Multiple factors contributing to an elevated risk for dislocation after total hip arthroplasty (THA) have been identified. Patient-related risk factors that have been identified are prior hip surgery, old age and female gender. However, there have been no prospective reports whether inflammatory arthritis (IA) is an independent risk factor.
From January 1996 to December 1999 427 primary total hip arthroplasties were carried out using one type of uncemented prosthesis: a hydroxyapatite coated EPF-PLUS® cup and a SL-PLUS® stem (PLUS Endoprothetik AG, Rotkreuz-CH). A 28 mm. ball head was used in every hip. To evaluate whether IA is a risk factor for dislocation the incidence and cause of early (<
2 year post-surgery) dislocation in IA hips was compared with those carried out for osteoarthrosis (OA). There were 341 THAs in 311 patients with OA and 69 THAs in 59 patients with IA (mainly rheumatoid arthritis) included in this study. The remaining 17 THAs were for various other reasons and excluded from this study. Statistical analysis of the dichotomous variables was carried out by the chi-square test and the Fisher’s exact test, Student’s t-test was used for the analysis of continuous variables.
Both groups were comparable with respect to the following risk factors: gender, approach (either straight-lateral or anterolateral), position of the acetabular component and experience of the surgeon. Mean age was lower in the IA group than in the OA group: 61. 0 vs 68. 1 years. Furthermore, the incidence of prior hip surgery was higher in the OA group. The incidence of dislocation was 7 out of 69 (10. 1%) in IA hips and 10 out of 341 (2. 9%) in OA hips (p=0. 006). All dislocations in IA where posterior, in OA 5 were posterior and 4 were anterior (1 unknown). No other mechanical factors leading to an increased instability of the hip in IA, such as trochanteric fractures, could be identified. Due to the relatively small numbers a statistical difference in the direction of dislocation could be identified (p= 0. 088). So, IA has to be considered as an independent risk factor for dislocation after THA. Both the polyarticular impairments and the lower quality of the soft tissues in IA could explain this elevated risk. To reduce the incidence of dislocation in IA it therefore seems advisable to pay detailed attention the soft tissues and the position of the prosthetic components in IA at the time of surgery. Also, consideration should be given to the use of an acetabular component with an elevated rim.
