In a small comparison of hip replacements performed after pelvic radiotherapy, trabecular metal cups were associated with higher revision-free survivorship than reconstruction cages. At the study's 10-year estimate, survivorship was 100% for the metal-cup group and 78.5% for the cage group. All 20 metal-cup hips remained free from revision, while 4 of 20 cage hips were revised. In this study, revision meant another operation involving the replaced hip.
The revision result was the only comparison the authors reported as statistically significant, with p = 0.040. The analysis also reported a hazard ratio of 5.18 and a 95% confidence interval from 0.82 to 32.74. A hazard ratio is a time-to-event comparison, while a confidence interval shows how widely the estimate could vary. The wide interval underscores how imprecise the size of the observed difference was.
Other measures were less decisive
The study's primary endpoint was survivorship free from aseptic loosening, meaning the implant remained free from the specific loosening event being tracked. At 10 years, that estimate was 100% with metal cups and 88.2% with cages. The difference was not statistically significant, with p = 0.182. A Firth penalized Cox analysis reported a hazard ratio of 3.42, with a 95% confidence interval from 0.52 to 22.45.
Function showed a similar numerical pattern. The postoperative Harris Hip Score, or HHS, was 88.9 for metal cups and 81.8 for cages, with p < 0.001. But the difference was below the minimal clinically important difference, the study's benchmark for judging whether a numerical change was clinically meaningful.
Complications were recorded in 10% of the metal-cup group and 25% of the cage group. The difference was not statistically significant, with p = 0.407. The figures therefore show a numerical gap, not a firm difference between the fixation groups.
A small, uneven comparison
The comparison drew on retrospective clinical records from one centre. It included 40 patients and 40 hips treated during 2008-2019, divided evenly between 20 hips with trabecular metal cups and 20 with reconstruction cages. The research question was whether the two fixation approaches differed in implant survivorship and function after pelvic radiotherapy. Because the cohort was retrospective and unmatched, the groups were compared as they appeared in the records.
Researchers used unpaired tests for group comparisons. For outcomes that unfold over time, they used Kaplan-Meier survivorship estimates with log-rank testing, along with Firth penalized Cox regression and sensitivity analyses. Kaplan-Meier analysis estimates how many implants remain free of a specified event as follow-up progresses.
The groups were reported as similar in age, sex and radiation dose, but their follow-up was not balanced. Median follow-up was 9.7 years in the cage group and 8.4 years in the metal-cup group, a difference reported as p = 0.036. The cage group was therefore observed longer, an imbalance that makes a direct comparison harder to interpret.
That design leaves several reasons for caution. The study was small, single-centre, retrospective and unmatched, and the authors say it was underpowered outside the revision comparison. The hazard-ratio confidence intervals were broad, pointing to imprecise estimates. As an observational cohort, the study can show an association between fixation type and outcomes in this group, but it cannot establish that one method caused the better result or identify the best fixation method overall.
Researchers call for confirmation
The authors describe the findings as hypothesis-generating. They say trabecular metal cups had numerically higher survivorship and function, but only the revision comparison was significant. They call for confirmation in larger, multicentre cohorts.
The study was supported by two Chang Gung Memorial Hospital research programs. The authors declared no competing interests, and the datasets generated or analysed during the study are available from the corresponding author on reasonable request.
Paper data and sources
Original title: Trabecular metal cups versus reconstruction cages for primary total hip arthroplasty in the irradiated acetabulum: a nine year comparative cohort study.
Authors: Yu-Chih Lin, Sheng-Hsun Lee, Shih-Hui Peng et al.
Journal/Repository: International orthopaedics
Status: Peer-reviewed
First online: 2026-08-21
DOI: 10.1007/s00264-026-07004-w
Original paper · Full text