axis: months since operation. Y-axis: proportion of components unrevised. For confidence intervals at ten years see text

Fig. 4

Cumulative incidence of failure of one or both components of THA in a competing risk setting, by diagnostic group (left panel RA group; right panel OA group). X-axis: time in months since operation. Y-axis: probability of failure. Red area: probability of failure due to aseptic loosening (both early loosening and late loosening with osteolytic lesions and PE wear). Blue area: probability of failure due to other causes such as peri-prosthetic fracture, infection, malposition and recurrent dislocation