A case series of modular hip hemiarthroplasties employing a metal-on-metal taper-trunnion junction : are they a source of metal particle release?

Aims: Hip hemiarthroplasty is a common procedure in the treatment of intracapsular displaced femoral neck fractures. Modular hemiarthroplasties have a separate stem, neck, and head component which gives the surgeon more combinations to try and accurately recreate the patient's original hip geometry. Despite regular use, little is known regarding susceptibility to metal-on-metal debris wear in this specific situation.

Methods: This single-centre, two-year prospective cohort study aimed to characterize in vivo wear and associated adverse reaction to metal debris (ARMD) in an uncemented CORAIL stem and Cathcart modular head hip hemiarthroplasty. The mean patient age was 80.5 years (62 to 96) and mean follow-up 2.2 years (1.0 to 4.6). Overall, 54 patients had a clinical, radiological, and serum metal ion (chromium (Cr) and cobalt (Co)) assessment. At follow-up radiological evidence of acetabular erosion was graded (0 to 3: normal to protrusio). Metal ion levels were considered high if ≥ 7 ppb as per current Medicines and Healthcare products Regulatory Agency guidelines.

Results: Final Cr and Co levels in ppb were 0.26 (IQR 1.33; 95% CI 0.67 to 5.16) and 0.68 (IQR 2.52; 95% CI 1.25 to 3.30), respectively. The mean one-year Oxford Hip Score was 35 (SD 10). Acetabular erosion was detected in 27 patients (50%). All eight patients (14.8%) with high metal ion levels had associated acetabular erosion, of which four (50%) had an ARMD lesion. Patients with high metal ion levels had a similar head size with the same taper size, similar OHS, and similar pre-fracture mobility to those with low metal ion levels.

Conclusion: Modular hip hemiarthroplasty patients may be susceptible to metallosis and ARMD despite being less active individuals than those who receive a total hip arthroplasty. Acetabular erosion was associated with a 2.5-times increased risk of raised metal ion levels but cause and effect have not been established.