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MSK Block > Biology of Fracture Healing > Flashcards

Biology of Fracture Healing Flashcards

1
Q

What are the four important bits of bone?

A

– Epiphysis, Physis, the Metaphysis and the Diaphysis.

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2
Q

How does bone size increase after ossification of the epiphysis?

A

An increase in bone girth occurs through appositional bone formation by generative cells in the deepest layer of the periosteum

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3
Q

What type of cartilage is found at synovial joints?

A

In synovial joints this is hyaline cartilage

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4
Q

What kind of cartilage exists in synarthroses?

A

Fibrocartaliginous

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5
Q

What are the four functions of bone?

A
  • Support
  • Protection
  • Leverage
  • Metabolic function (Mineral storage/Haemopoiesis)
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6
Q

What is found in bone matrix (non mineral bit)

A

o Type 1 collagen fibres, derived from tropocollagen molecules produced by osteoblasts, make up 80% of the un-mineralized matrix. They form a matrix which embodies a mucopolysaccharide ground substance (awry in Mucopolysaccharidosis) which acts as a scaffold on which minerals are deposited.

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7
Q

What are the main mineral components of bone?

A

Calcium and Phosphate in the form of Crystalline Hydroxyapatite, which is laid down in osteoid at the calcification front.

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8
Q

Define demineralization

A

to resorption of whole matrix, including collagenous component.

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9
Q

What does PTH do?

A

o Parathyroid hormone stimulates the osteoclasts to reabsorb bone matrix leading to calcium in the blood. When blood calcium levels are higher than normal calcitonin is released, which inhibits osteoclast activity and decreases bone reabsorption.

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10
Q

What do osteoblasts do?

A

Mature osteoblasts form rows of mononuclear cells along the free surfaces of trabeculae and haversian systems where osteoid is laid down prior to calcification. They are rich in alkaline phosphatase (raised in diseases of bone formation such as Paget’s Disease) and are response for the production of Type 1 Collagen.

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11
Q

Outline endochondral ossification

A

o Cartilage is reabsorbed and replaced with bone (e.g. long bones)
o Begins at the primary centre in the shaft (diaphysis) and later at each end (epiphysis – secondary centre)
o Growth in length is at epiphyseal growth plates
o A similar process takes place in the later stages of fracture repair

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12
Q

What are four mechanisms of injury for fractures?

A 
Direct force - Bone breaks at point of impact
Indirect force - Bone breaks at a distance from where force was applied
Repetitive stress
Abnormal weakening (pathological fracture)
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13
Q

Give four different types of indirect fracture and the movement associated

A

 Spiral fracture – Twisting
 Oblique fracture – Compression
 Butterfly fragment – Bending
 Transverse fracture – Tension

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14
Q

Give four different ways in which fractures are dispalced

A

Translation
Angulation
Rotation
Length

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15
Q

Give five stages of fracture repair

A

1) Tissue destruction and haematoma formation
2) Inflammation and cellular proliferation
3) Callus formation (Fibrocartaliginous Callus formation)
4) Consolidation (Bony Callus formation)
5) Remodelling

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16
Q

What happens in stage 1 of fracture repair?

A

1) Tissue destruction and haematoma formation
Vessels are torn and a haematoma froms around and within the fracture. Bone at the fracture surfaces, deprived of blood, dies back a millimetre or two

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17
Q

What happens in stage 2 of fracture repair? (inflammation and cellular proliferation)

A

2) Inflammation and cellular proliferation
Rapid acute inflammatory reaction and migration of inflammatory cells occurs. The fragement ends are surrounded by cellular tissue which creates a scaffold across the fracture site. Inflammatory mediators are released, causing new capillaries to grow across haematoma (granulation tissue)

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18
Q

What happens in stage 3 of fracture repair?

A

3) Callus formation (Fibrocartaliginous Callus formation)
Differentiating stem cells provide chondrogenic and osteogenic cell populations. Cartaliginous callous from forms woven (immature) bone, which becomes more densely mineralized and causes the fracture to “unite” at weak 4.

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19
Q

What happens in stage 4 of fracture repair?

A

4) Consolidation (Bony Callus formation)

With continuing osteoclastic and osteoblastic activity the woven bone is transformed into lamellar bone.

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20
Q

What happens in stage 5 of fracture repair?

A

5) Remodelling

Continues for many years.

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21
Q

Give three reasons for which fractures are splinted

A
  • Alleviate pain
  • Ensure that the union takes place in good position
  • Permits early movement of the limb and a return to function
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22
Q

Give one reason people commonly say fractures are splinted which is not true

A

They are NOT splinted to ensure union

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23
Q

What is driect union?

A

Direct union encourages bone healing through a very different mechanism to the one outlined above – and indeed, it could even be considered inferior. Plating, for instance, stabilizes the fracture immediately, but this prevents the micromovement which stimulates callus formation.

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24
Q

What is the gap between bones required to be less than in order to encourage osteogenesis

A

If the gap between bones is very narrow (

25
Q

How many weeks before callus is strong enough to be bridged?

A

By 3-4 weeks the fracture is solid enough to allow penetration and bridging of the area by cutting cones (osteoclastic cones followed by osteoblasts).

26
Q

What are the advantages of healing by callus over healing by direct union?

A

– It ensures mechanical strength while the bone ends heal, and with increasing stress the callus grows stronger and stronger. With rigid metal fixation the absence of callus means that there is a long period during which the bone depends entirely on metal for support. The implant also diverts stress from the bone which this may not fully recover until the metal is removed.

27
Q

How long does a bone take to heal?

A
  • A spiral fracture takes 6-8 weeks to consolidate (reach complete repair)
  • Lower limb needs twice as long
  • Add 25% if the fracture is not spiral or involves the femur
28
Q

What is Perkin’s timetable?

