Failure of a Modular Femoral Revision Stem in Hip Arthroplasty: A Rare Complication and Literature Review.

Introduction: Zimmer modular revision (ZMR)® femoral stems are widely utilized in revision total hip arthroplasty (rTHA) due to their intraoperative customization that offers surgical flexibility in reconstructing complex hip joints. However, despite these advantages, the modular junction is prone to localized stress concentration, which may transfer cantilever loads distally. This mechanical environment possibly causes a fracture, often in the body-stem junction, where the cross-sectional area is reduced. Moreover, patient-based factors in addition to implant-related factors can both contribute to such rare but catastrophic failure. Factors such as bone quality, implant design, and surgical technique must be evaluated. These assessments will help in the formulation of a long-term management plan, along with a strategy to prevent this issue. Case Report: In this report, we present a 70-year-old male patient with a past medical history of hypertension and a past surgical history of a left THA in 2011, a right THA in 2016, and a revision left THA using ZMR secondary to a periprosthetic fracture in 2021. In December 2023, he presented to the emergency department with a 2-day history of sudden atraumatic left groin pain. Imaging revealed a femoral stem fracture at the body-stem junction. Conclusion: Although rare, cantilever fatigue of the ZMR stem is a serious complication. It is linked to both patient related factors (advanced age, high BMI, poor proximal bone stock), and implant factors (shorter length, smaller diameter, extended offset), with failure oftern), with occurring at the body-stem junction.