Suspensory Ligament Injuries in Horses: Why They Happen and How to Manage Them

The Suspensory Ligament: Not Really a Ligament

Here is a fact that surprises most horse people: the suspensory ligament is technically a muscle. Or rather, it was a muscle. Evolutionary biologists call it the interosseous muscle, and in the ancient ancestors of the modern horse, it was a functioning muscle with contractile fibers that helped flex the digits. Over millions of years, as horses evolved from multi-toed forest browsers to single-toed grassland runners, that muscle gradually transformed into a dense, fibrous band of connective tissue. In the modern horse, only scattered remnants of muscle fibers remain. It functions as a ligament in every practical sense, so that is what we call it.

Understanding this origin matters because it explains something about how the suspensory ligament behaves when damaged. Unlike a true ligament (which is entirely collagenous), the suspensory retains some muscle tissue characteristics, particularly in the proximal region near its origin. This mixed composition affects healing, imaging appearance, and even treatment response. The proximal suspensory region often looks different on ultrasound than the body or branches, not because anything is wrong, but because the tissue composition changes along its length.

The suspensory ligament's job is deceptively simple: prevent the fetlock from hyperextending during weight bearing. When the horse's foot hits the ground at speed, the fetlock drops toward the ground. The suspensory ligament is the primary structure that limits how far it drops. Without it, the fetlock would contact the ground. That is not a theoretical scenario. Horses with complete suspensory ruptures have fetlocks that sink to the ground, a condition called breakdown. It is the catastrophic injury you sometimes see on racetracks.

Anatomy of the Suspensory Apparatus

The suspensory ligament originates from the back of the upper cannon bone (third metacarpal in the forelimb, third metatarsal in the hindlimb) and the lower row of carpal or tarsal bones. This origin point is called the proximal suspensory region, and it is where a large percentage of injuries occur.

From its origin, the suspensory runs down the back of the cannon bone, sandwiched between the cannon bone in front and the deep digital flexor tendon behind. About two-thirds of the way down the cannon, it divides into two branches: the medial (inside) and lateral (outside) branches. Each branch courses obliquely downward and forward to attach to the top of its respective proximal sesamoid bone at the back of the fetlock joint.

From the sesamoid bones, thin extensor slips continue forward and merge with the common digital extensor tendon on the front of the pastern. This creates a sling-like mechanism that supports the fetlock from below and connects to the extensor apparatus on top. The entire system, including the sesamoid bones, the distal sesamoidean ligaments below the fetlock, and the suspensory ligament above, is called the suspensory apparatus.

Trace the suspensory ligament from origin to sesamoid attachment in our interactive 3D model →

In the hindlimb, the anatomy is similar but the suspensory origin is slightly different in shape and the tissue contains more residual muscle fibers than the forelimb. Hindlimb proximal suspensory disease (PSD) is common in dressage horses and has its own diagnostic challenges because the normal ultrasound appearance in the hind is more heterogeneous than the fore, making it harder to distinguish pathology from normal variation.

Check the equine anatomy encyclopedia for detailed entries on each component of the suspensory apparatus and how they interact.

Types of Suspensory Injuries

Proximal Suspensory Desmitis (PSD)

Injuries to the origin of the suspensory ligament account for roughly 30 to 40 percent of all suspensory injuries. In the forelimb, PSD often presents as a subtle, poorly localized lameness that worsens with work. In the hindlimb, PSD is notorious for being difficult to diagnose because the lameness can mimic hock or stifle pain, and the horse may not show obvious swelling.

Hindlimb PSD is over-represented in dressage horses and sport horses that work in collection. The mechanics make sense: collected gaits demand more engagement of the hindquarters, which increases load through the proximal suspensory region as the hindlimb pushes off. Horses working at piaffe and passage are loading these structures at extreme levels, stride after stride.

Body Lesions

Injuries to the body of the suspensory (the straight section running down the cannon bone between origin and branch split) are less common than proximal or branch injuries. When they occur, the horse typically presents with palpable swelling on the back of the cannon bone and more obvious lameness than PSD. Body lesions tend to respond well to treatment because the tissue in this region is more uniformly collagenous and has a reasonable blood supply.

