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Equine Final Year > Equine Bone Healing > Flashcards

Equine Bone Healing Flashcards

1
Q

What is good about bone healing?

A

Bone has ability to heal completely after fracture and return to original structure and mechanical properties (if given the right mechanical environment to do so)

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2
Q

What is the immediate injury response <48h to bone injury?

A

Structural damage

  • Haematoma
  • Inflammatory mediators
    • Kinins, complement, histamine, serotonin, prostaglandins, leukotrienes
      • Promote vasodilation
      • Chemotaxis of white blood cells
      • Platelet aggregation and release
      • Mesenchymal cell proliferation
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3
Q

Name some inflammatory mediators that appear during the immedaite injury response in bone

A

Kinins, complement, histamine, serotonin, prostaglandins, leukotrienes

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4
Q

Inflammatory mediators are released in bone during the immediate injury response. What do they do?

A
  • Promote vasodilation
  • Chemotaxis of white blood cells
  • Platelet aggregation and release
  • Mesenchymal cell proliferation
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5
Q

What are the phases of fracture healing?

A
  1. Inflammation
  2. Repair
  3. Remodelling

The phases are not distinct –> lots of overlap

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6
Q

What happens during the inflammatory phase of bone healing?

When does it occur?

A
  • Occurs in first 2-3 weeks
  • Growth factors
  • Cytokines
  • Phagocytosis
  • Fragment end resorption
  • Inflammatory phase results in clearance of debris/necrotic/devitalised bone. Sets the stage for healing to occur. Fracture gap widens.
  • One of the first things that happens is fragment reabsorption
  • Fracture becomes more obvious during healing because of the resorption
  • On a radiograph a fracture will look its worst at 2-4 weeks post injury
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7
Q

At what point does the fracture become more obvious?

A

On a radiograph the fracture will look its worst at 2-4 weeks post injury

This is during the inflammatory phase

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8
Q

During the inflammatory phase, does the fracture get smaller or larger?

A

Fracture gap widens

Inflammatory phase results in clearance of debris/necrotic/devitalised bone

Fragment reabsorption

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9
Q

For how long does the reparative phase occur?

A

2-12 months duration

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10
Q

What happens during the reparative phase of bone healing?

A
  • Angiogenesis
    • Adjacent tissues (muscles)
    • Medulla
    • Angiogenesis –early supply from surrounding soft tissue, latterly from re- establishment of medullary blood supply.
  • Periosteal and endosteal callus formation
    • Interfragmentary stabilisation
    • Suppressed by
      • Rigid immobilisation –will be more likely to trigger 1y bone healing
      • Excessive mobilisation
    • Callus –cartilage and bone, stabilise fragments –> callus is really important for stabilisation
    • Cartilage component becomes mineralised, resulting in cancellous bony union (subsequently remodelled into lamellar bone)
  • Bone union
    • Cancellous bone, formed by a combination of intramembranous and endochondral ossification
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11
Q

What is periosteal and endosteal callus formation suppressed by?

A

Suppresed by:

  • Rigid immobilisation
  • Excessive immobilisation
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12
Q

What is this image showing with regards to bone healing?

A

Intramembranous ossification during the reparative phase

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13
Q

What happens during intramembranous ossification during the reparative phase of bone healing?

A
  • Peri/endosteal surfaces
    • low strain/motion
  • Fibrous scaffold
  • Buttress for ossification
  • Endochondral ossification can form between the bone ends
  • Intramembranous ossification goes straight from fibrous scaffold to mineralisation
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14
Q

What is this arrow pointing to with regards to bone healing during the reparative phase?

A

Soft callus - endochondral ossification

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15
Q

How does the haematoma formed during immediate injury response change during the reparative phase of bone healing?

A
  • Differentiation of haematoma
    • Fibroplasia
      • Chondrogenesis
        • Mineralisation
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16
Q

Briefly outline the steps in the indirect fracture healing process

A
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17
Q

Briefly, what happens during the remodelling phase of bone healing?

A

Bone resorption

Bone formation

Cortical callus - Haversian remodelling

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18
Q

During the remodelling phase of bone healing, how can there be some correction of malalignment possible in juveniles?

