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 preven