Age and component head size related to primary total hip arthroplasty dislocation

Researchers note that the type of bearing surface did not soley impact dislocation rates.

VIENNA — Clinical researchers studying the effect of bearing surface on a patient’s risk of revision for dislocation following primary total hip arthroplasty for osteoarthritis found patient age and femoral head size had greater impacts on dislocations than bearing type.

Shaun A. Sexton, FRCS, of England, and his co-investigators from Australia identified 862 total hip arthroplasty (THA) revisions performed for dislocations among data for 110,239 THAs in the Australian Orthopaedic Association National Joint Replacement Registry between September 1999 and December 2007.

Based on their findings, this represented a 0.8% revision rate, according to Sexton.

“This is the first large-scale analysis of dislocation rate by bearing type. Based on a literature review, we postulated that some bearing types may be at a higher risk for dislocation,” said Sexton, who presented the results at the 10th European Federation of National Associations of Orthopaedics and Traumatology (EFORT) Congress, here.

Adjusted analysis

Sexton and colleagues studied all revisions due to dislocations in the Australian Orthopaedic Association National Joint Registry by bearing type. This included 20,627 ceramic-on-ceramic, 14,001 ceramic-on-polyethylene, 12,208 metal-on-metal and 62,437 metal-on-polyethylene implants. Less than 1% of the registry records did not mention the bearing surface used.

The rate of revision due to dislocation was 0.3 per 100 component years, Sexton told Orthopedics Today.

After finding that the bearing type alone did not seem to impact dislocations, researchers adjusted their analysis using patient age, gender and femoral head size to detect other possible factors that might be related to THA dislocations. In doing that, they found ceramic-on-ceramic THA was associated with the highest revision rates for dislocation vs. a traditional metal-on-polyethylene bearing surface.

Metal-on-metal dislocations

Based on the study’s results, this difference was only seen with head sizes less than or equal to 28 mm used in patients younger than 65 years old and in heads greater than or equal to 28 mm implanted in patients older than 65 years old.

“Overall, ceramic does not have a higher dislocation rate,” Sexton noted. “But when we controlled for age and femoral implant head size, we found that is some subgroups ceramic-on-ceramic bearings had a higher revision rate due to dislocation.” Furthermore, he said, “We found that there was a higher revision due to dislocation in metal-on-metal compared with metal-on-polyethylene in the cases when a small head size was used in younger patients.”

Since the registry cases had only 7 years of follow-up, investigators theorized that more dislocations could still conceivably occur in the future in the metal-on-polyethylene group, possibly due to polyethylene-liner wear, which could alter the findings. Therefore, another analysis of the data to retest these findings may be required in the future, Sexton said.

One of the moderators asked whether the investigators observed a relationship between gender or surgical approach and THA dislocation rates in their study.

Sexton replied, “We controlled for gender in the statistical analysis. However the joint registry does not provide data on surgical approach and therefore we are unable to say whether approach was a risk factor.” He added, “Due to recent advances with improved offset and head size options now available with ceramic-on-ceramic bearings as well as a reduced risk of ceramic fracture, the higher revision due to dislocation may no longer be present when the joint registry data is revisited in the future.”

For more information:

• Shaun A. Sexton, FRCS, can be reached at shaunsexton@doctors.org.uk. Orthopedics Today was unable to determine if he has a financial interest in any product or company mentioned in this article.

Reference:

• Sexton SA, De Steiger R, Jackson M, et al. Bearing surface and risk of revision due to dislocation after primary total hip arthroplasty. Paper #F584. Presented at the 10th EFORT Congress. June 3-6, 2009. Vienna.