The hind fetlock is a high-motion joint that undergoes significant compression and force absorption when the horse is moving. This joint is highly susceptible to soft-tissue injuries and bone disorders. 
Horses with hind fetlock lameness often show signs of heat and swelling in this joint. In severe cases, horses may be unable to weight-bare on the limb. 
Performance horses such as racehorses and dressage horses are prone to hind fetlock injuries. Eventers are more prone to fore-fetlock injuries, likely due to the landing forces after large jumps. 
Hind fetlock disorders range from minor issue requiring temporary rest and ice to career-ending injuries.  Vigilance and quick intervention are necessary to give your horse the best possible chance of recovery.
You can help to prevent hind fetlock lameness in your horse with good care and management. Keep your horse at a healthy body weight, condition them appropriately for their job, and watch closely for any signs of soreness.
Always ensure that you support your horse’s joints with a good nutrition program and consider supplementing with anti-inflammatory nutrients that promote joint comfort.
Signs of Hind Fetlock Lameness
The hind end fetlock plays a critical role in supporting the horse’s weight. As a result, lameness can be seen even with minor injuries.
Lameness is relatively easy to notice in this joint because the soft tissue structures of the fetlock have limited protective coverings (i.e. fascia and fatty tissue).
- Reluctance to weight bear on the affected limb
- Reduced range of motion in the fetlock
- Pain on palpation
- Shortened stride in the affected limb
- A “dropping” of one or both fetlocks that is lower than normal
To diagnose hind fetlock lameness in your horse, your veterinarian will first palpate the fetlock for any swelling or heat.
The vet may also perform x-rays of multiple views of the joint to visualize any changes to the bones. An ultrasound may be used to check for soft-tissue injury.
If hind fetlock lameness is apparent, but neither x-rays nor ultrasound reveals any diagnosis, your veterinarian may refer the horse for additional imaging such as CT or MRI scans.
Anatomy of the Fetlock Joint
The fetlock joint in horses is known as the metacarpus. It lies at the distal (far) end of the third metacarpal (cannon bone) and the proximal (close) end of the first phalanx (long pastern).
The fetlock also contains the two proximal sesamoid bones, which are small bones that lie at the rear of the fetlock joint. 
The hind fetlock joint is classified as a hinge joint because its motion is restricted to forwards and backwards.
The fetlock is also a synovial joint surrounded by a joint capsule that contains lubricating synovial fluid. This fluid provides a slick, gliding surface for the joint to move over and provides nourishment to the articular cartilage pads within the joint. 
Image from Denoix, J.M. Essentials in Clinical Anatomy of the Equine Locomotor System.
1- third metacarpal bone (cannon bone); 11 – proximal phalanx 
The horse’s fetlock undergoes extreme forces and requires numerous ligaments to hold the joint in place. Strong collateral ligaments extend from the cannon bone to the long pastern, preventing side-to-side motion.
The fetlock also has cruciate ligaments, providing additional protection from rotation. The intersesamoidean ligament and the collateral ligaments hold the sesamoid bones in place. 
Ligaments also function as part of the suspensory apparatus, which absorbs the force applied to the hind legs from the horse’s body weight.
The suspensory apparatus at the back of the horse’s fetlock is important for maintaining the weight-bearing abilities of the horse.
This apparatus provides stability to the fetlock joint under stress and prevents the fetlock from collapsing when weight is applied to the hind limb.
This collection of ligaments also contributes to the stay apparatus, which allows the horse to sleep standing up.
- Suspensory Ligament: runs along the back of the cannon bone to the proximal sesamoid bones
- Palmar Ligament: connects the proximal sesamoid bones
- Straight & oblique ligaments: extend from the distal end of the cannon bone down the back of the long pastern
- Extensor branches of the suspensory ligament
The suspensory apparatus and all the ligaments of the fetlock are held together by an annular ligament, which wraps around the fetlock and prevents bowing out of the ligaments when the fetlock is not bearing any weight. 
The tendons in the fetlock joint can be grouped into two categories: flexor and extensor.
Flexor tendons travel down the back of the fetlock and bend the fetlock. This allows the horse to apply a force to the ground that propels them in the direction of choice.
The two flexor tendons are the:
- Superficial digital flexor tendon (SDFT) – arises from the superficial digital flexor muscle
- Deep digital flexor tendon (DDFT) – arises from the deep digital flexor muscle 
Extensor tendons travel down the front of the fetlock and straighten the joint, allowing the horse to place their foot back on the ground. 