Branch Injuries

The medial and lateral branches are vulnerable because they are relatively thin compared to the body and they absorb asymmetric forces. A horse that lands unevenly, rotates on a turn, or works on deep, uneven footing can overload one branch while the other stays intact.

Branch injuries are the most common suspensory injury overall, especially in racehorses, eventers, and show jumpers. The medial branch in the forelimb is injured more often than the lateral, partly because of the way the forelimb loads during landing from a jump or during turns. In the hindlimb, the lateral branch tends to be more commonly affected.

Severe branch injuries can involve avulsion of the branch from the sesamoid bone, tearing the fibers where they insert. These avulsion injuries carry a more guarded prognosis than mid-branch tears because the insertion point has limited blood supply and heals slowly.

Why These Injuries Happen

Speed and sudden load. The suspensory ligament absorbs more force at faster gaits. A galloping horse loads the suspensory at forces that approach the tissue's breaking point with every stride. Add fatigue (the horse tires, other stabilizers lose effectiveness, and the suspensory takes more load) and you have the setup for injury. Racehorses, eventers, and polo ponies are at highest risk.

Footing. Deep, heavy footing forces the fetlock to drop lower before the surface provides support, increasing suspensory strain. Conversely, hard footing increases concussive forces. The worst scenario is uneven footing, where one side of the foot sinks more than the other, creating asymmetric branch loading. Poorly maintained arenas, rutted fields, and ground that is deep in some spots and hard in others are injury factories.

Conformation. Horses with long, sloping pasterns and low-set fetlocks naturally load the suspensory more at rest and during movement. Horses with offset knees (bench knees) load the medial branch unevenly. Toed-out conformation creates rotational forces that stress the branches asymmetrically. You cannot change conformation, but you can recognize high-risk horses and manage their workload accordingly.

Learn more about how conformation faults predispose horses to specific injuries in our article on conformation faults and why they matter.

Poor hoof balance. A foot that is medial-lateral imbalanced (one side of the hoof is higher than the other) creates uneven forces up the leg. The branch on the overloaded side absorbs more force every stride. Corrective trimming and shoeing can mitigate this, but the horse needs a farrier who understands the connection between hoof balance and soft tissue strain.

Previous injury. Scar tissue from a prior suspensory injury is less elastic and weaker than original tissue. Reinjury rates are significant, particularly if the horse returns to work too quickly or at too high a level. Each subsequent injury tends to be worse than the last because the accumulated scar tissue compromises more of the functional ligament.

Recognizing Suspensory Problems

The clinical signs vary depending on which part of the suspensory is injured and how severely.

Branch injuries typically produce visible or palpable swelling over the affected branch, just above the sesamoid bone. The area feels thick, warm, and the horse flinches when you press firmly. Lameness ranges from mild to severe depending on the degree of fiber disruption. In acute cases, the horse may be significantly lame at the trot.

Body injuries produce swelling on the palmar (back) surface of the cannon region. You can feel a firm, enlarged structure between the cannon bone and the DDFT. The horse resists flexion of the fetlock and shows lameness that worsens on circles, particularly when the affected leg is on the outside of the circle.

Proximal injuries are the tricky ones. Swelling in the proximal region is buried under other structures and difficult to palpate. The horse may show subtle lameness that is hard to localize. Flexion tests may be positive for upper limb flexion. The horse might look sore behind but pass hock and stifle tests. Many proximal suspensory injuries are initially misdiagnosed as something else because the presentation is so nonspecific.

One useful field test: apply firm thumb pressure to the proximal suspensory region (just below the carpus in the fore, just below the hock in the hind). A normal horse tolerates this without reaction. A horse with PSD often snatches the leg away, shifts weight, or flinches. It is not definitive, but it points the vet in the right direction.

