Large diameter metal-on-metal hip replacements yield high failure rate, corrosion
One recent investigation from U.K. researchers has found an “unacceptable” high rate of failure among large diameter, hybrid metal-on-metal hip replacements studied, according to results presented at the British Orthopaedic Association and Irish Orthopaedic Association Combined Meeting 2011 in Dublin.
According to study author Ben JRF Bolland, MBBS, MD, FRCS(Tr & Orth), the findings also noted evidence of high wear at the head and trunnion surface in retrieval components, as well as passive corrosion to the stem surface — raising concerns over the use of large heads on conventionally utilized 12/14 tapers.
The cumulative survival rate in the study was 92.4% for revision for any reason at 5 years.
“This is a clinical single-surgeon series of a large diameter, hybrid, metal-on-metal total hip replacement,” Bolland said. “We wanted to try and establish whether there were some predictors of failure in the workup of these patients which could help the surgeon make a choice. We also wanted to get a retrieval analysis, so we could determine the mechanism of failure.”
Bolland’s study involved mid-term results in 199 hips (182 patients) through a mean follow-up of 62 months. He and colleagues examined clinical and radiological outcomes and analyzed retrieval findings, as well as metal ion levels.
At the time of his presentation, 17 patients (8.6%) had undergone revision with another 14 patients awaiting revision. Women comprised 68% of those having implant failures (21). Progressive radiological changes were identified in 24 cases of failure, with 14 revision cases demonstrating evidence of adverse reactions to metal debris. As a whole, the failure cohort was found to have “significantly higher” whole blood cobalt ion levels — but no significant differences were detected in size, inclination or version of those cups compared to the unrevised cohort.
In isolation, the presence of pain and radiographic changes were found to be significant predictors of failure, Bolland reported.
Increased wear was found at the trunnion/head interface and increased corrosion was seen within the proximal and distal stem surfaces, as noted in the study abstract.
“In summary, we have shown high failure rates with a high incidence of adverse reaction to metal debris,” Bolland concluded. “Females appear to be at increased risk. Component size and position does not seem as critical … pain and X-ray changes are strong indicators of failure. We showed evidence in retrievals that there is wear in the trunnion, as well as corrosion of the stem. How this fits in with methods of failure, we are not sure at the present time.”
- Bolland BJRF, Culliford DJ, Langton DJ, et al. High failure rates with a large diameter hybrid metal-on-metal total hip replacement: Clinical, radiological and retrieval analysis. Presented at the British Orthopaedic Association and Irish Orthopaedic Association Combined Meeting 2011. Sept. 13-16. Dublin.