The Role of Polyethylene Design on Postoperative TKA Flexion: An Analysis of 1534 Cases

Richard W. McCalden MD, MPhil (Edin), FRCSC, Steven J. MacDonald MD, FRCSC, Kory D. J. Charron MET, Robert B. Bourne MD, FRCSC, Douglas D. Naudie MD, FRCSC
Symposium: Papers Presented at the Annual Meetings of the Knee Society
Volume 468, Issue 1 / January , 2009

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Abstract

The range of motion after TKA depends on many patient, surgical technique, and implant factors. Recently, high-flexion designs have been introduced as a means of ensuring or gaining flexion after TKA. We therefore evaluated factors affecting postoperative flexion to determine whether implant design influences longterm flexion. We prospectively collected data on patients receiving a primary Genesis II™ total knee replacement with a minimum of 1-year followup (mean, 5.4 years; range, 1–13 years). We recorded pre- and postoperative outcome measures, patient demographics, and implant design (cruciate retaining [CR, n = 160], posterior stabilized [PS, n = 1177], high-flex posterior stabilized [HF-PS, n = 197]). Backward stepwise linear regression modeling identified the following factors affecting postoperative flexion: preoperative flexion, gender, body mass index, and implant design. Independent of gender, body mass index, and preoperative flexion, patients who received a HF-PS and PS design implant had a mean of 8° and 5° more flexion, respectively, than those who received a CR implant. Patients with low flexion preoperatively (< 100°) were more likely to gain flexion, whereas those with high flexion preoperatively (> 120°) were most likely to maintain or lose flexion postoperatively. Controlling for implant design, patients with high flexion preoperatively (> 120°) were more likely to gain flexion with the HF-PS design implant (HF-PS = 32.0%; PS = 15.1%; CR = 4.5%).

Level of Evidence: Level II, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.

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