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Detection difficulties using radiographs may lead to under-reported mismatches in hip component size
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An analysis of metal-on-metal hips showed a 1% prevalence of component size mismatch, an event that may be underreported due to difficulties in intraoperative and plain radiograph detection, according to researchers.
Through a review of 1,200 failed metal-on-metal hips, researchers found 11 cases failed due to possible component size mismatch (CSM). To determine at what stage and now CSM was detected, the researchers reviewed clinical data, operative details from the revision surgery and prerevision imaging data on implants labelled as CSM. The researchers also compiled a short questionnaire containing 10 radiographs with various pathologies and distributed it to three orthopedic consultants and three senior trainees to determine the effectiveness of plain radiographs to show CSM.
During routine clinical follow-up, none of the mismatched cases were detected on plain radiograph, according to the researchers.
High wear rates and blood metal ion levels above the Medicines and Healthcare products Regulatory Agency action level of 7 ppb were found in cases of CSM.
There was a 27.7% mean detection rate among surgeons, with four of six detecting at least one of the three cases and one identifying two out of three cases of CSM on radiograph.
Manufacturer, hospital and surgeon factors were identified by root cause analysis as those that need to be addressed to reduce the incidence of CSM, because the only method of confirming size mismatch is currently through retrieval analysis.
Disclosure: Hart and Skinner have received funding from the British Orthopaedic Association.
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