, Volume 467, Issue 7, pp 1898-1906
Date: 07 May 2009

2009 Marshall Urist Young Investigator Award: How Often Do Patients with High-Flex Total Knee Arthroplasty Use High Flexion?

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Although high-flexion TKA designs aim to safely accommodate deep flexion, it is unknown how often patients use deep flexion outside the laboratory. We used a validated smart-activity monitor to document the prevalence of knee flexion greater than 90° in 20 consecutive patients (21 knees) who had high-flexion TKAs, at a minimum of 2 years’ followup. Patients wore the device continuously for a mean of 35.7 ± 0.5 hours. The 21 knees flexed more than 90° for an average of 10 ± 3.8 minutes (0.5%). Activities performed with flexion greater than 90° were, on average, 70% in single-limb stance, 12% moving from sitting to standing, 8% walking, 7% moving from standing to reclining, 2% stepping, 0.9% moving from lying to standing, and 0.1% running. Eight knees flexed greater than 120° for an average of 2.2 minutes (range, 0.2–15 minutes), or 0.1% of the testing time. Activities performed with flexion greater than 120° were, on average, 90% in single-limb stance, 6% moving from sitting to standing, 3% walking, 0.6% moving from standing to reclining, 0.3% stepping, and 0.1% moving from lying to standing. Peak flexion used at any time during testing was, on average, 84% ± 11% of maximum postoperative flexion (125° ± 12°). These patients rarely used deep flexion.

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

Dr. Freiberg has received consulting fees and royalties from Biomet Inc, Warsaw, IN, and Zimmer, Inc, Warsaw, IN. Dr. Malchau has received institutional research support from Zimmer.
Each author certifies that his or her institution has approved the human protocol for this investigation, that all investigations were conducted in conformity with ethical principles of research, and that informed consent for participation in the study was obtained.
This work was performed at the Harris Orthopaedic Biomechanics and Biomaterials Laboratory and Stanford University Medical Center.