Diagnosis: Ultrasound, MRI, and What They Show

Ultrasound is the primary diagnostic tool for suspensory injuries and has been for decades. A skilled ultrasonographer can identify fiber disruption, enlargement, changes in echogenicity (brightness on the image), and periligamentous edema. For body and branch injuries, ultrasound is usually sufficient for diagnosis and monitoring.

The limitations show up with proximal suspensory injuries, especially in the hindlimb. The proximal suspensory origin is partially obscured by the splint bones and sits in a tight anatomical space that is difficult to image cleanly. Mixed tissue composition (those remnant muscle fibers) creates a heterogeneous appearance on ultrasound that can mimic pathology. An inexperienced ultrasonographer may over-read or under-read proximal suspensory images.

MRI resolves ambiguity when ultrasound is equivocal. Standing MRI of the distal limb provides superior soft tissue detail and can identify bone marrow edema in the proximal cannon bone that often accompanies PSD. MRI also reveals concurrent injuries (DDFT adhesions, sesamoid bone damage) that ultrasound might miss.

Nuclear scintigraphy (bone scan) can highlight areas of increased bone turnover associated with suspensory origin injuries. The ligament itself does not show on bone scan, but the stress reaction in adjacent bone does. It is useful as a screening tool to localize lameness before ultrasound or MRI.

Regardless of imaging modality, serial examinations are essential. A single ultrasound at diagnosis tells you what the injury looks like today. Repeat ultrasounds at 60, 90, and 120 days tell you whether the ligament is healing, stalled, or worsening. Treatment and rehabilitation decisions should be guided by imaging progress, not by how the horse looks in the paddock.

Treatment Options Old and New

Controlled rest remains the cornerstone of suspensory injury management, and nothing replaces it. An acutely injured suspensory ligament needs time for the inflammatory phase to resolve and for early fiber alignment to begin. Stall rest with hand walking for the first 30 to 60 days is standard for moderate injuries. The temptation to turn the horse out because it "feels good" leads to reinjury. Ligaments heal slowly and do not respect the horse's enthusiasm.

Cold therapy and anti-inflammatories manage the acute phase. Ice boots, cold hosing, and topical anti-inflammatory gels (diclofenac) reduce swelling and pain. Systemic NSAIDs for the first 7 to 14 days. Beyond that, excessive anti-inflammatory use may actually impede healing by suppressing the inflammatory signals needed for tissue repair.

Extracorporeal shockwave therapy (ESWT) delivers focused acoustic waves to the injury site, stimulating blood flow and cellular activity. Multiple controlled studies show accelerated healing and improved tissue quality in suspensory injuries treated with shockwave compared to rest alone. Treatments are typically given at two- to three-week intervals for three sessions. One important caveat: shockwave provides temporary analgesia (pain relief) at the treatment site, which is why most competition organizations require a withdrawal period after treatment. Do not interpret post-shockwave soundness as healing.

Therapeutic ultrasound and laser therapy are sometimes used, though the evidence base is thinner than for shockwave. Some horses seem to benefit. Controlled studies are limited.

Regenerative Medicine: PRP, Stem Cells, and IRAP

This is where equine sports medicine has changed dramatically in the past fifteen years.

Platelet-rich plasma (PRP) is prepared by drawing the horse's blood, concentrating the platelets through centrifugation, and injecting the concentrate directly into the lesion under ultrasound guidance. Platelets release growth factors that promote tissue healing. PRP is widely used, relatively affordable ($300 to $800 per treatment), and supported by a growing body of evidence. Most vets treating competitive horses consider PRP standard of care for significant suspensory injuries.

Stem cell therapy uses mesenchymal stem cells harvested from the horse's bone marrow (usually from the sternum) or adipose tissue (fat from the tail head). The cells are processed (either concentrated on the same day or cultured in a lab over 2 to 3 weeks to expand the population) and injected into the lesion. Stem cells differentiate into fibroblasts that produce collagen, ideally improving the quality of the repair tissue. The evidence for stem cells is promising but not yet definitive. Studies show improved tissue organization and reduced reinjury rates compared to rest alone. Cost is higher, typically $1,500 to $3,000, because of the harvesting and processing steps.

