Fractures--intro, internal & external fixators Flashcards Preview

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Flashcards in Fractures--intro, internal & external fixators Deck (97)

What is the difference between stress and strain?

  • Stress = external force applied to any cross-sectional area (cause)
  • Strain = deformation of a loaded material as compared to its original form (effect)


Define stiffness

Material's ability to resist applied force


What is tensile strain?

Force pulling two ends of bone apart


What is compressive strain?

Force pushing inwards


What is shear strain?

Force pushing laterally in opposite directions on the top and bottom; pushes bone into diagonal shape


How does bending strain occur?

Combination of tensile and compressive loading forces


How does torsion strain occur?

Combination of compressive, tensile, and shear loading forces; twisting force


What is the definition of deformation?

Change in shape due to application of a force (stress)


What is the difference between plastic and elastic deformation?

  • Elastic--reversible change in shape
    •  Material returns to original shape when force is removed
  • Plastic--permanent change in shape


How might elastic and plastic deformation properties come into play when thinking about implants for fracture repair?

  • Want to adjust stiffness of implants based on how likely it is for the bone to deform
  • Ex: 
    • High porosity cancellous bone has a longer elastic phase and low yield point-->want to make sure the yield point isn't reached-->need more fixation
    • Low porosity cortical bone has a steep and short plastic phase so it takes a high degree of stress to reach the yield point-->probably don't need as rigid fixation


What is a yield point?

Point where material begins to deform plastically. Strain exceeds the material's ability to recover rending it permanently deformed.

Occurs between elastic and plastic deformation


What is a failure point?

Point where material cannot withstand anymore strain and fails (breaks)


What are the characteristics of a type I fracture grade?

  • Least severe
  • Wound < 1cm
  • Typically created by bone fragment from inside that retracts back through skin
  • Mild/moderate soft tissue contusion
  • Might be more hesitant to place implants due to risk of infection


What are the characteristics of a type II open fracture?

  • Open wound > 1cm in size
  • Wound usually from external source
  • Mild soft tissue trauma w/o excessive soft tissue damage or loss
  • No flaps or avulsions


What are the characteristics of a type III open fracture?

  • IIIA
    • Adequate soft tissue for wound closure
    • Large ST laceration/flap
  • IIIB
    • Extensive loss of ST
    • Bone exposure
    • Stripped periosteum
  • IIIC
    • Arterial +/- nerve supply to distal limb compromised
    • Requires microvascular anastomosis or amputation
    • Most owners will elect for amputation at this point


Which fracture is more severe: open or closed?

Open fractures are more severe than closed due to risk of infection


What is the first priority when assessing and initially treating an open fracture?

Systemic stabilization is first priority

  • Cover wound with sterile dressing and evaluate better once patient is stable
    • Nosocomial organisms far more virulent than what already exists in wound


Once the patient is stable, what should be done for assessment/initial treatment of an open fracture?

  • Wear gloves
  • Assess tissue damage and vascular nerve supply
  • Assess neurovascular status of distal limb
  • Image
  • Clean wound, collect culture, and start treatment with Cefazolin in case of type I or II


Know which fracture type is which!


Know this chart!


Know Salter Harris:

Huck's remembrance device:

Prison Makes Every Boy Crazy

(physis, metaphysis, epiphysis, both physis & epiphysis, crush)


Why are salter harris fractures more concerning than fractures not involving the physis?

Salter Harris fractures can lead to growth abnormalities in young animals even after the fracture has healed


What are the goals of fracture fixation?

  • Restore length and alignment to promote normal bone healing and limb function
  • Minimize motion at fracture ends
    • Fracture ends rubbing against each other will lead to erosion and resorption
  • Permit early ambulation with use of as many joints as possible during healing period


What is Wolff's Law? What needs to be balanced?

  • Bone needs to withstand forces to permit healing
  • Balance the forces that promote bone healing vs. those that promote bone resorption


What are the pros of internal fixation?

