Transcript Spine Biomechanics

Fracture Fixation
Internal & External
Fracture Types
http://health.allrefer.com/health/bone-fracture-repair-fracture-types-1.html
Influencing Healing
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Systemic Factors
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Age
Hormones
Functional activity
Nerve function
Nutrition
Drugs (NSAID)
http://www.orthoteers.co.uk/Nrujp~ij33lm/Orthbonefracheal.htm
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Local Factors
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Energy of trauma
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Degree of bone loss
Vascular injury
Infection
Type of bone fractured
Degree of immobilization
Pathological condition
Stages of Fracture Healing
1.
Inflammation & Hematoma
Osteoprogenitor cells, Fibroblasts
2.
Callus Formation
Periosteal and Endosteal
Fibro-cartilage differentiation
3.
Woven Bone
Substitution of avascular and necrotic tissue
Haversian remodeling
4.
Remodeling
Lamellar or trabecular bone
Restoration of continuity and ossification
Bone union
**When compression is applied via implant, these stages are minimized**
http://www.orthoteers.co.uk/Nrujp~ij33lm/Orthbonefracheal.htm
http://www.ivis.org/special_books/ortho/chapter_03/03mast.asp?Type=IPRP&LA=1
Healing Complications
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Most often due to severe injury
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Energy dissipation to bone and soft tissue results in
damage to blood supply
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Compartment syndrome
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Severe swelling resulting in decreased blood supply can cause the
muscles around the fracture to die
Bad osmotic pressure lets blood out instead of across damaged muscle
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Neurovascular injury
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As pressure remains high, blood cannot get to damaged muscle
Arteries and nerves around the injury site are damaged
Infection
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Imbalance of bacteria and body’s ability to cope with it when amount of
necrotic tissue and contraction of bacteria are not being cleared (by
surgeon or patient)
http://www.hughston.com/hha/a.fracture.htm
Healing Complications (Cont’d)
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Delayed union
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Nonunion
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Abnormal alignment
Post-traumatic arthritis
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Failure to heal
Malunion
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Extended healing time
Fractures that extend into the joints can cause premature arthritis of a
joint
Growth abnormalities
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A fracture through an open physis, or growth plate, could result in
premature partial or complete closure of the physis; Part or all of a
bone will stop growing unnaturally early
http://www.hughston.com/hha/a.fracture.htm
Treatment
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When will a cast suffice?
Fracture is stable
 Patient preference
 No complications (Ex.-infection, burn)
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When is fixation necessary?
Fracture is unstable
 Quick Mobilization
 Occupation
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Athletes
http://www.defence.gov.au/dpe/dhs/infocentre/publications/journals/NoIDs/ADFHealthApr01/adfhealthapr01_2_1_24-28.pdf
Principles of fracture fixation
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Obtain and maintain alignment
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Reduction
Transmission of compressive forces
Minimum motion across fracture site
 Achieve stability
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Avoid tensile/ shear/torsion forces
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Across fracture site
Prevent motion in most crucial plane
Fixation: Internal vs. External
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Internal
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Plates, screws, etc. completely within the body
Less expensive
Types
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Comminuted – nail with interlocking screw
Transverse or Oblique –plates or screws
External
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Pins coming through skin interconnected by external
frame
Has complications
http://www.defence.gov.au/dpe/dhs/infocentre/publications/journals/NoIDs/ADFHealthApr01/adfhealthapr01_2_1_24-28.pdf
Internal Fixation
http://www.nlm.nih.gov/medlineplus/ency/imagepages/18023.htm
Internal Fixation Priciples
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Rigid, anatomic fixation
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Allows an early return to function
Reserved for those cases that cannot be
reduced and immobilized by external
means
Open reduction of a fracture
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Good blood supply to undisturbed tissues
http://www.umm.edu/ency/article/002966.htm
Physiological Response to IF
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Primary healing
Minimal extramedullary callus
 Minimal intra-medullary callus
 Sub-periosteal
 Rapid
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Related to motion
Crosses miniature gaps
 Depends on soft tissue viability
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Stress Concentrations
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Geometric discontinuities (hole, base of
threaded screw, corner)
Local disturbance in stress pattern
 High stresses at site of discontinuity
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Drilling a hole reduces the bone strength
by 10 – 40 %
Types of IF Devices
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Lag screws
Kirschner wire
Wire loop
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Tension band wiring
Combination of wire loop and screw
Combination of Kirschner and wire loop
Plate
Intramedullary rods and nails
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Interlocking screws
Hemi-Arthroplasty
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In the hip, used for
femoral neck fractures
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Avascular necrosis
Fractures of the proximal
humerus
Early mobilization is
facilitated
http://www.orthogastonia.com/patient_ed/html_pages/hip/hip_hemiarthrooplasty.html
Bilboquet Device
http://www.maitrise-orthop.com/corpusmaitri/orthopaedic/100_bilboquet/bilboquet_us.shtml
Problems in IF
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Infection
