Intrathecal adhesions represent a major complication of equine tendon injuries. Angiotensin-converting enzyme (ACE) inhibitors have been shown to improve fibrotic processes and may offer a new method for adhesion prevention. Our hypothesis was that intrathecal enalapril would 1) reduce digital flexor tendon sheath (DFTS) adhesion formation and 2) result in improved healing in a collagenase induced tendon adhesion model in horses. Eight horses were enrolled in this randomized, blinded, controlled, pilot study. Via standing ultrasonographic guidance, a collagenase adhesion induction model was performed in the deep digital flexor tendon (DDFT) of both forelimbs. Daily intrathecal injections with 5 mg enalapril (treatment) were performed in a randomly assigned forelimb for 5 days, with the contralateral limb receiving an equivalent volume of 0.9% NaCl (control). Lameness and limb circumference were recorded throughout the experiment. Horses were euthanized after eight weeks and evaluated for gross DFTS adhesions and histopathologic scoring of DDFT healing. Paired data were analyzed using a one-sided alternative sign test and longitudinal regression. The median number of gross DFTS adhesions in treated limbs was significantly less than control limbs (p = 0.0039), with no histologic differences in DDFT healing. The average reduction in limb circumference and lameness score over time was significantly greater in treated versus control limbs (p < 0.025). These results indicate that intrathecal enalapril reduces DFTS adhesion formation without histologic evidence of improved healing. Although this study was limited to artificially induced DFTS adhesions, intrathecal enalapril may reduce morbidity in horses with naturally occurring tendon injuries.
