Tendon Lesions in Horses: Treatment and Prognosis

If an owner finds his or her horse in the field, a foreleg covered in blood from the knee down, the animal's tendons might not be the first concern. But as Robert L. Linford, DVM, PhD, Dipl. ACVS, a professor in the Department of Clinical Sciences at the Mississippi State University College of Veterinary Medicine, explained at a recent veterinary conference, even the tiniest leg laceration can have dire consequences for nearby tendons if left untreated.

At the 2012 Western Veterinary Conference, held Feb. 19-23 in Las Vegas, Nev., Linford discussed the clinical signs associated with certain tendon lacerations, along with the treatment options and prognoses, during a presentation for a veterinary audience.

Where Are the Tendons?

"Tendon lacerations are serious injuries for horses because a seemingly simple wound may cause a crippling lameness," Linford explained. "Any laceration below the elbow or stifle has the potential to sever a major tendon."

The first step in understanding tendon injuries is to know, generally speaking, where some specific structures are positioned within the horse's lower legs:

  • Extensor tendons run down the front of the horse's legs and over the cannon bones;
  • Superficial digital flexor tendons run down the very back of the horse's legs (below the knee and hock), and in the hind limbs form part of the Achilles tendon (located above the hock);
  • Deep digital flexor tendons lie between the suspensory ligament and the superficial digital flexor tendon;
  • Suspensory ligaments run between the cannon bone and the deep digital flexor tendon; and
  • Distal sesmoidian ligaments connect the base of the proximal sesamoids to the back of the long and short pastern bones and connect both structures to the deep flexor tendon.

Clinical Signs

Linford said that often times diagnosing a tendon disruption isn't overly difficult. Some disruptions tend to cause characteristic signs, which he described:

  • Disruptions localized to the extensor tendons cause the horse to either "knuckle over" at the fetlock or "flip" his hoof in the affected leg to avoid knuckling over, he explained. Once the hoof is placed on the ground, the horse can bear weight successfully, he added.
  • A problem localized to the deep digital flexor tendon alone, Linford explained, will cause a subtle fetlock drop when bearing weight along with a slight toe elevation. Pain and lameness are evident during weight bearing, he said.
  • Superficial digital flexor tendon disruptions result in a "very slight" fetlock drop with pain and lameness during weight bearing, he said.
  • If both the deep and superficial digital flexor tendons are damaged, Linford said, the fetlock will drop more significantly than if either single structure is cut, and the toe will elevate upon bearing weight, with prominent lameness.
  • A disrupted suspensory ligament (with no damage to the digital flexor tendons) results in a significant fetlock drop when bearing weight, he said.
  • Finally, damage to the digital flexor tendons and the suspensory and/or distal sesmoidean ligaments results in the fetlock dropping to the ground and the toe pointing straight up during weight bearing, Linford said.

Once a veterinarian diagnoses the type of tendon injury, he or she can make recommendations for treatment and determine prognosis.

Prognosis, Treatment, and Recovery

Linford explained that without appropriate treatment, tendon injuries often don't heal properly, "leading to a loss of biomechanical function of the limb and, ultimately, a crippling injury." He reviewed a few general studies that looked at the treatment type and/or prognosis for specific tendon injuries:

  • One study found that of horses treated for lacerated extensor tendons, 95% survived and nearly 75% recovered sound enough to continue in their intended use. A similar study revealed that of horses treated for flexor tendon lacerations, 80% survived and 50% returned to their intended use.
  • Another study found that delaying treatment for more than 24 hours post-injury raised the injury's mortality rate from 19% to 26% of affected horses.
  • A recent study revealed that the odds of returning to the same level of work post-flexor tendon laceration depended on the number of tendons or ligaments involved. (Linford explained that horses had "significantly higher odds of an unsuccessful outcome when two or three structures were affected compared to when only one structure was involved.")
  • Most studies found that proper wound care and limb immobilization were critical for survival and return to function, while the effect of suturing versus not suturing a severed tendons had a limited effect on the likelihood of survival or return to function. Debriding and closing the wound "generally resulted" in less scarring and better post-injury performance than was seen when a wound could not be closed, he said.

Veterinarians treat most tendon injuries using broad-spectrum antibiotics and some type of surgery, Linford said. Some of these surgical procedures--such as for partial tendon tears with no synovial involvement or for extensor tendon lacerations--can be performed in the standing, sedated horse, he said. More complex procedures--such as those for completely lacerated flexor tendons--should be performed under general anesthesia, he noted.

In some cases, Linford noted, a tendon or ligament injury can involve a joint (or synovial structure). While early studies found these horses had a 2.5-fold greater chance of euthanasia, a more recent study showed that synovial involvement has little to no effect on patient survival when prompt, aggressive, appropriate treatment can be done. In the event a joint is involved in a tendon disruption, Linford recommended starting the horse on broad-spectrum antibiotics and lavaging (flushing) the affected joint to reduce the risk of sepsis development. He suggested debriding and closing wounds involving synovial structures, although he noted that veterinarians should not close "heavily contaminated and severely traumatized wounds" until healthy tissue has developed at the wound margins.

Linford reviewed the steps in surgically repairing lacerated tendons with the veterinary audience. Post-surgery the horse's affected leg needs to remain immobilized and the animal will require stall rest, but exact treatment protocol depends on the injury's severity.

Complete extensor and partial flexor tendon lacerations typically require four to six weeks of stall rest with the tendon immobilized in a Robert Jones bandage (a layered and padded bandage designed to limit limb mobility). Stall rest should be followed by 10 to 12 weeks of controlled exercise and a subsequent increase in turnout and gradual return to work, Linford said.

For complete flexor tendon lacerations, Linford suggested the horse be stabled with the limb immobilized in a flexion splint or a cast for six weeks. Following splint or cast removal, he recommended supporting the fetlock in a support sling shoe for 10 to 12 weeks. "Unrestricted turnout and free exercise are not recommended in the six to eight months following surgery," he cautioned. Mature, well-organized scar tissue should be visible on ultrasound and the horse should be sound for six weeks prior to turnout and free-exercise, he stressed. Linford recommended keeping the horse out of athletic training for 10 to 12 months following surgery to allow any completely severed tendon to fully heal.

A veterinarian should be closely involved with rehabilitating every horse after a tendon injury. He or she will prescribe stall rest, controlled exercise, free-choice exercise, and eventual return to work as each individual patient dictates.

Complications

No horse health procedure is without risk, however. Linford noted that common complications resulting from tendon injuries and subsequent treatment include pain from adhesions, joint disease, tendon sheath adhesions, annular ligament constriction, reinjury, and repair failure.

Take-Home Message

Although a lacerated or severed tendon is a nightmare for most horse owners, Linford relayed that veterinary technology now allows for many such injuries to be repaired successfully. Understand the risks and that not every horse will recover fully, but also know that working closely with a veterinarian can help an affected animal return to soundness and his intended use.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.

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