Structural and mechanical properties of tendon related to function.

Tendon normally fulfills its primary role as a flexible force transmitting element very effectively and yet failure of this passive tissue leads to great disability. As a connective tissue its structure is relatively simple and the peculiar helical arrangement of collagen fibres confers highly non-linear as well as time-dependent mechanical properties. Functional significance cannot be attributed to any facet of mechanical response until the physiological pattern of loading is established. In particular the rate of deformation and the minimum force experienced by tendon in normal locomotion have yet to be elicited. Most published values of maximum forces transmitted by tendon fall short of the measured quasi-static rupture strength. The fact that some estimates exceed this ultimate force illustrates the errors incurred in indirect assessment. Direct measurement techniques, which have now been demonstrated to be practicable, should yield valuable information when applied to tendons susceptible to spontaneous rupture. Other proposed mechanical functions of tendon are clearly of secondary importance. Much has yet to be learned of the response of muscle to rapid loading and extension before these hypotheses can be tested fully. With our scant knowledge of normal tendon function it is indeed fortunate that the techniques of repair and treatment of damaged tendon are rapidly advancing.