How Often Do Patients with High-Flex Total Knee Arthroplasty Use High Flexion?

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 degrees 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 degrees 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 degrees 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 degrees +/- 12 degrees). These patients rarely used deep flexion.