Mixing and matching femoral, acetabular components OK

Large outcomes study showed different manufacturers’ components are often combined.

Issue: November 2005

Although current recommendations caution against it, a large-scale patient outcomes database has indicated that mixing femoral stems and acetabular cups from different manufacturers had no statistically significant effect on surgical outcomes.

At the recent British Orthopaedic Association Annual Congress, J. Glynne Andrew, FRCS, senior lecturer at Hope Hospital, Manchester, told the audience of his analysis of data from the Exeter Primary Outcomes Study (EPOS).

“Mixing femoral and acetabular implants from different manufacturers in total hip replacements (THRs) is discouraged but its actual importance is unknown,” he reported. “This topic has been the subject of a certain amount of debate.” He said the theoretical risks associated with mixing and matching stems and cups would possibly be corrosion between different metal, mismatched tapers and size differences between the heads and the cups.

“As far as we know there is no good evidence to show that it is harmful in the metal-on-polyethylene bearing. However, there is evidence that it is harmful with the ceramic heads; in particular, some of the reports of failures with the ceramic heads have been associated with the use of ceramic heads from one manufacturer and the stem from another manufacturer,” he said.

The EPOS

Andrew and colleagues used the EPOS, which has data from 10 centers located throughout Great Britain. The investigation was prospective, nonrandomized and focused on 1600 patients who received the cemented Exeter stem with various approaches using various acetabular components. The implanting center chose the acetabular components. The investigators used several main components (more than 100 each) used including Exeter, Exeter Contemporary, Duraloc, Charnley, Charnley Elite, Cenator and Trilogy. They also used a small subset of miscellaneous cups, of which less than 20 of each were used.

Patients were followed for a minimum of three years and were assessed using the Oxford Hip Questionnaire at the preoperative, three months, one-, two-, and three-year postoperative milestones.

Most acetabular components were either Charnley or Exeter. Andrew said that the preoperative evaluations indicated differences between the patients who received certain cups, particularly the Charnley. Further investigation showed those patients were associated with two particular centers in northern England, where patients’ scores were worse on the preoperative assessments but were not reflective of any difference in outcomes measures. “Comparing the outcomes data with 1100 other patients, you can see that there is a difference in the outcomes questionnaire, with the worse outcomes for the Charnley cup,” he said. “But if you look at the changes in the questionnaire, between the preop and the postop there is absolutely no difference.”

Andrew said there was a marginal increase in range of motion for patients who received the Exeter cups. In terms of patient satisfaction there was no difference between the main cups, but there was a marginal difference in the miscellaneous subgroup. There was a marginal improvement in quality of life data for the Exeter and the Trilogy cups.

“The number of complications was relatively small; in fact there was no statistically significant differences, but there was a higher number of dislocations in the uncemented cups. There was no statistical significant difference in the revisions at two years,” he said.

For more information:

JG Andrew, D Beard, J Nolan and the Exeter Primary Outcomes Study Group. “Mix and match” of femoral and acetabular components in total hip replacement — no effect on initial clinical benefit of surgery. Presented at the British Orthopaedic Association Annual Congress. Sept. 20-23, 2005. Birmingham, England.