Bones Developmental - Pathology
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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
- 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
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)
- Lateral aspect of radius