Bones and Fractures

Question 1

What are the 5 functions of the skeleton?

Answer 1

1. Support
2. Protection
3. Movement
4. Mineral storage —> calcium phosphate
5. Produces blood cells —> 1 trillion/day

Question 2

What are the 2 sections of the skeleton?

Answer 2

1. Axial —> inner
   - cranium, vertebral column, rib cage
2. Appendicular —> outer
   - pectoral girdle, pelvic girdle, upper
   limbs, lower limbs

Question 3

What are the 2 components of bones?

Answer 3

1. Cells
2. Matrix (osteoid)

Question 4

What are the 4 components of bone matrix?

Answer 4

Organic (40%):
1. Type 1 collagen - 90%
2. Ground substance - 10%
—> proteoglycans
—> glycoproteins
—> cytokines
—> growth factors

Inorganic (60%):
3. Calcium hydroxyapatite
4. Osteocalcium phosphate

Question 5

What are the 4 types of bone cells?

Answer 5

1. Osteogenic = ‘stem’
   - in marrow + deep periosteum
2. Osteocyte = mature
   —> senses mechanical strain —> directs
   osteoblast/clast activity
   - osteoblast embedded in osteoid
   secretions
   - in matrix
3. Osteoblast = making
   —> secretes osteoid —> catalyses
   mineralisation
   - in growing periosteum + endosteum
4. Osteoclast = breaking
   —> dissolves bone —> resorb via
   phagocytosis
   - from bone marrow
   - in bone surface (old/injured/excess)

Question 6

What are the 2 pathways of bone development in utero?

Answer 6

1. Intramembranous
   
   • flat bones: skull, clavicle, mandible
   • mesenchymal cells —> bone
2. Endochondral
   
   • long bones, ribs, vertebrae
   • mesenchymal —> cartilage —> bone
   • takes longer

Question 7

How does intramembranous ossification occur? (5)

Answer 7

1. Mesenchymal cells differentiate to osteoblasts
2. Osteoblasts secrete osteoid —> trapped —>
   become osteocytes
3. Osteocytes cluster —> ossification center
4. Ossification centers fuse —> form trabecular matrix
   (branches) and periosteum (outer membrane)
5. Blood vessels between cavities in cancellous bone
   —> bring mesenchymal cells —> red marrow

Question 8

How does endochondral ossification occur?

Answer 8

1. Bone collar forms around hyaline cartilage
2. Cavity forms in centre of cartilage —> periosteal
   bud invades cavity
3. Spongy bone formed in cavity (primary ossification
   = diaphysis) —> grows —> elongation
4. Medullary cavities form at ends of bone —> bone
   formation (secondary ossification = epiphyseal)
5. Growth till cartilage only at ends —> articular
   cartilage

Question 9

What are the 2 categories of bone?

Answer 9

1. Immature = first bone produced
   - woven structure —> weaker
2. Mature = mineralised
   - lamellar structure —> stronger
   - cortical or cancellous

Question 10

What are the 2 types of mature bone?

Answer 10

1. Cortical —> compact and dense (outer)
   - suitable for weight bearing
2. Cancellous —> spongy (inner)

Question 11

What is the organisation of cortical bone? (5)

Answer 11

Composed of osteons compact together
- Haversian Canal —> central space
- contains blood vessels, nerves,
lymphatics
- Lamellae —> concentric layers around centre
- Lacunae —> small spaces between lacunae
- contain osteocytes
- Canaliculi —> tunnels connecting lacunae
- contain ECF
- Volkmans Canals —> transverse canals connecting
Haversian Canals

Question 12

What are the 3 mechanisms of bone fracture?

Answer 12

1. Trauma - high or low energy
2. Stress - abnormal stress on normal bone
3. Pathological - normal stress on abnormal bone

Question 13

What is the structure of long bones?

Answer 13

Top to bottom:
1. Epiphysis
2. Physis
3. Metaphysis
4. Diaphysis

Outer to inner:
1. Periosteum = connective tissue membrane covering
2. Outer cortex = cortical bone
3. Cancellous bone —> red marrow in spaces
4. Medullary cavity —> yellow marrow
+ nutrient artery
+ articular cartilage at joint ends

Question 14

What is the role of bones in calcium homeostasis?

Answer 14

Stores 99% of bodies calcium
- Calcium hydroxyapatite
- Store + release —> regulated by PTH, calcitriol,
calcitonin, vitamin D

Question 15

What are the 2 types of bond growth?

Answer 15

1. Interstitial —> length
2. Appositional —> thickness (intermembranous)

Question 16

What is interstitial bone growth?

