Treating wounds of the equine distal limbs

Treating wounds of the equine distal limbs

Healing those involving deep structures can be especially challenging
Sep 01, 2009

Photo 1: A wound more than eight hours old. The laceration is on the cranial and mid-portion of the radius, severing the extensor muscles, and includes the periosteum of the radius. (PHOTO: COURTESY OF DR. JAMES A. ORSINI, NEW BOLTON CENTER, UNIVERSITY OF PENNSYLVANIA)
Wounds of the lower limbs of the horse can be challenging to treat successfully, especially those that may involve the deep structures, such as tendons, ligaments and synovial (joint) spaces.

"Rapid and accurate recognition of damage to deep structures is mandatory for appropriate case management and a favorable prognosis," says Henry W. Jann, DVM, MS, Dipl. ACVS, at Oklahoma State University's Center for Veterinary Health Sciences.

"Our knowledge of how tendons and ligaments heal is constantly expanding and controversial," Jann says. "We're not really certain of the physio-logical mechanisms that turn tendon healing on and off, but we're learning more every day."

Veterinarians know that the healing process is controlled to a large extent by growth factors. To assist healing, practitioners have some new therapies in their armamentarium, including stem-cell and shock-wave therapy.

Photo 2: Second intention wound healing in the mid- to distal part of the front limb of a horse. Notice the healthy granulation tissue and an area at the level of the fetlock and pastern that needs surgical debridement. This wound would benefit from a skin graft. (PHOTO: COURTESY OF DR. JAMES A. ORSINI, NEW BOLTON CENTER, UNIVERSITY OF PENNSYLVANIA)
"But, in terms of the precise biomechanical pathways and how to turn them on and off, we've still got a lot to learn," Jann says.

While it is known that training and exercise help strengthen bones and muscles, just how tendons respond to exercise and the best way to train horses to prevent tendon injury are not well understood. Tendons do get stronger to a certain extent in young horses, but in the mature horse it's hard to get them healed well enough to attain the physical strength required of an equine athlete. With any tendon laceration, the potential for severe hemorrhage is always present because of the proximity of major arteries to the flexor tendons and their relatively superficial location.

"Ligament healing follows essentially the same pattern as tendon healing," Jann notes, "although the intrinsic and extrinsic patterns have not been as clearly defined."

Unlike tendons, ligaments do respond positively to exercise.


Photo 3: Fresh wound in the mid-cannon bone area as a result of a wire cut. These wounds can be problematic due to secondary problems with compromised blood supply and bone injury. (PHOTO: COURTESY OF DR. JAMES A. ORSINI, NEW BOLTON CENTER, UNIVERSITY OF PENNSYLVANIA)
When examining a wound in the lower extremities that has the potential of penetrating or compromising deep-tissue structures, the horse's posture and ambulation will provide clues to potential tendon, ligament or joint damage.

"When tendons are compromised, there is an alteration in limb conformation during ambulation or upon weight- bearing," Jann explains. Damage to each of the various tendons, ligaments and joints — superficial deep flexor tendon (SDFT), deep digital flexor tendon (DDFT), metatarsophylangeal or metacarpophylangeal joint (MP), fetlock joint, distal interphalangeal joint (DIP) and coffin joint — has its own specific presentation/appearance. "These changes in conformation are consistent and can be relied upon for categorization of compromise to a specific tendon or tendon group," Jann says.