Abstract
Background
The New Zealand Joint Registry was started in 1999. An audit in 2009 showed 98% compliance. Ten year results were published in 2009. For Total Hip Replacement it showed that dislocation was the most common cause for revision (35%).
Methods
We reviewed the rate of revision for dislocation in the two most common diagnostic groups, Osteoarthritis (86%) and Acute Fracture NOF (3.6%) relative to the two most common surgical approaches, posterior and lateral. We also sought to analyse whether larger femoral head sizes decreased the dislocation rate.
Results
In Osteoarthritis there was a highly significant increase (p< 0.001) in revision for dislocation for the posterior (307 of 27,219 or 1.1%) over the lateral approach (56 of 12,599 or 0.4%). The revision rate per 100 component years decreased with increasing head size in both surgical approaches. This was significant only in the posterior approach for 36mm over 22mm and 28mm heads (p< 0.05). In Acute Fracture NOF the revision rates are higher than for osteoarthritis (1.6% posterior and 1.1% lateral) but there is no statistical difference between the two approaches (p = 0.37). The NOF group shows a non-significant increase in dislocation for 32mm heads over 28mm in both approaches, but no dislocations for the small number of 36mm heads.
Conclusion
This review confirms that the posterior approach has a significantly higher revision rate for dislocation over the lateral approach in osteoarthritis. The posterior approach shows a significant advantage for the 36mm head over 22 and 28mm, but the rate for the 36mm head posterior was virtually the same as for a 28mm head via the lateral approach. Larger diameter heads could lead to later revision from greater volumetric wear, increased frictional torque and thinner poyethylene liners and should be used with caution. To reduce dislocation in osteoarthritis the lateral approach should be considered.
