Summary
This study compares the cumulative percentage of revision for large Exeter stems to smaller Exeter stems to evaluate an increased risk of late revision for larger stem sizes by loosening and peri-prosthetic fracture. The data confirms our initial hypothesis that a statistically significant increased risk of late revision for fracture exists for larger stem sizes (4-6) compared to smaller sizes.
Abstract
Introduction
Since 1970, the Exeter cemented femoral stem has demonstrated excellent clinical and radiographic outcomes as well as long-term survivorship for primary total hip arthroplasty. However, recent studies have shown a potential trend of increased late revisions for larger stem sizes (size 4-6) for loosening and for peri-prosthetic fractures. This study aims to compare the cumulative percentage revision of large Exeter stems (sizes 4-6) to other smaller Exeter stems (sizes 0-3) to evaluate whether there exists a statistically significant increased risk in late revision for larger sizes for loosening and peri-prosthetic fracture.
Methods
Data from the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) were analysed for all primary total conventional hip procedures undertaken for osteoarthritis using the Exeter stem for the period September 1999 to December 2019. The primary outcome measure was the cumulative percent revision (CPR) for all causes and the CPR for fracture. Results were adjusted for age and gender. A sub-analysis was performed comparing the Exeter stems by offset sizes 37.5mm, 44mm, 50mm and 56mm.
Results
There were 84,037 primary THA procedures undertaken for OA. Of these, 81,976 were size 0-3 and 2,061 were size 4-6. The CPR at 17 years was 7.8% (95% CI 7.3, 8.4) for the size 0-3 group and 10.7% (95% CI 7.9, 14.4) for the size 4-6 group. There was no difference in the risk of revision when the two stem size groups were compared (entire period HR=1.17 (95% CI 0.94, 1.45), p=0.169). There was a higher CPR for fracture for size 4-6 stems compared to size 0-3 from 3.5 years onwards (HR=2.23 (95% CI 1.41, 3.53), p<0.001), with no difference between the two groups prior to this time. Large offset size was a risk factor for revision, with size 56mm having a higher rate of revision when compared to offset size 37.5mm (entire period HR=1.68 (95% CI 1.00, 2.81), p=0.050). There were no other differences between the remaining offset sizes.
Conclusion
The data obtained confirms our initial hypothesis that a statistically significant increased risk of late revision for fracture exists for larger stem sizes (Size 4-6) as compared to smaller sizes (Size 0-3). Fracture was also identified as the commonest cause for late-stage revision in larger sizes, specifically starting from 10 years post-primary procedure.