The 2012 Frank Stinchfield Award: Decreasing Patient Activity With Aging: Implications for Crosslinked Polyethylene Wear

Patient activity influences polyethylene wear. However, it is unclear how individual activity changes with patient aging after THA. We quantified changes in individual gait cycles and gait speed, assessed age-related differences in these parameters, and determined their relationship to polyethylene wear. A microprocessor was worn on the ankle to quantify the activity of 14 healthy patients with a well-functioning THA at two time periods: early (within 3.5 years of implantation) and late (10-13 postoperative years). Wear was measured on serial radiographs using edge detection-based software. Mean activity decreased by 16% from the early to the late period: 2.04 million gait cycles/year to 1.71 million gait cycles/year. Mean gait speed decreased by 9%: 15.4 cycles/minute to 14.0 cycles/minute. The activity of the 10 patients who were younger than 65 years at surgery decreased by 14% (2.34 million gait cycles/year to 2.02 million gait cycles/year), while the four patients 65 years or older at surgery decreased by 28% (1.29 million gait cycles/year to 0.94 million gait cycles/year). Gait speed was 26% slower for patients 65 years or older than for patients younger than 65 years. The mean linear penetration rate decreased by 42% from the first 5 years (early wear rate) to the next 8 years (late wear rate, 5-13 years): 0.043 mm/year to 0.025 mm/year. The greatest patient activity and wear occurred during the first 5 years. Walking speed and gait cycles both decreased with aging, resulting in deceasing wear over time.