"Tendonitis of the superficial digital flexor tendon (SDFT) is a common injury in horses, especially racehorses and event horses," began Ty Wallis, DVM, a third-year resident in equine surgery at Colorado State University (CSU). "It's usually hyperextension-related, and affected horses have a prolonged convalescence and high rate of recurrence."

Wallis discussed tendonitis and a CSU study of acellular urinary bladder matrix (UBM; ACell Vet Powder) as an intralesional (injected within the lesion) treatment at the 2007 American Association of Equine Practitioners Convention, held Dec. 1-5 in Orlando, Fla. "Proposed actions of UBM include recruitment of growth factors and cells, promotion of a rapid angiogenic response (growth of new blood vessels into the lesion), providing a scaffold for collagen, and minimizing fibrous tissue formation," he said.

Eight sound adult horses had bilateral forelimb SDF tendonitis induced with a collagenase (enzyme tissue degradation) model, then 4 mL of UBM that was mixed according to the manufacturer's instructions was injected into one limb's lesion after 14 days (based on lesion size and time to lesion stabilization from previous studies). The manufacturer recommends 6 mL per lesion in a clinical case, but for standardization purposes 4 mL was used in this study to ensure the lesion was full, but not overfilled. The other limb was injected with 4 mL of saline as a control. Additional treatments included non-steroidal anti-inflammatory drugs, bandaging, cold hydrotherapy, and controlled exercise for 84 days. Horses were evaluated clinically and ultrasonographically throughout the study, and after the study their tissues were evaluated.

Researchers found no significant difference between UBM-treated and control limbs for any clinical parameters (lameness, limb circumference, etc.). There were trends toward smaller lesion size, higher (more severe) gross pathology scores, lower lameness scores, and smaller cross-sectional area of the tendon in treated limbs. Treated limbs showed some differences in neovascularization (establishment of new blood vessels in the lesion), but they were not significant.

Wallis noted that the 84-day study period might have been too short and the number of study horses too small to detect a significant treatment effect.

More to the Story ...

But while this study seemed to find that UBM neither helped nor hurt horses with tendonitis, Wallis said that perhaps the collagenase model of tendonitis might not be a suitable model because the lesions in treated and control limbs continued to enlarge for the first 42 days of the study, including 28 days of treatment.

"This is probably the most concerning data in this study," he noted. "It suggests that there may have been continued collagenase activity and degradation of tissue. Therefore, UBM may not have been an effective treatment for collagenase-induced SDF tendonitis because the UBM, which is primarily collagen, may also have been degraded." He also noted that the collagenase model induces relatively severe lesions that might be worse than those in the typical traumatic tendonitis case.

"Tendonitis remains a difficult problem; we have high hopes for some of the currently available treatment options such as bone-marrow-derived mesenchymal stem cells (stem cells that can differentiate into a variety of cell types) and for Dr. Michael Schramme's surgical lesion creation model (compared to the collagenase model) for studying potential therapies in the future," he concluded.

Investigators on this study included Wallis; Gary Baxter, VMD, MS, Dipl. ACVS; Natasha Werpy, DVM, Dipl. ACVR; Gary Mason, DVM, PhD, Dipl. ACVP; David Frisbie, DVM, PhD, Dipl. ACVS; and Nicolai Jarloev, DVM, PhD. The study was funded by ACell Europe, Alm Brand Insurance Company in Denmark, and the Gail Holmes Orthopaedic Research Center at CSU.

About the Author

Christy M. West

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

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