Diseases of bone and joints

Question 1

endochondral ossification

Answer 1

process of bone formation in which cartilage is replaced by bone (long bones, vertebrae)

Question 2

intramembranous ossification

Answer 2

formation of bone on or in fibrous connective tissue (skull, clavicle)

Question 3

6 types of bone/cartilage diseases

Answer 3

• abnormalities of development
• metabolic
• degenerative
• inflammatory
• unknown cause
• neoplastic

Question 4

3 types of generalized developmental disturbances (abnormalities of development)

Answer 4

-chondrodysplasias
-osteopetrosis
-osteogenesis imperfecta
(all have genetic basis, many are reflections of a cartilaginous disorder)

Question 5

primordial dwarfism

Answer 5

• proportionate body form
• recessive character fixed by selection
• cattle, dogs (often classified as distinct breeds)
• some disproportionate dwarfs also classified as breeds

Question 6

chondrodysplasias in cattle

Answer 6

• dexter bulldog: domed cranium, short face, mandible projects, short limbs (lethal if homozygous)
• snorter type: short legs, broad head, bulging forehead, protrusion of upper jaw, prominent eyes (non-lethal)

Question 7

chondrodysplasia in sheep

Answer 7

• spider lamb chondrodysplasia
• autosomal recessive
• may be aborted, stillborn, or born alive
• long, thin, angular legs
• tall, finely boned, poorly muscled
• small head, scoliosis, sternal deformity, valgus deformity
• single base change in the tyrosine kinase II domain of fibroblast growth factor receptor 3 –> removes inhibition of chondrocyte proliferation

Question 8

chondrodysplasia in dogs

Answer 8

• several breeds
• disproportionate short-limbed dwarfism with normal body length
• loss of normal cone shape of distal ulnar metaphysis
• enlarged carpal joints with lateral deviations of the paws

Question 9

osteopetrosis

Answer 9

• multiple species including humans
• autosomal recessive
• accumulation of primary and secondary spongiosa in marrow space due to defective osteoclastic resorption of mineralized tissue
• brachygnathia inferior, sloping forehead, impacted molars, protruding tongue
• diaphyses narrow, bones fragile

Question 10

osteogenesis imperfecta

Answer 10

• rare in domestic animals, important in humans
• bones are fragile and fracture under physiologic pressure
• inherited, may be autosomal dominant –> mutations in genes coding for type I collagen
• thin cortex, wide marrow cavity (growth plates normal)
• joint hypermobility, blue sclera, fragile teeth

Question 11

5 types of localized developmental disturbances

Answer 11

• polydactilia
• adactylia
• syndactilia
• cervical vertebral stenotic myelopathy (wobbler) in horses
• wobbler syndrome in dogs

Question 12

polydactilia v adactylia v syndactilia

Answer 12

• poly: increase in number of digits
• adac: absence of digits
• syn: fusion of digits

Question 13

cervical vertebral stenotic myelopathy

Answer 13

• equine wobbles
• incoordination and locomotor disturbances
• morphological or functional stenosis (narrowing) of vertebral canal
• compression/stretching of cervical spinal cord secondary to vertebral malformation
• ataxia (forelimbs less severely involved)
• LESIONS CONFINED TO SPINAL COLUMN (PRIMARY) AND CORD (SECONDARY)

Question 14

2 syndromes associated with cervical vertebral stenotic myopathy

Answer 14

• cervical vertebral instability (narrowing of spinal canal during flexion of neck –> more common)
• cervical static stenosis (less common, neck position is immaterial –> always narrow)

Question 15

wobbler syndrome in dogs

Answer 15

• similar to condition in horses
• large breed dogs, males mostly
• age of onset weeks to years
• spinal cord compression or stretching
• funnel-shaped vertebral canal, anterior stenosis

Question 16

thyroid hormone influences in metabolic bone diseases

Answer 16

• effects on growth cartilage maturation
• hypothyroidism: retardation of growth and bone development (severity depends on age and degree of deficiency)
• hyperthyroidism: acceleration of normal processes of maturation

Question 17

gonad hormonal influence in metabolic bone diseases

Answer 17

• estrogens and androgens affect growing skeleton
• accelerate epiphyseal closure
• hypogonadism leads to delayed epiphyseal fusion
• hypergonadism leads to premature epiphyseal closure and maturation of the skeleton
• regulators of bone mass in adults

Question 18

gonadectomy in immature dogs

Answer 18

• growth plate closure delayed in neutered groups, delayed longer in ones neutered earlier
• rate of growth unaffected by gonadectomy, but extended growth period resulted in greater final radial/ulnar length in all male dogs and bitches neutered early

