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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

Osteochondrosis
Frequent 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).
Epiphysitis

Generalized 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
Neoplasia
Osteosarcoma 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)

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