A
  • Convex surface; positive charge – attract osteoclasts
  • Concave surface; negative charge – attract osteoblasts (which are going to lay down bone)
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19
Q

Explain what is happening in these radiographs

A
  • Type II fracture extending through the growth plate
  • Dense cortex is re-establishing down dorsal and plantar aspect
  • Haversian remodelling is also taking place
20
Q

What are some regulatory molecules that are necessary in the regulation of fracture repair

A

Soz, too lazy to try and put this into bullet points so have the powerpoint slide instead

21
Q

Buddy the dog was wearing a 2 foot leash. He sees a squirrel and wants nothing more than to chase after it. Lucky for him Buddy was finally able to catch the squirrel. How did he accomplish this?

A

Because the leash is not tied on to anything else

22
Q

Name some regulatory molecules that are involved in bone healing, remodelling phase?

A
  • Growth factors
    • TGF-βsuperfamily (including BMPs) –progression
    • PDGF
    • IGF-1/2
    • FGF
  • Cytokines
    • IL1 (differentiation), IL3, CSF
  • Others
    • osteopontin, osteocalcin, osteonectin
    • PGs
23
Q

What are the 2 basic patterns of bone repair?

A

Direct (primary) repair

Indirect (secondary) repair

24
Q

What occurs during diirect (primary) fracture healing?

A
  • Exact alignment
  • Rigid fixation (usually internal fixation)
  • Sufficient blood supply
25
Q

What is contact healing and what is gap healing with regards to direct (primary) repair under stability?

A

Contact healing

  • Secondary osteonal (Haversian) remodelling of the fracture at interfragmentary contact points

Gap healing

  • Small gaps filled with woven then lamellar bone
  • Secondary osteonal remodelling
    • Grow across

In contrast, in primary bone healing we’re relying on residual strength of bone (if incomplete fracture) or strength of the surgical implants

26
Q

What are the arrows pointing at in this photo with regards to a bone structural unit - cutting cone

A

Multinuclested osteoclasts resorbing bone at the leading edge (white arrows)

New bone is in red along the edges (being put down by osteoblasts)

27
Q

What are the AO principles 196o for direct fracture repair

A

O principles 1960

  • Anatomic reduction
  • Stable internal fixation – interfragmentary compression
  • Preservation of blood supply
  • Aim is to achieve early active, pain-free mobilisation
28
Q

What are some methods of direct (indirect) bone repair?

A
  • External fixation
    • Casts and braces
    • External fixators
  • Internal fixation
    • Screws
    • Plates
    • Intramedullary nails

In horses external fixation has more associated complications and isn’t as useful for stabilisation

29
Q

When surigcally fixing an ulna in the horse, where should you avoid making the incision?

A

Avoid making incision over point of elbow –> problems with healing

30
Q

What is a dynamic compression plate?

How should it be placed?

A
  • Standard bone plate
  • Stability of construct relies on friction between the plate and bone
  • Plate must be contoured to the bone
    • Relies on contact between plate and bone to achieve stability
  • Accurate anatomic reconstruction necessary
  • Fixed to the bone with cortical screws
  • Sloping holes in the plate allow compression to be applied to the fracture
31
Q

What is indirect (secondary) bone repair?

A
  • Rapid stabilisation
  • Callus formation
  • Rapid restoration of mechanical integrity
  • Long period of remodelling
  • Repair pattern influenced by both biology and mechanics
32
Q

What are some problems in fracture repair?

A
  • Accurate anatomical reduction:
    • Articular misalignment (step) causes osteoarthritis and cyclical implant loading
    • Accurate reduction often difficult:
      • Eburnation
      • Muscle contraction
      • Severe comminution (may simply be unable to put all the pieces back in proper anatomical alignment)
  • For repair of articular fractures it is absolutely vital that the bones are properly aligned
  • Can be difficult to get accurate reduction in long bone fractures
  • Contraction of surrounding muscles can impact on reduction
33
Q

What happens if you have no motion at the fracture gap?

A

No callus

Atrophic non-union

34
Q

What happens if you have excessive motion at a fracture gap?

A

Hypertophic non-union due to persistence of fibrous tissue

35
Q

What is circled here with regards to union during indirect (secondary) bone repair?

