MSK Growth, Injury and Repair

Question 1

Define osteogenesis/ossification

Answer 1

Process of bone formation

Question 2

When does bone development continue until?

Answer 2

Adult life (repair of fractures/remodelling)

Question 3

What are the three types of bone cells?

Answer 3

Osteoclasts = breakdown bone and resorb it 
Osteoblast = produce bone 
Osteocytes = mature bone cells

Question 4

What are the two types of ossification?

Answer 4

Intramembranous = mesenchyme –> bone (flat bones, irreg bones)

Endochondral = hyaline cartilage model –> bone (long bones)

Question 5

What is interstitial growth?

Answer 5

Increase in length of the bone occurs at epiphyseal plate by mitosis

Chondrocytes next to diaphysis age and degenerate
Osteoblasts move in and ossify the matrix –> bone
(happens in early adulthood)

Question 6

What is appositional growth?

Answer 6

Increase in bone width
Happens past adulthood in response to increased muscle activity/wt

Osteoblasts in periosteum form compact bone around external bone surface

Question 7

Describe the long bone anatomy

Answer 7

Consists of:
Diaphysis - shaft
Epiphysis - ends
Metaphysis - flares at end of diaphysis
Physis - eipiphyseal growth plates (physis also on the lesser and greater trochanters)
Medullary canal (w. huge haematogenic potential)

Question 8

What sort of movement does cortical bone resist?

Answer 8

Bending/torsion

Question 9

What does cancellous bone resist?

Answer 9

Absorbs/resists compression

Question 10

What does the cancellous bone contain?

Answer 10

Red bone marrow

Question 11

How is cortical bone laid down?

Answer 11

Circumferentially

Question 12

Which of cortical bone and trabecular bone is more active?

Answer 12

Trabecular

Question 13

Define bone fracture

Answer 13

Break in structural continuity of the bone (crack, break, split, buckle, crumpling)

Question 14

Why do bones fail?

Answer 14

Normal bones req. high energy injuries or repetitive stress (–> stress fracture)

Abnormal bones (osteoporosis, osteomalacia, metastatic tumours) may only req. a little bit of energy

Question 15

Describe the process of fracture repair

Answer 15

Stage 1 - INFLAMMATION
Blood cells accumulate, pro-inflammatory cytokines released –> recruitment of platelets, monocytes, PMNs, neutrophils, macrophages etc. –> haematoma formation
Bone necrosis at fracture ends –> byproducts of cell death
Fibroblast replication in these areas
Osteogenic induction of muscle/soft tissue cells
Angiogenesis (low O2 in middle of fracture & macrophages produce angiogenic factors)
CAREFUL not to lose haematoma

Stage 2 - SOFT CALLUS FORMATION 
Pain and swelling subside 
Bony fragments become united by cartilage/fibrous tissue 
Stability by angulation can still occur 
Continued inc. in vascularity 

Stage 3 - HARD CALLUS FORMATION
Conversion of cartilage –> woven bone (bone grows in from edges until it meets in middle)
Obvious callus on XRay

STAGE 4 - BONE REMODELLING
Conversion of woven bone –> lamellar bone
Medullary canal reconstituted
Bone responds to loading characteristics (Wolff’s law)

Question 16

Why must you not give NSAIDs to patients straight after they fracture their bone?

Answer 16

Stop inflammatory process that is necessary for clot formation

Question 17

Distinguish between primary bone healing and secondary bone healing

Answer 17

Primary = cortical bone directly tries to form bone without formation of a callus

Secondary = as above with callus formation

Question 18

What is Wolff’s Law?

Answer 18

Bone in a healthy person will adapt to the loads under which it is placed

Question 19

Finish the sentence:

Degree of instability is best expressed as …

Answer 19

A magnitude of strain

Question 20

What happens if the amount of strain on the fracture is not right?

Answer 20

Too much - fracture won’t heal

Too little - won’t be enough mechanical induction of tissue differentiation

Question 21

What is delayed union?

Answer 21

Failure to heal in expected time

Question 22

What are the reasons for delayed union?

Answer 22

High energy injury 
Infection 
Distraction (osteogenic jumping) 
Steroids
Immune supressors 
Warfarin 
NSAIDs
Ciprofloxacin 
Smoking

Question 23

What is non-union?

Answer 23

Failure to heal

Question 24

What are the reasons for non-union?

Answer 24

Instability (xs osteoclasis)
Failure calcification fibrocartilage (too much movement) 
Abundant callus formation 
Pain and tenderness 
Sclerosis
Persistent fracture line

Question 25

What do you do if there is failed union or non-union?

Answer 25

Different fixation
Dynamisation - e.g. removing nails to increase movement of bone
Bone grafting - if haematoma fails or no callus formation can replace cartilage (demineralised bone matrix) or straight to bone (bone graft)

Question 26

What is the best kind of bone graft and why?

What is the other type of bone graft?

Answer 26

Autogenous cancellous as it is both osteoconductive and osteoinductive

Allosteric grafts are only osteoconductive but overtime bone remodelling will hopefully turn the allosteric graft into your own bone(creeping substitution)

Question 27

What does osteoconductive mean?

Answer 27

Serves as scaffolding for new bone growth

Question 28

What does osteoinductive mean?

Answer 28

Recruitment of immature cells & stimulation of these cells –> preosteoblasts

Question 29

What are the different types of allograft bones?

Answer 29

Cortical, cancellous, fresh, prepared, structural

Question 30

What layer from spinned blood do platelet concentrates come from?

Answer 30

Buffy coat

Question 31

How might you use the buffy coat?

Answer 31

Inject it into local tissue to release a no of factors (platelet derived growth factor, transforming growth factor beta, IGF, VEGF) that stimulate bone healing