The musculoskeletal system consists of bones, cartilage, muscles, ligaments, and tendons. Primary functions of the musculoskeletal system include support of the body, provision of motion, and protection of vital organs. The skeletal system serves as the main storage system for calcium and phosphorus and contains critical components of the hematopoietic system. Many other body systems, including the nervous, vascular, and integumentary systems, are interrelated, and disorders of any one of these systems may also affect the musculoskeletal system and complicate diagnosis.
Diseases of the musculoskeletal system most often cause lameness. Lameness is an abnormal stance or gait caused by pain, mechanical restrictions such as upward fixation of the patella in horses, or neuromuscular disease. The most common cause of lameness in all species is pain. The degree of impairment depends on the specific problem and its severity. Skeletal, articular, and tendon/ligament disorders are by far the most common cause of lameness and have the greatest economic impact.
In horses and dogs, musculoskeletal injuries are a major source of debilitating pain, economic loss, and loss of athleticism. Osteoarthritis is common in middle-aged and older animals and has a great economic impact to owners of affected horses. In young performance horses, acute traumatic injuries are the most common cause of musculoskeletal dysfunction. Several studies estimate that problems involving the fetlock and carpal joints in horses in race training account for 25%–28% of horses lost from training. Tendon and ligament injury is also a common debilitating injury in performance horses. In dogs, cranial cruciate ligament injury with resulting osteoarthritis is a common musculoskeletal injury resulting in lameness. Although perhaps less common, primary muscular diseases, neurologic deficits, toxins, endocrine aberrations, metabolic disorders, infectious diseases, blood and vascular disorders, nutritional imbalances or deficits, and occasionally congenital defects can adversely affect the musculoskeletal system.