Answer 16

Bone lengthening
- at physis:
epiphyseal side —> hyaline cartilage dividing to form
more matrix
diaphyseal side —> cartilage calcifies —> dies —>
replaced by bone

Question 17

What is appositional bone growth?

Answer 17

Bone thickening (deposition beneath periosteum)
1. Periosteal blood vessel through ridge
2. Periosteal ridges fuse —> endosteum-lined tunnel
3. Osteoblasts in endosteum build new concentric
lamellae towards tunnel —> new osteon
4. Osteon grows outwards —> bone grows
5. Osteoclasts resorb old/damaged bone
- happens to 5-10% bone each year

Question 18

What are the 4 stages of fracture healing?

Question 19

What are the 6 causes of pathological fractures?

Question 20

What are the 3 mechanisms of bone fracture?

Question 21

How do stress fractures occur?

Answer 21

Bone overused —> stress > remodelling capacity —> weakened bone —> fractures easily
- usually to weight-bearing bones:
femur, tibia, metatarsals, navicular
- activity related:
athletes, occupation, military etc.
female athlete triad —> eating disorder,
amenorrhea, osteoporosis

Question 22

What are the 6 causes of pathological fractures?

Answer 22

1. Osteoporosis/osteopenia:
   
   • osteoclast > osteoblast activity —> bones soft —>
     low energy trauma fractures (fragility)
   • use T-score —> normal > -1
     —> -1 > osteopenia > -2.5
     —> -2.5 > osteoporosis
   • female:male —> 4:1
   • causes: postmenopausal
     senile
     secondary —> hypogonadism, excess
     glucocorticoid, alcoholism
2. Malignancy:
   
   • primary —> osteosarcoma
     —> chondrosarcoma
     —> ewing sarcoma
     —> lymphoma
   • bone metastasis —> blastic: prostate
     —> lytic: kidney, thyroid, lung
     —> both: breast
3. Vitamin D deficiency:
   
   • inadequate calcium + phosphate —> insufficient
     matrix mineralisation
     —> rickets (children)
     —> osteomalacia (adults)
4. Osteomyelitis
5. Osteogenesis Imperfecta (Brittle Bones)
   
   • produce abnormal type I collagen —> insufficient
     osteoid production
   • hereditary
6. Paget’s Disease
   
   • excessive bone breaking
   • 4 stages: osteoclastic activity
     mixed osteoclastic-osteoblastic activity
     osteoblastic activity
     malignant degeneration

Question 23

What are the 4 stages of fractures healing?

Answer 23

1. Bleeding
2. Inflammation
   
   • haematoma forms, cytokines released,
     aniogenesis, granulation tissue formed
3. New tissue formation
   
   • soft callus (collagen —> type II collagen) to …
     hard callus (bone —> type I collagen)
   • involves: fibroblasts, osteoblasts, chondroblasts
4. Remodelling
   
   • callus responds to activity —> excess removed
   • involves: macrophages, osteoclasts, osteoblasts

Question 24

What is Wolff’s Law?

Answer 24

Bone grows and remodels in response to the forces placed on it

Question 25

What is primary bone healing?

Answer 25

Intramembranous healing
- stable
- direct woven bone produced

Question 26

What is secondary bone healing?

Answer 26

Endochondral healing
- not as stable
- responses in periosteum and external soft tissue
- more callous bone produced

Question 27

How long do fractures take to heal?

Answer 27

3-12 weeks (depends on site, age, co-morbidities)
- Phalanges —> 3 weeks
- Metacarpals —> 4-6 weeks
- Distal radius —> 4-6 weeks
- Forearm —> 8-10 weeks
- Tibia —> 10 weeks
- Femur —> 12 weeks

Question 28

How are fractures diagnosed? (3)

Answer 28

1. Patient history (+ bystander if trauma)
2. Examination —> skin, deformity, function,
   tenderness, neurovascular status
3. X-ray —> anterior-posterior + lateral view

Question 29

What are the 3 stages of fracture management?

Answer 29

1. Reduce - open
   - closed —> manipulation
2. Fixation - internal - intermedullary —> pins, nails
   - extramedullary —> plate,
   screws, pins
   - external - monoplanar
   - multiplanar
3. Rehabilitation - use —> pain relief, retrain
   - movement
   - strengthen
   - weight bear

Question 30

What are the 8 symptoms of a fracture?

Answer 30

1. Can’t weight bare
2. Severe pain
3. Swelling
4. Deformity
5. Abbrasions
6. Loss of movement
7. Wound - if open
8. Loss of feeling - if nerve injured