Equine Skeletal Diseases

Fibrous Osteodystrophy This condition was originally described by the name of Bran disease

as it occurred when horses, owned by flour-millers, were fed almost exclusively bran, a cheap by-product. Similar changes can be seen when animals fed grain are supplemented with hay of poor nutritional value rather than alfalfa that is high in calcium

Clinical features. ◦ Changes in the head and facial outlines are commonly the first signs of

the disease; it has therefore been called big head (fig. Ic-1). The disorder is the result of feeding diets low in calcium and high in phosphorus.

Pathology◦ macroscopic appearance. The sharp features of the head, especially in

the region of the zygomatic arch and upper and lower jaws, become rounded and indefinite, giving the appearance of more swelling than really exists (fig. Ib2-11). Dissection shows a rather uniform thickening and rounding due to diffuse proliferation of imperfect bone in the subperiosteal region. The teeth may loosen and fall out. There is also lameness and a general tenderness of the joints.

◦ microscopic appearance. Classic lesions of fibrous osteodystrophy with osteomalacia are most obvious in facial bones and the mandible (fig. Ib2-16), but the lesions are generalized throughout the skeleton

Salmonella Infection Is a frequent cause of acute osteomyelitis

that affects the long bones of foals (fig. Ic-2). It is characterized by necrosis and formation of sequestra in the epiphysis below the growing articular cartilage or in the metaphysis below the physeal plate

Equine Cervical Vertebral Deformity

Common cause of ataxia in young horses. The condition is often associated with degenerative arthropathy secondary to osteochondrosis

Pathogenesis of the condition is incompletely understood, but maldevelopment of the cervical vertebrae causes narrowing or functional stenosis of the spinal canal. Spinal cord injury causes incoordination, principally affecting the hind limbs. Although the shape and characteristics of each cervical vertebra varies among individual foals, the cervical deformity is divided into two main categories:

◦ Cervical vertebral instability. Occurs in animals from 8 to 18 months of age. There is dynamic compression of the

spinal cord by the vertebral body when the neck is flexed (fig. Ic-3). Characteristic findings are symmetrical overgrowth of the bilateral articular processes and enlargement of the epiphyseal end plate of the vertebral body. This narrows the diameter of the vertebral canal during neck flexion, usually from C3-C5

◦ Cervical vertebral stenosis. Hypertrophy of the ligamentum flavum, fibrocartilaginous hyperplasia of the ligamentous

attachment, and fibrous thickening of the joint capsule of the articular facets is associated with asymmetric overgrowth of these structures and results in stenosis of the spinal canal (figs. Ic-4, Ic-5). Dorsal or dorsolateral compression of the spinal cord occurs regardless of neck position. Lesions are frequently located at C5-C7

Angular Limb Deformity Lateral deviation of the distal portion of the limb, originating in the

distal radial physis, carpus or distal metatarsal physis, and it is seen more commonly in foals than other domestic animals (fig. Ic-6). It may be present at birth or be acquired later in life.

Causes include uterine malposition of the fetus, trauma, poor conformation, and hypothyroidism. Foals with hypothyroidism have mandibular prognathism and delayed ossification of carpal and tarsal bones.

Growth and modeling of cartilage prior to formation of the primary ossification center or of the physeal plate or AE complex (fig. Ia-13) of the epiphysis directly controls the bone's size and shape. If there is abnormal development of the chondral model, ossification only adds support to form an abnormally shaped bone.

Conditions such as malunion of fracture, osteochondrosis, or premature arrest of growth on one lateral side of the physeal plate can produce a varus bone deformity. Increase compressive loads on a portion of the physeal plate can increase or decrease local cartilage growth depending upon the load magnitude. If local growth is increased, there is correction of the original deformity. If growth is decreased, the deformity is magnified

OsteochondrosisFrequent cause of lameness in young horses

(fig. Ic-7). The femero-patellar and tibio-tarsal joints are most commonly involved. Other joints commonly affected include the shoulder and metacarpo-phalangeal joints. The condition is frequently bilateral.

Clinical signs◦ The joint is distended with synovial effusion in

animals 6 months to 2 years of age. Lameness may be mild to moderate. It is exacerbated by exercise.

Pathology◦ Typical equine lesions in the femoral head are

illustrated (figs. Ic-7, Ic-8, Ic-9, Ic-10, Ic-11).

EpiphysitisGeneralized bone disease of

growing horses that is characterized by enlargement of the physeal region in young animals. This condition is a misnomer in that it is not particularly inflammatory and is not caused by an infectious agent. It is associated with osteochondrosis of the physeal plate

NeoplasiaOsteosarcoma occurs much more

frequently in the head than in the appendicular skeleton.

The most common site of chondrosarcoma is the rib.

Ossifying fibroma is seen in young horses in the mandible, maxilla or nasal sinuses (fig. Ib6-6, Ib6-7, Ib6-8)

More diseases when we discuss Blemishes and Unsoundnesses