Modern diagnostics and good horsemanship could detect a problem before a breakdown occurs

ON JUNE 5, 1999, the world was focused on Belmont Park for the Belmont Stakes (G1). Charismatic, winner of that year's Kentucky Derby (G1) and Preakness Stakes (G1), was favored to be the first horse in 21 years to win the Triple Crown.

I was there at trackside that day when the D. Wayne Lukas trainee tragically broke down near the finish line. In fact, I was the first veterinarian to give assistance to jockey Chris Antley and Charismatic, as Antley cradled the horse's left foreleg to keep him from stepping down on his shattered bones.

Through the quick actions of many people and the miracles of modern veterinary science, Charismatic's life was saved.

Similarly, but more tragically, on July 6, 1975, during a match race with Foolish Pleasure at Belmont, Ruffian broke down and later was euthanized after an unsuccessful attempt to repair her fractured right foreleg.

On October 27, 1990, Go for Wand broke down while racing in the Breeders' Cup Distaff (G1) at Belmont. I was present that horrible day, as well. Her injury was so severe that it was decided to euthanize her right on the track.

All three horses were multiple champions; all three horses had significant earnings for their eras; and all three horses became victims in the fight of their lives. A common denominator of all three injuries was fractured sesamoid bones.

Thoroughbreds are powerfully physical machines that travel at fast speeds on fragile legs. The average-sized racehorse is approximately seven times the weight of the average adult person, but the size of the bones in their legs is only slightly greater than that of the average adult person.

So why do racehorses not break down more often? Largely, it is because the bones of racehorses, in general, are many times denser than those of humans, which makes their bones substantially stronger. Additionally, advancements in veterinary diagnostics and greater media attention to racing injuries have caused veterinarians, trainers, and owners to become more proactive in protecting their horses from catastrophic breakdowns.

What can go wrong

Sesamoid bone injuries can be minor and treatable; they can be severe and life threatening; or they can be part of a more complex, composite breakdown injury that involves other bones and supportive, elastic structures that comprise the ankle joint.

An intimate relationship exists among various anatomical parts that directly and indirectly contribute to the normal function of the ankle joint. The sesamoid bones, the suspensory ligament, the splint bones, the cannon bone, the long pastern bone, the intersesamoidean ligament, and the distal sesamoidean ligaments are all interconnected. Uncorrected cumulative damage to any one of these structures can lead to additional damage to one or more of the other interrelated parts. Subtle damage to any one structure, or combination of structures, eventually can culminate in severe injury.

At the height of a race, if any one of these structures is compromised, the cumulative damage caused by each additional step the horse takes can lead to a life-threatening, catastrophic breakdown.

Condylar fractures of the outside portion of the end of the cannon bone are the most commonly involved with complete breakdown injuries.

Sesamoiditis

Inflammation of the sesamoid bones is called sesamoiditis. Any associated lameness often is first noticed only after hard exercise.

Radiographs are helpful in identifying enlarged vascular channels within each sesamoid bone and arthritic changes, often seen as bone spurs, or both. Enlarged vascular channels cause local weakening of the sesamoid bone and can be precursors to impending fractures.

Nuclear scintigraphy is particularly accurate in diagnosing and quantitating the degree of sesamoiditis. It can identify early changes and can be helpful in determining the validity of a questionable radiographic finding.

Treatments for sesamoiditis include various physical therapies, medication to reduce inflammation and increase blood flow, and shock-wave therapy. Progressive sesamoiditis can lead to sesamoid fractures.

Sesamoid fractures

Six types of sesamoid bone fractures occur:

• Apical fractures affect the top one-third of the sesamoid bone;
• Midbody fractures occur within the middle third of the sesamoid bone and usually affect the inside sesamoid of the foreleg;
• Basilar fractures occur at the bottom, or base, of the sesamoid bone and can comprise fragments or can involve the entire bottom portion of the bone;
• Abaxial fractures involve the outside border of the sesamoid bone where the branch of the suspensory ligament attaches;
• Axial fractures involve the long axis of the sesamoid bone. They often are associated with lateral (outside border) condylar fractures of the cannon bone and occasionally with total disruption of the suspensory apparatus, also known as a breakdown injury; and
• Comminuted fractures comprise multiple pieces of the sesamoid bone. Fatigue, accumulated strain during a race, degeneration of the sesamoid bones from chronic sesamoiditis, associated damage to the other mechanical support structures of the ankle joint, uneven track footing, or a bad step can contribute, individually or collectively, to a sesamoid fracture.

Training often strengthens the suspensory ligament so that the weakest link then becomes the sesamoid bones. Therefore, racehorses more typically are predisposed to fracture of the sesamoid bones than they are to tearing of the suspensory ligament.

Fractures of the sesamoid bone tend to be more difficult to heal than those of other bones. The sesamoid bone naturally has a poor blood supply, and because it is subjected to continuous tensile forces, when a fracture occurs, the pieces tend to pull apart. It, therefore, is difficult for the sesamoid bone to heal by formation of a bony union, which is more typical of the means by which long-bone fractures repair. Instead, sesamoid fractures often heal with a weak, fibrous union that usually is insufficient to withstand a return to the strenuous exercise required for racing.

