The role of polyethylene design on postoperative TKA flexion: an analysis of 1534 cases.
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 degrees and 5 degrees more flexion, respectively, than those who received a CR implant. Patients with low flexion preoperatively (<100 degrees) were more likely to gain flexion, whereas those with high flexion preoperatively (>120 degrees) were most likely to maintain or lose flexion postoperatively. Controlling for implant design, patients with high flexion preoperatively (>120 degrees) were more likely to gain flexion with the HF-PS design implant (HF-PS = 32.0%; PS = 15.1%; CR = 4.5%).


METHODS
Level II, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.
McCalden
Richard W
RW
Division of Orthopaedic Surgery, University Hospital, University of Western Ontario, London, ON, Canada. richard.mccalden@lhsc.on.ca
MacDonald
Steven J
SJ
Charron
Kory D J
KD
Bourne
Robert B
RB
Naudie
Douglas D
DD
D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000295:instrumentation* / Q000534:rehabilitation; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology / Q000601:surgery*; D007720:Knee Prosthesis; D016014:Linear Models; D008297:Male; D020370:Osteoarthritis, Knee / Q000503:physiopathology / Q000601:surgery*; D020959:Polyethylene; D011474:Prosthesis Design; D016059:Range of Motion, Articular; D012189:Retrospective Studies
D020959:Polyethylene