Bone, Joint and Muscle Pathology

Question 1

What bones are formed by intramembranous ossification?

Answer 1

Flat bones (these have no growth plates)

Question 2

Describe intramembranous ossification

Answer 2

• 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

Question 3

What kinds of bones are formed via endochondral ossification?

Answer 3

• long bones
  
  • requires growth plates
  • predominantly incr length

Question 4

Describe endochondral ossification?

Answer 4

• 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

Question 5

What are the zones that make up the growth plate?

Answer 5

Superficial

• Resting zone
• Proliferating zone
• Hypertrophic zone
• Ossification zone
• Trabecular bone

Deep

Question 6

What does growth plate function require?

Answer 6

requires:

• angiogenesis
• adequately mineralized collage/cartilage
• adequate blood vessel quality

Question 7

Where does achondroplasia affect in the growth plate?

Answer 7

the zone of resting cartilage

Question 8

Where does rickets affect in the growth plate?

Answer 8

• columnar cartilage in the provisional zone of calcification

Question 9

What zone does osteogenesis imperfecta affect in the growth plate?

Answer 9

the zone of osteoid formation

Question 10

Where in the growth plate does osteopetrosis affect?

Answer 10

the zone of bone remodeling in compact bone

Question 11

Describe woven bone

Answer 11

• polarized (remodeling lines are highlighted)
• lines are going in many different directions
• more osteocytes
• more flexible
• could be immature bone (not oriented to stress)

Question 12

Describe laminar bone

Answer 12

• more organized
• mature bone - has been reoriented/reorganized to stress
• fewer osteocytes

Question 13

What is the mneumonic device you can use to remember descriptors for fractures?

Answer 13

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

Question 14

What are the four stages of fracture healing?

Answer 14

1. Hematoma
2. Fibrocartilagenous callus
3. Bony callus
4. Remodeling

Question 15

What do you see histologically with bone necrosis?

Answer 15

empty lacunae (osteocytes have died off)

Question 16

Why does bone necrosis occur with fractures?

Answer 16

loss of blood supply –> ischemia –> cell death

Question 17

What stage of healing will the bone be in at days 7-10?

Answer 17

granulation tissue formation, with evident bone necrosis

Question 18

What stage of healing will a fracture be at 3 weeks?

Answer 18

callus formation

Question 19

What are Salter Harris fractures?

Answer 19

​fractures through a growth plate

• can induce growth deformities
• classified by fracture location

Question 20

What is the mneumonic used to remember Salter Harris fracture classifications?

Answer 20

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)

Question 21

Describe craniomandibular osteopathy

Answer 21

• 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

Question 22

Describe osteogenesis imperfecta

Answer 22

• defect in matrix synthesis (e.g. type I collagen)
• characterized by excessive bone fragility
  
  • ​fractures

Question 23

What is osteopetrosis?

Answer 23

• failure of bone remodeling
• increased bone density

Question 24

Describe chondrodysplasia

Answer 24

• not just one syndrome
• achondroplasia
• disproportionate dwarfism

Question 25

Describe osteoporosis

Answer 25

* **bone loss -- resorption \> formation** * d/t disuse, malnutrition, corticosteroids, etc * susceptible to fracture

Question 26

What is osteopenia?

Answer 26

decreased #s of thin trabeculae; go from osteopenia to osteoporosis

Question 27

Describe scurvy

Answer 27

* **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

Question 28

What are some caues of fibrous osteodystrophy?

Answer 28

* Causes: * Primary hyperparathyroidism * functional parathyroid adenomas * parathyroid hyperplasia * Secondary hyperparathyroidism * Ca:P imbalance in feed * Kidney dz

Question 29

What is fibrillation?

Answer 29

* Forms vertical clefts in cartilage * dull, yellow-brown cartilage * can be problematic b/c cartilage is avascular —\> poor healing

Question 30

Define eburnation

Answer 30

Continued trauma over a bone that causes polishing of exposed subchondral bone

Question 31

Osteophytes are what?

Answer 31

Protuberant overgrowths of bone in attempts to stabilize an articular surface

Question 32

What is a joint mouse?

Answer 32

Fragment that breaks off of an articular surface

Question 33

What types of acute infections cause inflammatory arthritis?

Answer 33

* Penetrating wounds * septicemia

Question 34

What types of chronic infections cause inflammatory arthritis?

Answer 34

* Immune mediated * viral * Untreated acute arthritis

Question 35

Descreased viscosity of joint fluid is an indication of what disease process?

Answer 35

Arthritis (inflammatory or osteoarthritis)

Question 36

Describe osteoarthritis

Answer 36

* **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

Question 37

Describe osteochondritis dessicans

Question 38

What is an example of joint neoplasm?

Answer 38

* Synovial cell sarcoma * typically very aggressive, looks like osteosarcoma but **doesn’t cross the joint**

Question 39

Describe the structure of an intervertebral disc

Answer 39

* Outer annulus fibrosis * inner nucleus pulposis

Question 40

Describe what occurs with degeneration of an IVD

Answer 40

* Annulus fibrosis cracks, tears or can rupture * releases nucleus pulposus * Types: * I - sudden, more common in chrondrodysplastic breeds, most severe * II - gradual

Question 41

Describe dural ossification

Answer 41

Ossifying pachymeningitis; often incidental

Question 42

Describe hip dysplasia

Answer 42

* Degenerative, non-inflammatory * generally large breed dogs * deformation of the joint * subluxation of femoral head if severe enough

Question 43

Describe elbow dysplasia

Answer 43

* Degenerative, non-inflammatory * generally large breed- esp. GSD * Seen with: * ununited anconeal process * fragmented medial coronoid process * OCD of the elbow

Question 44

Describe Type I and Type II muscle fibers

Answer 44

* Type I * slow twitch * large # of mitochondria * postural and sustained activity * Type II * fast twitch * fewer mitochondria * rapid activity

Question 45

What are some autoimmune causes of myositis?

Answer 45

* Systemic lupus erythematosus * polymyositis * purpura hemorrhagica

Question 46

What are bacterial and parasitic causes of myositis?

Answer 46

Bacterial * mostly Clostridium (will cause emphysematous necrosis) * abscesses Parasitic * Toxoplasma gondii * Trichinella spiralis * Sarcocystis spp.