The fetlock is a high-motion joint that undergoes significant compression and force absorption when the horse is moving. This joint is highly susceptible injury of both the soft tissues and bones associated with the region. [2]

Horses with fetlock injury often show signs of heat, pain, lameness, and swelling. In severe cases, horses may be unable to bear weight on the limb. [1]

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. [3]

Fetlock disorders range from minor issues requiring temporary rest and ice to career-ending injuries. [1] Vigilance and quick intervention are necessary to give your horse the best possible chance of recovery.

You can help to prevent fetlock injury 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 Fetlock Lameness

The fetlock plays a critical role in supporting the horse’s weight. As a result, lameness can be seen even with minor injuries.

Injury 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).

You can look for swelling or heat around the fetlock as one of the first signs of injury. Other signs of injury include: [1][6]

  • Edema, or swelling in the soft tissue structures around the joint
  • Effusion, or swelling within the joint capsule
  • Reluctance to bear weight on the affected limb
  • Reduced range of motion in the fetlock
  • Pain on palpation
  • Lameness, such as a shortened stride in the affected limb
  • A “dropping” of one or both fetlocks that is lower than normal

Diagnosis

To diagnose fetlock injury in your horse, your veterinarian will performa a musculoskeletal exam. Palpation of the area will identify any heat, pain, or swelling. Additionally, passive flexion of the limb will help assess range of motion.

Next, your veterinarian will perform a lameness exam, watching the horse in motion on a straight line and circle. They may perform a flexion test to simulate stress on the joint. [14]

Once your vet is confident that the lameness is associated with the fetlock, a combination of diagnostics may be necessary to determine the type of injury present. Radiographs of the joint assess changes to the bones, such as fractures or osteoarthritis. Ultrasound of the soft tissue structures around the joint identify injuries to the tendons, ligaments, and joint capsule.

If fetlock injury 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.

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Anatomy of the Fetlock Joint

The fetlock in horses is known as the metacarpophalangeal joint. It lies at the distal (far) end of the third metacarpal bone (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. [4]

The hind fetlock joint is classified as a hinge joint because its motion is restricted to forwards and backwards.

The fetlock is surrounded by a joint capsule that contains synovial fluid. Synovial fluid lubricates the joint and provides nourishment to the articular cartilage. [4]

Image from Denoix, J.M. Essentials in Clinical Anatomy of the Equine Locomotor System.

1- third metacarpal bone (cannon bone); 11 – proximal phalanx [27]

Soft Tissue Structures

There are several soft tissue structures associated with the fetlock. Some of these stabilize the joint directly, while others simply pass by. All these structures work together to support the structure and biomechanical function of the limb.

Strong medial (inside) and lateral (outside) collateral ligaments extend from the cannon bone to the long pastern, preventing side-to-side motion of the joint.

There are several ligaments associated with the sesamoid bones, which are imbedded within the intersesamoidean ligament. The collateral sesamoidean ligaments and distal sesamoidean ligaments (short, cruciate, oblique, and straight ligaments) all work together to hold the sesamoid bones in place. [4]

Flexor tendons travel down the palmar/plantar aspect (back) of the limb and bend the fetlock. This allows the horse to apply a force to the ground that propels them in the direction of choice.

  • Superficial digital flexor tendon (SDFT) – arises from the superficial digital flexor muscle in the proximal limb
  • Deep digital flexor tendon (DDFT) – arises from the deep digital flexor muscle in the proximal limb [4]

The two flexor tendons are bundled together with the suspensory ligament, which runs along the back of the cannon bone, then branches to connect to each sesamoid bone.

The primary function of the suspensory ligament is to prevent hyperextension of the fetlock. It provides stability to the fetlock joint under stress and prevents the fetlock from collapsing when weight is applied to the hind limb.

All the soft tissues at the back of the fetlock are held together by an annular ligament, which wraps around the back of the fetlock and prevents these structures from bowing out when the fetlock is not bearing any weight. [4]

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 [4]

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

Lameness originating from the fetlock is usually a result of arthritis, fractures, or soft tissue injury. Improper hoof angles or genetically long pasterns can also predispose horses to fetlock injury. [7]

Below, we discuss some of the common causes of lameness in the fetlock and how different cases are treated.

