Researchers concerned by loosening rates with aluminium free surface grit-blasted THR stems
PRAGUE — Swiss investigators have found high early loosening rates in a double-blinded randomized prospective trial of AL203-free surface Zweymueller femoral stems, according to a presentation at the SICOT XXV Triennial World Congress 2011, here.
“The Zweymueller principle works … [The] stem with an altered surface just doesn’t work,” Lukas Dominik Burger, MD, a resident and research fellow at Kantonsspital Bruderholz, in Bruderholz, near Basel, Switzerland, said.
Burger and colleagues theorized that since some AL203 inevitably remains on the surface of these grit-blasted stems after grit-blasting is completed, which has been associated with some reports of loosening, those stems that undergo a special chemical and mechanical treatment to remove the AL203 may show improved fixation and osteointegration. Therefore, a single-center prospective randomized study was performed to compare results in 24 patients with AL203-free surface stems (trial group) to 25 patients with regular grit-blasted stems that did not undergo the AL203-removal process (standard group).
Based on follow-up bone mineral density (BMD) tests results from dual-energy X-ray absorptiometry testing, the trial group had higher overall BMD at 12 months postoperatively in Gruen zones 6 and 7 and at 24 months in zones 6 and 7, as well as zone 2.
“Zones 3, 4 and 5, which are considered most important for anchorage of the Zweymueller stem (SL Plus; Smith & Nephew), showed considerably higher BMD in the AL203 group [standard]. Now we interpret this as a sign of trouble with the stem, which showed that the primary replacement doesn’t really work in this modified stem as opposed to the standard stem,” Burger said.
“Nine of 24 patients were revised for loosening of the AL203-free surface stem,” he said. “We have more patients in the pipeline which are already now presenting with typical loosening.”
Two of 25 patients in the standard group were revised. It will take more research to determine whether the process of AL203 grit blasting or rendering the implant AL203-free after production is the real problem, Burger said.
- Burger LD, Hirschmann MT, Afifi FK, et al. Do not implant! Unexpected high loosening rate of AL203-FREE non-cemented titanium trial-hip-stems. A randomized, prospective study of a new surface technology in THR. Paper #29109. Presented at the SICOT XXV Triennial World Congress 2011. Sept. 6-9. Prague.
- Disclosure: The study was supported by a research grant from Plus-Surgical/Smith & Nephew.
Congratulations on presenting those data; it took courage to do it. Make sure you get your data published. I hope you will also ask the manufacturer to inform everyone of what they did [with the surface finish and treatment]. They won't do it again, but somebody else might.
— Daniel J. Berry, MD
President, American Academy of Orthopaedic Surgeons
Chair in the Department of Orthopaedic Surgery
Disclosure: Berry receives royalties from DePuy on certain hip and knee implants. His department receives research support from Biomet, DePuy, Smith-Nephew, Stryker and Zimmer.