  • Variety of fixation options to promote stable repair
  • Can promote normal muscle/joint function during bone healing
  • Typically fewer rechecks than with external fixation and external coaptation
  • Nothing external to monitor


What are the cons of internal fixation?

  • Expense
  • Requires training for appropriate application
  • May require second surgery for explatation in the case of infection or discomfort


What are the pros of external coaptation?

  • Limited supplies necessary for placement
  • Need for specialized training is limited
  • Avoids prolonged surgical procedure


What are the cons of external coaptation?

  • Requires frequent rechecks and bandage changes
  • Can only be utilized for very specific fractures
  • Risk of bandage morbidity  preventing continued use
  • Immobilized joints


Why is Wolff's law important when considering fracture fixation? How does the chosen implant/fixation method relate to Wolff's Law with regards to fracture healing?

Wolff's Law states that bone remodels based on the forces that are applied.

When fixing bone, must balance so that fixators will stabilize bone and maintain fixation but will still allow bone to bear force so that it will be able to heal and not be resorbed


What factors must be considered before choosing external coaptation as a fixation method?

  • Below the knee and elbow
    • Minimally displaced and amenable to reduction
    • Transverse, simple, closed
    • Greenstick
    • Non-articular
  • Expected to heal rapidly


Which types of fractures are not amenable to external coaptation?

Articular and open fractures

NEVER EVER EVER cast an open fracture!!!


What are the two approaches for internal fixation?

Open anatomic reduction/reconstruction

Biological osteosynthesis


What are the fundamental differences between open anatomic fracture reduction/reconstruction and biological osteosynthesis?

  • Anatomic fracture reduction
    • Primary bone healing (< 1mm gap at fracture ends)
    • Perfect bone reconstruction
    • Rigid fixation (2% strain) w/ compression at bone ends
  • Biological osteosynthesis
    • Avoid disruption of fracture hematoma (minimal iatrogenic trauma)
    • Less rigid fixation
    • Secondary healing


What fracture types MUST be repaired with anatomic reduction? Which type can NEVER be repaired with anatomic reduction?

  • MUST repair articular fractures with anatomic reduction
  • NEVER repair highly comminuted fractures via anatomic reduction


Which fractures is anatomic reduction most appropriate for?

Most appropriate for repair of transverse, oblique, segmental, and minimally comminuted fractures


What are the 4 factors that should be considered when choosing implants for fracture fixation?

  • Fracture type & location
  • Bone affected
  • Patient factors
  • Surgeon preference/experience


What aspects of fracture type and location influence choosing implants for fracture fixation?

  • Forces acting on bone
  • Articular vs. metaphyseal vs. diaphyseal
  • Comminuted vs. simple
    • Comminuted: fixture must act as bone until bone gets strong enough to not collapse under force


What patient factors influence the choice of implants for fracture fixation?

  • Age
    • Old bones won't heal quickly-->need rigid fixation
    • Young bones heal very quickly and are still growing-->too much rigidity can lead to resorption
  • Comorbidities
  • Environment
  • Size/weight of patient


How does a LC-DCP differ from a DCP plate?

  • LC-DCP is different from DCP because:
    • Has a contoured underside
      • Stress more evenly distributed along plate with less stress at the screw hole
      • Plate is less likely to break at the screw hole (can leave on empty, unlike DCP plates)
      • Less contact with bone = less disruption of periosteal vascularity


How can LC-DCP and DCP plates be used to achieve compression at the level of the fracture?

  • As screws are tightened to the plate it draws the fracture ends closer together
  • Screw holes designed to allow screw placement that promotes compression of fracture ends
  • Oval screw holes allow for angulation
  • All plate surfaces are flat-->fraction between bone and plate creates stability 


What types of fractures are amenable to being compressed without risking displacement or further bone damage?

Non-comminuted fractures


Short oblique


Why must conventional plates be perfectly contoured to the bone on which they are applied?

Why is this not the case for locking plates?

