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MSK block > Fracture Healing > Flashcards

Fracture Healing Flashcards

1
Q

What type of CT is bone?

A

Bone is is a specialised form of dense connective tissue

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2
Q

List 3 mechanical functions of bone

A
  1. skeleton rigidity
  2. function as attachment and lever for muscle
  3. supports the body against gravity
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3
Q

What is the chemical function of bone

A

Calcium homeostasis and metabolism

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4
Q

What is the haematological function of bone

A

Bone marrow manufactures stem cells and other substances, which in turn produce RBCs

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5
Q

Compare and contrast the 3 macroscopic types of bone

A
  1. Trabecular (cancellous/spongy) bone ➞ sponge like network
    * located at ends of long bones
  2. Compact (cortical) bone ➞ strong , dense bone
  • no spaces/hollows in bone matrix visible to the eye
  • stiffer but more brittle than cancellous bone, withstands less strain before failure
  1. Woven bone ➞ Immature, disorganised bone
  • absent from normal bone after age 4
  • seen in fracture callus in both children and adults
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6
Q

Compare and constrast the 3 types of bone cells

A
  1. Osteoblasts
  • formation, organization and mineralisation of bone ECM
  • synthesis of collagen and other bone proteins
  1. Osteocytes ➞ similar to nerve cells
  • regulates response of bone to mechanical environment
  • Intercellular communication via canaliculi
  1. Osteoclasts
  • responsible for resorption of bone matrix (osteoid)
  • large motile, multinucleated cell
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7
Q

Describe the constituents of bone

A

Organic component (40% dry weight of bone)

  • Collagen (90%)
  • Proteoglycans
  • Matrix Proteins
  • Cells

Inorganic component (60% dry weight of bone)

  • Calcium Hydroxyapatite
  • Osteocalcium Phosphate
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8
Q

What component of bone provides compressive strength?

A

Calcium Hydroxyapatite (Inorganic component)

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9
Q

List the 4 sources of blood supply to bone AND where each supplies

A
  1. Nutrient artery system ➞ inner 2/3 of cortex from within (endosteal)
  2. Periosteal system ➞ outer 1/3 of cortex
  3. Metaphyseal system ➞ ‘zone of provisional calcification’ in physis
  4. Epiphyseal system ➞ supplies physis by diffusion
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10
Q

Vessels from which system contribute to endochondral ossification in children?

A

Nutrient artery system - in the child, these vessels end on metaphyseal side of the physis and contribute to endochondral ossification

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11
Q

The Metaphyseal system anastomoses with which other system?

A

The nutrient artery system

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12
Q

Which system supplies blood to the femoral and radial heads?

A

Epiphyseal system

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13
Q

Why is blood supply to the femoral and radial heads tenuous?

A

Femoral and radial heads are almost entirely covered by cartilage

Vessels from the from epiphyseal system enter in region between articular cartilage and growth-plate cartilage

Hence, blood supply is tenuous

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14
Q

List the 3 stages of fracture healing

A
  1. Inflammatory response
  2. Reparative response
  3. Remodelling
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15
Q

What occurs during the Inflammatory response of fracture healing (Incl timeframe)|

A

Time of injury to 24-72 hours

  1. Injured tissues + platelets release vasoactive mediators, growth factors and other cytokines
  2. These cytokines influence cell migration, proliferation, differentiation and matrix synthesis
  3. growth factors recruit fibroblasts, mesenchymal cells and osteoprogenitor cells to fracture site
  4. Macrophages, PMNs and mast cells (48hr) arrive at fracture site to begin process of removing the tissue debris
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16
Q

What occurs during the reparative response of fracture healing (Incl timeframe)|

A

2 days to 2 weeks

  1. vasoactive substances cause neovascularisation and local vasodilation
  2. undifferentiated mesenchymal cells migrate to fracture site and form cells which in turn form cartilage, bone or fibrous tissue
  3. the fracture haematoma is organised, fibroblasts and chondroblasts appear between bone ends and cartilage is formed
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17
Q

What occurs during Remodelling of fracture healing (Incl timeframe)

A

Middle of repair phase up to 7 years (most occurs in 1st year)

  1. osteoclasts resorb bone and the resulting hole is filled by osteoblasts with new bone and osteocytes
  2. fracture healing is complete when there is repopulation of the medullary canal
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18
Q

What is remodelling of woven bone dependant on?

What ‘law’ does this follow

A

Remodelling of the woven bone is dependent on the mechanical forces applied to it

Wolff’s Law - ‘form follows function’

19
Q

List 4 local and 4 systemic factors which affect fracture healing

A
20
Q

The amount of callus formed is _________ to the amount of immobilisation of the fracture

What does this mean for fractures fixed with rigid compression plates?

A

inversely proportional

fractures fixed with rigid compression plates permits almost no movement resulting in primary bone healing with little or no visible callus formation

21
Q

Bone is viscoelastic, what does this mean?

A

time dependent property where the deformation of the material is related to the rate of loading

22
Q

Bone is anisotropic, what does this mean?

