Charnley Elite follow-up confirms high early failure rate predictions

Posterior head migration viewed as a ‘powerful’ predictor of failure.

Researchers have identified a 33% combined radiographic loosening and revision rate for the Charnley Elite Plus hip stem in a nine-year follow-up study, confirming failure rate projections from their initial two-year study.

Calling the stem “rotationally unstable,” the British researchers continue to advise against using it.

The Charnley Elite Plus (DePuy), introduced in 1992 as a later generation of the highly successful Charnley, had excess early posterior head migration Posterior Head Migration, which is a manifestation of internal rotation of the stem within the femur. The new study also presents Posterior Head Migration as a powerful predictor of failure based on its correlation to later stem loosening.

The original Charnley, a low-friction total hip replacement implant, has more than 30 years’ follow-up and less than 10% stem failure at 10 years. The new Elite Plus is more anatomical with an enhanced shoulder flange and a different surface finish.

RSA predictions correct

Questions first arose about the Elite in 1999 when Richie Gill, DPhil, and colleagues showed in a two-year radiostereometric analysis (RSA)-based study comparing the Elite with the Exeter stem (Stryker), that the Elite’s Posterior Head Migration measured two-and-a-half times that of the Exeter stem on average. The researchers first recommended against using the Elite back then, noting that one subset (20%) of early Elite patients showed particularly high Posterior Head Migration — averaging 2.8 mm per year vs. 0.26 mm for Exeter patients.

Distal migration, although four times higher in the Exeter than in the Elite Plus, did not necesarilly correlate with failure, said Gill, a university research lecturer at the Nuffield Department of Orthopaedic Engineering Collaboration, Nuffield Orthopaedic Surgery, University of Oxford in Oxford, England.

“Our RSA predictions eight years ago were correct," Gill told Orthopedics Today. Rotationally unstable stems fail early and the Charnley Elite Plus is rotationally unstable.

The new nine-year study, conducted in 2004, tracked 118 patients with Charnley Elites implanted at the Nuffield Orthopaedic Centre between 1994 and 1997, including some from the initial RSA study. Surgeons used the Hardinge approach and CMW3G cement on all patients and either the Charnley LPW or Ogee cup.

Researchers found a 17% revision rate at eight years. When they added all radiological failures to the revisions, overall failure rate escalated to 33% at eight years. When researchers then looked at the patient subgroup from the original RSA study, they found that four out of five failures occurred in patients who “had been recorded with high posterior head migration,” Gill said.

The researchers reported a 100% loosening rate for the subgroup of patients with high-posterior head migration at two years. Yet those with low posterior head migration had only a 7% failure rate.

In response to a question following Gill’s presentation, co-investigator David W. Murray, FRCS (Orth), noted: “Our feeling is that the Charnley Elite [Plus] stem is not very forgiving. When used with perfect cementing it can have a good long term outcome. However, even the best surgeons occasionally have sub-optimal technique. Under these circumstances a more rotationally stable device such as the Exeter probably has a better outcome. Hip replacement stems are now so good that it is best to use devices that are forgiving.”

Editor's note: This article was updated on Oct. 5, 2005 to include editorial changes to its original version.

For more information:
Gill HS, Hauptfleisch JT, Glyn-Jones S, et al. Early failure of Charnley Elite: verification of RSA predictions? Presented at the 7th European Federation of National Associations of Orthopaedics and Traumatology Congress. June 4-7, 2005. Lisbon, Portugal.