Os metatarsale III (MT3)
The third metatarsal bone (cannon bone of the hindlimb) is functionally identical to the forelimb third metacarpal bone but slightly longer and rounder in cross-section. It bears the full weight of the hindlimb between the hock and fetlock. The distal condyles articulate with the proximal phalanx at the fetlock joint. The proximal end articulates with the distal row of tarsal bones.
Condylar fractures of the distal metatarsal bone can occur but are less common than in the forelimb. Stress fractures and other injuries can cause hindlimb lameness. Diagnosis is radiographic. Relevant in evaluations of hindlimb lameness and after trauma.
## 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 Dorsal cortex fatigue refers to stress-related remodeling or microdamage of the dorsal cannon bone, more commonly recognized in the forelimbs of young racehorses (bucked shins). Hind-limb
## 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 hind cannon bone after work needs immediate evaluation. Do not attempt to walk the horse long distances until assessed.
## 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 Dorsal cortex fatigue refers to stress-related remodeling or microdamage of the dorsal cannon bone, more commonly recognized in the forelimbs of young racehorses (bucked shins). Hind-limb involvement is less frequent. It represents the bone’s response to repetitive high-strain loading before full adaptation has occurred. ## Causes Cyclical compressive loading during high-speed training in immature bone. ## Diagnosis Clinical soreness over the dorsal cannon after fast work, plus radiographs evaluating periosteal reaction or cortical stress fracture. ## Treatment Modification of the training schedule, rest until soreness resolves, and anti-inflammatories. Controlled return to speed work allows remodeling. ## Recovery and Prognosis Good with appropriate training adjustments. Progression to stress fracture is the main risk if ignored. ## Prevention Gradual introduction of high-speed work in young horses. Signs include: pain and swelling over the front of the cannon after fast work; warmth; more common in young racehorses; less frequent in hind limbs
## 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 metatarsal bone can occur but are less common than in the forelimb. Stress fractures and other injuries can cause hindlimb lameness. Diagnosis is radiographic. Relevant in evaluations of hindlimb lameness and after trauma.
Acute severe lameness with swelling of the hind cannon bone after work needs immediate evaluation. Do not attempt to walk the horse long distances until assessed.
See the Third Metatarsal Bone / Cannon Bone (Left Hindlimb) on our interactive 3D horse model. Open 3D Model