High Subsidence Rate Found for Elance Hip Stem: New Study

A research team from Japan has found evidence that Zweymüller-type noncemented total hip arthroplasty implant—an Elance stem—with a sand-blasted surface and an alkali and heat treatment—had a high rate of subsidence in patients. Their work, “High Subsidence Rate After Primary Total Hip Arthroplasty Using a Zweymüller-type Noncemented Implant With a Matte Surface,” appears in the Journal of the American Academy of Orthopaedic Surgeons Global Research & Reviews.

Co-author Toshiyuki Kawai, M.D., Ph.D., with the Department of Orthopedic Surgery, Kyoto University Graduate School of Medicine, Sakyo-ku in Japan, explained the genesis of the study to OTW. “Total hip femoral components of various materials and a multitude of designs are currently available. It is important to share surgical findings of less than good results in order to alert the public of possible issue with certain implants and to understand potential risk factor for early failure.”

“We had unfavorable results with a stem that had a widely used geometry but a relatively smaller surface roughness than stems with the similar geometry. This study included only 30 hips that were followed up only 6.3 years; however, we thought we should share those results now to give a caution rather than waiting until we get 10 years or 15 years of results.”

The 30 total hip arthroplasties (THAs) (27 patients) employed the Elance stem (manufacturer: Kyocera) from September 2012 to October 2014. Surgical indications were as follows: osteoarthritis (OA) secondary to hip dysplasia (23 hips), osteonecrosis of the femoral head (5 hips), primary OA in one hip, and rheumatoid arthritis in one hip.

“The survival rate of the Elance stem (a Zweymüller-type noncemented femoral implant) with stem revision for any reason was 86.4% (95% confidence interval, 68.9%-94.8%) at 5 years,” stated Dr. Kawai to OTW. “In comparison, the control group (THA done using stems other than the Elance stem) had a significantly higher survival rate of 99.5% (95% confidence interval, 96.2%-99.9%) at 5 years. Stem subsidence >5 mm was noted in 17 hips (56.7%) for the Elance stem. The survival rate with stem subsidence >5 mm as the end point was 46.6% (95% confidence interval, 29.9%-64.2%) at 5 years.”

“The Elance stem had a sandblasted matte surface with a target Ra of 1.0 to 2.5 micrometers, whereas the other Zweymüller stems had a higher roughness with a target Ra of 4 to 8 micrometers for SL-PLUS (Smith & Nephew) and Alloclassic (Zimmer-Biomet). This difference in surface roughness may have affected the initial fixation of the stem. A previous report described that an implant with a rough surface has a favorable effect on early and strong bonding to the bone.”

“According to previous reports, the mean migration of SL-PLUS implants was 0.3 mm at 2 years. The survival rate for the Alloclassic stem with subsidence > 5mm as the end point was 88.5% at 12 years. Elance had a similar stem design (geometry) to Alloclassic and SL-PLUS but had a significantly poorer implant survival than them. One biggest difference was the surface roughness (1.0 to 2.5 vs 4 to 8 micrometers), which could have caused the early subsidence.”

“Hip surgeons need to be aware of the importance of surface topography of an implant even when the device had a widely accepted geometry that yielded an excellent long-term survival. This caution should also be for medical device manufacturers who are going to make modifications on an existing stem or to conceive a new prosthesis.”