Question 19

adrenal cortex hormonal influence on metabolic bone diseases

Answer 19

• hyperadrenocorticism commonly causes osteoporosis in humans and dogs
• effects vary with species, exposure, source of compound
• reduction of rate of bone formation and amount of bone produced

Question 20

osteopenia

Answer 20

decreased amount of bone tissue in skeleton (does not always equal osteoporosis)

Question 21

osteoporosis

Answer 21

• disease in which osteopenia leads to fractures
• imbalance between formation and resorption
• 30% bone loss for radiographic detection
• mainly cancellous (not cortical) bone
• trabeculae reduced in number/size

Question 22

causes of osteoporosis/osteopenia

Answer 22

• usually nutritional in origin

- starvation, disuse (atrophy), old age, intestinal parasitism, Ca deficiency, Cu deficiency

Question 23

rickets (metabolic dz)

Answer 23

• disease of GROWING bones
• caused by deficiency of P or vitamin D
• basic lesions are failure of mineralization of osteoid and cartilaginous matrix
• increased depth of physis, distortion of metaphysis/epiphysis
• cortex is soft with curvature and fx, joint enlargement
• histological changes heal rapidly if deficiency is corrected

Question 24

osteodystrophia fibrosa (fibrous osteodystrophy, FOD)

Answer 24

• hyperparathyroid disorder (prolonged/excessive secretion of PTH)
• excessive osteoclastic resorption of bone and formation of fibro-osseous tissue
• primary: parathyroid hyperplasia/neoplasia
• secondary (nutritional or renal): derangements that lower Ca and increase PTH

Question 25

nutritional hyperparathyroidism

Answer 25

- deficiencies of Ca and/or vitamin D, excess P - each causes hypocalcemia - limited to young, rapidly growing animals (except horses) - horses: "big head" --> diets with lots of grain, corn, bran - swine: unsupplemented grain rations - dogs/cats: diets of meat or offal

Question 26

renal osteodystrophy

Answer 26

- fibrous osteodystrophy in chronic renal failure - well known in dogs, uncommon in other species - retention of phosphate due to reduced glomerular filtration - reduced plasma ionized calcium stimulates PTH release

Question 27

2 types of fractures

Answer 27

- tramuatic: fracture of a bone that initially is normal - pathologic (spontaneous): fracture occurring in response to mild physiologic stress (bone structure altered by disease, strength reduced)

Question 28

repair of a closed, complete fracture

Answer 28

- blood clot - organization of clot - production of callus (woven bone) - remodeling of callus (osteoclastic bone resorption and lamellar bone production) - remodeling of callus (replacement by lamellar bone) - process takes months or years depending on site and age

Question 29

complications of fracture repair

Answer 29

- misalignment, infection, necrosis - pseudoarthritis (nonosseous union - permits continued mobility at fracture site) - premature closure of growth plate (skeletal deformities)

Question 30

osteosis

Answer 30

- bone necrosis - most common cause is ischemia (secondary to trauma with fx) - histo: death and disappearance of osteocytes (lacunae are empty)

Question 31

legg-calve-perthes disease

Answer 31

- necrosis/collapse of femoral capital epiphysis - small dogs - lameness of insidious onset, 4-8mo of age - osteonecrosis initiated by episodes of ischemia - may lead to collapse of femoral head - degenerative arthropathy is long-term outcome

Question 32

actinomycosis

Answer 32

- actinomyces bovis - gram pos, branching filamentous organism - "lumpy jaw" (mandibular osteomyelitis) - periosteal proliferation

Question 33

metaphyseal osteopathy

Answer 33

- canine hypertrophic osteodystrophy (HOD) - young, fast growing dogs, large breeds - fever, anorexia, lameness, swelling in metaphyseal regions of long bones (distal radius and ulna esp) - most dogs recover with supportive care - underlying genetic defect (CLAD deficiency) --> neutrophil entrapment

Question 34

canine panosteitis

Answer 34

- eosinophilic panosteitis - large breed dogs (german shepherds) - shifting lameness, remission/exacerbation, self-limiting - abnormalities of diaphysis of long bone - expanding fibrovascular tissue in bone marrow, replaced by woven bone

Question 35

hypertrophic osteophathy

Answer 35

- hypertrophic pulmonary osteopathy - diffuse periosteal osteophytosis secondary to chronic lesion, usually intrathoracic - inflammatory or neoplastic - initial signs related to secondary bone changes - bone lesions regress of primary thoracic lesion removed