Repetitive Microtrauma:
- Mechanical Overload: Show jumping imposes significant and repetitive loads on the fetlock joints. Impact and torsional forces during takeoff and landing can cause microtrauma to the articular cartilage and subchondral bone, accelerating joint degeneration.
- Shear Forces: The nature of the motion and mechanics of jumping can create shear forces on the pastern joint, contributing to cartilage wear. This force occurs when the articular surfaces move oppositely due to the dynamics of motion.
Conformation and Biomechanics:
- Skeletal Conformation: Horses with conformations that predispose to an uneven distribution of forces on the pastern joint, such as improper limb angle, are at increased risk of developing OA.
- Biomechanical Alterations: Deficiencies in the biomechanics of movement, such as improper jumping technique or poor training, can increase stress on the joint.
Acute and Chronic Injuries:
- Traumatic Injuries: Acute injuries such as sprains, fractures and ligament tears can damage the pastern joint and predispose to the development of OA.
- Chronic Inflammation: Chronic inflammatory conditions, such as synovitis and tendonitis associated with the pastern joint, can contribute to joint degeneration.
Genetic Factors:
- Genetic Predisposition: Some bloodlines may have a genetic predisposition to OA due to the quality of articular cartilage and collagen structure, increasing susceptibility to joint degeneration.
Age and Prolonged Use:
- Aging: The natural aging process decreases the regenerative capacity of cartilage and the elasticity of joint tissues, which favors the occurrence of OA.
- Competition History: Horses that have been subjected to intensive training and competition for many years are at an increased risk of developing OA due to accumulated wear and tear on the joints.
Synovial Inflammation:
- Chronic Synovitis: Persistent inflammation of the synovial membrane can release inflammatory mediators that degrade articular cartilage, promoting the progression of OA.
Pathological Mechanisms
Articular Cartilage Degradation:
- Osteoarthritis involves the loss of proteoglycans and collagen in articular cartilage, carried out by degradative enzymes such as matrix metalloproteinases (MMPs).
Subchondral Bone Changes:
- Sclerosis of subchondral bone and osteophyte formation are adaptive responses to increased mechanical stress, contributing to joint stiffness and pain.
Joint Inflammation:
- Inflammation of the synovial membrane results in the production of proinflammatory cytokines, such as interleukin-1 (IL-1) and tumor necrosis factor-alpha (TNF-α), which exacerbate cartilage degradation.
Conclusion
Osteoarthritis in the pastern joint of jumping horses is a multifactorial condition influenced by mechanical, genetic, and environmental factors. Identification and management of these factors are essential to prevent the onset and progression of OA. Management strategies include correcting conformation, optimizing training and jumping techniques, proper injury management, and utilizing anti-inflammatory and chondroprotective treatments under veterinary supervision.
