QUANTITATIVE ASSESSMENT OF WALKING ACTIVITY AFTER TOTAL HIP OR KNEE REPLACEMENT

Accumulating data suggest that the amount of use, and not simply the d uration in situ, influences the wear and survival of total joint repla cements. An electronic, digital pedometer was used to record the numbe r of steps taken by 111 non-randomized volunteers who had had at least one total hip or knee replacement. The patients averaged 4988 steps p er day, which extrapolates to approximately 0.9 million cycles per yea r for each joint of the lower extremity. Average activity ranged widel y from 395 to 17,718 steps per day, an approximately forty-five-fold d ifference. The most active patient walked more than 3.5 times the aver age number of steps per day. Age was significantly associated with act ivity (p = 0.048), but there was a high degree of variability (standar d deviation, 3040 steps per day). Patients who were less than sixty ye ars old walked 30 per cent more on average than those who were sixty y ears old or more (p = 0.023). Men walked 28 per cent more on average t han women (p = 0.037), and men who were less than sixty years old walk ed 40 per cent more on average than the rest of the patients (p = 0.01 1). These data indicate that individual differences in the activity of the patient can be a substantial source of variability in rates of po lyethylene wear in vivo. The pedometer is an inexpensive investigation al tool with many potential applications, including standardizing wear measurements of joint replacements on the basis of gait cycles rather than time. This quantitative approach may provide prognostic informat ion regarding the survival of joint prostheses. Pedometer data may als o be useful for quantitative assessment of walking ability in outcome studies.