Fractures Flashcards
Stress
External force applied to any cross sectional area
Stiffness
Ability of a material’s ability to resist an applied force
Strain
Deformation of a loaded material as compared to its original form.
Typically measured in length
Tensile Strain
a change in length longwise
Compressive Strain
shortening of the length
Shear
a stress is applied that results in a change from side to side
Bending
Combination of tensile and compressive loading forces
Torsion
Combination of compressive, tensile, and shear loading forces
Deformation
change in shape due to application of a force (stress)
Elastic Deformation
a reversible change in shape
Material returns to original shape when load is removed
Plastic Deformation
a permanent change in shape
Material does not return to original shape when load is removed
Yield Point
point when material begins to deform plastically
Strain exceeds the material ability to recover rendering it permanently deformed
Occurs between elastic and plastic deformation
Ultimate failure point
material cannot withstand anymore strain and fails
Porosity
ratio of volume of open space to volume of total bone
High Porosity
Long elastic phase
Lower yield point
Low Porosity
Steep and short plastic phase (brittle)
Viscoelastic
Increased speed of loading (stress application) increases material stiffness
Anisotropic
Elastic modulus is dependent upon the direction of loading (stress application)
Bone is stronger and stiffer in compression
Bone is weakest when shear stress is applied
Type 1 open fracture
Wound smaller than 1 cm
Typically created by bone fragment from inside that retracts back through skin
Mild/Moderate soft tissue contusion
Type 2 Open Fracture
Open wound greater than 1 cm in size
Mild soft tissue trauma without extensive soft tissue damage
No flaps or avulsion
Type IIIA Open Fracture
Adequate soft tissue for wound coverage
Large ST laceration/flap
Type IIIB Open Fracture
Extensive ST loss
Bone exposure
Stripped periosteum
Type IIIC Open Fracture
Arterial +/- nerve supply to distal limb compromised
Requires microvascular anastomosis or amputation
What is the first priority of Open Fracture Management?
Systemic Stabilization: Cover the wound and stabilize patient
Greenstick Fracture
Incomplete Fracture
Long Oblique
Length of fracture (mm) greater than 2.0 x diameter of diaphysis (mm)
What type of animal does a Physeal fracture occur in?
Young animals ONLY
Articular
Fracture runs through a joint surface
Displaced Fracture
If fracture ends do not line up then fracture is considered displaced
What are the goals of fracture fixation?
Restore length and alignment to promote healing and limb function
Minimize motion at fracture ends
Permit early ambulation with use of as many joints as possible during healing period
Balance the forces that promote bone healing versus those that promote bone resorption
Wolff’s Law
Bone remodels based on the forces that are applied
Bone remodels and thickens in response to increased sustained forces
Bone resorbs and weakens in response to decreased sustained forces
What are the advantages of Internal/External Fixation?
Variety of fixation options to promote stable repair
Can promote normal muscle/joint function during bone healing
Typically fewer rechecks than with external coaptation
Nothing external to monitor
What are the disadvantages of Internal/External Fixation?
Expense to clinic and owner
Requires training for appropriate application
May require second surgery for explanation
What are the advantages of External Coaptation?
Limited supplies necessary for placement
Need for highly specialized training is limited
Avoids prolonged surgical procedure
What are the disadvantages of External Coaptation?
Requires frequent rechecks ($$) and bandage changes
Limited effective applications
Risk of bandage morbidity preventing continued use
Immobilized joints
Indications for External Coaptation
Fractures below the know or the elbow: Minimally displaced fractures and those amenable to reduction
Non-articular fractures
Fractures expected to heal rapidly: Greenstick fractures
What fractures should not be casted?
Comminuted fractures
What kind of bone healing takes place with Open anatomic reduction/reconstruction?
Primary bone healing with less than 1 mm gap
What is required for articular fractures?
Open Anatomic Reconstruction
What is most appropriate for repair of transverse, oblique, segmental, and non or minimally comminuted fractures?
Open Anatomic Reconstruction
What should you consider when selecting implants?
Fracture type and location
Bone affected
Patient factors
Surgeon preference and experience
Primary Implants
Bone Plates
Interlocking Nails
External Skeletal fixators (ESF)
Secondary Implants
Kirschner wires (K-wires)
Cerclage wire
Interfragmentary screws
What is the most common material used for Bone plates?
Stainless steel
What material is better fatigue resistant for bone plating?
Titanium
Dynamic Compression Plate (DCP)
Screw holes designed to allow screw placement that promotes compression of fracture ends
Tightening of the screws moves fracture ends closer together
Limited Contact DCP
Contoured underside that allows stress to be more evenly distributed across plate
Less contact with bone = less disruption of periosteal vascularity
Locking Plates (LCP)
Threaded locking screw head locks into threaded screw hole on plate
What plate type is commonly used for MIPO?
Locking Plates (LCP)
What kinds of bones are Locking Plates good to use in?
Osteoporotic bone
Soft bone
Comminuted fractures
What is the advantage of Locking Plates?
Greater force if required to cause implant failure
Pull out of screws only happens under significantly higher forces
What are cannulated screws used for?
Hollow for driving over pins
What is the goal of using screws?
Achieve as much contact with bone with a significantly stable implant of minimal size
What is the rule for measuring screws?
Screw diameter should not exceed 40% of bone diameter when used in diaphyseal bone
What are Cancellous screws best used for?
Metaphyseal and epiphyseal bone
Characteristics of Cancellous Screws
Increased outer diameter to core diameter ratio
Deeper thread
Larger pitch
Characteristics of Cortical Screws
Decreased outer diameter to core diameter
More shallow thread
Decreased pitch
Core diameter
does not include the threads
Outer diameter
does include the threads
When do you use Cortical Screws?
Dense cortical bone
What forces do Cortical screws overcome?
Bending forces
Self-tapping screws characteristics
Fluted tip
Does not require tapping
What screws are most resistant to bending forces than Cortical screws?
Locking screws
Locking plates
Tightening of the screws “locks” the screw into the plate creating a construct that converts shear and bending stress into compressive forces at bone-screw interface
Lag Screws
Placed perpendicular across an oblique or sagittal fracture line to promote compression of the fracture ends
Lag Screw uses
certain articular fractures
oblique
causes compression across the fracture
Position Screws
Screw placed across a fracture line to hold fragments in place
No compression across the fracture is achieved
What is the application rule for conventional plates?
Stable repair requires screw purchase of at least 6 cortices above and below fracture
What is the application rule for locking plates?
Stable repair requires screw purchase of at least 4 cortices about and below fracture
Compression mode
Plate applied to achieve compression across the fracture
On what types of fractures do you use Compression mode?
Used for transverse or short oblique fractures
What type of bone healing is promoted with compression mode?
Primary bone healing
Neutralization Mode
Plates that are used in addition to primarily placed lag or positional screws
Plates act to protect/neutralize against shearing, bending, and rotational forces
Buttress Mode
Used in metaphyseal fractures to prevent collapse fractures to prevent collapse of the adjacent articular surface
Bridging Mode
Plate spans fractured area which cannot be anatomically reconstructed
Plate bears all load at level of fracture
What mode is used in biological osteosynthesis/MIPO?
Bridging Mode