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Saturday, March 3, 2001

Males' wear rate after THR found higher than females'

An analysis of the ambulatory activity of patients with total hip replacements to determine the effect on polyethylene wear finds wear per million cycles is significantly higher in males than females (p = 0.006). Even after adjustment for greater height and weight in males, the males' wear rate was still significantly higher, according to the study in poster exhibit 331.

Males walked at a higher average speed (p = 0.07), spent 33.9 percent more time walking fast or very fast, had 4 percent more starts/stops per day, with 13 percent less strides between stops.

The patients wore the Step Activity Monitor (SAM), a microprocessor placed on the ankle, that measures ambulatory activity in real time. Activity magnitudes, speed parameters and activity patterns were analyzed in 31 patients with 37 primary total hips. Wear was measured from digitized radiographs using a validated two-dimensional, edge detection-based computer algorithm.

On average, patients walked 5.6 hours per day (range: 1.9-9.8); averaging 5,266 gait cycles (range: 1,737-11,805), at 20 cycles/minute (range: 12.7-32.8) with a maximum speed of 63 cycles/minute (range: 45.0-88.0). Fast and very fast walking (30-49 and > 50 cycles/minute) accounted for 9.4 percent and 4.4 percent of total walking time.

Patients started and stopped walking about 66 times per day (range: 34-113), with about 81 cycles between stops (range: 28.1-200.1) in average active intervals of 5.3 minutes (range: 3.3-10.3).

"Similar to a set of automobile tires, polyethylene wear is a function of the amount and type of use," say the researchers. "Faster walking with more frequent starting and stopping is associated with a higher polyethylene wear rate. As the clinical performance of crosslinked polyethylenes is being monitored, it is critical to consider the influence of the amount and type of patient activity on wear."

The researchers are Mauricio Silva, MD; Walter O. Jackson, MD; Eric F. Shepherd, MD; Mylene A. dela Rosa, BS; and Thomas P. Schmalzried, MD, all of the Joint replacement Institute at the Orthopaedic Hospital, Los Angeles, Calif.

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2001 Academy News March 3 Index C

Last modified 16/February/2001 by IS