A

Different mechanical properties when loaded along different axes

This is because the structure of bone is dissimilar in the transverse and longitudinal directions

Ie. cortical bone is stronger in compression than tension and weakest in shear

23
Q

When a tension force is applied to bone, what fracture results?

Explain the mechanics of this AND state the most common locations this occurs in

A

Transverse fracture

Failure due to debonding at the cement lines and pulling out of the osteons

Tends to occur in areas with a large proportion of cancellous bone eg. calcaneum, 5th metatarsal

24
Q

When a compression force is applied to bone, what fracture results?

Explain the mechanics of this AND state the most common locations this occurs in

A

Oblique fracture at 30o angle (b/c shear forces at this angle are responsible for the failure)

Failure due to oblique cracking of the osteons (few fractures occur purely due to compression)

Fractures tend to occur in the metaphyses of bones where there is more cancellous bone which is weaker

25
Q

What is a bending force and, what fracture results?

Explain the mechanics of this

A

Combination of compression and tension

Results in transverse fractures

Tensile stresses and strains on one side of the neutral axis and compressive stresses and strains on the other side ➞ failure on the tension side progresses transversely across the bone and the neutral axis shifts

26
Q

When a torsion force is applied to bone, what fracture results?

Explain the mechanics of this

A

Spiral fracture

A load is placed on a structure so that twisting occurs about an axis. A torque or moment is produced within the structure

27
Q

List 5 surgical treatment options for fractures

A
  1. Plaster fixation and Traction
  2. Bone Screw
  3. Plates
  4. Intra-Medullary Nails
  5. External Fixation
28
Q

What are the 2 types of screws used in surgical treatment of a fracture?

CHECK THIS - are wood screwes even used?!

A

Wood screw ➞ inserted into a small pilot hole. The screw threads compress the wood, which is less stiff than the screw, resulting in an elastic force

Machine screw (bone screw) ➞ inserted into a pre-drilled and pre-tapped hole. The screw itself deforms plastically when inserted into metal

29
Q

Give 2 benefits and 3 disadvantages of ‘plates’ in the surgical treatment of fractures

A

Benefits:

  1. anatomical reduction of the fracture with open techniques
  2. stability for early function of muscle-tendon units and joints

Disadvantages:

  1. risk of bone refracture after their removal
  2. stress protection and osteoporosis beneath a plate
  3. plate irritation
30
Q

What are the 2 types of Intra-Medullary nails and what is the benefit to using these

A

Reamed or unreamed

Preserves soft tissues

31
Q

Give 4 advantages and 4 disadvantages to using external fixation

A

Advantages

  • apply quickly
  • allows adjustment
  • soft tissues not disturbed
  • access to wounds
  • joints can be mobilised

Disadvantages

  • pin tract infection
  • malunion
  • patient compliance required
32
Q

List the steps of wound management (8)

A
  1. ATLS Protocols
  2. Assess NV status of the limb
  3. Swab wound
  4. Photograph and Cover wound
  5. Give Tetanus prophylaxis and IV antibiotics
  6. Operative debridement and copious irrigation (within 6 hrs)
  7. Stabilisation of the fracture (reduces rates of infection)
  8. Coverage and closure of the wound (by 5-7 days)
33
Q

What is the Gustillo Anderson Classification?

A

Most commonly used classification system for open fractures

34
Q

List the criteria of the Gustillo Anderson Classification

A
35
Q

What are physeal Injuries?

A

Injuries Involving the growing region of childs bone (epiphyseal growth plate)

36
Q

Give 2 complications of physeal injuries

Why must we be concerned about these

A

Non-union and Mal-Union

Can risk premature growth arrest and deformity of growth if not accurately reduced

37
Q

What is Compartment Syndrome?

A

When circulation and function of tissues within a closed space are compromised by an increased pressure within that compartment

38
Q

Give 4 clinical features of compartment syndrome

A
  1. Pain out of proportion to the injury
  2. Pain on passive stretching of the involved compartment (cardinal sign)
  3. Pallor
  4. Pulselessness
  5. Paralysis
  6. Paraesthesia

(Last 4 appear very late and we should not wait for these)

39
Q

How do we diagnose compartment syndrome?

A

Intra-compartment pressure measurement

  • Normal compartment pressure is zero
  • Value above 40mmHg or within 40mmHg of diastolic is diagnostic
40
Q

How do we treat compartment syndrome?

A
  1. Split bandages / POP down to skin
  2. Fasciotomy – urgent surgical decompression of the involved compartments
41
Q

What is the biggest concern following long bone and pelvic fractures?

How would this present?

A

Fat embolism syndrome (high index of suspicion needed)

Presents with pulmonary and neurologic manifestations combined with petechial hemorrhages - often fatal

42
Q

Aside from the fracture itself, when else must we be concerned about FES

A

Surgery - FES is associated with movement of unstable bone fragments and reaming of the medullary cavity during placement of an internal fixation device

43
Q

What is the most effective prophylactic measure and treatment for Fat embolism syndrome

A

Most effective prophylactic measure is to reduce long bone fractures ASAP after injury + supportive treatment

MSK block (30 decks)

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