If your horse is showing signs of fetlock injury, consult with your veterinarian for an accurate diagnosis and an appropriate rehabilitation program.

Osteoarthritis

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 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. [5]

Over many years, the concussive forces can break down the protective joint cartilage. This also causes thinning of the lubricating synovial fluid. [9]

With this deterioration in the joint, bone-on-bone contact can lead 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. [9]

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. [10]

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. [11]

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. [12]

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. [13]

Fetlock Fusion:

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. [19]

Most arthritic pain occurs when there is bone-on-bone contact during movement of the joint. Fetlock fusion prevents the joint from moving to eliminate pain. This procedure generally carries a good prognosis for pasture soundness.

Physitis

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. [16]

When these growth plates become inflamed, permanent damage to bone growth can occur, and future soundness may be affected. [16]

Physitis is usually seen in 3-9 month old foals, particularly in larger foals that experienced a growth spurt. [15]

This condition presents as painful swelling in a foal’s fetlock. The foal will frequently shift weight to offload the affected joints.

Causes

Physitis can be caused by improper nutrition, exercise that overloads the growth plates, trauma, or infection. [15]

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. [16]

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.

Mineral imbalances in the diet may also contribute to the development of physitis in foals. Underfeeding copper and over-feeding calcium may both contribute to physitis risk. [17][18]

Fetlock physitis is treated with veterinarian-directed stall rest, non-steroidal anti-inflammatory drugs (NSAIDS), and re-balancing of the diet. [15]

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. [20] It is common in racehorses due to the trauma experienced while racing.[20]

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 and porous.

Together, these two types of bone aid in force absorption upon impact. [20] 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. [20]

If left untreated, condylar fractures of the distal end of the cannon bone may appear due to bone weakening. [20]

Subchondral bone disease cannot be detected on x-rays until it results in a fracture. A presumptive diagnosis may be made by your veterinarian if your horse’s lameness is isolated to the fetlock, but radiographs and ultrasound do not reveal any abnormalities. [14]

Subchondral bone disease is usually treated with extended time off and NSAIDs to relieve pain. If a fracture has occurred, surgery may be required. [21]

Traumatic Injuries

Lameness associated with the fetlock can be caused by traumatic injury to the joint, including bangs, bruises and fractures.

Because horses live within a hierarchical social structure, bangs and bruises are commonplace. If the fetlock has been knocked hard, the region can swell. This swelling and heat are often not permanent and resolve with cold hosing, rest, and anti-inflammatories. [8]

Chip Fractures

Chip fractures occur when small pieces of bone break off due to glancing trauma, repeated stress to the joint, or avulsion at a ligamentous attachment. The bone fragments can become displaced within the joint, causing pain and inflammation.

Chip fractures are usually treated through arthroscopic 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 complicating injuries. [1]

Large Fractures

Fractures occur when direct trauma is inflicted on the bone or when extreme force is transmitted at an angle through the bone.

A simple fracture involves a break through some portion of the bone. The break can be complete, meaning it completely separates the bone into two or more parts, or incomplete, where the bone is still in one piece.

A comminuted fracture (also called a compound fracture) is when the bone breaks into multiple pieces or fragments. [1]

Fractures may also be displaced, when the fractured pieces of bone don’t align along the fracture plane; articular, when the fracture communicates with the joint; or open, when bone punctures through the skin.

Large 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 of a fracture associated with the fetlock joint depends on the severity. Generally, simple condylar fractures have a good athletic prognosis. Complicating factors such as comminution, displacement, and contamination (open fractures) decrease the prognosis.

Horses are heavy animals and not well-suited to bear weight on three legs. Complications during recovery include laminitis in the opposite limb, misalignment of the fracture, failure of the implants (i.e. screws becoming dislodged or infected), and secondary arthritis. [1]

Sesamoiditis

The sesamoid bones are embedded within the intersesamoidean ligament at the back of the fetlock. Sesamoiditis involves pain and chronic inflammation in the sesamoid bones or surrounding soft tissues.

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 suspensory apparatus.

