October 06, 2017
2 min read

Findings support use of thresholds to identify patients at risk for adverse reactions to MoM hip implants

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Results from this study indicated patients with blood metal-ion levels that did not meet implant-specific thresholds had a low risk for adverse reactions to metal debris following metal-on-metal hip procedures.

Gulraj S. Matharu

“Our large, multicenter validation study confirmed that patients with [Birmingham hip resurfacing] BHR or Corail-Pinnacle [metal-on-metal] MoM implants and blood metal-ion levels below newly devised implant-specific thresholds were at a low risk of having [adverse reactions to metal debris] ARMD,” Gulraj S. Matharu, BSc(Hons), MRCS, MRes, told Healio.com/Orthopedics. “These new thresholds missed fewer patients with ARMD compared with current fixed thresholds proposed by worldwide regulatory authorities. We, therefore, now have good evidence supporting the use of implant-specific blood metal-ion thresholds when managing patients with MoM hip arthroplasties.”

Researchers performed a validation study of 803 MoM total hip arthroplasties. Of these, 323 were unilateral BHR), 93 were bilateral BHRs and 294 were unilateral procedures done with Corail-Pinnacle implants. Investigators performed whole-blood metal-ion sampling in all patients and categorized patients into either an ARMD group or those without ARMD. Investigators used thresholds of 2.15 g/L of cobalt for the unilateral BHRs, a 5.5 g/L ceiling for cobalt or chromium for the bilateral BHR and 3.57 g/L for unilateral procedures that used the Corail-Pinnacle.

Results showed investigators missed 20 patients with an ARMD when they used the implant-specific thresholds. For the ability to differentiate between patients with an ARMD and those without, the area under the curve, sensitivity, specificity and positive and negative values for each implant-specific threshold for unilateral BHR was 89.4%, 78.9%, 86.7%, 44.1% and 96.9%, respectively; 89.2%,70.6%, 86.8%, 54.5% and 93%, respectively, for bilateral BHR; and 76.9%, 65%, 85.4%, 24.5% and 97.1%, respectively, for unilateral Corail-Pinnacle implants.

According to researchers, more patients with an ARMD were missed when they used thresholds recommended by regulatory authorities compared with 35 patients when researchers used the U.K. threshold of 7 g/L for both cobalt and chromium, 21 patients when the U.S threshold of 3 g/L for both cobalt and chromium was used. Forty-six patients were missed with the U.S. threshold of 10 g/L for both cobalt and chromium. – by Monica Jaramillo


Disclosures: Matharu reports he receives financial or material support from the Arthritis Research UK (Clinical Research Fellowship), The Orthopaedics Trust (Research Grant), The Arthritis Research Trust (Surgical Research Fellowship) and The Royal Orthopaedic Hospital Hip Research and Education Charitable Fund Research Grand. Please see the full study for a list of all other authors’ relevant financial disclosures.