Most conventional plates work by creating friction between the plate and bone--the plate stabilizes the bone and forces are transmitted through the plate to the bone so they must be in close contact.

Locking plates don't need contact with bone.  This is because the stability comes from the purchase of the screw in the bone and the head of the screw being locked into the plate


What bone types are locking plates better for?

Osteoporotic bone

Soft bone

Comminuted fractures


T/F: Locking plates are used most comminly in MIPO



What is a lag screw and how is it used in fracture repair?

  • Placed perpendicular across an oblique or sagittal fracture line to promote compression of the fracture ends
    • Can use a cortical or partially threaded screw
    • Glide hole drilled in near cortex
      • Far cortex (trans cortex) is drilled to the core for the core diameter of the screw
  • Tightening the screw pulls the trans cortex closer to the cis cortex-->compression
  • Can be placed through conventional screw holes


Which fractures are lag screws used for?

Certain articular fractures

Oblique fractures


How are position screws different from lag screws? Which is stronger?

  • Screw placed across a fracture line to hold fragments in place
  • No compression across the fracture is achieved
  • Weaker repair compared to lag screw


What characteristics of cancellous bone screws make them better for use in cancellous bone/metaphyseal bone compared to cortical screws (i.e. why does the cancellous screw have improved pull out strength)?

  • Cancellous screws have a smaller core diameter but a larger outer diameter due to having larger threads and a longer pitch
  • Since core diameter determines bending strength and outer diameter determines pull-out strength, this means cancellous screws are less likely to be pulled out and cortical screws are less likely to bend
  • Cancellous bone is softer--need the extra pull-out strength

(Insert that's what she said/pull-out game strong joke)


Which of the 3 types of screws discussed (cortical, cancellous, locking) is the strongest against bending stress?

Locking--have the largest core diameter


T/F: Plates should be applied to the tension side of bone



What are the general guidelines for the application of conventional plates?

  • Should be precisely contoured to match the shape of the normal shape of the bone surface
    • Maximizes contact-->inc. strength of repair
    • Prevents distraction of fracture ends during screw placement
  • Stable repair requires screw purchase of at least 6 cortices above and below fracture


What are the general guidelines for the application of locking plates?

  • Minimal to no contouring required
  • Stable repair requires screw purchase of at least 4 cortices above and below fracture


What are the differences (tightening screw, loading of limb) between conventional and locking plates?

  • Conventional
    • Tightening the screw generates friction between bone and plate
    • Loading of the limb results in force shared between plate and bone
    • Friction between plate and bone is necessary for stability of fixation
  • Locking
    • Tightening the screw "locks" it into the plate creating a construct that converts shear and bending stress into compressive forces at the bone-screw interface
    • No load sharing (NEVER use in young animal)


What are the 4 modes achievable with plate application?

  • Compression
  • Neutralization
  • Buttress
  • Bridging


Can a locking plate (placed ith locking screws) be applied in a compression mode?


Plate bears all of the load at the level of the fracture


When is placing a plate in bridging mode most pertinent?

Biological osteosynthesis/MIPO


What is unique about buttress plating compared to the other plating modes?

  • Used in metaphyseal fractures to prevent collapse of the adjacent articular surface
  • Will frequently incorporate lag screws
  • Plate is subject to full loading due to fraction configuration
    • Axial forces don't help with fracture compression and do not promote load sharing (by the bone)
    • Plate supports the cortex and resists displacement
  • Most or all screw holes should be filled


What are the characteristics of compression mode plating?

  • Plate applied to achieve compression across the fracture
  • Used for transverse or short oblique fractures
    • Compression will not cause 'shear'
  • Eccentrically loaded screws
  • Load carried mostly by the bone and to a lesser extent by the plate
  • May promote primary bone healing


Explain what neutralization mode plating does

  • Plates used in addition to primarily placed lag or position screws
  • Plate acts to protect/neutralize against shearing, bending, or rotational forces which would otherwise damage the intrafragmentary repair achieved by screws
  • Plate itself is not stabilizing--just neutralizing forces that would cause damage to the stabilization


Explain bridging mode plating

  • Plate spans fractured area which cannot be anatomically reconstructed (comminuted area)
    • Plate must "bridge" fracture gap
  • Plate bears all load at level of fracture
    • No load sharing at fracture level
    • Screw holes left empty at level of fracture
    • Micro-motion at fracture site promotes secondary bone healing
  • Longer plate with fewer screws 


What forces are overcome by external coaptation?

