Study shows direct correlation between linear wear of hip implants and patient activity

Issue: Issue 5 2012

German and American researchers have conducted one of the first studies indicating a direct link between patient activity and the rate of linear wear in total hip replacements using alumina heads and conventional polyethylene.

The results of [our] measurements were in the expected range of conventional polyethylene with the linear wear rate of 0.1 mm per year," Alexandra Finn, of the Orthopädisches Krankenhaus Schloss Werneck in Werneck, Germany, said during presentation at the 13th EFORT Congress 2012. "We considered an average activity of 1.8 million load cycles per year in the range of 200,000 to 5 million steps, and the regression analyses have shown that the activity influenced the linear wear rate by 18%. The questionnaires [used] implied a higher estimated functionality of the total hip replacement by the observer [than] the patient himself; however, the objective inquiry of the activity was much better."

Long-term follow-up

Finn and colleagues followed 82 patients (104 hips) who underwent total hip replacement at a mean age of 58 years. The acetabular component consisted of a titanium hemispherical design (Harris-Galante Porous, Zimmer; Freiburg, Germany) and 28 mm alumina heads were used. The investigators took digitized radiographs of the patients yearly to calculate wear characteristics over time. An electronic step accelerometer was used to record patient activity levels, and function was assessed using the Daily Activity Questionnaire, Harris Hip Score, UCLA score and Extra Short Musculoskeletal Function Assessment questionnaire. Patients had an average follow-up of 12 years and 1,203 radiographs were taken during the study.

Finn and colleagues found that patients took between 200,000 and 5 million steps, with a mean of 1.8 million steps per patient per year. They found a linear wear rate of 0.1 mm per year, and volumetric wear measured an average of 52.9 mm³ per year.

Using univariate regression analysis, Finn and colleagues were able to assess weight, age at surgery, peak activity, medium intensity steps, high intensity steps, inclination angle and acetabular anteversion, according to the abstract. Age, weight, gender and cup position were not associated with the linear wear rate.

Study limitations

She cited the retrospective nature of the study and older cohort as study limitations. Although the study involved older patients, she said the research design would predict higher wear rates in cases with more active, younger patients and those with worse bearing couples.

"We consider that the linear wear rate is influenced by the activity of the patient in retirement with 18% and 0.1 mm per year is in the expected range," Finn said. – by Jeff Craven

Reference:

Finn A, Mahlmeister F, Martell JM, Hendrich C. Long-term effect of patient’s activity upon wear in THR. Paper #12-3422. Presented at the 13th EFORT Congress 2012. May 23-25. Berlin.

For more information:

Alexandra Finn can be reached at the Orthopädisches Krankenhaus Schloss Werneck, Balthasar-Neumann-Platz 1, Werneck, Germany; email: alexandra.finn@web.de.
Disclosure: Finn has no relevant financial disclosures.