Os metacarpale/metatarsale III
The cannon bone is the large, single weight-bearing bone of the lower limb: third metacarpal (MC3) in the forelimb and third metatarsal (MT3) in the hindlimb. Horses evolved to run on one digit, so this bone carries the entire load. The smaller splint bones (MC2/MC4 and MT2/MT4) run alongside it as vestigial remnants of the second and fourth digits. Because the cannon bone lies just under the skin with little muscle covering, it is easily palpated and vulnerable to direct trauma, kicks, and overreaching. Its dorsal cortex is a common site of dorsal metacarpal disease (“bucked shins”) in young horses entering speed training. The distal condyles are a frequent site of catastrophic condylar fractures in racehorses, especially Thoroughbreds.
Origin: N/A (bone)
Insertion: N/A (bone)
Action: Bears the entire body weight on a single digit; key structural adaptation for speed
Bucked shins (dorsal metacarpal periostitis/stress remodeling) are common in 2-year-old racehorses; they can progress to dorsal cortical stress fractures if training continues. Condylar fractures (especially lateral) are high-speed injuries that cause acute severe lameness and fetlock effusion; lag-screw fixation is standard for many. Medial condylar fractures can spiral; fixation may use lag screws or a plate, depending on the fracture. The bone is also susceptible to direct trauma fractures and periosteal reactions from splints or kicks.
## 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.
## 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
Fractures or bony growths (splints) on the second or fourth metacarpal bones. Splints are common in young horses beginning work and are caused by tearing of the interosseous ligament between the splin
Heat, swelling, or pain on the front of the cannon bone after fast work in a young horse suggests bucked shins; rest and veterinary evaluation are needed before more speed work. Sudden severe lameness with a swollen fetlock after racing or hard exercise is an emergency (possible condylar fracture). Protect the cannon bones with boots when working on hard or uneven ground.
## 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
## 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
Fractures or bony growths (splints) on the second or fourth metacarpal bones. Splints are common in young horses beginning work and are caused by tearing of the interosseous ligament between the splint and cannon bones. Signs include: Warm, painful swelling on the inside or outside of the cannon bone; lameness in acute phase; bony hard lump after healing (cosmetic blemish); usually resolves with rest; rarely causes long-term lameness unless near the knee or suspensory.; Consult veterinarian for specific symptoms.; Hard, warm, painful swelling on the side of the cannon bone; lameness (may be temporary); cosmetic blemish after healing; splint fractures can irritate the suspensory ligament if displaced.
Bucked shins (dorsal metacarpal periostitis/stress remodeling) are common in 2-year-old racehorses; they can progress to dorsal cortical stress fractures if training continues. Condylar fractures (especially lateral) are high-speed injuries that cause acute severe lameness and fetlock effusion; lag-screw fixation is standard for many. Medial condylar fractures can spiral; fixation may use lag screws or a plate, depending on the fracture. The bone is also susceptible to direct trauma fractures and periosteal reactions from splints or kicks.
Heat, swelling, or pain on the front of the cannon bone after fast work in a young horse suggests bucked shins; rest and veterinary evaluation are needed before more speed work. Sudden severe lameness with a swollen fetlock after racing or hard exercise is an emergency (possible condylar fracture). Protect the cannon bones with boots when working on hard or uneven ground.
See the Cannon Bone (Third Metacarpal/Metatarsal) on our interactive 3D horse model. Open 3D Model