The prognosis depends on the severity of damage to the suspensory ligament and to the distal sesamoidean ligaments, rather than on the size of the fracture alone.

Simultaneous fracture of both sesamoid bones in the same limb results in catastrophic disruption of the entire suspensory apparatus and loss of ankle support. Such catastrophic breakdown injuries warrant a decision by the owner to humanely destroy the horse or to attempt to salvage him or her for breeding.

Repair of sesamoid fractures

Horses with any type of fracture of the sesamoid bone should be evaluated for additional musculoskeletal injuries before surgery is attempted. The size of the fracture fragment and the amount of attachment of the suspensory ligament to the detached portion of the sesamoid bone determine its prognosis and treatment. The prognosis decreases as the size of the defect on the joint surface increases and as the amount of detached suspensory ligament damage increases.

Prognosis and treatment for the various types of sesamoid fractures are:

• Apical fragments of less than one-third of the total sesamoid bone, in general, have a good prognosis for return to racing following surgical removal. However, racing performance following removal of the fragment is poor if additional suspensory damage is present before surgery. Small, apical sesamoid fragments often can be removed by arthroscopic surgery;
• Midbody sesamoid fractures heal poorly because of their inadequate blood supply and/or because the fragments are pulled apart by continuous tension generated by the suspensory apparatus. Singular midbody fractures are serious injuries that could severely limit future athletic performance.

Treatment options include combinations of bone grafting, fixation with a lag screw, repair using cerclage wire, shock-wave therapy, placing the limb in a cast, and various splinting and bandaging options.

If both sesamoid bones in the same leg sustain midbody fractures, there is an even greater loss of the supportive suspensory apparatus, and the condition is considered life threatening. Damage to associated blood vessels usually occurs, which disrupts or diminishes the blood supply to the horse's lower leg.

An external support bandage or Kimzey splint can be applied to stabilize the injury, but saving the horse's life often depends on the success of an internal fixation, such as fusion of the ankle joint (arthrodesis);

• Basilar sesamoid fractures can be smaller than apical fractures, but they usually have a worse prognosis because of their attachments to the lower portion of the distal sesamoidean ligaments. Small, articular (joint) fragments can be removed surgically, including arthroscopically, but they require a longer period of post-surgical rest.

  If basilar sesamoid fractures involve the entire articular width of the bottom portion of the sesamoid bone, they are poor surgical candidates.

  The prognosis for horses with large, displaced, or comminuted (multiple-piece) basilar fractures is poor for a return to racing soundness;

• Abaxial sesamoid fractures often follow sesamoiditis. Abaxial fractures affecting the joint can be treated by removal of the fragment, if it is small. If the fragment is large, however, treatment involves inserting a lag screw, performing a bone graft, or both.

  Fractures not involving the joint can be managed by stall confinement alone. The prognosis is related to the size of the fragment, the extent of damage to the suspensory ligament, and the severity of sesamoiditis;

• Axial sesamoid fractures occur in a more vertical plane and usually are associated with a condylar fracture of the cannon bone or with breakdown injuries. They occur on the same side of the limb as the condylar fracture. The first step to repair the injury is surgical reconstruction of the condylar fracture. Then internal fixation of the two fracture fragments of the affected sesamoid is performed. The prognosis for a return to racing soundness is poor; and
• Comminuted sesamoid fractures have a poor prognosis for future racing soundness. Unfortunately, they often are associated with traumatic disruptions of the suspensory apparatus and catastrophic breakdowns./ul>

  Condylar fractures can occur alone or accompany sesamoid fractures. Complete breakdown injuries might be amenable to conservative, long-term, bracing techniques or they could require internal fixation techniques of fusing the ankle joint, using stainless-steel plates, screws, and wires.

  Prevention of sesamoid fractures

  Sesamoid fractures occur more often when the footing is deep. Running on a deep track, combined with speed, sets the stage for a sesamoid fracture during a breeze or a race. Fatigue of the flexor muscles (leg weariness), usually at the end of exercise, also may be a factor, as well as a bumping incident involving the horse during the race or the animal having taken a bad step.

  Uneven track footing also has been suggested as a contributing factor. Improper shoeing, especially with a lower heel and a longer toe, including excessive toe grabs, also might be predisposing factors.

  A horse's legs should be monitored routinely for heat and swelling, especially in the fetlock region. Actual lameness often is one of the later signs of a problem. Icing a horse's ankles might be warranted, as well as administering the anti-inflammatory phenylbutazone alone or in combination with the vasodilator isoxsuprine.

  Use of good support wraps during exercise and overnight standing bandages can give added relief.

  Early preventive diagnostics include high-detail radiographs, ultrasonography, and nuclear scintigraphy.

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  Gregory Beroza, D.V.M., is a board-certified surgeon and practitioner. He is director of the Long Island Equine Medical Center in Huntington Station, New York, and he has an office at Belmont Park. He often writes articles under the title HorseDoc Reports. His website is www.horsedoc.com