The two extensor tendons are the:
- Common or long digital extensor tendon – arises from the long digital extensor muscle
- Lateral digital extensor tendon – arises from the lateral digital extensor muscle 
Together, these tendons enable locomotion by allowing the horse to step forwards and keep limbs high enough off the ground to avoid tripping.
Causes of Fetlock Lameness
Given the importance of the fetlock in locomotion, it is typically easy to notice when your horse has become lame in this joint.
Fetlock lameness is usually a result of arthritis, fractures or injuries of the suspensory apparatus. This structure is susceptible to damage because of the high concussive forces on the fetlock joint when moving.
Improper hoof angles or genetically long pasterns can also predispose horses to fetlock lameness.  Knocks or bangs to the joint, sprains, and strains can also cause fetlock lameness.
Below, we discuss some of the common causes of lameness in the hind fetlock and how different cases are treated.
If your horse is showing signs of fetlock lameness, consult with your veterinarian for an accurate diagnosis of the cause and an appropriate rehabilitation program.
Osteoarthritis is a degenerative joint disease and the most common form of arthritis. It is caused by gradual wear and tear on the joints.
The hind fetlock is part of the suspensory apparatus of the hind end, meaning the joint takes the burden of high forces with every step the horse takes.
Over many years, the concussive forces can break down the protective cartilage pad at the end of the bone. This also causes thinning of the lubricating synovial fluid. 
With this deterioration in the joint, the end of the cannon bone can rub directly against the long pastern bone leading to pain and inflammation.
The inflammation triggers the horse’s body to produce bony outgrowths in and around the joint. These outgrowths can “catch” when the fetlock moves, resulting in more pain and inflammation and potentially leading to lameness. 
If your horse’s fetlock lameness is diagnosed as osteoarthritis, your veterinarian may suggest treatment with one of the following joint injections or fetlock fusion (in severe cases).
Hyaluronic acid and corticosteroids:
These compounds have anti-inflammatory effects, reducing pain in the joint. 
Interleukin-1 Receptor Antagonist Protein (IRAP):
IRAP is a protein naturally produced by the horse’s body that has been shown to reduce inflammation and promote cartilage regeneration. 
Platelet Rich Plasma (PRP):
PRP is a component of the horse’s blood that can stimulate and repair damaged cartilage when injected into the joint space. 
Autologous Protein Solution (Pro-stride):
Pro-stride is a derivative of the horse’s blood that can reduce inflammation, stimulate tissue repair, and reduce pain. 
In extreme cases of lameness, a surgery called fetlock fusion (fetlock arthrodesis) may be performed. This surgery involves placing plates and screws to permanently immobilize the fetlock. 
Most arthritic pain occurs when the joint moves and the bones rub together. Fetlock fusion prevents the joint from moving to eliminate pain.
Physitis is a condition involving inflammation of the growth plates – regions at the end of bones that transform cartilage into bone tissue. This process known as endochondral ossification is how bones grow longer. 
When these growth plates become inflamed, permanent damage to bone growth can occur, and future soundness may be affected. 
Physitis is usually seen in 3-9 month old foals, particularly in larger foals that experienced a growth spurt. 
This condition presents as painful swelling in a foal’s hind fetlock. The foal will frequently shift weight weight to offload the affected joints.
Physitis can be caused by improper nutrition, exercise that overloads the growth plates, trauma or penetrating wounds. 
Foals undergoing a rapid growth phase can experience inflammation in the growth plates as the bones struggle to support the increased bodyweight.
This is why it is important not to overfeed the mare or foal. Overfeeding the mare during pregnancy or lactation can cause her milk to be too nutrient-rich, while overfeeding the foal leads to excessive growth. 
Avoid exercising your foal at a young age. Foals exercised too early cannot bear the increased loads, resulting in inflammation of the immature growth plates.
Subchondral Bone Disease
Subchondral bone disease is a chronic fatigue injury that occurs in the subchondral and trabecular bone tissue of the distal cannon bone.  It is common in racehorses due to the trauma experienced while racing.
Subchondral bone tissue sits directly under the cartilage pad at the end of a long bone. Below this is a layer of trabecular bone tissue, which is spongey, porous and full of small holes.
Together, these two types of bone aid in force absorption upon impact.  However, subchondral bone disease can develop when these tissues experience repeated trauma.
Subchondral bone disease is not technically a disease but rather the result of micro-injuries to the subchondral and trabecular bone. 
If left untreated, slab fractures of the distal end of the cannon bone may appear due to bone weakening. 
Subchondral bone disease is often diagnosed with a nerve blocking of the suspected limb. If your horse’s lameness after blocking the hind fetlock, your veterinarian will conclude that the fetlock is causing your horse pain.
