Histology and gene expression of extensor tendons and pathobiology of extensor tendon tendinopathy using an ovine model

Tendons function to transmit the forces generated by muscle to bone, resulting in movement of a joint. However some tendons have more specialized functions. Functionally distinct tendons have differences in tissue composition that relate to differences in function. However, it is unclear whether functionally distinct tendons also behave differently following injury. This study aims to investigate the normal characteristics of ovine forelimb extensor tendons and the changes that occur following injury using a combination of histological and gene expression analysis. The lateral digital extensor tendon (LDET) and two branches of the common digital extensor tendons (CDET) in the forelimb of 6 sheep were collected to study normal extensor tendon characteristics. In another 6 sheep, the LDET and two branches of the CDET were transected and harvested 8 weeks later to evaluate the characteristics of injured extensor tendons. In the third group of 6 sheep, the LDET and two branches of the CDET were harvested 8 weeks after partial transection of the superficial digital flexor tendon (SDFT) in the same limb to evaluate the effects of tendinopathy of the SDFT on the normal extensor tendon characteristics. Samples were assessed using histology and gene expression. The results demonstrate that there are gene expression differences between the extensor tendons in the ovine forelimb and the changes in the ovine extensor tendons following surgery are similar to that of other tendons studied including the “energy storing” tendons. Partial transection of the SDFT had no effect on the extensor tendons