37 – THE ROLE OF POLYETHYLENE DESIGN ON POST-OP TKR FLEXION: AN ANALYSIS OF 1534 CASES

Abstract

Purpose: 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 long-term flexion.

Method: 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]).

Results: Backward stepwise linear regression modeling revealed the following factors that significantly affected 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 resulted in 8° and 5° more flexion, respectively, than those who received a CR implant. Based on analysis examining pre-operative flexion categories, 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%).

Conclusion: In summary, our data demonstrate postoperative range of motion after TKA is related to several factors, confirming the important role of the patient’s preoperative range of motion. In addition, our review suggests knee design and, in particular, the use of a so called “high-flexion” PS polyethylene design may be advantageous in maintaining or improving flexion postoperatively, especially in those patients with good pre-operative range of motion.