Clinical and Ultrasonographic Findings of Collagenase Induced Tendinitis in the Horse

The aim of this study was to assess the clinical and ultrasonographic alterationsin the superficial digital flexor tendon (SDFT) of horses with collagenase-inducedtendinitis.Design- Experimental study.Animals- Five clinically normal adult horse.Procedures- Two thousand units of collagenase were injected in the center of the SDFT offorelimbs of each horse under ultrasound guidance. Clinical examinations were performedto evaluate heat, response to palpation, presence of swelling, and lameness grade.Ultrasound images of the SDFT were recorded prior to injury and at 1, 3, 5, 7, and 14 daysafter injection. Images were digitized, and percentage of lesion, the echogenicity score(ES), and the fiber alignment score of the fibers (FS) at the maximum injury zone (MIZ)were measured. The sum of the core lesion from 8–20 cm distal to the accessory carpalbone was also measured.Results- Collagenase resulted in anechoic core lesion involving 20%-35% of the tendoncross section at MIZ. There were not any significant difference in the size, ES, and FSbetween all the days except between the first day and the other days. There were nosignificant differences between observations made of each structure in the left and rightforelimbs of the same horse.Conclusions and Clinical Relevance- Collagenase-induced injury is ultrasonographicallysimilar to naturally occurring injury and causes the same tendinitis in both left and rightforelimbs and also in different horses. Tendon lesions using collagenase injection representan experimental model for tendon injury in research trials.