This disease cannot be detected on x-rays until it results in a fracture. 
Subchondral bone disease is usually treated with extended time off and NSAIDs to relieve pain. If a fracture has occurred, surgery may be required. 
Fetlock lameness can be caused by trauma to the joint, including bangs, bruises and fractures.
Because horses live within a hierarchical social structure, bangs and bruises are commonplace. When the hock has been knocked hard, the joint can swell.
This swelling and heat is often not permanent and resolves with cold hosing and rest. 
Two main types of fractures can occur within the fetlock joint: chip fractures and comminuted fractures.
Chip fractures occur when small pieces of bone break off due to glancing trauma or repeated stress to the joint. The bone fragments can become displaced within the fetlock, causing pain and inflammation.
Chip fractures are usually treated through endoscopic surgery. A small incision is made into the joint, through which a camera is introduced. The chip is visualized, grasped with forceps, and removed.
Prognosis after chip removal is excellent as long as there are no other complicated injuries. 
A comminuted fracture (better known as a broken bone) involves a complete fracture through a bone’s main body. Fractures can occur at the following locations: 
- Long pastern bone
- Short pastern bone
- Distal cannon bone
- Sesamoid bones
Comminuted fractures occur when direct trauma is inflicted on the bone or when extreme force is transmitted at an angle through the bone.
Comminuted fractures are more complex to treat than chip fractures. The bone must be surgically stabilized with plates and screws to ensure the fracture remains aligned.
The leg is then cast, and the horse is placed on stall rest to give the bone time to heal and avoid further injury.
The prognosis is guarded for horses with comminuted fractures. Horses are heavy animals and not well-suited to bear weight on three legs.
The sesamoid bones are located within tendons and allow for smooth movement of the tendon over the joint.
Sesamoiditis involves pain and chronic inflammation in the sesamoid bones or surrounding tendons. Because this structure is constantly moving, it is highly susceptible to inflammation.
Sesamoiditis can occur in every type of performance horse. While the exact cause is not completely understood, it is thought to be brought on by overuse and stress to the sensory apparatus.
Sesamoiditis is treated with stall rest and symptom management to control pain with NSAIDS. 
Villonodular synovitis occurs when the cartilage pad in the joint capsule becomes inflamed and thickened because of repetitive stress.
This condition is mostly seen in Thoroughbred and Standardbred racehorses.
Villonodular synovitis can be diagnosed through ultrasound, and treatment involves surgical excision of the thickened area. 
Suspensory Ligament Disorders
The suspensory ligament is a crucial component of the suspensory apparatus that supports the fetlock. Disorders of this ligament can result in the hind fetlock dropping due to the lack of support.
Most suspensory disorders are diagnosed through ultrasound and symptom reporting (i.e. dropping the fetlock, swelling around the ligament, heat, and lameness).
Suspensory Ligament Tears:
Like any ligament, the suspensory ligament is susceptible to complete and partial tears.
Minor tears can be treated with rest, corrective farriery, and anti-inflammatory drugs to bring the horse back to prior performance. Severe tears can force the horse to retire from all riding.
Consult with your veterinarian for an accurate diagnosis and to understand the prognosis for your horse. 
Suspensory Ligament Desmitis:
Suspensory ligament desmitis is characterized by lesions that can occur on any part of the suspensory ligament.
This condition is usually diagnosed via nerve block as it typically does not present with swelling or heat.
Treatment consists of shockwave application, local anti-inflammatory medications, stem cell injections, and corrective farriery. 
Degenerative Suspensory Ligament Desmitis:
DSLD is a chronic condition of the connective tissue within the suspensory ligament. It is thought to be caused by genetic factors, but research is still ongoing.
This condition results in a complete failure of suspensory ligaments on both hind limbs, producing catastrophic dropping of the fetlock.
DSLD is incurable and often results in the euthanasia of the horse. 
How To Prevent Hind Fetlock Issues
The first step to preventing hind fetlock issues is ensuring your horse has correctly balanced feet. Horses with altered balance are susceptible to hyperextension of the fetlock, straining the structures within the fetlock.
Hoof issues including toes that are too long or too short and collapsed heels can increase the risk of injury. Ensure you provide your horse with regular farrier care from a qualified practitioner. 
Training regimes should be balanced to minimize over-exertion of the hind fetlock structures. Avoid extreme loading of the hind fetlock caused by frequent jumping at a significant height or overuse of collection exercises.
Keep your horse at a healthy body condition and schedule regular veterinary check-ups to catch and address any health issues early.
