Abstract
Introduction
Numerous studies have reported on clinically significant volumes of material loss and corrosion at the head-stem junction of metal-on-metal (MOM) hips; less is understood about metal-on-polyethylene (MOP) hips. We compared the effect of bearing type (MOM vs MOP) on taper material loss for a hip system of a single design (DePuy Pinnacle).
Methods
We recruited retrieved MOM (n=30) and MOP (n=22) bearing hips that were consecutively received at our centre.
We prospectively collected associated clinical and imaging data. We measured the severity of corrosion and volumes of material loss at each head taper surface and used multivariate statistical analysis to investigate differences between the two bearing types.
Results
The median rate of material loss for the MOM and MOP groups was 0.81 mm3/year (0.01–3.45) and 0.03 mm3/year (0–1.07) respectively (p<0.001). 29 out of 30 MOM hips were revised for adverse metal reactions, compared with 1 out of 22 MOP hips.
Discussion
MOP hips lost significantly less material from their taper junctions than MOM hips. We suggest that the metal-metal interaction at the bearing surface of MOM hips enhances the corrosive environment at the head-stem junction.
Conclusion
Our results can reassure patients with MOP Pinnacle hips that they are unlikely to experience clinically significant problems related to material loss from the taper junction.