Bending, rotational


Which forces are overcome by plating?

Plating neutralizes all forces (shear, bending, tension, rotation)


What forces are overcome by interlocking nails?

Bending, torsion


What appendicular bone cannot be repaired by an interlocking nail? Why?

Radius--it is impossible to place without penetrating the joint


What complications are associated with internal fixation?

  • Implant failure
    • Loosening
    • Breaking
    • Migration
  • Osteomyelitis
  • Impingement of nerves
    • Femoral IM pins
  • Osteopenia
    • Secondary to implants that are too strong
  • Delayed, non-union, or malunion


When might it be necessary to remove implants?


What principles must be followed when applying cerclage wire to a fracture?

  • Only use on long oblique or spiral fractures
    • If you tighten around fragments that don't fit together bone will collapse
    • Fracture length > 2x bone diameter
    • Must be able to reconstruct bone column
  • Place at least 2 cerclage wires to stabilize fracture
  • Place 0.5cm from fracture ends, spaced ~0.5-1x bone diameter apart
  • Place wire perpendicular to bone
    • Tighten by twisting-->rigid fixation
    • Maintain tension and pull up as twisting
  • Cut wires leaving 2-3 twists
    • Do not bend twist over (loosens wire)


Why are skewer pins used in conjunction with cerclage wire?

Short oblique fractures

  • Aids in maintenance of reduction
  • Promotes compression across fracture line
  • Incorporates full cerclage wire and K-wire


What is the main method of action of a pin and tension band implant configuration in providing stability at a fracture?

Distractive forces of tendon or ligament are converted into compressive forces


What types of fractures are best repaired with the tension band implant configuration method?

Avulsion fractures, some osteotomies


What lends the most strength in tension band implant configurations?

Most strength is from fixation neutralizing the pull of the muscles/tendons on the fracture fragment and converting it to compressive forces


What types of bone are best suited for repair with interfragmentary wiring?

Used for simple fractures of flat, non-weight bearing bones that interdigitate

Most commonly used for mandibular and maxillary


What forces are neutralized with the application of an intermedullary pin?



What fracture configuration is an IM pin best suited to?

What is it contraindicated in?

Transverse or oblique fractures

Can be used in humerus, femur, tibia, ulna, metatarsals and metacarpals

Contraindicated in the radius!


What percentage of the intramedullary canal should be filled if an IM pin is the primary source of fixation?




What is the difference between normograde and retrograde pinning?

  • Normograde--goes through at proximal end of bone towards distal end
    • Must be used with the tibia (either can be used for humerus, femur, ulna, or MT/MC's)
  • Retrograde--from fracture site (distally) to proximal end
    • Must take pin out and re-insert proximal-->distal , then push through fractured piece


What types of fractures are suited to be repaired/stabilized via cross pinning?

  • Simple, transverse fractures that are close to the joint
  • Typically good for Salter Harris type I and II fractures
  • Fractures must have good contact to provide load sharing


What types of fractures are suited for repair/stabilization via the diverging pin technique?

Salter Harris I fractures of proximal humerus or femoral head


What are the primary benefits of external skeleton fixation compared to plating?

  • Variety of construction options
  • Can be placed with minimal disruption of the fracture fragments because of percutaneous pin placement
  • All implants are removed upon healing
  • Useful for treatment of grade II and III open fractures
  • Implants can be removed in stages to slow increase loading on bone (dynamization)
  • Cost is relatively low compared to some internal fixation devices


What type of fracture would necessitate fixation with an external skeletal fixator?

