What Are Splints in Horses? A Complete Guide for Horse Owners

A hot, swollen lump on the inside of your horse's cannon bone, usually with a few unhappy strides of lameness, is one of the most common veterinary calls in any UK livery yard. More often than not the diagnosis is a splint: an inflammatory bony reaction along the splint bone. Splints in horses are rarely catastrophic, but they are uncomfortable, slow to heal, and, if mismanaged, can compromise a young horse's future career. Worse still, what looks like "just a splint" is occasionally a fracture of the splint bone itself, which is a different and more serious problem.

This guide explains exactly what splints in horses are, what causes them, how they progress through the body's healing stages, how UK vets diagnose and treat them, how long recovery really takes, and what the implications are for pre-purchase examinations and competition. The aim is to give you enough working knowledge to recognise what you are looking at, manage it sensibly, and know when to call the vet immediately.

What Are Splints in Horses?

A splint is an inflammatory or bony swelling of the splint bone, or of the interosseous ligament that binds the splint bone to the cannon bone. The two splint bones (medial on the inside, lateral on the outside) are slim, tapering bones that run down either side of the back of each cannon bone. Anatomically they are the second and fourth metacarpal bones in the forelimb, and the second and fourth metatarsal bones behind: evolutionary remnants of the toes that once supported the ancestors of the modern horse.

In a young horse the interosseous ligament between each splint bone and the cannon is elastic and slightly mobile. As the horse matures, this ligament gradually ossifies and the splint bones fuse to the cannon, usually by around six or seven years of age. A splint typically develops when that ligament is strained or damaged during the years before fusion is complete, triggering inflammation and then a localised bony reaction that owners feel as a firm lump.

The condition is often called splints in the plural because it can appear as a chain of small bony bumps along the splint bone rather than a single defined lump. Vets may refer to it as metacarpal exostosis in the forelimb, or tarsal exostosis in the rare hindlimb cases. By a wide margin the most common form is on the inside of a front cannon bone, in horses aged two to five years old. As the Horse & Hound veterinary library (edited and approved by an MRCVS vet) notes, splints are one of the most common reasons for mild forelimb lameness in young UK horses.

Types of Splint

UK vets generally distinguish between four types of splint, each with a different prognosis and management plan.

The blind splint is the classic trap. Because there is "nothing to see", owners and yard staff dismiss it and the horse goes back to work too soon, while the underlying inflammation rumbles on. If lameness persists more than ten days after an apparent splint, a veterinary assessment with imaging is essential.

What Causes Splints in Horses?

Splints are an inflammatory response, almost always to one of three main triggers.

• Concussion. Repeated impact on hard ground (schooling on dry summer arenas, hacking on tarmac, working or racing on firm going) strains the interosseous ligament between the splint and cannon bones. The inflammation this causes triggers a localised bony reaction.
• Direct trauma. A kick from another horse in the field, or a horse striking its own opposite leg (brushing). This is why splints often appear after a turnout incident, or in horses that move close behind.
• Conformation. Faults such as being toe-out or bench-kneed transfer more concussive force onto the inside of the cannon, predisposing the horse to splints. Poor limb conformation is one of the strongest risk factors.

Less common, but worth knowing:

• Mineral imbalance, particularly a low calcium-to-phosphorus ratio in young, growing horses. UK grazing is generally well balanced, but cereal-heavy diets without adequate calcium can predispose youngstock to splints.
• Inappropriate workload. Asking too much of a two- or three-year-old, especially tight schooling on hard surfaces, is the single most preventable cause.
• Poor farriery. Long toes, low heels or asymmetric mediolateral foot balance shift load onto the inside of the cannon.

Most splints occur in horses aged two to five years. By six or seven the bone has matured and the splint bone is fully fused to the cannon, so fresh splints in older horses are usually traumatic in origin and warrant closer investigation.

Symptoms: How to Spot a Splint

Splints progress through three phases, each with characteristic signs.

Acute Phase (Days 1 to 14)

• A warm, soft, painful swelling on the inside of the cannon bone
• Mild to moderate forelimb lameness, usually grade 1 to 2 out of 5, worse on a hard surface or a tight circle
• The horse may flinch or pull the leg away when the area is palpated
• Heat in the area that persists for at least the first week
• No firm bony lump yet: the swelling is fluid and inflammatory

Subacute Phase (Weeks 2 to 8)

• The soft swelling reduces and a firmer lump becomes palpable
• Lameness eases, and most horses are sound at walk and trot in straight lines
• Heat reduces but is still detectable on direct palpation
• The horse may still feel sensitive to circle work on hard ground

Chronic Phase (After 8 Weeks)

• A hard, well-defined bony lump remains
• The horse is sound in straight lines and in normal work
• The lump is cold to the touch and not painful under firm pressure
• Cosmetic rather than functional: most chronic splints never cause lameness again

A word on the splint that shows a lump but no lameness. An old, cold, hard splint that has never caused a lame step is almost always a cosmetic blemish and needs no treatment. A new, warm splint that is not yet causing obvious lameness still needs rest, because working on it is what turns a small quiet splint into a large angry one. If lameness persists into the chronic phase, or returns as work increases, suspect a knee splint, a splint bone fracture, or interference with the suspensory ligament, all of which require imaging.

