The health of musculoskeletal system has a substantial role in determining the future performance potential of a horse. Lameness is the main causes of loss performance in young sport horses. Joint disorders are among the most prevalent problems in horses and considered as the causes of pain, lameness, poor performance, early retirement, and economic losses in athletic horses. Developmental orthopedic disease (DOD) is the term used to describe a variety of important disorder in growing horses. These include osteochondrosis (osteochondritis)/ dissecans (OCD), subchondral bone cyst, flexural deformity, angular deformity, incomplete cuboidal bone ossification, physitis, wobblers syndrome, and juvenile osteoarthritis. Osteochondrosis is a common developmental orthopedic disease and is a major source of lameness in young horses, leading to decreased athletic potential. This disorder has become a major concern in the equine industry. The pathophysiology of osteochondrosis is complex. Osteochondrosis develops as the result of disturbance in the process of endochondral ossification during skeletal growth. The disturbance may eventually lead to the formation of a defect, semi-loose or even completely loose fragments within a joint, that this condition is described as osteochondrosis dissecans (OCD). Proposed etiological risk factors include trauma/exercise, growth rate, a large body size, vascular failure, dietary imbalance, endocrine factors, and genetic predisposition. Vascular failure at the bone-cartilage interface can cause to defect in blood supply that contribute to the pathogenesis of OCD. It has been recognized that biomechanical trauma and exercise precipitate the onset of clinical signs of OCD, that involve in formation, loosening and avulsing of OCD flap. Also, young horses with a rapid growth rate and large body size are more at risk of developing of OCD. Dietary factors are one of the most important of OCD risk factors. High intake energy and imbalance in trace minerals, can result in an increased incidence of OCD. Imbalance in certain hormones including insulin and thyroid hormones, involved in the development of OCD. Although the inheritance pattern of OCD is not well defined, genetics can also be responsible for OCD. Different breeds of horses have different incidences of OCD and also different patterns of OCD in different joints indicate that genetics is an important factor for OCD. In addition, different molecular events have been described in OCD pathophysiology. Although OCD can occur in any joint on any part of the articular surfaces, but some joints and anatomical sites most frequently affects. The most common joints affected by OCD are the stifle, tarsus, fetlock, and shoulder. Lateral trochlear ridge of the femur and distal intermediate ridge of the tibia are the prominent sites for OCD in stifle and tarsal joints, respectively. The predilection site of OCD in fetlock joint is the distal sagittal ridge of the third metacarpal/ tarsal bone. Shoulder OCD frequently affects the glenoid and the humeral head. OCD may occur unilaterally, bilaterally or affect different joints. Clinical signs of OCD can be appeared as early as 4 months of age, or may be noticed until 2 to 4 years of age as the horse begins training. Some horses with OCD do not show the clinical signs but may be identified coincidentally during radiographic examinations. Poor performance, joint distention, and lameness are the common clinical signs of OCD. These symptoms vary with the location and severity of OCD. Diagnostic imaging techniques such as radiography and ultrasonography as well as arthroscopy can be used to identify OCD lesions. The choice of treatment depends on a variety of factors, including the severity of clinical signs, the location of the OCD, and the age of the horse. Conservative treatments and arthroscopic surgery are used for management of OCD. Conservative treatments including rest, restricted exercise, intraarticular medication, and nutritional management may be appropriate for mild cases or when radiographic lesions are seen without clinical signs. Arthroscopy is recommended for horses with persistent clinical signs, unstable lesions, or loose osteochondral fragments. Removal, surgical debridement or repair the OCD fragments performed during arthroscopy. Prognosis for athletic performance is good to excellent for most horses with OCD that treated surgically. However, it depends on the joint location, the severity of the OCD, and the extent of damage to the joint. Early diagnosis and appropriate treatment prior to the premature degeneration of the joint are important to improve athletic performnce. Nutritional balance, careful management of growing foal, controlled exercise, and screening program are should be considered for prevention and management of OCD. Awareness of OCD and its different aspect is essential in order to management of the effect of OCD on equine industry.

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