Bone grafts and open fractures Flashcards
Most common types of bone graft used in small animal orthopaedics
Cancellous autograft
Autograft
From the same animal
Allograft
From a different animal of the same species
Xenograft
Graft from a different species
Functions of a bone graft
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
Where is a cancellous bone graft most commonly collected from
Proximal humerus or iliac crest
Medial tibia and greater trochanter can also be used
Why is a cancellous bone graft used?
To stimulate bony union
To fill bone cysts
Arthrodeses
Delayed or non-union fractures
Treatment of osteomyelitis
Enhancement of vascularisation of cortical grafts
Autogenous cancellous bone graft
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
Indications for use of a cortical bone graft
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
limitations of cortical bone grafts
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.
Freeze dried cancellous bone chips
commercially available allograft
Some osteoinduction
Good osteoconduction
No osteogenesis
Demineralised bone matrix
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
Bone morphogenic protein (BMP)
Group of cytokines
Recombinant human BMP (rhBMP) is available
Used off label as an alternative to bone graft
Good osteoinduction
No osteoconduction
No osteogenesis
When should radiographs be taken in the assessment of fracture healing?
after 4 weeks, and then every 4 weeks until healing is documented
Four As in radiographic evaluation of fracture healing
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
Gustillo-Anderson classification of open fractures - grade I
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.
Gustillo-Anderson classification of open fractures - grade II
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.
Gustillo-Anderson classification of open fractures - grade III
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
Initial stabilisation of an open fracture
Triage the patient - ABC
Pain relief
Manage life threatening conditions
Haemostasis is rarely required but may be a priority
Systemic antibiotic therapy in an open fracture
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
Emergency open fracture care
- Haemostasis
- Cover wound with a sterile dressing whilst preparing for lavage
- Wear sterile gloves (& hat, mask, gown)
- Apply water soluble gel or saline soaked swabs to the wound
- Clip away hair, working from the wound outwards if possible. Clean skin using diluted chlorhexidine.
- Flush wound with copious amounts of sterile saline to remove debris & dilute bacteria
- Take a deep bacterial swab for culture
- Apply a sterile dressing & bandage
Osteoconduction
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.
Osteoinduction
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).
Osteogenesis
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.
What dressing should you use for a small puncture wound, clean laceration, or superficial wound?
Non-adherent dressing prior to bandaging
What dressing should you use for a contaminated or infected wound?
Wet-to-dry to aid in suerficial debridement
What is the period of time that is crucial for surgical stabilisation of open fractures?
24 hrs
Wound treatment should be carried out ASAP though
Debridement in open fractures
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.
Fixation methods for open fractures
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.
Summary of how to deal with an open fracture
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
