Bones Developmental - Pathology

()Map MUSCULOSKELETAL SYSTEM (Map) BONES

Generalised

Proportionate dwarfism

• Miniature breeds
• Due to growth factor deficit

Chondrodysplasia

• Literally means “abnormal cartilage development”
• Defective cartilage growth at the physis
• Usually genetic cause
• Occurs in cattle, dogs, sheep, pigs and cats
• Leads to disproportionate dwarfism (contrast with miniature breeds)
  • Generally, growth is disproportionate because only the growth of bones which form from cartilage models is retarded – growth of other bones is normal (i.e. long bones shorter than normal)

In Dogs:

• Localised forms occur in dogs (e.g. affecting skulls of Pekingese and Bulldogs or the limbs of Dachshunds and Bassett hounds)
• Occasionally seen in immature Beagles, Poodles, Alaskan Malamutes, Scottish Deerounds and Norwegian Elkhounds

In Cattle:

• Dexter cattle
  • Are heterozygous for incompletely dominant gene
  • When homozygous - lethal, producing 'buldog calf'
  • Usually aborted prior to seven month of pregnancy
  • Also occurs in Holstein, Jerseys and Charolais
  • Grossly:
    • Limbs and vertebral column are short
    • Domed cranium
    • Protruding tongue
    • Absent hard palate
    • Large umbilical hernia with eventrated abdominal organs
  • Histologically:
    • Proliferative and hypertrophic zones in the physes are irregularly separated by fibrovascular tissue
    • Chondrocytes are not properly arranged
    • Irregular ossification and mineralisation

• Telemark type
  • Cattle of Norwegian origin
  • Also seen in Jersey cows
  • Calves born alive, unable to stand and die soon after birth
  • Grossly:
    • Domed cranium
    • Brachygnatic face
    • Protruding tongue
    • Cleft palate
    • Short neck and limbs

• Brachycephalic 'Snorter' type
  • Hereford and Aberdeen Angus
  • Show nasal dyspnoea and chronic rumenal tympany
  • Grossly:
    • Short, broad head
    • Prominent, laterally displaced eyes
    • Short and compressed vertebral column
    • Distal long bones shorter than proximal
  • Histologically:
  • Physes appear normal
  • Pallisading chondrocytes fewer in number
  • Less hypertrophy

In Sheep:

• Ancon type
  • Short limbs due to premature closure of growth plates
  • Now rare
• Spider lamb
  • Hereditary (autosomal recessive) in Suffolk and Hampshire breeds in North America
  • Long, thin, angular limbs
  • May be born alive or dead, aborted or develop symptoms within a month of birth
  • Grossly:
    • Fine bones, poor musculature, small heads, scoliosis
  • Histologically:
    • Abnormal centres of endochondral ossification
    • Nodular cartilage hypertrophy

In Pigs:

• Occurs in Danish Landrace
• Autosomal recesive inheritance
• Dwarfs with short legs, forelegs shorter than hind legs
• Abnormal movement is noticable at weaning
• Sequel is arthrosis

Osteopetrosis (Marble bone disease)

• Occurs in sheep, dogs, cattle, horses
• Failure of resorption by osteoclasts -> failure of remodelling of cancellous bone
• Bones become thickened and dense but brittle
• Marrow cavites are full of unresorbed primary spongiosa
• Thickened intramembranous bones of skull -> altered shape of brain
• Associated with severe viral infections, e.g. FeLV, BVD
• Hereditary in Angus cattle

Lysosomal storage disease

• Excess accumulation of metabolites in lysosomes
• Affects mainly nervous system
• Also affects growth of cartilage

Osteogenesis Imperfecta

• Cause of fragile bones in humans, very rarely in animals
• Reported in Holstein and Charolais calves
• Poor mineralisation of bones and teeth
• Fractures are often present at birth

Congenital hyperostosis of pigs

Hyperostosis (Image sourced from Bristol Biomed Image Archive with permission)

• Rare, genetic
• Diaphysial dysplasia
• Excessive periosteal intramembranous bone, particularly in long bones
• Grossly:
  • Greatly thickened long bones
  • Tense, shiny skin, closely adherent to tissues below
• Born dead or die soon after birth

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)

Developmental abnormalities