Feeding & Nutrition
Finally, you can support your horse’s joints and mobility by feeding a balanced diet that meets all of their nutrient requirements.
Your horse’s feeding program needs to provide adequate levels of amino acids and the minerals copper and zinc to form collagen proteins that make up joint cartilage.
Your horse’s diet also needs to provide calcium and phosphorous in the correct ratio to support optimal bone growth and strength.
Nutritional supplements such as methyl-sulfonate-methane (MSM), hyaluronic acid, and omega-3 fatty acids have also been shown to improve joint health and reduce inflammation.
Work with a qualified equine nutritionist to design a balanced feeding program that provides adequate nutrients without over-supplying energy. You can submit your horse’s information online for a free diet balancing.
Looking for more ways to support your horse’s joint health and reduce the risk of lameness? Check out our article on the 8 Key Principles for Supporting Joint Health in Horses.
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- Brokken, M. Disorders of the Fetlock and Pastern in Horses. Merck Manual. 2019.
- Holmstrom, M. et al. Biokinematic analysis of the Swedish Warmblood riding horse at trot. Equine Vet J. 1994.
- Marneris, D. and Dyson, S. Clinical features, diagnostic imaging findings and concurrent injuries in 71 sports horses with suspensory branch injuries. Equine Vet Edu. 2014.
- Budras, K. et al. Anatomy of the Horse: An Illustrated Text. Schluetersche. 2003.
- Dyson, S. and Genovese, R. The Suspensory Apparatus. Veterian Key. 2016.
- Davidson, E. Lameness Evaluation of the Athletic Horse. Vet Clinics: Equine Prac. 2018.
- Ross, M. and McIlwraith, W. Conformation and Lameness. Veterian Key. 2016.
- Dyson, S. et al. Osseous Trauma in the Fetlock Region of Mature Sports Horses. AAEP Proceedings. 2006.
- McIlwraith, W. et al. The horse as a model of naturally occurring osteoarthritis. Bone Joint Res. 2012.
- Auer, J. et al. Effect of hyaluronic acid in naturally occurring and experimentally induced osteoarthritis. Am J Vet Res. 1980.
- Machado, T. et al. Effects of blood-derived products and sodium hyaluronate on equine synovial fluid cells and on synovial fluid from osteochondrotic joints of horses after arthroscopy and administration of treatment. Am J Vet Res. 2019.
- Textor, J. et al. Synovial fluid growth factor and cytokine concentrations after intra-articular injection of a platelet-rich product in horses. The Vet J. 2013.
- King, W. et al. The Use of Autologous Protein Solution (Pro-Stride®) and Leukocyte-Rich Platelet-Rich Plasma (Restigen®) in Canine Medicine. Vet Med. 2021.
- Ross, M. and Dyson, S. Diagnosis and Management of Lameness in the Horse. Saunders. 2011.
- Bramlage, L. Physitis in the horse. Equine Vet Edu. 2011.
- Mackie, E. et al. Endochondral ossification: How cartilage is converted into bone in the developing skeleton. Int J Biochem Cell Bio. 2008.
- Pearce, S. et al. Effect of copper supplementation on the evidence of developmental orthopaedic disease in pasture-fed New Zealand Thoroughbreds. Equine Vet J. 1998.
- Pagan, J. Nutrition of the Growing Horse: Feeding Management to Reduce DOD. Appl Equine Nutr. 2005.
- Parente, E. et al. Stress Protection Afforded by a Cast on Plate Fixation of the Distal Forelimb in the Horse In Vitro. Vet Surgery. 1995.
- Kawcak, C. et al. The role of subchondral bone in joint disease: a review. Equine Vet J. 2001.
- Lowe, J. Treatment of subchondral bone disease in the equine fetlock joint. Arthramid Vet. 2020.
- Brokken, M. Sesamoiditis in Horses. Merck Manual. 2016.
- Nickels, F. et al. Villonodular synovitis of the equine metacarpophalangeal joint. J Am Vet Med Assoc. 1976.
- Dyson, S. Diagnosis and Management of Common Suspensory Lesions in the Forelimbs and Hindlimbs of Sport Horses. Clin Tech Equine Pract. 2007.
- Brokken, M. Suspensory Desmitis in Horses. Merck Manual. 2016.
- Halper, J. Degenerative Suspensory Ligament Desmitis – A New Reality. Pakistan Vet J. 2010.
- Balch, O. et al. Balancing the normal foot: hoof preparation, shoe fit and shoe modification in the performance horse. Equine Vet Edu. 2010.
- Denoix, J-M. Essentials in Clinical Anatomy of the Equine Locomotor System. CRC Press. 2019.