The carpus actually involves 3 joints, any of which could be a cause of a carpal or metacarpal disorder. Veterinarians use a number of diagnostic techniques to pinpoint disorders in the area, including examination of any lameness, swelling, fluid buildup, or pain in the joint. 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.
X-rays of the carpus are critical for specific diagnosis of fractures within the joint, osteochondritis dissecans, cysts beneath the cartilage, osteoarthritis, septic (infectious) arthritis, and benign tumors containing both bone and cartilage.
Bucked Shins (Sore Shins, Saucer Fractures)
Bucked shins is a painful inflammation of the connective tissues on the shinbones. The condition most often affects the forelimbs of young Thoroughbreds in training and racing, and less commonly Standardbreds and Quarter Horses.
Strains sustained during high-speed exercise usually cause this condition in young horses whose bones are not fully conditioned. The condition may begin with microfractures (such as stress fractures) that can develop into major fractures. Affected bones will show a warm, painful swelling. The horse usually becomes lame, with a shortened stride. Exercise may worsen the lameness.
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. Older horses not responding to rest and medication may require surgical screws to treat the fractures.
Degeneration of the Carpal Bones beneath the Cartilage
Most fractures that occur within the joint are likely preceded by the death of cells in the carpal bone. This degeneration of cells is believed to be caused by recurring trauma. Bone disease beneath the cartilage elsewhere in the carpus may also cause degeneration of carpal bones. Depending on the location, degeneration can be diagnosed either by using x-rays or by surgically inspecting the inside of the joint with an endoscope. Treatment involves surgically removing any dead, damaged, or infected tissue. The outlook for recovery is relatively good.
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. 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 conservatively in the past, but more recently veterinarians have surgically cut the ligament (called sectioning) with good results.
Fracture of the Carpal Bones
Fractures of the carpal bones may include chip fragments, slab fractures, and fractures of the accessory bones.
Chip fragments of bone and cartilage are the most common fractures in the carpal joints of racehorses. They occur less commonly in working Quarter Horses and sport horses. The primary cause is trauma, usually associated with fast exercise. 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 is excellent. However, 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 is repaired with lag screws (placed surgically with an endoscope). Such a fracture is considered routine if the joint does not collapse, and the treatment returns many horses to full athletic activity.
However, slab fractures can also lead to a collapse of a row of carpal bones. If untreated, the affected leg gradually turns inward, causing laminitis (founder) in the hoof of the opposite forelimb. Collapsing slab fractures require surgery. Immobilization in a cast for up to 6 weeks helps minimize the chance of another collapse of the joint.
Accessory Carpal Fractures
These 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 lame. Diagnosis requires x-rays for confirmation. With rest and conservative treatment, the fracture may heal. 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 Bone, Joint, and Muscle Disorders in Horses: Inflammation of the Suspensory Ligament (Suspensory Desmitis)) 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 may affect a supporting leg. It may go away after several days' rest but return after work.
Longstanding fractures lead to lameness in the supporting leg, which is apparent when the horse is worked at speed. The suspensory ligament thickens at and above the fracture site, where a considerable amount of callus may build up without the fracture actually healing.
X-rays confirm the diagnosis. Surgical removal of the fractured tip and 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. 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 Bone, Joint, and Muscle Disorders in Horses: Bucked Shins (Sore Shins, Saucer Fractures)).
A hygroma is inflammation of an acquired bursa. Acquired bursas are fluid-filled sacs that develop as a result of trauma. Excessive fluid accumulates in the bursa, and the bursal wall thickens with fibrous tissue. The condition rarely produces lameness. Diagnosis is made by feeling the swollen bursa together with x-ray confirmation. Hygromas can be treated in the early stage with drainage, steroid injections, and bandaging. At later stages, drains must be implanted.
Osteoarthritis (Degenerative Joint Disease)
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 that may become severe. Treatment of severe osteoarthritis is limited mostly to pain relief, but removal of dead or damaged tissue from the joint, followed by joint and whole system treatment may help (see Bone, Joint, and Muscle Disorders in Horses: Osteoarthritis).
Osteochondroma of the Distal Radius
The formation of an osteochondroma (a benign tumor containing both bone and cartilage) at the lower end of the radius usually occurs in young animals. In affected horses, the carpus will typically swell after exercise, with the swelling subsiding after a few hours. Moderate lameness during exercise is also seen. Deep inside, the carpal joint may be tender, and the area is sensitive to pressure. Rapid bending of the carpus causes pain. Diagnosis is usually made with x-rays, but ultrasonography may be necessary to define the extent of the osteochondroma. Treatment is generally successful when the osteochondroma, along with any resulting damage to the deep flexor tendon, is removed with an endoscope.
Rupture of the Common Digital Extensor Tendon
This developmental problem is present at birth or is seen shortly after. Foals usually 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 confirms the condition by feeling the swollen, disrupted ends of the extensor tendon. 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.
Splints is a condition in which painful, bony outgrowths occur on the upper part of the cannon bones, usually on the inner sides of the legs. 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.
Cysts Beneath the Cartilage and Septic Arthritis
Cysts beneath the cartilage (see Bone, Joint, and Muscle Disorders in Horses: Cysts beneath the Cartilage (Subchondral Cysts)) may be seen in the lower part of the radius or the carpus. Many of these cysts cause no problems; however, in certain areas of the carpus they can cause signs. They are diagnosed using x-rays, and if conservative treatment does not solve the problem, surgically removing them using an endoscope is recommended.
