Lame - bone pathology

Question 1

What are the two causes of fracture?

Answer 1

Traumatic - normal bone with excessive force
Pathological - abnormal bone with minimal trauma

Question 2

What are the 3 locations of bone fractures?

Answer 2

Growth plate
Trabecular bone
Cortical bone

Question 3

What do fractures that cross/crush the growth plate cause?

Answer 3

Angular limb deformities

Question 4

What type of fractures of the growth plate are more likely to heal easily?

Answer 4

Fractures that involve only the growth plate and primary bone trabeculae

Question 5

What type of fractures of the growth plate are more likely to cause irreversible damage?

Answer 5

Fractures crossing growth plate through metaphysis/epyphisis
Crush of growth plate

Question 6

What is the first step of fracture repair?

Answer 6

Formation of a haematoma around fracture site

Question 7

What does damage to blood vessels from a fracture cause?

Answer 7

Reduced blood flow
Necrosis of bone fragments
Release of growth factors by macrophages from dying bone

Question 8

What is formed from the haematoma in fracture repair?

Answer 8

Soft tissue callus/procallus

Question 9

How is the procallus formed in fracture repair?

Answer 9

Blood vessels proliferate and undifferentiated mesenchymal cells penetrate, forming loose collagenous tissue

Question 10

What is formed from the procallus in fracture repair? How?

Answer 10

A primary callus - metaplasia of the collagenous tissue into cartilage and woven bone

Question 11

What is the secondary callus made of? What is it?

Answer 11

Replaces the primary callus over time with lamellar bone

Question 12

What does the makeup of the primary callus depend on?

Answer 12

Blood an oxygen supply
The poorer the blood and o2 supply, the greater amount of cartilage in a callus - takes bone longer to heal

Question 13

How does the bone return to its original shape over time?

Answer 13

The portions of callus that dont undergo physical stress are reabsorbed over time

Question 14

What can complicate bone repair?

Answer 14

Insufficient bone supply
Instability
Infection poor nutrition

Question 15

What happens when there is instability during bone repair?

Answer 15

Non union - procallus cant mature into bone so forms fibrous tissue instead
Fibrous tissue not strong enough

Question 16

What can be formed by a non-union of bone due to instability?

Answer 16

Cysts
False joints
Pseudoarthritis

Question 17

What is common in open fractures?

Answer 17

Septic bone inflammation/infection

Question 18

Why is it easier for bacteria to invade under the articular epiphyseal cartilage complex?

Answer 18

Capillaries bend sharply to joining veins so there is turbulent blood flow and a discontinuous endothelial lining - easier for bacteria to invade

Question 19

What pathogens cause osteomyelitis?

Answer 19

Almost always bacterial eg. strep, staph, truperella, E. coli

Question 20

What causes inflammation during osteomyelitis?

Answer 20

Bacteria invade
Neutrophils recruited to the site causing inflammation

Question 21

What does inflammation stimulate during osteomyelitis? What does this cause?

Answer 21

Inflammation stimulates osteoclasts to reabsorb bone and enzymes released - bone loss

Question 22

What does the density of bone cause during osteomyelitis?

Answer 22

Density of bones means exudate cant get out of bone - the increased pressure is very painful, compresses blood vessels
Leads to thrombosis and infarction of intramedullary fat, marrow and bone

Question 23

What is deposited at the side of osteomyelitis?

Answer 23

Fibrous tissue

Question 24

What are sequelae?

Answer 24

Complications of osteomyelitis

Question 25

What are some sequelae?

Answer 25

Inflammation extending to the surrounding soft tissues causing abcesses Skin fistula Septic arthritis Sepsis Pathologic fractures Bone sequestra

Question 26

Where can osteomyelitis spread to?

Answer 26

Surrounding soft tissues Adjacent bones Across joints Into the bloodstream

Question 27

What are bone squestra?

Answer 27

fragments of pale, chalky necrotic bone that are cut off from their blood supply and surrounded by exudate Have no blood supply so cant resorb

Question 28

Why are bone sequestra bad?

Answer 28

They can interrupt/undermine bone healing

Question 29

What can cause bone sequestra?

Answer 29

Bone fractures Osteomyelitis

Question 30

What mechanism causes bone growth in width?

Answer 30

Intramembranous bone formation - osteoblasts for new concentric layers of cortical bone

Question 31

What mechanism causes bone growth in length?

Answer 31

Endochondral ossification in the metaphyseal growth plates

Question 32

When are growth plates thickest?

