Vertical impact increase in middle age may explain idiopathic weight-bearing joint osteoarthritis.

Abstract

To test the hypothesis that ground reaction force increases when a standard stepping task is performed in late middle age. Consecutive sample. Internal medicine practice. Thirty-six male patients (age range, 17-72yr) from an internal medicine practice. Subjects performed 20 consecutive footfall impacts onto a force platform while barefoot and while wearing shoes. Ground reaction forces were recorded for each footfall. Impact is positively related to age both when barefoot (r = .84, p < .001) and when wearing shoes (r = .71, p < .001). Impact remains constant until age 50, after which it increases by 13.3% for barefoot subjects. Barefoot impact was significantly lower and less variable than impact when shod (barefoot = 1.18 body weight [BW]; shod = 1.22 BW; F(1,5) = 169.91, p < .001). An increase in impact force during locomotion was identified that occurs in late middle age, when stability declines and idiopathic weight-bearing joint osteoarthritis develops. Because impact is negatively related to stability, the impact rise is probably caused by postural adjustments to instability resulting from irreversible neurologic decline. This heightened impact may account for the accelerated rate of weight-bearing joint osteoarthritis that begins in late-middle age.