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.
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
"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.
"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
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)
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.
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.
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
"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.