Polyethylene wear (linear penetration) in 37 hip replacements was assessed
from digital images using a validated two-dimensional, edge detection-based
computer algorithm. Patient activity was assessed with a pedometer, a step
activity monitor and a simple visual analog scale. Joint use was related t
o wear at the 90% confidence level. Without three recognized outliers, wear
was highly correlated to use. The visual analog scale activity rating was
significantly related to wear for the 24 hip replacements with standard pol
yethylene, Univariate regression analysis indicated that male gender, heigh
t, weight (which were both highly correlated to male gender) and hip center
of rotation were significantly correlated to wear. Multivariate regression
analysis indicated that male gender, femoral off-set, and Hylamer(R) were
significantly correlated to wear. Based on the wear and activity data from
the 24 hip replacements with standard polyethylene, the average volumetric
wear rate per million cycles with a 70 kg patient weight was 30 mm(3). This
unique in vivo result can be considered a target wear rate for standard po
lyethylene in hip simulator studies.