Intrathecal enalapril reduces adhesion formation in experimentally induced digital flexor tendon sheath injuries in horses.

Objective: The objectives of the study were to describe a standing percutaneous adhesion induction model in the digital flexor tendon sheath (DFTS) of horses and to evaluate the effect of intrathecal administration of the angiotensin-converting enzyme (ACE) inhibitor enalapril on tendon healing and adhesion formation.

Study design: Randomized, blinded, controlled experimental study.

Animals: Eight healthy horses.

Methods: A collagenase-induced adhesion model was implemented in the deep digital flexor tendon (DDFT) of both forelimbs under standing ultrasonographic guidance. Daily intrathecal injections of 5 mg enalapril (the treatment condition) were administered to a randomly assigned forelimb for 5 days, with the contralateral limb receiving an equivalent volume of 0.9% NaCl (the control). Lameness and limb circumference were recorded weekly. Horses were euthanized after 8 weeks and evaluated for gross digital flexor tendon sheath (DFTS) adhesions. Tendons were collected for histopathologic scoring of DDFT healing. Paired data were analyzed using a one-sided alternative sign test and longitudinal regression.

Results: Multiple DFTS adhesions were formed in control limbs of all horses. The median number of gross DFTS adhesions in treated limbs was less than in control limbs (p = .0039). The average reduction in limb circumference and lameness scores over time occurred faster in treated versus control limbs (p < .025). There were no differences in DDFT histopathologic scores between groups.

Conclusion: The standing percutaneous DFTS adhesion induction model demonstrated that intrathecal enalapril reduced DFTS adhesion formation, lameness scores, and limb circumference over time.

Clinical significance: Intrathecal enalapril administration may reduce morbidity in horses with naturally occurring tendon injuries.