The suspensory apparatus is one of the most important support structures in the horse’s limb, and yet it’s also one of the most commonly injured. For us as rehabilitation therapists, understanding this region is vital. It helps us communicate clearly with veterinary colleagues, educate owners, and guide patients through recovery in a way that gives them the best possible chance of returning to soundness.
The Anatomy
The suspensory apparatus is made up of three main parts:
- The suspensory ligament (interosseous medius): originates at the top of the cannon bone and distal carpal or tarsal bones. It contains muscle fibres in its proximal portion and splits distally to insert on the proximal sesamoidean bones with medial and lateral extensor branches traveling to join the common digital extensor tendon and lateral digital extensor tendons to insert on the extensor process of the middle and distal phalanges.
- The proximal sesamoid bones
- The distal sesamoidean ligaments: Including short, cruciate, long and oblique ligaments.
Together, these structures form a sling that supports the fetlock, preventing it from over-extending under load. The apparatus also stores elastic energy, acts as a spring, stabilises the distal limb, and is a crucial part of the stay apparatus. In the forelimbs, the suspensory is loaded during landing, while in hindlimbs, it is loaded during push-off.
How and Where It Breaks Down
The suspensory apparatus is vulnerable to cumulative microtrauma. Over time, repeated strain can exceed the strength of the ligament fibers. Fatigue, poor conformation, hoof imbalance, and discipline-specific demands all contribute to strain.
Common sites of injury include:
- Proximal suspensory desmitis (PSD): occurs in the forelimb and hindlimb, but is a very different condition in each of these areas.
- Mid-body desmitis: Often acute strain, more common in forelimbs.
- Branch desmitis: Especially in high-performance horses, can coexist with proximal lesions.
- Distal sesamoidean ligament desmitis: Less common but can destabilise the fetlock.
- Sesamoiditis or sesamoid fractures: Sometimes part of the picture.
Let’s take a closer look at each of these
Proximal Suspensory Desmitis (PSD): Forelimb
Often seen in jumpers or eventers, PSD in the forelimbs can be linked to conformational faults such as long sloping pasterns; long-toe-low-heel; upright pasterns; over at the knees; or a base narrow stance.
Horses often present with a transient lameness that resolves with rest and returns with work, lameness that worsens on soft ground or when the affected linb is on the outside of a circle.
Prognosis for these cases is generally good, with around 80% returning to work in 6-9 months.
Proximal Suspensory Desmitis (PSD): Hindlimb
PSD in the hindlimbs is often bilateraly and most commonly occurs in dressage horses. It can be a primary injury or a secondary injury.
Primary injury to the PSD in the hindlimb usually occurs as a result of repetitive strain coupled with poor conformation such as straight hocks, long-toe-low-heel, poor hoof balance, negative plantar angle, or hyperextension of the fetlocks.
Secondary injuries can occur concurrently with hock osteoarthritis, sacroiliac dysfunction, or pathology in the distal limb. We should always look for concurrent pathologies when presented with PSD in the hindlimbs.
Horses often present with a low-grade persistent lameness that does not resolve with rest, a reluctance to collect, difficulty in canter transitions, and poor push-off or reduced impulsion. They are worse under saddle than in-hand. Pathology is often bilateral, which can make lameness difficult to identify, especially when it occurs as a secondary pathology.
Prognosis is usually poor with rest alone, and usrgery may be needed to improve outcomes.
Mid-Body Desmitis
Endurance horses are more likely to experience desmitis in the mid-body of the suspensory, usually as an acute onset after strenuous work. They may present with acute pain, swelling and heat.
Prognosis is generally good, with horses returning to work in 6-9 months.
Branch Desmitis
Commonly occurs in performance horses, especially showjumping, endurance and racing. Poor conformation can increase risk, incl poor hoof balance, long sloping pasterns, and offset knees. Other risk factors include working past fatigue, excessive fetlock extension, working on hard surfaces, and a history of Proximal Suspensory Desmitis.
Prognosis depends on the severity of the lesion. Mild thickening does well, but core lesions or multiple branch involvement is more guarded and requires longer rehabilitation.
Distal Sesamoidean Ligament Desmitis
Straight or oblique sesamoidean ligaments are most often affected. When oblique or cruciate ligaments are affected, fetlock instability will be worsened as tears will extend into the joint capsule. Risk factors include conformational faults such as long, sloping pasterns, long-toe-low-heels, and poor medio-lateral hoof balance.
Prognosis can be good for mild thickening or partial tears; and guarded for complete tears or multiple ligament involvement.
Diagnosis
- Palpation: Helpful in some cases, but can be unreliable, especially hindlimb PSD where the ligament is too deep. Pain on palpation can be present in the absence of lameness and pathology.
- Diagnostic blocks: Used by vets to localise pain.
- Ultrasound: First-line diagnostic tool shows thickening, fiber disruption, lesions, adhesions.
- Radiographs: Useful in chronic proximal lesions to identify bone sclerosis or avulsion. Rule out fractures of the sesamoid bones.
- MRI: Best for early lesions and bone involvement.
Pain on palpation of the suspensory apparatus correlates poorly with clinical pathology and lameness.
Treatment Strategies
Treatment always revolves around a progressive controlled exercise program (CEP). Other strategies include:
- Acute phase: Rest, cryotherapy, NSAIDs, compressive support.
- Progressive loading: Exercise guided by ultrasound monitoring – never time alone.
- Adjuncts: Shockwave therapy (especially hindlimb PSD), PRP or stem cells for certain lesion types.
- Farriery: Shorten toe, improve breakover, support heel, correct mediolateral balance.
- Surgery: In hindlimb PSD, plantar fasciotomy ± neurectomy when conservative care fails.
The Rehab Role
Our role as rehabilitation therapists is crucial. We:
- Guide the controlled exercise program, progressing only when the horse and imaging say it’s safe.
- Monitor quality of movement, focusing on symmetry, push-off power, fetlock control, and fatigue signs. These are just as important as lameness grade.
- Support the team by communicating with vets and farriers about changes in load tolerance or new concerns.
- Educate owners so they understand the time frames, risks of reinjury, and the importance of patience.
Conclusion
The suspensory apparatus is both powerful and vulnerable. Injuries here can be career-limiting, but with a thorough understanding of anatomy, pathology, diagnostics, and rehabilitation, we can give our patients the best possible chance of recovery. Clear communication with veterinary colleagues and owners, combined with a disciplined rehab program, makes us an essential part of the team.
Resources
Equine Tendinopathies: Evidence-Based Treatment And Its Limits
Deep Digital Flexor Tendon Injury for Vet Rehab Therapists
Superficial Digital Flexor Tendon (SDFT) Injuries: A Practical Reference for Vet Rehab Therapists
A Shift in Perspective From Mechanics to Tensegrity
Selected Cases of Ligament/Tendon Injury in Horses and their Rehabilitation, Melanie Perrier
The Equine Limbs: 4 part series, Robyn Crighton, Jennifer Williams
Re-Thinking Functional Anatomy: What We Have Failed To Notice, Elizabeth W. Uhl, Michelle Osborn
References
Ovendale, T., Desfontaines, B. 2025. Organ Systems – Tendon: Equine Pathology & Surgery [Lecture to EPS226]. Equine-librium College, Plettenberg Bay, 2025.
OpenAI. (2025). ChatGPT [Large language model]. https://chat.openai.com/chat
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