IRAP (interleukin-1 receptor antagonist protein) is an autologous blood product that targets inflammation rather than tissue repair. The horse's blood is incubated in special tubes that stimulate white blood cells to produce anti-inflammatory proteins, which are then concentrated and injected. IRAP is more commonly used for joint inflammation than ligament injuries, but some practitioners use it in combination with PRP for suspensory lesions with significant periligamentous inflammation.

ProStride and similar commercial kits combine PRP and IRAP-like components in a single preparation processed chair-side. They simplify the procedure and reduce cost compared to separate PRP and IRAP treatments.

None of these therapies replace rest. They accelerate and improve the quality of healing that occurs during controlled rehabilitation. A horse that gets PRP and goes back to full work in six weeks will reinjure. A horse that gets PRP and follows a proper 9- to 12-month rehab program has the best chance of a durable recovery.

The Rehabilitation Timeline

This is the part that tests every horse owner's patience. Suspensory ligament rehabilitation takes 9 to 12 months for moderate injuries and longer for severe ones. Rushing is the single biggest cause of reinjury.

A typical protocol looks something like this (adjusted based on imaging and clinical progress):

• Weeks 1 to 4: Stall rest, hand walking 10 to 15 minutes once or twice daily. Ice therapy, NSAIDs as needed. Repeat ultrasound at 30 days.
• Weeks 5 to 8: Increase hand walking to 20 to 30 minutes. Begin walking under saddle on firm, flat footing if cleared by ultrasound. No circles, no hills, no lateral work.
• Weeks 9 to 16: Walking under saddle 30 to 45 minutes. Introduce small paddock turnout (not a big field where the horse gallops). Recheck ultrasound at 90 days.
• Weeks 17 to 24: Begin trot work, starting with 2-minute trot sets and increasing by 2 minutes every one to two weeks. Continue walking on non-trot days. Straight lines only initially, then gradual introduction of large circles.
• Weeks 25 to 36: Build trot work to 20 to 30 minutes. Introduce canter in 2-minute sets, progressing slowly. Recheck ultrasound at 6 months. Adjust timeline based on imaging.
• Weeks 37 to 48: Gradual return to discipline-specific work. Introduce jumping (small), collected work, or speed work at very conservative levels. Final ultrasound before return to full work.

Every step up in work should be followed by palpation of the suspensory region the next day. Any heat, swelling, or pain means you went too far too fast. Drop back one level and hold there for two weeks before trying again.

The hardest part is month 4 to month 8. The horse feels great. It bucks and plays in the paddock. It pulls the handler on walks. It looks sound. The ultrasound shows a healing lesion that is not yet mature. And you have to hold the line. So many injuries re-tear during this phase because the horse's behavior convinces the owner that it is ready. It is not. Ligament maturation lags behind clinical comfort by weeks to months.

Prevention and Risk Reduction

You cannot injury-proof a horse. But you can reduce risk substantially.

• Maintain footing. Drag arenas regularly. Fill holes in turnout areas. Avoid working on ground that is too deep, too hard, or inconsistent.
• Condition progressively. Ramp up workload over weeks, not days. A horse coming back from a break needs time for connective tissues to adapt. Muscles strengthen in weeks; tendons and ligaments take months.
• Prioritize hoof balance. A well-balanced foot distributes forces evenly. Schedule farrier visits every 5 to 6 weeks, not 8.
• Warm up properly. Walk for 10 minutes before asking for anything strenuous. Cold, stiff ligaments are more vulnerable than warm, pliable ones.
• Know your horse's limits. A horse with previous suspensory injury, poor conformation, or advanced age is at higher risk. Adjust expectations and workload accordingly.
• Monitor regularly. Run your hands down the legs after every ride. You should know what your horse's legs feel like normally so that abnormalities stand out immediately.

For a comprehensive look at how leg structures relate to each other and where injuries commonly occur, study our horse leg anatomy guide and explore the structures directly in the 3D model.