In vivo and in vitro measurement of tendon strain in the horse.

Strains gauges were applied to the superficial flexor tendon, deep flexor tendon, and suspensory ligament of sound adult horses. Maximum tendon strain occurred during full weight bearing while walking, when the forelimb was perpendicular to the group surface. There was decrease in tendon strain with increase in hoof angle for the deep digital flexor, but no change in tendon strain for the superficial digital flexor and suspensory ligament with changing hoof angle. At physiologic rates of strain, tendons were able to withstand large loads without yielding. Load strain curves developed in vitro indicated that during walking, the deep digital flexor was calculated to load to 416.8 kg; the superficial flexor tendon to 362.9 kg; and the suspensory ligament to 172.4 kg. This study shows that in the horse, strain in flexor tendons during walking was in excess of 5%, indicating strains within the visco-elastic range.