Walking activities and wear of prostheses.

A study of the walking activities of 243 individuals was carried out. The individuals came from four different occupations and had an age range of 17-83 years. The survey carried out in this investigation showed surprisingly little correlation between variables such as age, height, and weight of individuals and their speed of walking, length of stride, or distance walked. Correlation matrices were obtained for the whole sample and then for each sex, showing similar trends. The most significant correlation was between the height of an individual and the length of the stride, and there was a lesser correlation between age and the number of steps walked by an individual per day. Further statistical analyses showed that males in manual occupations walked most and those in sedentary occupations walked least. On the other hand, in the female groups housewives seemed to walk least and those in technical occupations walked most. The average number of steps walked per day by a male individual for the whole sample was 9537; that for females was 9839. The corresponding distances walked per day were 6.7 and 6.5 km. The differences were not statistically significant. Predictions of wear of prosthetic components made of ultrahigh molecular weight polyethylene were made on the basis of the above data and other variables affecting wear, such as the weight of the subject and the area available for contact during walking. Charts have been constructed of the penetration of the metallic component into the plastic one for both hip knee prostheses, thus enabling predictions of the wear of the plastic components of these two most widely used prostheses. Owing to the wide ranging values of the variables used in making the predictions of wear, these latter should be regarded only as 'safe' first estimates.