Sesamoiditis is treated with stall rest and anti-inflammatories. [22]

Villonodular Synovitis

Villonodular synovitis occurs when the articular cartilage 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. [23]

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 clinical presentation (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 be carrier-limiting or even result in early retirement.

Consult with your veterinarian for an accurate diagnosis and to understand the prognosis for your horse. [24]

Suspensory Ligament Desmitis:

Suspensory ligament desmitis describes chronic inflammation and injury to the suspensory ligament. It can be further categorized by region- proximal (top one third), body, and branches.

When considering lameness associated with the fetlock region, the suspensory branches are the structures of interest. The medial and lateral suspensory branches attach to the apical (top) portion of the medial and lateral sesamoid bones, respectively.

Injury to the suspensory branches is relatively common and usually occurs to a single branch of a single limb. However, both branches of the same limb may be affected, which is more common in the hind limbs.

Foot imbalance is thought to be a predisposing factor for suspensory branch desmitis.
Horses with suspensory branch desmitis and injury typically present with heat, pain, swelling, and lameness. Diagnosis is confirmed with ultrasound.

Treatment consists of shockwave application, local anti-inflammatory medications, stem cell injections, and corrective farriery. [25]

Degenerative Suspensory Ligament Desmitis:

DSLD is a chronic degenerative 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. [26]

How To Prevent Fetlock Issues

The first step to preventing hind fetlock issues is ensuring your horse has correctly balanced feet. Horses with improper 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. [26]

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 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.

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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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References

  1. Brokken, M. Disorders of the Fetlock and Pastern in Horses. Merck Manual. 2019.
  2. Holmstrom, M. et al. Biokinematic analysis of the Swedish Warmblood riding horse at trot. Equine Vet J. 1994. View Summary
  3. 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.
  4. Budras, K. et al. Anatomy of the Horse: An Illustrated Text. Schluetersche. 2003.
  5. Dyson, S. and Genovese, R. The Suspensory Apparatus. Veterian Key. 2016.
  6. Davidson, E. Lameness Evaluation of the Athletic Horse. Vet Clinics: Equine Prac. 2018. View Summary
  7. Ross, M. and McIlwraith, W. Conformation and Lameness. Veterian Key. 2016.
  8. Dyson, S. et al. Osseous Trauma in the Fetlock Region of Mature Sports Horses. AAEP Proceedings. 2006.
  9. McIlwraith, W. et al. The horse as a model of naturally occurring osteoarthritis. Bone Joint Res. 2012. View Summary
  10. Auer, J. et al. Effect of hyaluronic acid in naturally occurring and experimentally induced osteoarthritis. Am J Vet Res. 1980. View Summary
  11. 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.View Summary
  12. 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.View Summary
  13. 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.
  14. Ross, M. and Dyson, S. Diagnosis and Management of Lameness in the Horse. Saunders. 2011.
  15. Bramlage, L. Physitis in the horse. Equine Vet Edu. 2011.
  16. Mackie, E. et al. Endochondral ossification: How cartilage is converted into bone in the developing skeleton. Int J Biochem Cell Bio. 2008.
  17. 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. View Summary
  18. Pagan, J. Nutrition of the Growing Horse: Feeding Management to Reduce DOD. Appl Equine Nutr. 2005.
  19. 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. View Summary
  20. Kawcak, C. et al. The role of subchondral bone in joint disease: a review. Equine Vet J. 2001. View Summary
  21. Lowe, J. Treatment of subchondral bone disease in the equine fetlock joint. Arthramid Vet. 2020.
  22. Brokken, M. Sesamoiditis in Horses. Merck Manual. 2016.
  23. Nickels, F. et al. Villonodular synovitis of the equine metacarpophalangeal joint. J Am Vet Med Assoc. 1976. View Summary
  24. Dyson, S. Diagnosis and Management of Common Suspensory Lesions in the Forelimbs and Hindlimbs of Sport Horses. Clin Tech Equine Pract. 2007.
  25. Brokken, M. Suspensory Desmitis in Horses. Merck Manual. 2016.
  26. Halper, J. Degenerative Suspensory Ligament Desmitis – A New Reality. Pakistan Vet J. 2010.
  27. Denoix, J-M. Essentials in Clinical Anatomy of the Equine Locomotor System. CRC Press. 2019.