Bone, Joint and Muscle Pathology Flashcards
What bones are formed by intramembranous ossification?
Flat bones (these have no growth plates)
Describe intramembranous ossification
- ossification center begins in the fibrous CT membrane
- osteoid is secreted into the fibrous membrane
- entrapped osteoblasts become osteocytes
- form woven bone and periosteum
- final layer of compact bone
What kinds of bones are formed via endochondral ossification?
- long bones
- requires growth plates
- predominantly incr length
Describe endochondral ossification?
- start with hyaline cartilage “model”
- develops periosteum and primar ossification center in the middle of the bone
- then dev. secondary ossification center at the ends
- hyaline cartilage trapped b/t the two = growth plate
- bone grows outwards from ossification centers
What are the zones that make up the growth plate?
Superficial
- Resting zone
- Proliferating zone
- Hypertrophic zone
- Ossification zone
- Trabecular bone
Deep
What does growth plate function require?
requires:
- angiogenesis
- adequately mineralized collage/cartilage
- adequate blood vessel quality
Where does achondroplasia affect in the growth plate?
the zone of resting cartilage
Where does rickets affect in the growth plate?
- columnar cartilage in the provisional zone of calcification
What zone does osteogenesis imperfecta affect in the growth plate?
the zone of osteoid formation
Where in the growth plate does osteopetrosis affect?
the zone of bone remodeling in compact bone
Describe woven bone
- polarized (remodeling lines are highlighted)
- lines are going in many different directions
- more osteocytes
- more flexible
- could be immature bone (not oriented to stress)
Describe laminar bone
- more organized
- mature bone - has been reoriented/reorganized to stress
- fewer osteocytes
What is the mneumonic device you can use to remember descriptors for fractures?
OLD ACID
O: Open vs. closed
L: Location
D: Degree (complete vs. incomplete)
A: Articular extension
C: Comminution/Pattern
I: Intrinsic bone quality - pathologic fracture
D: Displacement, angulation, rotation
What are the four stages of fracture healing?
- Hematoma
- Fibrocartilagenous callus
- Bony callus
- Remodeling
What do you see histologically with bone necrosis?
empty lacunae (osteocytes have died off)
Why does bone necrosis occur with fractures?
loss of blood supply –> ischemia –> cell death
What stage of healing will the bone be in at days 7-10?
granulation tissue formation, with evident bone necrosis
What stage of healing will a fracture be at 3 weeks?
callus formation
What are Salter Harris fractures?
fractures through a growth plate
- can induce growth deformities
- classified by fracture location
What is the mneumonic used to remember Salter Harris fracture classifications?
SALTR
S: Straight - Type 1
A: Above (thru and above GP) - Type 2
L: Lower (thru and above GP) - Type 3
T: Through (passes through GP) - Type 4
R: cRush (causes most damage)
Describe craniomandibular osteopathy
- Craniomandibular osteopathy
- also called ‘lion jaw’
- primarily in Westies and Scotties
- autosomal recessive
- 3-7 mo, stops @ 11-13 mo
- C/S: jaw pain, difficulty opening jaws
Describe osteogenesis imperfecta
- defect in matrix synthesis (e.g. type I collagen)
- characterized by excessive bone fragility
- fractures
What is osteopetrosis?
- failure of bone remodeling
- increased bone density
Describe chondrodysplasia
- not just one syndrome
- achondroplasia
- disproportionate dwarfism
Describe osteoporosis
- bone loss – resorption > formation
- d/t disuse, malnutrition, corticosteroids, etc
- susceptible to fracture
What is osteopenia?
decreased #s of thin trabeculae; go from osteopenia to osteoporosis
Describe scurvy
- only in species lacking L-gulonolactone oxidase (e.g. guinea pigs)
- Pathogenesis:
- lack of Vit C
- weakened vessel walls and physeal cartilage deformity
- periarticular hemorrhage and osteochondrodysplasia
What are some caues of fibrous osteodystrophy?
- Causes:
- Primary hyperparathyroidism
- functional parathyroid adenomas
- parathyroid hyperplasia
- Secondary hyperparathyroidism
- Ca:P imbalance in feed
- Kidney dz
- Primary hyperparathyroidism
What is fibrillation?
- Forms vertical clefts in cartilage
- dull, yellow-brown cartilage
- can be problematic b/c cartilage is avascular —> poor healing
Define eburnation
Continued trauma over a bone that causes polishing of exposed subchondral bone
Osteophytes are what?
Protuberant overgrowths of bone in attempts to stabilize an articular surface
What is a joint mouse?
Fragment that breaks off of an articular surface
What types of acute infections cause inflammatory arthritis?
- Penetrating wounds
- septicemia
What types of chronic infections cause inflammatory arthritis?
- Immune mediated
- viral
- Untreated acute arthritis
Descreased viscosity of joint fluid is an indication of what disease process?
Arthritis (inflammatory or osteoarthritis)
Describe osteoarthritis
- Degenerative joint dz
- typically an aging lesion
- lesions:
- fibrillation, cartilage erosion, osteophytosis, eburnation, synovial hyperplasia
- Mechanical and biochemical aspects:
- Decreased proteoglycan synthesis
- Increased metalloenzyme synthesis — degrade proteoglycans
Describe osteochondritis dessicans
What is an example of joint neoplasm?
- Synovial cell sarcoma
- typically very aggressive, looks like osteosarcoma but doesn’t cross the joint
Describe the structure of an intervertebral disc
- Outer annulus fibrosis
- inner nucleus pulposis
Describe what occurs with degeneration of an IVD
- Annulus fibrosis cracks, tears or can rupture
- releases nucleus pulposus
- Types:
- I - sudden, more common in chrondrodysplastic breeds, most severe
- II - gradual
Describe dural ossification
Ossifying pachymeningitis; often incidental
Describe hip dysplasia
- Degenerative, non-inflammatory
- generally large breed dogs
- deformation of the joint
- subluxation of femoral head if severe enough
Describe elbow dysplasia
- Degenerative, non-inflammatory
- generally large breed- esp. GSD
- Seen with:
- ununited anconeal process
- fragmented medial coronoid process
- OCD of the elbow
Describe Type I and Type II muscle fibers
- Type I
- slow twitch
- large # of mitochondria
- postural and sustained activity
- Type II
- fast twitch
- fewer mitochondria
- rapid activity
What are some autoimmune causes of myositis?
- Systemic lupus erythematosus
- polymyositis
- purpura hemorrhagica
What are bacterial and parasitic causes of myositis?
Bacterial
- mostly Clostridium (will cause emphysematous necrosis)
- abscesses
Parasitic
- Toxoplasma gondii
- Trichinella spiralis
- Sarcocystis spp.