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Delayed union
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Non-union
External Fixation
http://www.nlm.nih.gov/medlineplus/ency/imagepages/18021.htm
External Fixation
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Method of immobilizing fractures
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Employing percutaneous pins in bone
attached to
Rigid external metal
 Plastic frame
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For treatment of open and infected
fractures
Indications for EF
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Open grade III fractures
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Compound tibia fractures
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Generally from motorcycle injuries
Gunshot wounds
Major thermal injuries
Open fractures associated with polytrauma
Management of infected nonunions
Forces in an External Fixator
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Compression
Neutralization
Distraction
Angulation
Rotation
Translation or displacement
Compression
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For transverse
fractures
Adds stability
at nonunion
site
Neutralization
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For comminuted
fracture
Compression may
lead to excessive
shortening
Used to maintain:
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Length
Alignment
Stability
Distraction
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For distal
metaphyseal or
intra-articular
injuries
Same principle of
traction
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Distraction of
fragments
Alignment of injury
Angulation
A – unacceptable alignment B – loosening clamps; loss of distr. and compr. force
C – after frames completely loosened; angulation is corrected
D - compression on distraction forces are reapplied
Rotation
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Exert rotational
force
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Along longitudinal axis
Release of forces
first
Can be done with
repositioning pins
Most of present
frames cannot apply
rotational forces
Translation or Displacement
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Volkov apparatus
Double ring unit
 Moves one ring in
parallel to other
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For translation
Types of EF Devices
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Unilateral
Bilateral
Triangular
Quadrilateral
Semicircular & Circular ring
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Ilizarov
http://www.ilizarov.org.uk/content.htm
Unilateral EF
Bilateral EF
Triangular EF
Quadrilateral EF
Semicircular and Circular EF
Advantages of EF
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Easy application
Good stability
Excellent pain relief
Adjustable
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Alignment, Angulation, Rotation
Access to open wounds
Frequent dressing change
 Monitoring of damaged tissue
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Disadvantages of EF
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Application may cause soft tissue damage
Lacks advantages of cyclic loadings as
seen in casts
Constrained in time
Pins may drain
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Infection
The End
Granulation
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Tissue damage repair
begins with growth of
new capillaries
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Red dots are new
clusters of capillaries
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Bleed easily
Bright red tissue of a
healing burn is
granulation tissue
http://medweb.bham.ac.uk/http/depts/path/Teaching/FOUNDAT/repair/grantiss.html
Hematoma
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Blood collection localized to an organ or tissue
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Usually clotted
Example: Contusions (bruises), black eye, blood
collection beneath finger or toenail
Almost always present with a fracture
http://www.healthscout.com/ency/68/677/main.html
Fibrocartilage
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Cartilage with a fibrous matrix and approaching
fibrous connective tissue in structure
Produced by fibroblasts
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Forms in areas where size of the fracture gap is 1mm
or greater
Subsequently replaced by bone
Mechanical properties inferior to other types of
cartilage
Contains:
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Large amounts of collagen type I
Reduced amounts of proteoglycans
Collagen type II, found only in cartilage
http://www.vetmed.ufl.edu/sacs/notes/Cross-Healing/page9.html http://wberesford.hsc.wvu.edu/histolch6.htm
http://www.nuigalway.ie/anatomy/wilkins/practicals/bone/html/bone_1.html
http://www.bm.technion.ac.il/courses/336529/web/Cartilage/major%20types.htm
Inflammation & Hematoma
http://www.ivis.org/special_books/ortho/chapter_03/03F2.jpg
Inflammation & Hematoma
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Inflammation begins immediately after a fracture
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Initially consists of hematoma and fibrin clot
Hemorrhage and cell death at location of
fracture damage
Fibroblasts, mesenchymal cells, osteoprogenitor
cells appear next
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Formation of granulation tissue
Ingrowth of vascular tissue
Migration of mesenchymal cells
http://www.aans.org/education/journal/neurosurgical/apr01/10-4-1.pdf
Simon, SR. Orthopaedic Basic Science. Ohio: American Academy of Orthopaedic Surgeons; 1994.
Inflammation & Hematoma (Cont’d)
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Primary nutrient and oxygen supply provided by
exposed cancellous bone and muscle
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Use of anti-inflammatory or cytotoxic medication
during first week may alter the inflammatory
response and inhibit bone healing
http://www.healthscout.com/ency/68/677/main.html
Callus Formation
http://www.ivis.org/special_books/ortho/chapter_03/03mast.asp?Type=IPRP&LA=1
Callus Formation
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Begins when pain and swelling subside
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Ends when bone fragments are immobilized by
tissue
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Size inversely dependent on immobilization of
fracture
Mesenchymal cells form cells which become
cartilage, bone, or fibrous tissue
Increase in vascularity
Stable enough to prevent deformity
Callus does not appear on x-ray images
http://www.orthoteers.co.uk/Nrujp~ij33lm/Orthbonefracheal.htm
Simon, SR. Orthopaedic Basic Science. Ohio: American Academy of Orthopaedic Surgeons; 1994.
