Catastrophic Femoral Head-Stem Trunnion Dissociation Secondary to Corrosion.

BACKGROUND Modular femoral heads provide procedural enhancement by allowing accurate restoration of hip offset and limb-length equalization. However, corrosion may lead to adverse local tissue reactions. Severe trunnion corrosion can also lead to femoral head dissociation and catastrophic implant failure following primary total hip arthroplasty. METHODS We describe 5 cases, from our institution, in which the femoral head became dissociated from the femoral stem trunnion secondary to severe corrosion. Possible causes are evaluated. RESULTS Demographic commonalities among the 5 patients included a body mass index (BMI) of ≥30 kg/m(2) and male sex. All femoral heads were made of cobalt-chromium alloy and were larger-diameter implants (≥36 mm). Four of the 5 patients had a femoral head that increased the neck length above the default on a so-called standard head and 3 of the 5 had a stem with a 127° neck-shaft angle. CONCLUSIONS Although dissociation of the femoral head from the femoral trunnion following total hip arthroplasty is exceedingly rare, the prevalence may increase with longer follow-up. The dissociation is likely related to multiple factors, including a BMI of ≥30 kg/m(2), male sex, and corrosion resulting from the use of a larger metal head with a neck length of greater than the default and a stem with high offset. It is critical that surgeons be able to recognize this mode of implant failure and appropriately prepare to remove the femoral component during revision surgery. LEVEL OF EVIDENCE Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.