Effects of age upon the mobility of human finger joints.

Few measurements have been made of the frictional forces within living joints. Barnett and Cobbold (1962) recorded that the coefficient of friction at the distal interphalangeal joint of the middle finger in six healthy adults could be as low as 0 0075, a figure of the same order as that in excised joints (Jones, 1936; Charnley, 1959). Rydell (1965) measured, in a patient fitted with a hip prosthesis, the coefficient of friction between the artificial femoral hip and the intact acetabulum; he gave a figure 0021 ± 0-0014. The present paper is concerned with the variation observed in the coefficient of friction, as reflected by joint mobility, among individuals of different ages.