How UK Vets Diagnose Splints

Most splints are diagnosed clinically: the history (young horse, increased work, hard ground, recent kick), palpation that finds heat and a swelling, and a trot-up that confirms forelimb lameness. The diagnosis is usually unambiguous within a few minutes. Imaging is reserved for cases that do not fit the pattern or that fail to improve.

• Radiography (X-ray) to rule out a splint bone fracture, check for bony bridging to the cannon, and assess the suspensory ligament insertion. Always done on suspicion of fracture, on high knee splints, and on any splint that fails to settle within three weeks.
• Ultrasonography to assess the interosseous ligament and rule out suspensory ligament involvement, particularly in blind splints.
• Nerve blocks, occasionally used to confirm the splint is the true source of lameness, particularly in low-grade chronic cases where more than one problem may coexist.

Persistent or atypical lameness is worth taking seriously, because the differential diagnoses include more significant conditions such as proximal suspensory desmitis and general hindlimb lameness. Owners can use the RCVS Find a Vet service to locate a registered equine practice.

Treatment of Splints in Horses

The principle of splint treatment is simple: reduce inflammation in the acute phase, then allow controlled rest while the bony remodelling completes. There is no shortcut. The faster you try to bring the horse back, the larger and uglier the final bony lump tends to be, and the higher the risk that a small unstable splint becomes a chronic problem.

Acute Phase Management

1. Box rest or restricted turnout for 7 to 14 days. A small starvation paddock is generally fine, using stall rest if the horse will not settle; full grass turnout that lets the horse gallop is not.
2. Cold therapy twice daily for the first 5 to 7 days: cold hosing, ice boots or cold packs, for 15 to 20 minutes per session.
3. NSAIDs, such as phenylbutazone ("bute"), at the lowest effective dose, on veterinary prescription, for 5 to 10 days. NSAIDs reduce inflammation and pain but also slow bony remodelling, so vets generally avoid extended courses.
4. Support bandaging of the affected limb, particularly in the stable. Apply with care to avoid creating pressure points.
5. No ridden work until heat and pain have fully subsided.

Returning to Work

After 30 to 45 days most splints are ready for a gradual return. A typical UK rehabilitation programme starts with hand walking and builds slowly from there.

Advanced Treatments

For splints that fail to settle, or for high knee splints near the carpal joint, UK vets may use:

• Shockwave therapy, focal extracorporeal shockwave applied to the splint to accelerate bony remodelling and reduce pain. Many UK equine hospitals now offer it as standard.
• Local corticosteroid injection, occasionally used for persistent inflammation, with due awareness of the systemic risks in young horses.
• Surgical splint bone removal, for fractures, infected splints, or splints causing persistent suspensory ligament interference. Recovery is around three months with a good chance of full return to work.

How Long Does a Splint Take to Heal? Recovery Timeline

This is the question owners ask most, and the honest answer is that a splint heals in two overlapping stages. The inflammatory phase, when the heat, pain and lameness resolve, usually settles within 30 to 45 days of appropriate rest. The remodelling phase, when the bony lump hardens, shrinks and stabilises, continues quietly for several months afterwards but does not stop the horse working.

• Simple true splint: sound and back in light work within 4 to 6 weeks, full work by 8 weeks.
• Blind or slow-to-settle splint: often 8 to 12 weeks, because the inflammation lingers.
• High knee splint: longer and less predictable, because of the proximity to the joint.
• Splint bone fracture with surgery: typically 10 to 14 weeks to full work.

The single biggest factor that lengthens recovery is going back to work too early. Patience genuinely shortens the total timeline.

Splint Bone Fracture: Why It Matters

A fractured splint bone is the diagnosis owners most fear, and rightly. Common causes are kicks in the field, direct trauma during racing or jumping, or interference between a horse's own legs at speed. The break is most often in the lower third of the splint bone.

