Os metacarpale III (MC3)
The third metacarpal bone (cannon bone) is the primary weight-bearing bone between the carpus and fetlock. It is robust and well-developed, bearing the entire weight transferred through the forelimb. The distal end has a condylar articular surface with a sagittal ridge that articulates with the proximal phalanx, ensuring only sagittal movement at the fetlock joint. The proximal end articulates with the distal row of carpal bones.
Condylar fractures of the distal cannon bone are a serious injury in racehorses and can be life-threatening if unstable. Bucked shins (dorsal cortical stress fractures) are common in young racehorses. Diagnosis is radiographic. Prognosis depends on fracture configuration and soft-tissue damage.
## Overview Dorsal metacarpal disease, commonly called bucked shins, is painful periostitis and stress remodeling of the front of the third metacarpal bone. It occurs almost exclusively in young race
## Overview Stress fractures are incomplete cracks from repetitive loading rather than a single traumatic event. They are common in racehorses in bones such as the tibia, humerus, pelvis, and cannon.
## Overview Periostitis is inflammation of the periosteum, the membrane covering bone. It causes local heat, pain, and swelling and leads to new bone production if prolonged. Common sites include the
## Overview A keratoma is a benign tumor of keratin-producing cells within the hoof capsule. Although most keratomas occur in the hoof wall or sole, rare lesions can involve the coronary band or exte
## Overview Condylar fractures of the third metacarpal or metatarsal bone (cannon bone) are sagittal-plane fractures of the distal condyle, most often the lateral condyle in Thoroughbred racehorses.
Acute severe lameness with swelling of the cannon bone after fast work needs immediate evaluation. Do not attempt to walk the horse long distances until assessed.
## Overview Dorsal metacarpal disease, commonly called bucked shins, is painful periostitis and stress remodeling of the front of the third metacarpal bone. It occurs almost exclusively in young racehorses (especially 2-year-old Thoroughbreds) entering high-speed training. The bone is adapting to new loading demands. ## Causes Repetitive high-strain compression before the dorsal cortex has remodeled sufficiently. ## Diagnosis Clinical soreness and swelling over the dorsal cannon after fast work. Radiographs assess periosteal reaction and rule out cortical stress fracture. ## Treatment Rest from training until soreness resolves, anti-inflammatories, cold therapy, and a modified return to speed work (short bursts rather than sustained galloping). ## Recovery and Prognosis Good. Most horses adapt and return to training. Ignoring the condition risks progression to stress fracture. ## Prevention Gradual introduction of high-speed exercise in young horses. Signs include: pain and swelling over the front of the cannon; worse after fast work; warm to touch; common in 2-year-old Thoroughbreds
## Overview Stress fractures are incomplete cracks from repetitive loading rather than a single traumatic event. They are common in racehorses in bones such as the tibia, humerus, pelvis, and cannon. Early signs are subtle lameness or poor performance. Bone scan detects them before complete fracture occurs. Rest allows healing. ## Causes Cyclical fatigue of bone. ## Diagnosis Nuclear scintigraphy. Radiographs may be normal early. ## Treatment Strict rest, often 60 to 90 days or longer depending on the bone. ## Recovery and Prognosis Excellent if rested before propagation. Catastrophic if the fracture completes. ## Prevention Monitoring of racehorses and modification of training when early soreness appears. Signs include: subtle lameness or poor performance; positive bone scan; radiographs often normal early; risk of catastrophic completion
## Overview Periostitis is inflammation of the periosteum, the membrane covering bone. It causes local heat, pain, and swelling and leads to new bone production if prolonged. Common sites include the cannon bones (bucked shins in young racehorses) and splint bones. ## Causes Repetitive concussion, direct trauma, or infection. ## Diagnosis Palpation and radiographs showing periosteal reaction. ## Treatment Rest, anti-inflammatories, and modification of training. Most cases resolve with time. ## Recovery and Prognosis Good. ## Prevention Gradual introduction of high-speed work in young horses. Signs include: local heat, pain, and swelling over bone; radiographic periosteal reaction; lameness if painful
## Overview A keratoma is a benign tumor of keratin-producing cells within the hoof capsule. Although most keratomas occur in the hoof wall or sole, rare lesions can involve the coronary band or extend in a manner that affects the cannon region externally. They produce pressure necrosis of the underlying coffin bone and recurrent abscesses or lameness. Note: the term is sometimes loosely confused with cannon keratosis (stud crud), which is a completely different skin condition. ## Causes The etiology is unknown. Chronic irritation, trauma, or inflammation of the germinal epithelium is suspected. ## Diagnosis Lameness, recurrent hoof abscesses, and distortion of the white line or hoof wall are typical. Radiographs show a well-defined area of bone lysis. Definitive diagnosis requires histopathology after surgical removal. ## Treatment Surgical excision of the keratoma and affected hoof wall is the treatment of choice when lameness or recurrent infection is present. The defect is protected while the hoof regrows. ## Recovery and Prognosis Prognosis is good after complete removal. Recurrence is uncommon if the entire lesion is excised. Hoof wall regrowth takes many months. ## Prevention No specific prevention is known. Signs include: intermittent or persistent lameness; recurrent hoof abscesses; distortion of the white line or hoof wall; radiographic bone lysis
## Overview Condylar fractures of the third metacarpal or metatarsal bone (cannon bone) are sagittal-plane fractures of the distal condyle, most often the lateral condyle in Thoroughbred racehorses. They result from fatigue failure of subchondral bone under repetitive high-speed loading. Acute lameness and fetlock effusion after exercise are classic. ## Causes Repetitive loading during race training produces microdamage that coalesces into a propagating fracture. Lateral condylar fractures predominate in the forelimb; medial fractures are more likely to spiral proximally. ## Diagnosis Acute lameness after work, marked fetlock effusion, and pain on flexion are typical. Radiographs (including flexed views) confirm the fracture. Standing computed tomography is more sensitive for early stress changes. ## Treatment Lag-screw fixation is the treatment of choice for most lateral condylar fractures. Medial fractures can spiral; fixation may use lag screws or a plate, depending on the fracture. Conservative casting is occasionally used for very short, incomplete fractures. ## Recovery and Prognosis Many horses return to racing after uncomplicated lateral condylar repair, although osteoarthritis can limit performance. Spiral medial fractures and those with significant joint damage have a more guarded outlook. ## Prevention Screening with advanced imaging in high-risk racehorses and careful training management may reduce catastrophic propagation, although evidence is still developing. Signs include: acute lameness after exercise; marked fetlock joint effusion; pain on fetlock flexion; swelling of the distal cannon
Condylar fractures of the distal cannon bone are a serious injury in racehorses and can be life-threatening if unstable. Bucked shins (dorsal cortical stress fractures) are common in young racehorses. Diagnosis is radiographic. Prognosis depends on fracture configuration and soft-tissue damage.
Acute severe lameness with swelling of the cannon bone after fast work needs immediate evaluation. Do not attempt to walk the horse long distances until assessed.
See the Third Metacarpal Bone / Cannon Bone (Right Forelimb) on our interactive 3D horse model. Open 3D Model