PAIN FOLLOWING HIP RESURFACING: IS THE ANGLE OF ACETABULAR CUP INCLINATION TO BLAME?

Abstract

Introduction: Hip resurfacing is a successful pain-relieving procedure which restores function in young patients. However, some patients have persisting pain. We suggest that load characteristics in relation to position of the cup may influence these symptoms. We aimed to determine the effect of acetabular cup inclination angle on pain following hip resurfacing.

Methods: 92 consecutive hips in 81 patients were resurfaced with the ASR prosthesis. The average age was 56.5 years (35–72). 33 were female hips. Harris Hip Scores (HHS) and UCLA activity scores were recorded pre-operatively and at last follow-up. Patient satisfaction was recorded. Acetabular cup inclination angle was measured. An acceptable angle for hip replacement is 45 degrees +/− 5 degrees. We therefore grouped cups into those above 50 degrees and those below. Average follow-up was 17.9 months (8–31). There were 39 hips with an angle less than 50 degrees (A), and 53 greater than 50 (B). Patients in each group were comparable for age, sex, follow-up and BMI.

Results: In group A HHS improved from 53.4 to 98.7 and UCLA activity score improved from 4.2 to 7.5. All patients were extremely or very pleased. In group B HHS improved from 49.0 to 94.0 and UCLA activity score improved from 3.9 to 7.1. 48 of 53 patients were extremely or very pleased. At follow up 37 of 39 (95%) of patients in group A had no pain. In group B 35 of 53 had no pain (66%). This is a statistically significant difference when analysed with Fisher’s exact test (p< 0.05).

Discussion: This study shows that an excessively open acetabular cup may contribute to persisting pain and patient dissatisfaction. This may be a result of excessive eccentric wear and metal ion deposition, and may lead to early failure of the prosthesis.