  • Fractures of the appendicular skeleton (mostly below stifle and elbow)
  • Spinal fractures/luxation
  • Mandibular fractures



What are some other uses for external skeletal fixation?

  • Correction of angular limb deformities
  • Limb lengthening (distraction osteogenesis)
  • Arthrodesis (joint fusion)
  • Joint immobilization


What complications are associated with external skeletal fixation?

  • Pin tract drainage
    • +/- infection of soft tissues
  • Loosening of pins/wires
  • Osteomyelitis
  • Ring sequestrum
  • Nerve or vascular damage


What must be done if pins/wires become loose from an external skeletal fixation?

  • Remove loose pins/wires
    • Pin bone interface sustains high stress loads resulting in bone resorption


Explain the ring sequestrum complication with external skeletal fixators

The pin can get hot when placing into bones that are fairly hard--if you don't properly lavage the bone when placing the pin and it gets too hot, you can kill all the bone surrounding the pin-->nerve/vascular damage


What increases ESF stability?

  • Frame type (I-III)
  • Double bar
  • Interconnecting bars
  • Reduce bone-connecting bar distance
  • Pin distribution
    • Close to ends of bone and fracture = most stable
  • Increased # of pins
  • Larger diameter of pins and connecting bar


What decreases ESF stability?

  • Frame type
  • Pin distribution
  • Decreased # of pins 
  • Smaller diameter of pins and connecting bar


What is a type IA ESF? How strong is it?

  • Unilateral-uniplanar
  • Bar only on one side of bone
  • Pins exit only on one side of bone
  • All pins in one plane
  • Most basic
  • Weakest


What is a type IB ESF?

  • Unilateral-biplanar
  • Pins placed 60-90 degrees from each other
  • Only type IA and IB can be used on humerus and femur
  • Interconnecting bars increase rigidity
  • Weakest


What is a type IIA ESF

  • Bilateral-uniplanar
  • Stiffer than type I
  • Full pins pass fully out either side of the bone and skin so external fixators can be placed on both sides


What is a type IIB ESF?

  • Bilateral-uniplanar
  • Same as type IIA, except some half pins are included in the construct
  • Stiffer than type I


What is a type III ESF?

  • Bilateral-biplanar
  • Strongest
  • Full pins pass fully out either side of the bone and skin so external fixators can be placed on both sides
  • Pins placed in 2 planes


What are the basic guidelines for placement of transfixation pins?

  • Pin diameter should be no more than 25% of bone diameter
  • Pins are placed percutaneously through small incisions
    • In areas with little soft tissue
    • Avoiding neurovascular structures
  • At least 2 pins per bone segment are required (3 pins per segment is ideal for optimal stabilization)
  • Pins should be placed 1/2 bone diameter away from the fracture and each other
  • Pins are connected in various forms to connecting rods
    • Clampls connecting the pins and rods should be at least 1cm away from skin
    • Connecting rod should be as close to bone as possible


T/F: When placing connecting rods (ESF), increased distance from skin = increased construct stability

FALSE--increased distance from skin = decreased construct stability


How does the use of dynamization promote bone healing?

  • Dynamization = incremental destabilizatoin of the construct (decreasing ESF stability on purpose)
  • Allows axial loading of the fracture to enhance callus hypertrophy and remodeling of fracture 
  • Must make sure there is a callus in the first place in order for this to be effective


When is dynamization best applied with regards to the timing of fracture healing?

Typically recommended at 6 weeks post repair

(can vary between patients)


Why are hybrid fixators particularly useful for treatment of fractures that are close to articular surfaces?

  • Utilizes components of linear and circular ESFs
  • Thin wires or circular fixator allow for multiple sites of bone purchase in a smaller bone fragment


What are the benefits of using an acrylic frame?

  • Can connect pins in various planes
    • Mandibular fractures
  • Lightweight
    • Good for toy breed dogs, cats, and exotics
  • Eliminates need for fixation clamps