The cannon bone and splint bones make up the metacarpus in the horse. The carpus ("knee") actually involves 3 joints, any of which could be a cause of a carpal disorder. Signs of carpal or metacarpal injury include lameness, swelling, fluid buildup, or pain in the joint. Veterinarians use a number of diagnostic techniques to pinpoint disorders in the area, including examination, xrays and ultrasound. Sometimes the only observable evidence of carpal problems is fluid buildup (swelling) and minor gait problems. Regional analgesia may be used, injecting directly into the joint and observing a spread of the anesthetic throughout the connected joints.
Bucked Shins (Sore Shins, Saucer Fractures)
Bucked shins is a sudden, painful inflammation of the connective tissues on the cannon bones (shinbones). The condition most often affects the forelimbs of young Thoroughbreds in training and racing, and less commonly Standardbreds and Quarter Horses.
Excessive stress to the bone sustained during high-speed exercise usually causes this condition in young horses whose bones are not fully conditioned. The bone cannot tolerate the stress placed on it and forms a new, but weaker, layer of bone to compensate. The outer surface elevates and becomes inflamed. The condition usually begins in the left forelimb and progresses to the right. Microfractures (such as stress fractures), which can develop into major fractures, can occur in some cases. Affected bones will show a painful swelling. The horse usually becomes lame, with a shortened stride. Exercise may worsen the lameness.
The diagnosis is made based on the history, examination findings, and x-rays. Treatment usually involves altering the training schedule to short bursts of speed work 2 to 3 times a week. Rest from training is important until the soreness and inflammation go away. Severe inflammation may be relieved by anti-inflammatory, pain-relieving drugs and application of cold packs. Surgical screws are used to treat any fractures.
Desmitis or Sprain of the Inferior Check Ligament
Desmitis (inflammation) of the inferior check ligament is a common diagnosis, but it can be easily confused with inflammation of nearby ligaments. It can occur on its own or in conjunction with an injury to a flexor tendon. This injury is more common in adult or aged horses, suggesting that degeneration associated with aging may predispose the ligament to injury. It is relatively uncommon in racehorses and is common in ponies and Warmbloods (show jumpers and dressage horses). It usually only occurs in one limb. The injury typically causes swelling in the upper third of the cannon bone. Ultrasonography can help confirm the diagnosis. The primary sign is lameness, which is lessened by the use of injected anesthetic. This condition has been treated with rest, controlled exercise, and possibly shockwave therapy or injections of plasma or stem cells. For horses that do not respond to other treatments, surgically cutting the ligament (called sectioning) may be an option.
Fracture of the Carpal Bones
Fractures of the carpal bones may include chip fragments, slab fractures, and fractures of the accessory bones.
Chip Fragments (Carpal Chip Fractures)
Chip fragments of bone and cartilage are the most common cause of lameness in racehorses. They occur less commonly in working Quarter Horses and sport horses. The primary cause is trauma, usually associated with fast exercise. Although they can occur in many locations, chips often occur on the front portion of the joint. Diagnosis generally involves examination of the inflamed joint membranes together with x-rays that reveal the chip fragments. Surgery using an endoscope is the treatment of choice. The overall outlook for recovery depends on the amount of damage done to the joint cartilage. In conditions persisting over a long time, the loss of joint cartilage and bone will be greater, lowering the horse’s chances of returning to previous performance levels.
Carpal Slab Fractures
Slab fractures extend from one joint surface to another joint surface. The most common slab fracture occurs on the third carpal bone. Slab fractures are repaired with lag screws (placed surgically with an endoscope). Bone fragments that are too thin to be repaired are removed.
Accessory Carpal Fractures
The accessory carpal bone is located on the back side of the carpus. Fractures of this bone are less common than other fractures in the carpus. Accessory carpal fractures may lead to an increase in fluid in the joint and will usually make the horse severely lame. Diagnosis requires x-rays for confirmation. With rest and conservative treatment, the fracture may heal. However, if the fracture extends into the joint or creates fragments, the fragments may need to be surgically removed. The formation of a fibrous union at the site of the fracture may allow a horse to return to athletic activity.
Fractures of the Splint Bones
Fractures of the splint bones (the second and fourth metacarpal and metatarsal bones) may occur as a result of direct trauma or, more often, after inflammation of the suspensory ligament (see below) and the resulting buildup of fibrous tissue at the end of the bone. Immediately following fracture, severe inflammation (usually involving the suspensory ligament) may occur. Lameness is usually present and may be severe at first. It may go away after several days’ rest but return after work.
X-rays confirm the diagnosis. Ultrasound examination of the suspensory ligament is also helpful and can help direct treatment. Surgical removal of the fractured tip and any new bone growth (callus) is the treatment of choice. The outlook for recovery depends on the severity of the suspensory desmitis (inflammation), which has a greater bearing on future performance than the splint fracture itself.
Fracture of the Cannon Bone
The most common reason for fractures of the third metacarpal bone (cannon bone) is the cyclic trauma of racing. Fractures occur into the fetlock joint (condylar fractures); stress fractures are also possible in the body of the cannon bone. An affected horse usually becomes suddenly lame after exercise or a race and has significant swelling of the fetlock joint. X-rays are used to confirm diagnosis of cannon bone fractures.
These fractures are treated with surgery using compression plates and bone screws. More conservative treatments risk delayed healing and the development of osteoarthritis (see below).
Hygroma
A carpal hygroma is a swelling under the skin on the front of the carpus. It usually develops as a result of trauma. The condition rarely produces lameness. Infections are not usually present at first but may develop after the hygroma is drained or injected. Diagnosis is made by feeling the swelling together with x-ray confirmation. Your veterinarian will determine whether the hygroma connects with the joint. Hygromas can be treated in the early stage with drainage, steroid injections, and bandaging. When infection is present, the infected tissue needs to be surgically removed.
