Carpal Bone Injuries

In the horse, the carpus is the knee. It is composed of three joints and two rows of bones. The carpal tunnel is the canal through which the tendons and ligaments pass. Common injuries to the carpus include carpal fractures, carpal tunnel syndrome and carpitis.

Carpus Fractures

Factors predisposing a horse to fractures of the carpus include poor conformation, immaturity, lack of fitness and constant stress over a long duration. Carpus fractures are most often seen in racehorses, and occur most frequently on the outside of the left knee and the inside of the right knee. All races are run counterclockwise putting the most stress on these two areas. There are three types of carpus fractures seen in the racehorse: chip fractures, slab fractures, and fractures of the accessory carpal.

Chip fractures occur only on one surface of any given bone in the carpus. They can be loose within the joint, partially attached, or completely adhered to the bone. Pain, inflammation and lameness occur to varying degrees depending on the location and length of time the chip has been present.

Graphic example of internal fixation of a slab fracture of the third carpal bone.Slab fractures extend from one side of the bone to the other ( see figure). There is a higher incidence of slab fractures when corticosteroids are repeatedly injected into the joint. They generally start as small fissures that, with repeated stress to the bone, can turn into a complete fracture. The horse will have mild lameness at the fissure stage, but as soon as it progresses to a fracture this changes to marked lameness and severe pain.

With fractures of the accessory carpal, the horse is immediately lame and unable to bear any weight on the affected limb. These generally occur vertically and most often multiple fracture lines are noted.

Treatment for Carpus Fractures

Chip fractures are typically arthroscopically removed with post-operative care consisting of systemic antibiotics, anti-inflammatories and sodium hyaluronate. More conservative methods call for stall rest instead of surgery, but have not been shown to be as effective in returning the horse to competition and can lead to complications.

Early treatment of a slab fracture with internal fixation ( see figure) has a good prognosis. When treatment is delayed, degenerative joint disease (DJD) can develop. In this case, the prognosis is poor and the chance that the horse will return to full athletic ability is doubtful.

Fractures of the accessory carpal can be treated conservatively with stall rest and bandaging with immobilization, or can be treated surgically with internal fixation.

Carpal Tunnel Syndrome (CTS)

Graphic example of cross-section of the equine carpus (knee).Lameness in carpal tunnel (canal) syndrome is caused by inflammation and pressure within the carpal tunnel ( see figure). There is no room for swelling in the carpal tunnel, so when it does occur, there is an interruption of blood flow and normal nerve impulses to the area, causing pain and lameness in the affected limb. CTS can result from tendonitis, desmitis of the superior check ligament, or a fracture of the accessory carpal. CTS is very common among jumpers and trainers often complain of an intermittent lameness.

Swelling occurs on the front of the leg just above the knee at the base of the radius (a bone that forms a joint with the carpus), and includes inflammation of the tendons in the area. The horse experiences pain when the knee is flexed and the carpal tunnel can be palpated.

Treatment for Carpal Tunnel Syndrome

Conservative treatment methods call for systemic anti-inflammatories and physical therapy designed to decrease inflammation, including warm moist heat, cold therapy, therapeutic ultrasound, low light therapy, massage, and passive exercise with stretching. Surgical treatment may relieve the pressure (and thus the pain) within the carpal tunnel. Training can generally resume four to six weeks after surgery.

Carpitis

Graphic example of Carpitis.Overextension of the carpus can cause inflammation to several of the carpal bones, predisposing the horse to arthritis within the carpal joint. Inflammation causes swelling on the front of the knee accompanied by pain upon palpation and when the joint is flexed. The horse may have some lameness, but in most chronic cases lameness is not seen. Diagnosis is made through radiography or infrared thermography. If lameness is noted nerve blocks are used to determine its origin.

Treatment for Carpitis

Mild cases of carpitis require rest, physical therapy and non-steroidal anti-inflammatories (NSAIDs). More severe cases may also require intra-articular (into the joint) or systemic sodium hyaluronate and systemic glucosamines. Further measures are necessary if degenerative joint disease (DJD) is present. Treatment is determined by the severity of the DJD.