Mechanical Role
 Enlarge diameter at fracture site
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Reduces mobility
Reduces resulting strain
Granulation Replaces Hematoma
Granulation differentiates into
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Connective tissue
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Random orientation of collagen fibrils
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Their direction reflects the direction of tensile forces
Fibrocartilage
Deformation of Callus
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Strength of initial
reparative tissue is low
If forces surpass the
strength of callus
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Unstable fracture
Functional load deforms
fracture
Fracture fixation is
recommended
Woven Bone
Woven Bone
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Callus changes from cartilaginous tissue to
woven bone
Callus mineralized but internal architecture is not
fully matured/arranged
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Connective tissues and fibrocartilage thickens
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Osteon organization is not complete
Fracture becomes increasingly stable
Mineralization is sensitive to strain
Mechanically stable scaffold
Increased strength and stiffness with increase of
new bone joining fragments
Simon, SR. Orthopaedic Basic Science. Ohio: American Academy of Orthopaedic Surgeons; 1994.
Bone Remodeling
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Woven bone becomes lamellar bone
Bone union occurs at fracture gap
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Callus gradually reabsorbed by osteoclasts
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Replaced by bone
Medullary canal reconstitutes
Begins within 12 weeks after injury
May last several years
http://www.glaciermedicaled.com/bone/bonesc3p2.html
Simon, SR. Orthopaedic Basic Science. Ohio: American Academy of Orthopaedic Surgeons; 1994.
Mesenchymal Cells
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Source of cells for new bone production
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Derived from bone marrow cells
Intramembranous bone formation
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Formation of bone directly from mesenchymal cells
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Cells become osteoprogenitor cells then osteoblasts.
Development of Cartilage model
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Mesenchymal cells form a cartilage model of the bone
during development
http://www.grossmont.edu/shina.alagia/lectures/144/Bone%20physiology.ppt
http://www.ecmjournal.org/journal/supplements/vol005supp02/pdf/vol005supp02a07.pdf
Fracture Stability
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Direction of fracture & material (type of bone)
define stability
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Stable
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Definition of direction of force important
Fissure (Hairline) – not complete break, minimal
trauma
Greenstick – crack on outside of “bend”
Unstable
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Comminuted – many bone fragments
Oblique – break at an angle
Spiral – corkscrew-like crack pattern
http://pain.health-info.org/Pain%20Pages/fractures.htm
Lag Screw
Lag Screw
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Stability
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Exerts inter-fragmentary
compression
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Static compression
Distal head must be
engaged
Screw Holding Force
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Increase in area of bone
within screw threads
Decrease in pilot hole
size
Increase in length of
engaged threaded
portion
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Area available to resist
shear
Kirschner Wire
Kirschner Wire (Cont’d)
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Rotational stability
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May be a problem
Anchorage to tension band
Twisting of wires on both sides
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Almost equally distributed compression
Tension Band
Tension Band (Cont’d)
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Dynamic compression
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When tension applied
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Compressive forces are at the fracture site
Used
Substitutes torn ligaments & tendons
 Allows injured ligaments to heal
 When fragments too small to be screwed
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http://www.wheelessonline.com/o2/1536.htm
Tension band & Screw
Tension Band & Screw
Plating of Vertebral Column
Vertebral Column
Intramedullary Pin
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Types
Open
 Closed
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3-point fixation
End fixed in epiphyses
Intramedullary Pin (Cont’d)
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Stability is dependant
on
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Friction / pressure
between
Deformable nail (elastic
recoil)
 Endosteal surface of
medullary canal
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Fracture “personality”
Intramedullary Pin (Cont’d)
Blood
supply is from the medullary canal
Compromised
More
by intramedullary fixation
care has to be taken
Open Fracture
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Bone ends have penetrated through and
outside skin
Important features
Polytrauma victims
 Varying soft tissue damage
 Contaminated wound
 Requires emergency treatment
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Types of Open Fracture
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Type I – Low Energy
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Type II
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Puncture wound (1 cm dia. or lesser)
Not much soft tissue contusion
Usually simple transverse, short oblique fracture
No crushing component
Laceration (more than 1 cm long )
Not extensive soft tissue damage
Not severe crushing component
Type III – High Energy
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Extensive damage to soft tissue
High velocity injury or severe crushing component
Type I
Type II
Type III