Head-neck modularity in total hip arthroplasty (THA) components confers several advantages, including intraoperative flexibility and precision that allow surgeons to adjust leg length and femoral offset. Also, in this age of “value-based purchasing,” modular hip implants may help hospitals reduce their implant inventory.
But modularity has its drawbacks, one of which is the increased number of interfaces at which wear and corrosion can occur. These metallurgical phenomena increase the risk of mechanical failure, metallosis, and adverse soft-tissue reactions.
In the April 22, 2015 edition of JBJS Case Connector, Arvinte et al. describe the case of a 64-year-old man who presented with a sudden onset of left groin pain and an inability to bear weight. Fourteen years earlier surgeons had performed a left THA using a modular titanium-alloy stem with a 6-degree trunnion taper and 32-mm cobalt-chromium head. The patient described intermittent but painless clunking in the same hip beginning five years after THA.
Radiographs showed a clear dissociation between the femoral head and neck. During revision, surgeons noted metallosis but no evidence of infection. Macroscopic examination of the removed components revealed substantial fretting and corrosion wear at the proximal part of the trunnion, leading the authors to conclude that chronic failure of the trunnion caused the eventual dissociation of the modular head. They speculated that the failure process may have begun with the clunking in the hip five years after the initial THA.
The patient made an unremarkable recovery and had excellent clinical and radiographic outcomes at the nine-year follow-up. The authors suggest that the onset of clicking or clunking in a modular hip “should be investigated as it may be a harbinger of head-neck dissociation.”