A

Large mass of callus is disproportionate to the size of the fracture and the fracture line has persisted

Hypertrophic delayed union

36
Q

What is going on here?

A

Fibrous Malunion

Rather than getting an ossified repair it just forms a fibrous bridge that persists

Not as stable or strong so high risk of re-fracture

37
Q

What is the problem with excessive motion on implants for fracture repair?

A

Excessive motion - implant cycling

Excessive motion is something we are always fighting against in the horse because of the mechanical loads We need the bone to heal within 2-3 months otherwise the implants will reach their fatigue point and break

38
Q

What are some problems in fracture repair in horses?

A
  • Large animals (often >500kg)
  • Enormous mechanical loads on recovery from general anaesthesia
  • Rapid weight bearing
  • Bed rest not an option

A recipe for disaster!!

39
Q

What are some problems in fracture repair in horses with regards to soft tissues?

A
  • Condition of the soft tissues
  • Integrity of soft tissue cover:
    • Protection against infection
    • Integrity of blood supply
  • Tendency to open fractures:
    • Poor soft tissue cover distal limbs
    • Explosive nature of fractures
    • Poor first aid stabilisation
  • Prox. Limb fractures –> they have a lot of muscle coverage In the distal limb there isn’t much more than subcutaenosu tissue covering the bone
  • Can get problems with implants impinging on the skin and closing the skin can be an issue too
40
Q

What are some problems in fracture repair in horses with regards to load?

A
  • Contralateral overload (‘fracture disease’) in the horse:
    • Laminitis
    • Angular deformity (in younger animals)
    • Elongation of the stay apparatus
    • Cartilage degeneration
  • Pain-free weight bearing is necessary objective of fracture repair in the horse
    • Requires accurate reduction and rigid fixation
41
Q

What are some problems with contralateral limb overload in horses with fracture repair?

A
  • Contralateral overload (‘fracture disease’) in the horse:
    • Laminitis
    • Angular deformity (in younger animals)
    • Elongation of the stay apparatus
    • Cartilage degeneration
42
Q

What are some problems in fracture repair with prolonged immobilisation (‘cast disease’)?

A
  • Prolonged immobilisation (‘cast disease’):
    • Osteoporosis (loss of bone density) –> reversible but have to be careful because if they have developed severe osteoporosis they have increased risk of re-fracture
    • Joint laxity
    • Tendon laxity
    • Cartilage degeneration
    • Pressure or rub sores (be very careful not to apply bandages too tightly)
43
Q

What are some problems in fracture repair with regards to infection?

A
  • Infection (osteomyelitis)
    • Open fractures
    • Destruction of blood supply in overlying soft tissues
    • Prolonged surgery time
    • Implants are ‘foreign bodies’
    • Osteomyelitis could be considered as one of the most major causes of fracture repair failure
44
Q

What is and what are the pros and cons of biological fracture healing?

A

Minimally invasive surgery

  • Small incisions
  • Minimal disruption to fracture haematoma
  • Periosteum largely left intact
  • Quicker and better fracture healing

BUT

  • Increased reliance on complex (expensive) intra-operative imaging (CR/DR/fluoroscopy)
  • Increased technical demands
  • Expensive implants
  • Less accurate anatomic reduction –increased reliance of implants to load share

Can slide under the soft tissues and screw them in via small stab incisions –> good for maintaining blood supply and avoiding damage to the periosteum

45
Q

How can you help enhancement of fracture repair?

A
  • Cancellous Bone Grafting
    • Gold standard
    • Morbitity?
    • Availability
  • Osteoconduction -scaffold
  • Osteoinduction –stimulation of osteogenesis
  • Source of osteoblasts / osteoprogenitor cells
  • Alternatives
    • Active area of research due to desirability in human field
    • No risk of disease transmission
    • No morbidit
    • Ready availability
  • Synthetic osteoinductive agents
    • Bone morphogenic proteins
    • Deminaralised bone matrix
    • Parathyroid hormone gene
  • Synthetic osteoconductive agents
    • Beta tricalcium phosphate (lots of products)
  • Mesenchymal stem cell based techniques
  • Gene therapy (BMP, VEGF)

Equine Final Year (102 decks)

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