Osteoarthritis (Degenerative Joint Disease) of the Carpus
In the carpus, osteoarthritis typically occurs together with a longterm thickening of the joint. The range of motion of affected joints is decreased, and x-rays reveal a gradual loss of joint cartilage and bony changes that may become severe. Treatment of severe osteoarthritis is limited mostly to pain relief and anti-inflammatory drugs. Osteoarthritis between the carpus and the cannon bone is sometimes treated by surgically fusing the bones together.
Rupture of the Common Digital Extensor Tendon
This developmental problem is present at birth or is seen shortly after. Foals may show a carpal or fetlock deformity, forcing the joint to remain in a flexed position. If not noticed immediately, the condition may cause an abnormal tightening of the flexor muscle-tendon unit. A veterinarian suspects the condition by feeling the swollen, disrupted ends of the extensor tendon and confirms the diagnosis with ultrasonography. Treatment involves stall rest. When appropriate, splints are used to prevent the secondary tightening of the tendons that can lead to knuckling. The outlook is good for a full recovery in foals that do not have additional abnormalities.
Splints
Splints is a condition in which painful, bony outgrowths (exostoses) occur on the upper part of the cannon bones, usually on the inner sides of the legs along the splint bones (the second metacarpal bones). Trauma from a jarring injury, strain from excess training (especially in young horses), poor conformation, imbalanced diet or excessive food intake, or improper shoeing may be factors that contribute to the condition.
Lameness is seen only when the bony outgrowths are forming. It is seen most often in young horses and is more obvious after the horse has been worked. In the early stages, there is no visible enlargement of the affected area, but your veterinarian may be able to feel some local, painful swelling. In the later stages, a calcified growth appears. Lameness disappears, except in rare cases in which the growth interferes with the suspensory ligament or the carpal joint. X-rays are necessary to differentiate splints from fractured splint bones.
Complete rest and treatment with appropriate anti-inflammatory drugs is recommended. Injected corticosteroids, together with counterpressure bandaging, may reduce inflammation and prevent excessive bone growth. If the growth affects the suspensory ligament, however, it may be necessary to remove the growth surgically.
Inflammation of the Suspensory Ligament (Suspensory Desmitis)
Injuries of the suspensory ligament, which supports and protects the fetlock, are common in both fore limbs and hind limbs. These injuries are classified by the region in which they occur: the top one-third of the ligament, the body of the ligament, and one or both ligament branches.
Inflammation of the Top Third of the Suspensory Ligament (Proximal Suspensory Desmitis)
Inflammation of the top one-third of the suspensory ligament (and upper third of the cannon bone) is relatively common and can affect the forelimbs or hind limbs of athletic horses of all ages. It can affect one or more limbs. Inflammation of the upper third causes lameness, poor performance, or poor action.
Lameness can vary from mild to severe and is usually not severe unless there is substantial damage. In early cases, the sudden lameness seems to improve within a few days. If limbs on both sides are affected, the lameness may be less apparent, and loss of performance may be more obvious. The lameness may be more obvious on soft ground.
Affected horses do not usually show signs of heat, pain, or swelling that can help pinpoint the location of the injury. Veterinarians must use a thorough lameness examination and nerve blocks (local anesthesia) to identify the location of the injury. X-rays, ultrasonography, scintigraphy, and magnetic resonance imaging (MRI) may help in the diagnosis of this condition. Treatment is stall rest, followed by a graduated program of exercise combined with correction of foot imbalance. Premature return to work typically results in recurrence of the lameness. Horses with longterm disease may require a longer rehabilitation program and additional therapies (such as medications, shockwave treatments, or stem cells).
Inflammation of the Body of the Suspensory Ligament
This is an injury seen mostly in racehorses, affecting usually the forelimbs of Thoroughbreds and both the forelimbs and hindlimbs of Standardbreds. Signs vary and may include enlargement of the ligament, local heat, swelling, lameness, and pain. The diagnosis is based on signs and can be confirmed using ultrasonography. Treatment is aimed at reducing inflammation by using nonsteroidal anti-inflammatory drugs, hydrotherapy, and controlled exercise. Shockwave therapy, platelet-rich plasma, and stem-cell therapy have also been used.
Inflammation of the Branches of the Suspensory Ligament
This relatively common injury can affect the forelimbs and hindlimbs in all types of horses. Usually only a single branch in a single limb is affected, although both branches may be affected, especially in hindlimbs. Horses that develop this condition often have imbalanced feet.
Signs depend on the degree of damage and how long the condition has existed. The affected area may be hot, and fluid buildup in the affected branch can cause swelling. Swelling of the fetlock or digital tendon sheath may also be present. Direct pressure applied to the injured branch may cause pain, as may bending the fetlock. Lameness varies and is sometimes absent altogether.
Diagnosis is based on observation of the signs, response to nerve blocks, and ultrasonography. Management of the condition depends on the severity of signs as well as on the breed and use of the horse. Corrective trimming and shoeing may be necessary, because proper foot balance is critical. Treatments may also include shockwave therapy, anti-inflammatory drugs, stem cell therapy, and surgery. The outlook for recovery depends on the horse’s job; pleasure or sport horses have a better prognosis than do racehorses. Injuries are slow to heal; some signs take 6 months or more to improve, after which the condition may return.
For More Information
Also see professional content regarding disorders of the carpus in horses and disorders of the metacarpus in horses.
