Independence Day
The Fourth of July Parade in Pagosa Springs, Colorado, is always a mix of fire trucks, dogs, donkeys, and horses, a few floats, and anyone who wants to put on the red white and blue. The grand champion entry for two years running was Bob and Janice Moomaw’s American Spotted Draft Horse, Wahoo, pulling a beautifully decorated cart and driven by Janice’s Dad, Pete Milan. Wahoo has the demeanor of a Budweiser Clydesdale—dignified, unhurried, and unflappable. In fact, I don’t think I’ve ever seen Wahoo canter.

Two months after the parade in 2006, Wahoo was trotting up the hill to his barn with his pasture mates when he suddenly began to limp badly on his left hind leg. Pete was there to feed the horses and he called our practice as soon as he saw Wahoo limp into the barn. Pete had seen the horses get into kicking matches before and he guessed that Wahoo had been kicked. My husband and partner, Dr. Jim Latham, drove out to take a look at the big horse.

Wahoo’s left hind leg was swollen and tender to palpation on the back and inside of his cannon bone. There was pitting edema over the inside of the superficial and deep digital flexor tendons. Pitting edema is fluid within the soft tissues and it implies generalized inflammation in the area. An indentation is left on the skin and soft tissues after pressure is put on the area of edema with fingertips.

Jim directed Pete to confine Wahoo to his paddock, massage a liposomal diclofenac crème (Surpass) directly to the swelling twice daily and give Wahoo phenylbutazone twice daily in his feed. Surpass is a topical anti-inflammatory that seems to help with edema and only acts locally. He planned a recheck for a few days.

We both went out to check Wahoo four days later. We watched him walk and trot and palpated the reduced swelling. He was greatly improved and Jim planned to decrease and then stop the Bute. We rechecked him a few days after the Bute treatment ended. The medication had been masking Wahoo’s pain and once again Wahoo was significantly lame. He was short strided at the walk and quick to get off weight bearing at the trot. We immediately requested Wahoo be transported to our clinic for x-rays and ultrasound.

Wahoo’s x-rays were normal, but ultrasound of the deep digital flexor tendon of the left hind leg demonstrated a 1.2x 1.0 cm core lesion, a loss of normal fiber pattern—at the level of the distal third of the cannon bone about 5 inches above the sesamoid bones. Normal fibers run up and down the axis of the limb and are parallel and closely spaced. Tendonitis is recognized by the loss of this regular pattern. When fibers are torn, blood and serum fill the spaces between fibers, resulting in a visible deficit or “core lesion” seen on ultrasound. Jim wrapped Wahoo’s leg in a support wrap and referred the big horse to Littleton Large Animal Clinic near Denver, Colorado.

Dr. Earl Gaughan, DVM, Dipl ACVS and staff at LLAC examined Wahoo and confirmed the ultrasound diagnosis of deep flexor tendonitis. Stem cell injection was recommended to help resolve this very large lesion. Following regional anesthesia, a 3 inch incision was made to the side of Wahoo’s tail and subcutaneous fat was dissected out. The incision was closed and the fat was sent to Vet-Stem in Poway, California, for processing. Two days later, stem cells harvested from Wahoo’s fat were returned to LLAC and after a sterile skin prep, the cells were injected into the deep digital flexor tendon lesion. Wahoo remained in a stall at LLAC for a month and a follow up ultrasound showed significant reduction of the tendon core lesion deficit. He returned home for rehab.

Rest is the primary treatment for tendon injury. Total time to return to use may not be greatly reduced with stem cell therapy but the quality of healing is said to be superior with less likelihood for recurrence—less scar tissue, more directed, quality fiber pattern. Controlled exercise after two months is important to discourage adhesions and encourage elasticity.

Wahoo was kept wrapped for two months and confined for another four months with daily hand walking. His space and walking were then gradually increased. He was fed grass hay at frequent intervals throughout the day to encourage gut motility and keep him busy, but the amount was controlled so that he did not gain weight.

At the end of six months, we went back to see Wahoo at his barn. (On clinical exam, Wahoo was walking normally and trotting with a spring in his step and great forward motion. Fetlock flexion did still bother him. Jim palpated Wahoo’s injury site and there was no sensitivity. We reclipped the back of Wahoo’s left hind cannon bone area but a thick, crusty dermatitis like heavy, dry seborrhea impeded ultrasound exam. The dermatitis may have been reaction from the prior clipping and long term wraps or a fungal or bacterial infection. We elected to treat it. After skin cleaning and treatment for two weeks, Jim repeated an ultrasound of the deep digital flexor tendon. The prior lesion was filling in well—75% healed, and the tendon had returned to normal size. The fiber pattern was not totally normal, as expected, but the healing was impressive for only six months time.

The digital flexor tendons of the horse support a large amount of weight because of the angle of the fetlock and they also function to flex the lower limb and store energy for efficient motion. They are also shock absorbers. The tendons are mostly composed of a protein called collagen that is organized in fibers. The fibers can stretch as much as 10% in length, and even walking causes a strain of 2-4%. Overstretching and chronic wear as well as age lead to serious strain or rupture of the tendon fibers. It is reported that as many as 43% of horses in National Hunt training develop tendonitis and “bowed” tendon is a common race horse injury. There are very few cells, called fibroblasts, in the tendon to initiate repair.

Sudden overextension of the metatarsal-phalangeal (fetlock) joint may cause tearing of the deep digital tendon and cumulative fatigue can certainly lead to serious strain. In Wahoo’s case, he may have caught his left hind hoof on a tree stump or downed branch, or he may have stepped in a prairie dog hole. He’ll never tell.

In the first two weeks after sudden tendon injury there is hemorrhage and inflammation in the tendon itself where the fibers have ruptured. This is seen as a black hole on ultrasound. Surrounding the tendon there is edema and inflammation. Then, the few fibroblasts in the area begin to produce irregularly arranged scar tissue. Tendon tissue itself is not well regenerated and the healing scar tissue is initially weak. At 15-18 months after injury, the tendon is as strong as it is going to be, but it has poor elasticity compared to normal. Reinjury is common because scar tissue is inelastic and tends to tear rather than stretch like normal tendon fibers along the long axis of the limb when stressed by repeated or excessive flexion. Hopefully the improved fiber repair from stem cell therapy and careful reconditioning would reduce the incidence of recurrence for Wahoo.

Historically, therapy for flexor tendon strain has been rest and confinement. Alternate therapies have included:

  • Blistering: irritants to increase local blood flow (an outmoded ineffective procedure)
  • Wraps with magnets (ineffective)
  • Tendon splitting—surgically lancing the injury site to relieve pressure of the blood clot and allow increased entrance of blood vessels and hopefully fibroblasts and growth factors for repair.
  • Injection of hyaluronans into or around the injury site, with or without steroids (questionable results).
  • Extracorporeal shock wave therapy which may increase vascularization at tendon insertions and recruit cells and growth factors into tendon and bone in the area.

Preliminary investigations suggest that stem cells seem to hasten the healing process with less inflammatory cells and aid in improved tendon repair fiber architecture-- improved tendon fiber density and alignment. It is hoped that stem cell therapy will increase the percent of horses who can return to work successfully with less reinjury.

Wahoo was cleared for daily excursions pulling a light cart on level surfaces, just in time.

Fourth of July, 2007, First Place: Wahoo
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