Fracture Healing Flashcards
What type of CT is bone?
Bone is is a specialised form of dense connective tissue
List 3 mechanical functions of bone
- skeleton rigidity
- function as attachment and lever for muscle
- supports the body against gravity
What is the chemical function of bone
Calcium homeostasis and metabolism
What is the haematological function of bone
Bone marrow manufactures stem cells and other substances, which in turn produce RBCs
Compare and contrast the 3 macroscopic types of bone
- Trabecular (cancellous/spongy) bone ➞ sponge like network
* located at ends of long bones - 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
- Woven bone ➞ Immature, disorganised bone
- absent from normal bone after age 4
- seen in fracture callus in both children and adults
Compare and constrast the 3 types of bone cells
- Osteoblasts
- formation, organization and mineralisation of bone ECM
- synthesis of collagen and other bone proteins
- Osteocytes ➞ similar to nerve cells
- regulates response of bone to mechanical environment
- Intercellular communication via canaliculi
- Osteoclasts
- responsible for resorption of bone matrix (osteoid)
- large motile, multinucleated cell
Describe the constituents of bone
Organic component (40% dry weight of bone)
- Collagen (90%)
- Proteoglycans
- Matrix Proteins
- Cells
Inorganic component (60% dry weight of bone)
- Calcium Hydroxyapatite
- Osteocalcium Phosphate
What component of bone provides compressive strength?
Calcium Hydroxyapatite (Inorganic component)
List the 4 sources of blood supply to bone AND where each supplies
- Nutrient artery system ➞ inner 2/3 of cortex from within (endosteal)
- Periosteal system ➞ outer 1/3 of cortex
- Metaphyseal system ➞ ‘zone of provisional calcification’ in physis
- Epiphyseal system ➞ supplies physis by diffusion
Vessels from which system contribute to endochondral ossification in children?
Nutrient artery system - in the child, these vessels end on metaphyseal side of the physis and contribute to endochondral ossification
The Metaphyseal system anastomoses with which other system?
The nutrient artery system
Which system supplies blood to the femoral and radial heads?
Epiphyseal system
Why is blood supply to the femoral and radial heads tenuous?
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
List the 3 stages of fracture healing
- Inflammatory response
- Reparative response
- Remodelling
What occurs during the Inflammatory response of fracture healing (Incl timeframe)|
Time of injury to 24-72 hours
- Injured tissues + platelets release vasoactive mediators, growth factors and other cytokines
- These cytokines influence cell migration, proliferation, differentiation and matrix synthesis
- growth factors recruit fibroblasts, mesenchymal cells and osteoprogenitor cells to fracture site
- Macrophages, PMNs and mast cells (48hr) arrive at fracture site to begin process of removing the tissue debris
What occurs during the reparative response of fracture healing (Incl timeframe)|
2 days to 2 weeks
- vasoactive substances cause neovascularisation and local vasodilation
- undifferentiated mesenchymal cells migrate to fracture site and form cells which in turn form cartilage, bone or fibrous tissue
- the fracture haematoma is organised, fibroblasts and chondroblasts appear between bone ends and cartilage is formed
What occurs during Remodelling of fracture healing (Incl timeframe)
Middle of repair phase up to 7 years (most occurs in 1st year)
- osteoclasts resorb bone and the resulting hole is filled by osteoblasts with new bone and osteocytes
- fracture healing is complete when there is repopulation of the medullary canal
What is remodelling of woven bone dependant on?
What ‘law’ does this follow
Remodelling of the woven bone is dependent on the mechanical forces applied to it
Wolff’s Law - ‘form follows function’
List 4 local and 4 systemic factors which affect fracture healing
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?
inversely proportional
fractures fixed with rigid compression plates permits almost no movement resulting in primary bone healing with little or no visible callus formation
Bone is viscoelastic, what does this mean?
time dependent property where the deformation of the material is related to the rate of loading
Bone is anisotropic, what does this mean?
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
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
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
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
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
What is a bending force and, what fracture results?
Explain the mechanics of this
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
When a torsion force is applied to bone, what fracture results?
Explain the mechanics of this
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
List 5 surgical treatment options for fractures
- Plaster fixation and Traction
- Bone Screw
- Plates
- Intra-Medullary Nails
- External Fixation
What are the 2 types of screws used in surgical treatment of a fracture?
CHECK THIS - are wood screwes even used?!
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
Give 2 benefits and 3 disadvantages of ‘plates’ in the surgical treatment of fractures
Benefits:
- anatomical reduction of the fracture with open techniques
- stability for early function of muscle-tendon units and joints
Disadvantages:
- risk of bone refracture after their removal
- stress protection and osteoporosis beneath a plate
- plate irritation
What are the 2 types of Intra-Medullary nails and what is the benefit to using these
Reamed or unreamed
Preserves soft tissues
Give 4 advantages and 4 disadvantages to using external fixation
Advantages
- apply quickly
- allows adjustment
- soft tissues not disturbed
- access to wounds
- joints can be mobilised
Disadvantages
- pin tract infection
- malunion
- patient compliance required
List the steps of wound management (8)
- ATLS Protocols
- Assess NV status of the limb
- Swab wound
- Photograph and Cover wound
- Give Tetanus prophylaxis and IV antibiotics
- Operative debridement and copious irrigation (within 6 hrs)
- Stabilisation of the fracture (reduces rates of infection)
- Coverage and closure of the wound (by 5-7 days)
What is the Gustillo Anderson Classification?
Most commonly used classification system for open fractures
List the criteria of the Gustillo Anderson Classification
What are physeal Injuries?
Injuries Involving the growing region of childs bone (epiphyseal growth plate)
Give 2 complications of physeal injuries
Why must we be concerned about these
Non-union and Mal-Union
Can risk premature growth arrest and deformity of growth if not accurately reduced
What is Compartment Syndrome?
When circulation and function of tissues within a closed space are compromised by an increased pressure within that compartment
Give 4 clinical features of compartment syndrome
- Pain out of proportion to the injury
- Pain on passive stretching of the involved compartment (cardinal sign)
- Pallor
- Pulselessness
- Paralysis
- Paraesthesia
(Last 4 appear very late and we should not wait for these)
How do we diagnose compartment syndrome?
Intra-compartment pressure measurement
- Normal compartment pressure is zero
- Value above 40mmHg or within 40mmHg of diastolic is diagnostic
How do we treat compartment syndrome?
- Split bandages / POP down to skin
- Fasciotomy – urgent surgical decompression of the involved compartments
What is the biggest concern following long bone and pelvic fractures?
How would this present?
Fat embolism syndrome (high index of suspicion needed)
Presents with pulmonary and neurologic manifestations combined with petechial hemorrhages - often fatal
Aside from the fracture itself, when else must we be concerned about FES
Surgery - FES is associated with movement of unstable bone fragments and reaming of the medullary cavity during placement of an internal fixation device
What is the most effective prophylactic measure and treatment for Fat embolism syndrome
Most effective prophylactic measure is to reduce long bone fractures ASAP after injury + supportive treatment