A
  • A spiral fracture in the upper limb unites in 3 weeks
  • For consolidation multiply by 2
  • For the lower limb multiply by 2 again
  • For transverse fracture multiply again by 2
29
Q

What are the three stages of fracture treatment?

A

Reduce
Hold
Exercise

30
Q

Give three overall methods of maitaining fracture reduction

A
  • External Splints including plaster
  • Internal Fixation
  • External Fixation
31
Q

Give two methods of external splinting?

A

Continous traction

Plaster of paris

32
Q

Outline continous traction

A

o Continuous traction is one potential method of promoting bone repair – traction is applied to the limb distal to the fracture. The patient will often have to stay in hospital for this method of holding a reduction.

33
Q

Outline three complications of continous traction

A

Complications include circulatory embarrassment, nerve injury and pin site infection.

34
Q

Outline plaster of paris

A

o Plaster of Paris is widely used as a splint, especially for distal limb fracture and most children’s fracture. This allows the patient to go home sooner than with continuous traction

35
Q

Give four complications of plaster of parris

A

Complications include stiffness (which occurs as a result of joint immobilisation and muscle adhesions), a tight cast (causing vascular compression), pressure sores (pressing on a bony prominence) and skin abrasions.

36
Q

What is internal fixation?

A

Bone fragments may be fixed with screws, a metal plate held by screws, a long intramedullary nail or a combination.

37
Q

What are six indications for internal fixation?

A
  • Fractures that cannot be reduced except by operation
  • Inherently unstable fracture (mid-shaft forearm fractures and ankle)
  • Fractures that unite poorly and slowly (femoral neck fractures)
  • Pathological fractures
  • Multiple fractures
  • Fractures in patients with nursing difficulties
38
Q

What are the three main advantages of internal fixation?

A

Precise reduction, immediate stability and early movement.

39
Q

What is the big risk of internal fixation?

A

Infection

40
Q

What are three ways to avoid infection in internal fixation

A

1) The patient – devitalized tissue, a dirty wound and unfit patient
2) The surgeon – thorough training, high degree of surgical dexterity, adequate assistance
3) The facilities – a guaranteed aseptic routine, a full range of implants and staff familiar with use

41
Q

Give three complications of internal fixation other than infection

A

non-union, implant failure and refracture (on removal of the metal implants.

42
Q

Give three methods of internal fixation?

A

Intramedullary nail
Screws and plates
Wires

43
Q

Outline intramedullary nails

A

Internal fixators responsible for long bones, primarily the femur and tibia. A nail is inserted into the medullary cannal to splint the fracture, and rotational forces are resisted by introducing rotational locking screws that transfix the bone cortices and the nail proximal and distal to the fracture.

44
Q

Outline screws and plates

A

This form of fixation is useful for treating metaphyseal fractures of long bones and diaphyseal fractures of the radius and ulnar.

45
Q

Outline wires

A

Transfixing wires can hold major fractures together, and simple k-wires can be used for fractures around the elbow and wrist. Tension band wiring is useful for olecranon or patellar fractures.

46
Q

What is external fixation and what is it used for?

A

A fracture may be held by transfixing screws or tensioned wires that pass through the bone above and below the fracture and attached to an external frame. This is especially applicable to the tibia and pelvis.

47
Q

Give four indications for external fixation?

A
  • Fractures associated with sever soft-tissue damage (open fractures) or those that are contaminated, where internal fixation is risky and repeated access is needed for wound inspection, dressing or plastic surgery
  • Fractures around joints where soft tissue is too swollen for safe internal fixation
  • Multiple injuries
  • Infected fractures for which external fixation is not suitable
48
Q

What are three complications of external fixation?

A
  • Damage to soft tissue structures, no-contact between fragments, pin-track infection (pin site care required).
49
Q

Give five factors which cause non- and mal-union

A

1) Distraction and separation of the fragments, sometimes the result of interposition of soft tissues
2) Excessive movement at the fracture line
3) A severe injury that enders the local tissues non-viable
4) A poor local blood supply
5) Infection

50
Q

What is bone morphogenic protein?

A

BMP can be used as an alternative to autologous bone grafting. It is usually impregnated in a carrier, which may be allograft, demineralized bone matrix, collagen or bioactive bone cementand serves to induce new osteoblast formation from mesenchymal cells. The new bone produced is of the same quality and quantity as that produced from autologous bone grafting.

51
Q

What are the two benefits of bone grafts

A

Bone grafts are both osteoinductive and osteocondutive. They are able to stimulate osteogenesis through the differentiation of mesenchumal cells into osteoprogenitor cells and they provide linkage across defects and a scaffold upon which new bone can form.

52
Q

What are two types of bone graft?

A

Autograft

Allograft

53
Q

What are two types of autograft and what is an autograft?

A

Bone is transferred from one site to another in the same individual.
Two types are cancellous and vascularized grafts

54
Q

What is an allograft?

A

Consist of dead bone transferred from one individual ot another of the same species

55
Q

What are the potential risks of allografts?

A

Potential risks include infection/malignancy transfer – HIV, syphilis and hepatitis must be performed on the donor.

56
Q

Why is demineralization of allografts good?

A

Demineralization reduces anti-genecity and enhances the osteoinductive properties of the graft.

57
Q

What is the use of ultrasound in stimulating fracture healing?

A

There is evidence to suggest that daily low intensity ultrasound can speed up fracture healing in broken bones by stimulating bone cells to grow and repair.
A meta-analysis of 13 RCTs totalling 563 patients found a 34% overall mean reduction in healing time.

58
Q

How does smoking effect fracture healing?

A

Meta-analysis revealed that smoking is associated with a higher rate of nonunion in all long-bone fractures, tibia fractures, and open fractures.

MSK Block (15 decks)

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