Date Published: April 23, 2019
Publisher: Public Library of Science
Author(s): Albert S. Tsang, Andrew J. Dart, Sara A. Biasutti, Leo B. Jeffcott, Margaret M. Smith, Christopher B. Little, James H-C Wang.
Following injury to a tendon little is known about potential for pathology to develop in other regional tendons from overloading or altered function. The aim of this study was to investigate the gene expression and histopathological changes that occur 1) within the deep digital flexor tendon (DDFT) after injury to the superficial digital flexor tendon (SDFT) and 2) within the flexor tendons (SDFT and DDFT) after injury to the extensor tendons. Merino wethers [Ovis aries] (n = 18) were divided into three equal groups and underwent either partial transection of the SDFT, complete transection of the extensor tendons or were left as non-operated controls. Tendons were harvested and sampled regionally for gene expression (real time PCR) and histologic analysis eight weeks after surgery. Transection of the SDFT resulted in increased expression of collagen III, versican, biglycan, lumican and MMP1 (P<0.026 for all genes) within the DDFT. There was no effect of transecting the extensor tendons on the expression of any gene tested in either the SDFT or the DDFT. The DDFT had elevated histopathology scores induced by transection of the SDFT, eight weeks previously. There were minimal histological differences in either the SDFT or DDFT after transection of the extensor tendons. Transection of the SDFT results in a mild, subclinical tendinopathy within the DDFT with potential implications on treatment and rehabilitation of SDFT injuries. Injury to the extensor tendons has minimal measured effect on the SDFT or DDFT.
Tendon injuries are a common problem in human and equine athletes [1–3]. They are the most common form of musculoskeletal injury in the horse and have been reported to account for up to 46% of all musculoskeletal injuries in athletic horses . These injuries can be split into two main groups distinguished by clinical presentation and aetiology, into either traumatic lacerations or strain-related injuries.
It has recently been identified that there are widespread histopathological changes in the equine and ovine SDFT after focal surgical injury [1, 18]. From the results of this study, it has now been demonstrated that the DDFT sustains a mild tendinopathy following surgical injury to the SDFT and similar to previous findings [1, 18], these changes are not focal but in fact widespread throughout the entire tendon. Aspects of the tendinopathic changes observed in the SDFT, such as cellularity, collagen fibre malalignment and vascularity, did not appear to resolve over time and the authors considered that this pathology is likely to persist in the long term and have implications on the structure and function of the tendon [1, 18]. If these histopathologic changes within the SDFT do persist for the long term, the combined effect of pathology within both the SDFT and DDFT may contribute to the high recurrence of re-injury and the poor prognosis for return to athletic performance observed in equine athletes.