Deviation of carpus

Deviation of carpus may be palmar, dorsal, media or lateral in animals.

Palmar (backward) deviation of carpus

Palmar (backward) deviation of carpus also known as hyperextended knees, calf knees, or sheep knees.

Backward deviation of the carpus (back at the knee) is thought to place increased stress on the palmar soft tissue structures and increase compression on the dorsal aspect of the carpus. Backward knee conformation is thought to make horses working at speed more susceptible to carpal injuries but this is not widely accepted, especially in Europe. Hyperextension of the carpus is not the only reason for carpal injuries; long toes were associated with carpal problems in Thoroughbred racehorses in one study. Additionally, injury to the palmar soft tissue structures of the carpus may contribute to this conformation, suggesting that it may not be a strictly genetic influence.

Dorsal (forward) deviation of carpus

Dorsal (forward) deviation of carpus also known as bucked knees or knee sprung.

Dorsal (forward) deviation of carpus condition may also be called “goat knees” or “over in the knees.” It is generally believed that “bucked knees” is a less serious problem than the calf-knee condition and may protect against carpal disease in racehorses. However, severe dorsal deviation may be more dangerousfor the rider because the horse’s knees are on the verge of buckling forward.

Forward deviation of the carpus may be caused by contraction of the carpal flexors (i.e., ulnaris lateralis, flexor carpi ulnaris, and flexor carpi radialis) in young horses and may place increased strain on the extensor carpi radialis and the suspensory ligament. Congenital forms are nearly always bilateral and may be accompanied by a forward knuckling of the fetlocks.

The condition is often present at birth and usually disappears by 3 months of age if it is not severe. One study documenting the variations in conformation in Swedish Warmblood horses found considerably more elite sport horses were “buck kneed” than “calf kneed,” while the reverse was true in riding school horses.

Medial deviation of carpus

Medial deviation of carpus also known as knock knees, carpus valgus, or knee-narrow conformation.

Medial angular deviation of the carpus (or lateral deviation of the distal limb) can result from abnormalities of the distal metaphysis, physis, and epiphysis of the radius; from abnormal development and alignment of the carpal bones; or from carpal joint laxity. This deviation contributes to increased tensional strain on the medial collateral ligaments of the carpus and compression forces on the lateral (concave) surface of the carpus.

Varying degrees of stresses are also transmitted to the joints proximal and distal to the carpus. Varying degrees of outward rotation of the cannon bone, fetlock, and foot may accompany this entity.

Mild carpal valgus (5° to 7°) may have a protective mechanism against carpal injuries, and is preferred over completely straight front limbs. The odds for carpal fracture and effusion decreased with an increase in carpal angle in Thoroughbred racehorses. In general, carpal valgus appears to be less problematic in performance horses than carpal varus.

Lateral deviation of carpus

Lateral deviation also known as bowlegs, carpal varus, or bandy-legged conformation.

Carpal varus is an outward deviation of the carpus (or inward deviation of the distal limb) when viewed from the front of the horse. It may be accompanied by a base-narrow, toe-in conformation. This condition increases tension on the lateral surface of the carpus and compression on the medial surface of the carpus and carpal bones.

This deviation may be correctable in young horses but growth of the knee reached a plateau at approximately 140 days of age in Thoroughbreds, suggesting that carpal deviations (lateral or medial) should be corrected before this age.

Bench Knees (Offset knees)

Bench knee is a conformation in which the cannon bone is offset to the lateral side and does not follow a straight line down from the radius when viewed from the front. Increased weight bearing on the medial splint bone is thought to occur in benched kneed horses. This is thought to contribute to increased stress on the interosseous ligament predisposing to “splints.” The combination of bench knees and carpal valgus is common, and offset knees has been associated with fetlock problems in racing Thoroughbreds.