Late dislocations after total hip arthroplasty: Is the bearing a factor?
- Shah SM, Walter WL, Tai S, Lorimer M, deSteiger R
- The Journal of Arthroplasty (2017), accepted manuscript. doi: 10.1016/j.arth.2017.04.037.
- Level of Evidence:
- None given. Registry-based study.
Shah et al. investigated the risk of revision due to late dislocation in THA with ceramic-on-ceramic (CoC) bearings compared to ceramic-on-highly cross-linked polyethylene (CoXPE) and metal-on-highly cross-linked polyethylene (MoXPE) bearings analyzing tdata from the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR). Their hypothesis was that CoC bearings should have a lower incidence of late dislocation because of reduced wear and osteolysis.
All primary THA were included in the study for osteoarthritis utilizing MoXPE (101,915), CoXPE (30,256), and CoC (60,104) bearings with sizes 28, 32 and 36mm. The data was adjusted for age and gender. At 13 years 1,219 THA were revised for dislocation. The cumulative percentage revision (CPR) calculated for the 3 groups (MoXPE, CoXPE, CoC) at 2 years was 0.6, 0.4 and 0.5, respectively. At 13 years it was 1.2, 1.0 and 0.9, respectively.
For all head sizes, there was an increased risk of revision for dislocation for MoXPE bearings compared to CoXPE during the whole observation period, and for MoXPE compared to CoC after 3 months. Further analysis showed no effect of the bearing for head size 28mm, except during the first 3 months in which CoC bearings had a higher revision rate for dislocation. No differences were found for 32mm bearings. For 36mm bearings, MoXPE had the highest revision rate for dislocation after 3 months (Hazard Ratio 1.6 vs. CoC).
The authors conclude that overall the bearing surface had little influence on revision for dislocation, apart from a higher rate for 36mm MoXPE bearings. They speculate that this may be an effect of the release of corrosion products from modular junctions.
- Only revisions (for dislocation) included
- Only primary interventions due to osteoarthritis included
- No p-values given
- Dislocation risk depends – among many other things – on approach, positioning, laxity of the joint or capsule retention. None of these confounding factors were assessed or analyzed.
- There may also be a selection bias. Due to cost issues MoXPE bearings are more likely to be used in public hospitals.