In vitro mechanical properties of equine tendons in relation to cross-sectional area and collagen content.

The mechanical properties of the deep digital flexor tendon (DDFT), the superficial digital flexor tendon (SDFT) and the suspensory ligament (SL) of the hindlimb of the horse were studied in vitro. The tendons were observed at several morphologically distinct sites. The loaded tendon is homogeneously strained, in spite of large variations in cross-sectional area. Consequently the modulus of elasticity was inversely proportional to the corresponding cross-sectional area and ranged from 738 MPa (megaPascal, N mm-2) to 1398 MPa within the DDFT, from 1000 MPa to 1282 MPa within the SDFT and from 576 MPa to 669 MPa within the SL. The collagen content was inversely proportional to the cross-sectional area and proportional to the modulus of elasticity. This stresses the influence of tendon composition on the mechanical properties, and also demonstrates the difficulty in judging the strength of a particular tendon or site within a tendon from its cross-sectional area. The respective tendons ruptured at strains of 10.0 per cent (DDFT), 12.3 per cent (SDFT) and 11.0 per cent (SL). The influence of strain rate on the modulus of elasticity is small, and these tendons may therefore be considered as non-linear elastic structures. The average hysteresis is about 5 per cent.