Bones Developmental - Pathology

Generalised

Dwarfism

Retention of elongated primary trabeculae

• Happens due to impaired osteoclastic activity
• Primary trabeculae do not transform into secondary and tertiary
• Continue to elongate
• Form a dense band beneath growth plate - growth retardation lattice
• Dense spikules apparent on radiographs
• Can be caused by distemper virus, bovine viral diarrhoea virus

Localised

• Hemimelia - abscence of one of limb bones
• Syndactylia - fusion of toes
• Polydactylia - increased number of digits
• Ectrodactylia - cleft in paw extending to metacarpus of dogs and cats

Cervical Vertebral Stenotic Myelopathy (Wobblers)

• Equine disease
• Narrowing of the vertebral canal due to malalignment or maldevelopment of the vertebrae
• Fast growing male TBs ranging from 8 months to 4 years
• Hind limb ataxia due to cord compression

Angular limb deformity

• Lateral deviation of distal portion of limb (valgus)
• Medial deviation of distal portion of limb (varus) - more rare
• Most common in foals
  • Carpal joint
  • Tarsal joint
  • Fetlock joint
• Congenital or acquired
• Due to:
  • Malpositioning in utero
  • Excessive joint laxity
  • Hypothyroidism
  • Trauma
  • Overnutrition
  • Defective endochondral ossification
  • Poor conformation
  • Disruption of blood supply to one side of bone
  • Secondary to physitis in horses
• Usually resolves spontaneously in one to two weeks of life
• More severe cases exceding compensatory capabilities will persisist
• Cartilage development is affected

Fibrous dysplasia

• See Bones and Cartilage - hyperplastic and neoplastic

Physitis

• In horses
• Often associated with angular limb deformity
• Also called epiphysitis and physeal dysplasia
• Problem of endochondral ossification
• Two age groups
  • Weanlings
  • Yearlings in early training and two-year-olds
• May cause contracted tendons and flexural deformities
• Factors probably involved in its development:
  • Genetically fast growth rate
  • Large quantities of imbalanced, high energy feed
  • Imbalanced weight-bearing on joints
  • Excessive activity
  • Growth spurts
• Histologically: (appearance similar to angular limb deformity)
  • Lateral aspect of radius
    • Thickened metaphyseal part of physeal cartilage
    • -> Delay or disturbance of endochondral ossification
    • Compression
  • Central part
    • No obvious deformity
  • Medial aspect
    • Tension
    • -> Transverse fractures and repair
  • Laxity of periarticular attachements in young foals allows angular limb deformity; not occuring in older foals and young horses
  • (Sustained trauma produces similar lesions)

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Developmental abnormalities