Bone grafts and open fractures

Question 1

Most common types of bone graft used in small animal orthopaedics

Answer 1

Cancellous autograft

Question 2

Autograft

Answer 2

From the same animal

Question 3

Allograft

Answer 3

From a different animal of the same species

Question 4

Xenograft

Answer 4

Graft from a different species

Question 5

Functions of a bone graft

Answer 5

Osteoinduction - recruitment of osteogenic cells

Osteoconduction - providing a scaffolding structure for bone to grow onto or into

Osteogenesis - graft contains live cells capable of producing bone

Question 6

Where is a cancellous bone graft most commonly collected from

Answer 6

Proximal humerus or iliac crest

Medial tibia and greater trochanter can also be used

Question 7

Why is a cancellous bone graft used?

Answer 7

To stimulate bony union
To fill bone cysts
Arthrodeses
Delayed or non-union fractures
Treatment of osteomyelitis
Enhancement of vascularisation of cortical grafts

Question 8

Autogenous cancellous bone graft

Answer 8

Most convenient, inexpensive, non-immunogenic

Harvested from proximal humerus, proximal tibia, greater trochanter, ilial wing

Can be unrewarding in small patients

Cells die rapidly, store for as little time as possible

Blood soaked swab is the best medium

Question 9

Indications for use of a cortical bone graft

Answer 9

treatment of multifragmented diaphyseal long-bone fractures

limb lengthening procedures

management of malunion or non union fractures

limb salvage procedures for primary bone tumours

after resection of a radial osteosarcoma

graft in vertebral fusion - wobblers

arthrodesis

RARELY USED

Question 10

limitations of cortical bone grafts

Answer 10

Cortical autografts - only a limited amount of bone can be taken without compromising the donor site

Cortical allografts –a healthy donor needs to be euthanased

Bone is usually collected under aseptic conditions and stored in the freezer (-70°C)

Viable cells are rejected so there is no osteogenesis

The cortical grafts are revascularised much more slowly than cancellous grafts

Its strength gradually declines as a result of osteoclastic resorption

Do not completely incorporate and remain as mixtures of necrotic and viable bone.

Question 11

Freeze dried cancellous bone chips

Answer 11

commercially available allograft

Some osteoinduction

Good osteoconduction

No osteogenesis

Question 12

Demineralised bone matrix

Answer 12

Commercially available

Cortical allograft is morselized, cleaned, and decalcified

The decalcifation process exposed the proteins, making the graft more osteoconducive

Good osteoinduction

Good osteoconduction

No osteogenesis

Question 13

Bone morphogenic protein (BMP)

Answer 13

Group of cytokines

Recombinant human BMP (rhBMP) is available

Used off label as an alternative to bone graft

Good osteoinduction

No osteoconduction

No osteogenesis

Question 14

When should radiographs be taken in the assessment of fracture healing?

Answer 14

after 4 weeks, and then every 4 weeks until healing is documented

Question 15

Four As in radiographic evaluation of fracture healing

Answer 15

Activity – evidence of bone healing and callus formation

Alignment – the alignment of the joint above and below of the fractured bone should be unchanged since the surgery

Apposition – only concerns ‘reducible’ fractures- the apposition of the bone on the fracture site should be unchanged

Apparatus – the implants used should not have changed, e.g. not have moved, bent or broken

Question 16

Gustillo-Anderson classification of open fractures - grade I

Answer 16

A small puncture wound caused by a bone end penetrating skin from the inside-out, without skin loss – if animals with grade I injuries are presented within a few hours of they may be treated in a similar manner as a closed fracture.

<1cm wound.

Question 17

Gustillo-Anderson classification of open fractures - grade II

Answer 17

Larger skin wound caused by external trauma with loss of skin. Contamination and soft tissue injury greater than with a grade I injury.

> 1cm wound.

Question 18

Gustillo-Anderson classification of open fractures - grade III

Answer 18

Extensive skin and soft tissue damage. Often associated with severe comminuted fractures and risk of complications high.

Can be further classified based on damage to periosteum and neurovascular structures

Question 19

Initial stabilisation of an open fracture

Answer 19

Triage the patient - ABC

Pain relief

Manage life threatening conditions

Haemostasis is rarely required but may be a priority

Question 20

Systemic antibiotic therapy in an open fracture

Answer 20

Early intravenous antibiotic administration in humans has demonstrated a massive reduction in infection rates

Ideally antibiotics are given within 3 hours of the injury

Must be intravenous

Broad spectrum - consider the likely contaminants

Question 21

Emergency open fracture care

Answer 21

1. Haemostasis
2. Cover wound with a sterile dressing whilst preparing for lavage
3. Wear sterile gloves (& hat, mask, gown)
4. Apply water soluble gel or saline soaked swabs to the wound
5. Clip away hair, working from the wound outwards if possible. Clean skin using diluted chlorhexidine.
6. Flush wound with copious amounts of sterile saline to remove debris & dilute bacteria
7. Take a deep bacterial swab for culture
8. Apply a sterile dressing & bandage

Question 22

Osteoconduction

Answer 22

the three dimensional process of in-growth of capillaries, perivascular tissues and osteoprogenitor cells (mesenchymal cells) from recipient bed into the structure of graft.

The trabeculae act as a scaffold over which host elements migrate.

Question 23

Osteoinduction

Answer 23

The recruitment and differentiation of fibroblast-like mesenchymal cells or pluripotential cells into osteoclasts and blasts induced by contact with the bone matrix.

Bone produces many growth factors that act as potential determinants of local bone formation. E.g. the bone morphogenetic protein (BMP).

Question 24

Osteogenesis

Answer 24

A function of donor cells that survive the transplant (possibly only about 10% will survive). Those that survive are critical in the early stages (first 6-8 weeks) of bone healing.

Question 25

What dressing should you use for a small puncture wound, clean laceration, or superficial wound?

Answer 25

Non-adherent dressing prior to bandaging

Question 26

What dressing should you use for a contaminated or infected wound?

Answer 26

Wet-to-dry to aid in suerficial debridement

Question 27

What is the period of time that is crucial for surgical stabilisation of open fractures?

Answer 27

24 hrs

Wound treatment should be carried out ASAP though

Question 28

Debridement in open fractures

Answer 28

Devitalised tissue should be removed with minimal debridement of tendon, ligament, blood vessels, nerves and bones.

Fat, and muscle (and skin) can be aggressively debrided.

Serial debridements may be necessary and better than performing radical debridement on day one.

If tissue viability is dubious then it is better to perform minimal debridement & then reassess the following day & then debride only if it becomes definitively necrotic.

Question 29

Fixation methods for open fractures

Answer 29

External Skeletal Fixation should be considered and is often the primary choice.

External Coaptation is rarely ideal

ORIF ( = OPEN REDUCTION and INTERNAL FIXATION) may be preferable in some cases particularly with simple fractures and grade I open fractures.

Question 30

Summary of how to deal with an open fracture

Answer 30

Look for and manage associated injuries - life before limb

IV broad spectrum antibiotics immediately and continued as per data sheet

Sedation is essential for appropriate irrigation

Wide clip and clean

Copious irrigation

Protect the wound