Infectious or septic arthritis (see Bone, Joint, and Muscle Disorders in Horses: Septic Arthritis) of the carpal joints is relatively rare. It most commonly follows injections given to the joint. Horses show severe lameness as well as fluid buildup and swelling in the joint. The veterinarian will detect heat, pain, and fluid in the joint. Treatment with appropriate antibiotics is required.
Inflammation of the Suspensory Ligament (Suspensory Desmitis)
Injuries of the suspensory ligament, which supports and protects the fetlock, are common in both forelimbs and hindlimbs. Signs often are restricted to the top one-third of the ligament, to the body of the ligament, or to one or both ligament branches.
Inflammation of the Top Third of the Suspensory Ligament
Inflammation of the top one-third of the suspensory ligament is relatively common and can affect the forelimbs or hindlimbs of horses of all ages. Unlike inflammation of other portions of the ligament, inflammation of the upper third causes lameness, poor performance, or poor action. It is often seen in horses with poor foot balance. Straight hock conformation or hyperextension of the fetlock joints may make a horse more prone to this type of injury.
Lameness can vary from mild to severe and, in early cases, is generally worsened by work and improved by rest. Forelimb lameness may be more noticeable by bending the fetlock and interphalangeal joints but is generally unaffected by bending the carpus, whereas hindlimb lameness may be increased by bending the fetlock and interphalangeal joints or by bending the hock and stifle joints.
In severe cases, localized heat may be felt just below the back of the carpus (or tarsus). Swelling may or may not be present. In more chronic cases, often no obvious abnormality can be detected.
Local anesthesia and ultrasonography 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.
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 can be confirmed using ultrasonography. Treatment is aimed at reducing inflammation by using nonsteroidal anti-inflammatory drugs, hydrotherapy, and controlled exercise.
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. 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 and ultrasonography. Management of the condition depends on the severity of signs as well as on the breed and use of the horse. The outlook for recovery is guarded. Injuries are slow to heal; some signs take 6 months or more to improve, after which the condition may return.
Hernias, Lumps, and Splints in the Synovial Joint Membrane
These conditions are relatively uncommon but must be considered when fluid-filled swellings occur across the back of the carpus. A synovial hernia is a swelling arising from the rupture of the synovial membrane by a defect in the joint capsule or the tendon sheath. Diagnosis is confirmed using contrast x-rays. When it is accessible, the hernia or splint is surgically repaired.
Torn Medial Palmar Intercarpal Ligament
This injury, first described in 1990, is usually diagnosed when there is an inflammation of the membranes of the carpal joint that does not respond to treatment. Bone chips may be present in the carpus, and the horse may be exceedingly lame. Diagnosis is made by surgical inspection of the joint using an endoscope. An endoscope is also used for treatment to remove the torn fibers. If the ligament is torn less than 50%, the outlook for recovery is excellent.
Inflammation of the Tendon Sheaths Associated with the Carpus
There are several forms of inflammation that can affect the tendon sheaths, including those caused by trauma, infection, and others whose cause is unknown (in which there is no evident lameness). The only sign may be joint fluid buildup around the tendon sheath. Inflammation caused by trauma is usually seen in older animals. In the acute form, a fluid-filled swelling appears; in the chronic form, the connective tissues may show abnormal thickening and scarring.
Treatment consists of generalized and local anti-inflammatory treatment. Surgical removal of any dead or damaged tissue may be helpful in treating the chronic form seen in jumpers. The infectious (septic) form of inflammation is rare. When it is seen, the signs include lameness, heat, and swelling as seen in septic arthritis.
Inflammation of the Synovial Membrane and Fibrous Joint Capsule
Inflammation of the membrane and capsule surrounding the carpal joint is a common condition and is usually the result of training or racing in athletic horses. In addition to affecting the joint membrane and capsule, the inflammation can also affect the ligaments and cause bone and cartilage damage.
Signs include varying degrees of lameness with heat and swelling around the joint. In longterm inflammation of the synovial membrane, x-rays may show bony growths, but in many instances no significant changes show up on x-rays. Treatment is as described under osteoarthritis (see Bone, Joint, and Muscle Disorders in Horses: Osteoarthritis). The most common treatments are corticosteroids injected into the joint, either alone or in combination with hyaluronic acid, as well as appropriate nonsteroidal anti-inflammatory drugs. If the inflammation does not respond to joint treatment, diagnostic surgery using an endoscope to inspect the inside of the joint may be necessary to exclude other causes of inflammation.
Last full review/revision July 2011 by Russell R. Hanson, DVM, DACVS, DACVECC; Joerg A. Auer, DrMedVet, Dr h c, MS, DACVS, DECVS; Andrew P. Bathe, MA, VetMB, DACVS, DEO, MRCVS; Leo B. Jeffcott, MA, BVM, PhD, FRCVS, DVSc, VD; Svend E. Kold, DMV, MRCVS, RCVS Specialist in Equine Surgery (Orthopedics); C. Wayne McIlwraith, BVSc, PhD, DSc, FRCVS, DACVS; Dale A. Moore, MS, DVM, MPVM, PhD; Sheldon Padgett, DVM, MS, DACVS; Tracy A. Turner, DVM, MS, DACVS, DABT; Stephanie J. Valberg, DVM, PhD, DACVIM; John F. Van Vleet, DVM, PhD