WHAT IS DEVELOPMENTAL ORTHOPEDIC DISEASE?
Overview of Developmental Orthopedic Disease
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Developmental Orthopedic Disease (DOD) is a set of conditions which encompasses all skeletal diseases observed in growing foals [1]. These diseases are habitually observed in developing horses as they experience rapid growth and formation of principal musculoskeletal structures [2]. DOD can thus affect the equid’s growth plates, joints, cartilage and it can present as bone conformation abnormalities, joint swelling, lameness, muscle atrophy, and incoordination [1,3]. The onset of DOD is multifactorial and includes the equid’s nutrition, exercise, body weight, genetic predisposition, and mechanical stress to the joints [3]. While a wide range of afflictions may be defined under DOD, the most common forms include osteochondrosis (OC), osteochondritis dissecans (OCD), physitis, wobbler syndrome, and acquired flexural deformities [1]; However, this proves to be controversial as other studies have also reported subchondral bone cysts as a highly common form of DOD, specifically in warmbloods, standardbreds, and thoroughbreds suggesting breeds have specific risk factors [3,4]. DOD is particularly problematic in horses used for performance purposes (ie. show jumping) as it may disrupt their athletic motility. Consequently the sales price of DOD-affected horses is reduced by an average of 48% [5]. Furthermore, DOD constitutes a welfare issue as these horses' quality of life is reduced. For example, a young horse diagnosed with DOD may experience conformation malformities, joint swelling, lameness, muscle atrophy, and may lack coordination [3]. As DOD affects equids worldwide, and because increasing incidence and prevalence are being reported, action to mitigate equine DOD is becoming increasingly necessary [6].
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The remainder of this introduction will provide a brief overview of the main forms of DOD. For specific information regarding clinical signs, prevention, nutrition, treatment, and risk factors please direct yourself to the respective sections at the top of the webpage.
Osteochondrosis
Osteochondrosis (OC) has repeatedly been observed to be the most important type of DOD as OC has an incidence rate of 25% in growing horses [2,7]. OC arises within the cartilage of the joints, at the ends of long bones, and results when this soft tissue differentiates and matures improperly [8,9]. While the affected horse grows, their abnormal soft tissue ossifies and results in improper bone formation. Osteochondrosis is especially problematic as it can lead to other complications such as fragments within the joint, bone distortion, cysts, an abnormal narrowing of the vertebral canal, and uncoordinated muscle movements [3,10]. Furthermore, osteochondritis dissecans, a second form of DOD, arises when osteochondrosis causes detached cartilage fragments [11].
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Photo By: The American College of Veterinary Surgeons
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Photo By: Horses and Us
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Physitis
Physitis is characterized by swelling around the cartilaginous growth plates of long bones in young horses and it can occur alongside osteochondrosis [10].
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Photo By: Jackson et. al., 2011
Subchondral Bone Cysts
Subchondral bone cysts (SBC) occur within the ends of bones that are located within joints, specifically, in the medial femoral condyle of the stifle. The pathogenesis of SBC is largely unknown; however, SBC tends to form following osteochondrosis or trauma to the articular surface of the bone which is where two bones meet [12].
Limb Deformities
Angular limb deformities present as the development of crooked legs, specifically in regards to the carpus and tarsus joints [3]. Alternatively, flexural limb deformities are the result of excessively relaxed or contracted tendons causing conformation problems.
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Cervical Vertebral Malformations / Wobbler Syndrome
Wobbler syndrome, formally referred to as cervical vertebral malformation, is the development of a narrowed spinal canal due to malformed vertebrae, resulting in ataxia which is characterized by balance [3].
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Scapulohumeral Dysplasia
Scapulohumeral dysplasia results from a mismatch in size between the humerus and glenoid socket resulting in lameness and instability (Thomas, 2022). Note, this condition only occurs in Shetland ponies and thus is less relevant to the broader equid community [10].
