Abstract
Introduction
Dislocation after primary total hip arthroplasty (THA) is a devastating and frequent postoperative complication. Many risk factors for dislocation have been identified, however, thus far there has been no consensus whether inflammatory arthritis is a risk factor for dislocation or not. We carried out a prospective study assessing the prevalence of dislocation within 2 years after primary total hip arthroplasty for osteoarthrosis and inflammatory arthritis.
Patients and Methods
Between 1996 and 1999 312 patients (342 hips) with either a primary or a posttraumatic osteoarthrosis (OA group) and 59 patients (69 hips) with rheumatoid arthritis or other forms of inflammatory arthritis (IA group) were operated. One single type of prosthesis was implanted (EPF-PLUS® cup and SL-PLUS® stem) using an anterior approach. All dislocations in the two years following surgery were recorded. Both diagnostic groups were compared for known risk factors such as old age, female gender, prior hip surgery, and experience of the surgeon. Radiographs were examined for avulsion fractures of the tip of the trochanter and signs of loosening. The abduction and anteversion angles of the acetabular component were measured. Statistical analysis was performed with the Chi-square test and Student’s t-test.
Results
The dislocation rate for inflammatory arthritis patients was significantly greater than that in patients with osteoarthrosis: 10. 1% (7 hips) in the IA group, 2. 9% (10 hips) in the OA group (p = 0. 006). There were no other differences in risk factors favouring dislocation in the IA group, such as old age, female gender, prior hip surgery, experience of the surgeon, trochanteric fractures or malposition of the prosthetic components. All dislocations in the IA group were posterior and occurred without any kind of trauma. In contrast, nearly half of the dislocations in the OA group were anterior and two were of traumatic origin.
Discussion
Taking into account the fact that there are no differences in known risk factors for dislocation between our two groups and no differences in complication rate, except for dislocation, we can say that inflammatory arthritis has to be considered an independent risk-factor for dislocation after primary total hip arthroplasty. It may be that inferior quality of the (pseudo) capsule and the muscles stabilising the hip joint due to inflammatory arthritis leads to inadequate soft tissue tension. Another factor can be the concomitant impairments in rheumatoid patients, such as impairments of the upper extremity, ipsilateral knee or contralateral hip, leading to hyperflexion in the operated hip causing a posterior dislocation without trauma.
