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Greater implant damage seen with high flexion vs posterior stabilized tibial inserts
Implants with similar locking mechanisms, femoral components and methods of sterilization were studied.
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Results of an award-winning retrieval analysis revealed greater post, notch and backside damage in high flexion tibial inserts compared with posterior stabilized tibial inserts of the same manufacturer.
“The [high flexion] HF cohort demonstrated greater notch site damage and tibial post site damage compared to the [posterior stabilized] PS group,” study investigator Douglas D. R. Naudie, MD, FRCSC, of the University of Western Ontario, said. “Backside damage scores were higher in the high flexion group. Primary damage [was] burnishing and scratching. This is not what we expected. Both groups had similar locking mechanisms, femoral and tibial components and methods of sterilization.”
Naudie presented the results of the Mark Coventry Award-winning study at the Knee Society 2012 Specialty Day in San Francisco.
In their retrieval analysis, Naudie and colleagues compared 20 high flexion Genesis 2 (Smith & Nephew, Memphis, Tenn.) polyethylene tibial inserts with 20 posterior stabilized tibial inserts from the same manufacturer. The researchers matched groups for duration of implantation, and patients’ body mass index and age.
The investigators divided the implants into 16 zones and assessed them for microscopic damage. On microscopic analysis, several of the implants showed damage to the posts. Therefore, they used micro CT to confirm the damage.
The researchers found no differences between groups for gender, age, time in vivo, reason for revision, revision history, insert size or thickness. The HF cohort showed greater notch site, backside and tibial post damage compared with the PS group.
In both groups, Naudie said they identified post notching of 0.5 mm to 2 mm in selected cases.
Naudie and his colleagues found burnishing and scratching on the back sides of the HF implants and burnishing, scratching and deformation on the tibial posts — but the deformation was mainly on the posterior medial aspects of the posts in most cases, Naudie said.
“We recognized the limitations of the study,” Naudie said. “It is a retrieval study. Those implants that were retrieved during revision may not be representative of well functioning implants and, of course, our matching is confined by the inserts we have retrieved at our own institution. We did not evaluate clinical flexion in these patients or the radiographic position in these groups.” Strengths of the study included use of the same femoral component, tibial base plate, locking mechanism and sterilization process for both groups, he said. – by Renee Blisard Buddle
Reference:
- Paterson NR, Teeter MG, MacDonald SJ, et al. A retrieval analysis of high flexion versus stabilized tibial inserts. Presented at the Knee Society 2012 Specialty Day. Feb. 11. San Francisco.
For more information:
- Douglas D. R. Naudie, MD, FRCSC, can be reached at the Division of Orthopaedic Surgery, London Health Sciences Center, University Campus, University of Western Ontario, 339 Windermere Rd., London, Ontario, Canada N6A 5A5; 519-661-2111; email: douglas.naudie@lhsc.on.ca.
- Disclosure: Naudie is a consultant for Smith & Nephew and Stryker, and receives royalties from Smith & Nephew that are not related to the implant described in this study. The researchers’ institution, London Health Sciences Center, University Campus, receives educational and research support from Smith & Nephew, Depuy and Stryker.