Signs that point towards a fracture rather than a routine splint include:

• Significant lameness lasting beyond two weeks despite rest
• Marked swelling that fails to reduce after 7 to 10 days of cold therapy
• Pain on direct, firm palpation persisting into the third or fourth week
• A visible deformity of the splint bone in some cases

X-rays confirm the diagnosis. Surgical removal of the fractured fragment, particularly in the lower splint bone, has an excellent prognosis, with most horses returning to full work in 10 to 14 weeks. Without surgery, fractures often heal with a large unstable callus that continues to interfere with the suspensory ligament, a problem that becomes harder to manage over time. This is exactly why any lameness that does not settle warrants proper imaging rather than more rest and hope.

Should You Buy a Horse With a Splint?

A "fired" splint (old, hard, cold and not associated with lameness) is rarely a deal-breaker at a vetting. Experienced UK vets distinguish clearly between a chronic cosmetic splint and an active one. The questions they weigh during a five-stage vetting include:

• Is the lump cool, hard and well-defined?
• Is the horse sound on a circle on hard ground?
• Is there any sign of suspensory ligament involvement on palpation?
• Is the splint high (near the knee) or close to the suspensory ligament insertion?

If all the answers are reassuring, an old splint is a cosmetic finding. If the splint is high, close to the suspensory ligament, or shows any heat at all, a radiographic assessment is sensible before purchase. As Horse and Rider Magazine notes, an old quiescent splint is almost always a non-issue; it is the active or atypical ones that justify caution.

How to Prevent Splints in Horses

Splints are easier to prevent than to cure. A combination of controlled workload, balanced diet and good farriery dramatically reduces the incidence in young horses. Practical steps:

• Build conditioning gradually. A young horse should not be schooling intensively on a hard arena before its fourth or fifth year.
• Use a fibre or sand-fibre arena rather than a dry, hard summer school for the majority of schooling.
• Have a competent farrier balance the foot mediolaterally every five to seven weeks. Asymmetric balance is a leading cause.
• Feed a balanced diet with adequate calcium, and avoid cereal-heavy, unbalanced feeds in growing horses.
• Use splint or brushing boots if your horse moves close behind or in front. They will not prevent every splint, but they cut down the trauma-induced ones.
• Be honest about turnout. A young horse galloping with a domineering field mate is a common cause.

Splints in Horses FAQ

How long does a splint take to heal in a horse?

Most splints settle within 30 to 45 days of rest, after which the horse can begin a gradual return to work. The bony lump continues to remodel for several months but is no longer painful. High knee splints and splint bone fractures take longer, typically 8 to 14 weeks for full recovery.

Can you ride a horse with a splint?

Not in the acute phase. While the lump is warm and painful and the horse is lame, the answer is unequivocally no. Once the area is cold, the horse trots up sound, and at least 30 days of rest have passed, a graduated return to work is appropriate. Riding through an active splint nearly always makes the final lump larger and the recovery longer. An old, cold, sound splint is no barrier to ridden work.

Do splints in horses go away?

The bony lump itself usually does not disappear: it remodels and shrinks somewhat but remains palpable for life. The pain, heat and lameness, however, do resolve. A chronic splint is a cosmetic finding rather than a soundness problem in the vast majority of cases.

What is the difference between a splint and a splint bone fracture?

A splint is inflammation of the ligament and bone that produces a reactive bony lump over weeks. A splint bone fracture is a true break of the bone itself. The fracture is more painful, more persistently lame, and usually needs an X-ray to diagnose. Splint bone fractures often benefit from surgical removal of the fractured fragment.

Are splints in horses hereditary?

Splints themselves are not directly inherited, but the conformational traits that predispose a horse to them, such as toe-out or bench knee, are. Two splint-prone parents are more likely to produce a splint-prone foal.

Will a splint stop my horse competing?

An old, cold splint will not. The horse will be passed sound at any BHS or FEI competition vetting provided the splint is quiet and the horse is sound. An active splint will sideline the horse for four to eight weeks, and a fractured splint bone somewhat longer.

The Takeaway

Splints in horses are common, manageable and usually cosmetic, but the temptation to dismiss the heat and the brief lameness costs more horses more time than almost any other "minor" lameness. Cold therapy, rest, a gradual return, and a sober look at why the splint happened in the first place (work, ground, conformation, farriery) will see almost every case through to a sound chronic state.

If lameness persists more than two weeks, if the splint sits high up the cannon near the knee, or if the lump simply refuses to settle, call the vet for imaging. Catching a fracture early, and getting an unstable splint properly stabilised, is the difference between a six-week setback and a six-month problem. This article is general guidance and is not a substitute for veterinary advice: always consult your own vet for a diagnosis and treatment plan tailored to your horse.

For more on related leg conditions and structures, see our guides to curbs in horses, windgalls, bone spavin, sidebone and desmitis (ligament inflammation), as well as our overview of lameness in horses. For young-horse conditioning, read our piece on building an equine fitness plan.