Answer 32

When growth is most rapid, closes at skeletal maturity

Question 33

What are the 4 different cartilage zones in the growth plate?

Answer 33

The reserve/resting zone Proliferative zone Hypertrophic zone Calcifying zone

Question 34

What is the reserve/resting zone for?

Answer 34

A source of cells for the proliferating zone

Question 35

What happens in the proliferative zone?

Answer 35

Cells multiply Produce matrix Become arranged in longitudinal columns

Question 36

What happens in the hypertrophic zone?

Answer 36

Chondrocyte volume expands Chondrocytes modify the matrix to allow capillary invasion Initiation of matrix mineralisation

Question 37

What happens in the calcifying zone?

Answer 37

Blood vessels from metaphysis invade into advancing growth plate Cartilage mineralisation

Question 38

What do the invading blood vessels from the metaphysis allow?

Answer 38

They provide entry for the osteoblasts - critical step

Question 39

What is the primary spongiosa?

Answer 39

The junction between cartilage and bone in the metaphysis A fragile lattice of bone covered spicules of calcified cartilage

Question 40

What is the secondary spongiosia? What is it made up of?

Answer 40

More mature trabeculae when growth plate advances - fewer, thicker and made up of mostly bone

Question 41

What is chondrodysplasia?

Answer 41

Hereditary disorders of bone growth - primary lesions in growth cartilage of the physeal/epiphyseal cartilage of long bones

Question 42

What are some disorders of bone growth in chondrodysplasia?

Answer 42

Growth plates reduced Disorganised chondrocytes Cartilage matrix less dense Trabeculae/spongiosa thickened Cartilage retained in the secondary spongiosa

Question 43

What type of dwarfism is caused by chondrodysplasia?

Answer 43

Disproportionate dwarfism - normal sized head with short legs

Question 44

Why does disproportionate dwarfism not affect the head?

Answer 44

Bones of the head are not formed by endochondral ossification

Question 45

What is not caused by chondrodysplasia?

Answer 45

Proportionate dwarfism - due to endocrine disease, malnutrition, or artificial breeding selection instead Just small dogs

Question 46

What causes angular limb deformities?

Answer 46

Partial or complete premature closure of growth plates

Question 47

What is the most common site of angular limb deformities?

Answer 47

Distal ulnar physis - most stress on this growth plate

Question 48

What causes angular limb deformities in horses?

Answer 48

Physeal osteochondrosis

Question 49

What area is the most commonly affected thing in physeal osteochondrosis?

Answer 49

Hypertrophic cartilage layer

Question 50

What is the result of physeal osteochondrosis?

Answer 50

A well demarcated wedge of retained cartilage in the physis - columns of chondrocytes that dont mineralise Can cause growth plate fractures?

Question 51

What is the weakest part of the bone?

Answer 51

Metaphyseal cortex adjacent to the growth plate

Question 52

What breed of dogs most commonly get elbow dysplasia?

Answer 52

Large to giant breed dogs

Question 53

What are some elbow abnormalities that cause elbow dysplasia?

Answer 53

Medial coronoid disease Humeral osteochondrosis Ununited anconeal process Elbow instability

Question 54

What disease does a short radius cause?

Answer 54

Medial coronoid disease

Question 55

What disease does a short ulna cause?

Answer 55

Ununited anconeal process

Question 56

What can cause aseptic/ischaemic necrosis?

Answer 56

Trauma causing vascular damage Neoplasm infiltration Thromboembolism

Question 57

What does ischaemic necrosis of the metaphysis of the bone and bone marrow cause?

Answer 57

Retained growth cartilage - conversion of epiphyseal cartilage to bone is impaired

Question 58

What does ischaemic necrosis of the epiphysis of the bone cause?

Answer 58

Premature growth plate closure - death of the proliferating chondrocytes

Question 59

What can aseptic/ischaemic necrosis lead to?

Answer 59

Avascular necrosis of the femoral head (legg-calve-perthes)

Question 60

What breeds are predisposed to avascular necrosis of the femoral head (legg-calve-perthes)?

Answer 60

Minature poodle Yorkie

Question 61

Why does ischaemic necrosis cause avascular necrosis of the femoral head?

Answer 61

Ischaemia causes dead femoral head bone to be replaced by fibrous tissue - this is not supportive enough so femoral head collapses

Question 62

What does not happen in avascular necrosis of the femoral head because it is a sterile disease?

Answer 62

Bone sequestra