Osselets in horses is a type of arthritis affecting the fetlock joint, commonly seen in young, active horses involved in high-performance activities like racing and jumping. This condition develops as a result of repetitive, high-impact stress on the fetlock joint, leading to inflammation and eventual bony outgrowth. [1]

Affected horses typically have swelling and heat around the fetlock joint, accompanied by pain or sensitivity to touch. Early signs include stiffness, especially after rest. In advanced cases, osselets can cause lameness and restricted joint movement, leading to changes in the horse’s gait.

For horse owners and trainers, recognizing the signs of fetlock arthritis is key to early detection and treatment. Timely intervention can significantly improve the prognosis and help preserve long-term joint health.

Effective management of fetlock arthritis may involve joint injections, pain medications, nutritional support and adjustments to the horse’s training regimen. Keep reading to learn more about osselets to support your horse’s performance at home and in the show ring.

Osselets in Horses

Osselets in horses is a degenerative joint disease that affects the fetlock joint (metacarpophalangeal or metatarsophalangeal joint), primarily involving inflammation and bony growth on the front of the fetlock.

This condition results from stress-induced inflammation of the articular cartilage and subchondral bone within the joint capsule. It primarily affects exercising horses participating in high-impact activities, such as racing or jumping.

Over time, chronic inflammation leads to the formation of bony exostoses (bony outgrowths) along the front and sides of the fetlock joint. As the condition progresses, fibrosis and calcification can restrict joint movement, leading to pain, lameness, and an altered gait.

Diagnosis typically involves clinical examination, palpation of the fetlock joint for heat and swelling, and diagnostic imaging such as radiographs to assess the extent of bony changes.

Treatment focuses on anti-inflammatory medication, rest, and modified training to manage symptoms and slow progression, along with long-term changes to reduce high-impact stress on the joint.

Fetlock Anatomy

The fetlock joint, known for its flexibility and strength, is a high-motion joint located in both the forelimbs and hindlimbs of horses. In the forelimb, it is referred to as the metacarpophalangeal joint (MCPJ), and in the hindlimb, it is called the metatarsophalangeal joint (MTPJ). [1][2]

The fetlock joint has an extensive range of motion, allowing up to 120 degrees of flexion and extension, which is essential for shock absorption and forward propulsion. However, this wide range of motion also makes the fetlock prone to stress and injury. [3]

In fact, the fetlock joint is the most commonly injured joint in horses due to the intense stress it endures during high-impact activities, making it particularly susceptible to degenerative conditions and traumatic injuries. [4][5][6][7]

Key Structures

The fetlock joint is composed of several key components that provide stability and functionality, enabling smooth movement and resilience under the stresses of athletic activity: [8]

  • Metacarpal/Metatarsal bone: Also known as the cannon bone, this bone articulates with the proximal phalanx (P1) to form the joint.
  • Sesamoid bones: Two small sesamoid bones are located at the back of the joint. They provide surfaces for tendon movement and enhance joint stability.
  • Articular cartilage: The joint is lined with articular cartilage, which allows for smooth movement.
  • Synovial capsule: The joint is enclosed within a synovial capsule filled with synovial fluid, providing lubrication.

In addition to the bones and cartilage, several supporting structures maintain the stability and function of the fetlock joint: [9]

  • Collateral ligaments: These ligaments provide lateral stability to the fetlock joint, helping resist inappropriate movement and reduce injury risk during athletic activities.
  • Suspensory ligament: Positioned at the back of the fetlock, this ligament prevents overextension
  • Flexor tendons: These tendons connect to flexor muscles, allowing the horse to flex the fetlock joint and absorb shock while supporting its weight during movement.

Repetitive stress or inflammation in any of these components can contribute to degenerative conditions like osselets, where bony growth develops in response to chronic joint strain.

Causes

Osselets result from repetitive strain and stress on the fetlock joint, a high-motion area that is especially vulnerable in athletic horses. This condition develops as key joint structures gradually deteriorate due to continuous use and the impact of high-performance activities. [1][5][7]

As the condition progresses, bony growths (osteophytes) may form around the fetlock joint, leading to discomfort and restricted movement. Cartilage loss can cause the joint space to narrow, and damage to surrounding tissues such as ligaments and tendons may occur. Without treatment, these