The metatarsal bones are the long bones of the hind cannon region, running from the hock joint down to the fetlock. In the horse, there are three metatarsal bones: the large metatarsal (cannon bone) and two small metatarsals (splint bones) — the medial (inside) and lateral (outside). This structure mirrors the equivalent metacarpal bones in the foreleg and forms the essential weight-bearing column of the hind limb below the hock.
Anatomy of the Metatarsal Region
The large metatarsal, commonly called the hind cannon bone, is a single, dense, cylindrical bone that bears the full weight of the hindquarters. It sits between the hock joint above and the fetlock joint below. Like its forelimb equivalent, it is flanked on either side by the small metatarsals — vestigial remnants of the outer toe bones that disappeared through equine evolution. The small metatarsals articulate with the cannon bone along their length via a fibrous attachment and taper to a blind end approximately two-thirds of the way down the limb.
The metatarsal region is covered by dense periosteum — the fibrous outer layer of bone — and surrounded by the tendons and ligaments of the lower hind limb, including the deep digital flexor tendon, the suspensory ligament originating behind the cannon, and the digital extensor tendons running over the front surface.
Metatarsal Injuries and Conditions
The most common metatarsal pathology is a splint — a bony enlargement that develops when periosteal reaction occurs between the small metatarsal and the cannon bone. Hind splints are less common than fore splints and tend to form on the medial aspect (inside) of the limb. During formation they can cause heat, swelling, and lameness. Once fully developed and no longer active, most splints are cosmetically obvious but clinically insignificant, unless positioned close enough to the suspensory ligament or a joint to cause ongoing interference.
Stress fractures of the cannon bone can occur in young horses in heavy training, particularly racehorses. These require prompt veterinary assessment — a fracture confirmed by X-ray typically requires box rest and careful rehabilitation. If your horse presents with sudden-onset hind limb lameness localised to the cannon region, veterinary assessment should not be delayed. See our disease entry on cannon bone stress fractures for more detail.
Periostitis — inflammation of the periosteum — can occur following kicks, knocks against fencing, or from the limbs hitting each other (brushing). It presents as localised heat and swelling on the surface of the bone and should be assessed by a vet to rule out fracture.
The Metatarsal Region in Performance Assessment
When assessing a horse for purchase or soundness, veterinarians and experienced buyers examine the metatarsal region carefully. The amount of bone — the circumference measured around the cannon just below the knee or hock — is considered an indicator of a horse’s capacity to carry weight in work. A light-boned horse of 500kg carrying a 70kg rider is at greater risk of limb problems than one with proportionately denser bone. The BHS recommends pre-purchase veterinary examinations that include careful palpation and if necessary radiography of the cannon region. See the BEVA guidance on pre-purchase examinations for detail on what a five-stage vetting covers.
For related anatomy, see our entries on fetlock and hock.
Frequently Asked Questions
What is the difference between the metacarpal and metatarsal?
Metacarpal refers to the cannon and splint bone region of the foreleg — between the knee (carpus) and the fetlock. Metatarsal refers to the equivalent region of the hind leg — between the hock (tarsus) and the fetlock. The bones are anatomically similar, serving the same structural role in their respective limbs, but the hind cannon is generally slightly longer than the fore cannon. The prefix meta- means “after” in Greek, whilst carpal refers to the wrist (foreleg) and tarsal to the ankle (hind leg).
Can a horse work with a splint on the hind metatarsal?
In most cases, yes, once the splint has fully calcified and is no longer active. An active splint — producing heat, sensitivity to pressure, and lameness — requires rest and veterinary guidance before resuming work. A cold, hard, inactive splint that does not impinge on any soft tissue structure is typically considered a cosmetic blemish rather than a clinical problem. The exception is a splint positioned directly over the suspensory ligament, where ongoing pressure can cause chronic soft tissue irritation. Any hind limb splint should be assessed by a vet before the horse returns to work.
How is metatarsal bone density measured?
Circumference of the cannon bone below the hock is measured with a tape in a routine conformation assessment — this provides a relative guide to bone density. More accurate assessment requires radiography or, in specialist contexts, bone scanning using nuclear scintigraphy. Radiographs show the density, structure, and any pathological changes in the bone. For horses with a history of limb problems or those being considered for intensive competition careers, detailed radiographic assessment of the cannon region is a sound investment.