Abstract
355 non-cemented MOM arthroplasties, of a single surgeon, with a follow up of 3–16 years (avg. 7.5 years) were retrospectively reviewed for evidence of pseudotumor and aseptic mechanical failure. There were 186 with 28 mm heads, 126 with 34 mm heads, 47 with 38 mm heads, from a single manufacturer.
There were 5 revisions of 38 mm heads for atraumatic painful “metalosis” 4–8 years after implantation (10.7%).
There were 4 revisions of 34 mm heads for post-traumatic instability (dislocation) with secondary metalosis 4–7 years after implantation (3.1%)
There were 2 revisions of 28 mm heads for post-traumatic instability (dislocation) with secondary metalosis 6–12 years after implantation (1.1%).
There were 5 patients, all with 38 mm heads, with asymptomatic “psoas bursae” with elevated serum CR and Co levels (1.0–3.0).
All of the failed THR's had acetabular components with lateral tilt <50 degrees (35–50), and anteversion angles <15 degrees (0–15). 2 of the 34 mm and both 28 mm instabilities were the consequence of injuries sustained in motor vehicle accidents. The remaining 2 instabilities with 34 mm implants were the result of mechanical falls.
Particulate debris, whether secondary to polyethylene, ceramic or metal articulations has been well documented as a cause of synovitis and damage to bony and soft tissues adjacent to a THR. This debris appears to be the result of material wear and mechanical failure with use over time. Unlike native articular cartilage, these materials are incapable of self-lubrication. Therefore THR articulations are dependent upon the penetration of ambient synovial fluid to provide lubrication of the replacement surfaces. This study suggests that increase in head diameter may reduce penetration of synovial fluid between the articulating surfaces of a THR, compromising the lubrication of bearing surfaces; thereby contributing to accelerated wear and premature failure of larger MOM arthroplasties.
