Prospective cohort study of 660 metal-on-metal hip resurfacings and large-diameter THRs (ASR and BHR). The study asks why some patients develop adverse reactions to metal debris (ARMD) requiring early revision. It tests whether excess bearing wear or systemic metal hypersensitivity is the primary mechanism.
The MoM debate centered for years on whether ARMD was an allergy or a wear problem. This paper answers it: the mechanism is excess wear from edge loading, not pre-existing immune sensitization to metal ions.
The ASR's reduced arc of cover (151° vs 162° for a size-matched BHR) places the contact patch structurally closer to the acetabular rim. Add a small femoral head or excess anteversion and edge loading becomes inevitable, regardless of surgical skill.
When you see an ASR patient with groin pain, check whole blood cobalt immediately. A level 20 times normal means the bearing is failing, not the patient's immune system. Low threshold for revision applies — tissue necrosis can be extensive even in patients who are still ambulatory and initially satisfied.
This paper is foundational to understanding why the ASR was eventually recalled and why arc of cover became a core design criterion for MoM bearings. It also established blood metal ion surveillance as standard of care for all MoM patients.
Prospective cohort study of 660 metal-on-metal hip resurfacings and large-diameter THRs (ASR and BHR). The study asks why some patients develop adverse reactions to metal debris (ARMD) requiring early revision. It tests whether excess bearing wear or systemic metal hypersensitivity is the primary mechanism.
The MoM debate centered for years on whether ARMD was an allergy or a wear problem. This paper answers it: the mechanism is excess wear from edge loading, not pre-existing immune sensitization to metal ions.
The ASR's reduced arc of cover (151° vs 162° for a size-matched BHR) places the contact patch structurally closer to the acetabular rim. Add a small femoral head or excess anteversion and edge loading becomes inevitable, regardless of surgical skill.
When you see an ASR patient with groin pain, check whole blood cobalt immediately. A level 20 times normal means the bearing is failing, not the patient's immune system. Low threshold for revision applies — tissue necrosis can be extensive even in patients who are still ambulatory and initially satisfied.
This paper is foundational to understanding why the ASR was eventually recalled and why arc of cover became a core design criterion for MoM bearings. It also established blood metal ion surveillance as standard of care for all MoM patients.