Bone Plating Flashcards
What are the 2 types of fracture fixation?
- NON-SURGICAL: external coaptation (splinting)
- SURGICAL: external skeletal fixator, pins, wires, plates, screws
What are the goals of fracture fixation (immobilization)?
- align joints and bones to restore length
- maintain some stress on bone and permit early ambulation to promote healing
- minimize motion at fracture ends
- balance forces that promote bone healing vs. those that promote bone resorption
What is Wolff’s Law?
bone remodels based on the forces applied to it
- remodels and thickens in response to increased sustained forces
- resorbs and weakens in response to decreased sustained forces
What are 4 pros to 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 (except with external coaptation)
- nothing externally to monitor (except with external coaptation
What are 3 cons to internal/external fixation?
- expense to clinic and owner - requires lots of specialized equipment and inventory
- requires training for appropriate application
- may require second surgery for explantation due to infection, loose/broken implants, or irritation/rejection
What are 3 pros to external coaptation?
- limited supplies necessary for placement
- need for highly specialized training is limited
- avoids prolonged surgical procedure - diaphyseal and transverse fractures heal well
What are 5 cons ot externap coaptation?
- requires frequent rechecks and bandage changes ($$$)
- limited effective applications - only below elbow and stifle
- risk of bandage morbidity preventing continued use
- immobilized joints
- bandage sores
What are some indications for external coaptation?
- fractures below the elbow or stifle
- minimally displaced fractures
- transverse, simple, closed fractures
- non-articular fractures
- fractures expected to heal rapidly - Greenstick fractures
What are 2 approaches to internal fixation?
- open anatomic reduction/reconstruction - primary bone healing with perfect bone reconstruction and rigid fixation
- biological osteosynthesis - plates placed away from the callus, avoiding disruption of fracture hematoma —> less rigid, secondary healing
What fractures require open anatomic reconstruction?
- articular fractures
- transverse, oblique, segmental, and non/minimally comminuted
What is the open but do not touch approach to biological osteosynthesis?
fracture is surgically approached and visualized, but the fracture ends are NOT manipulated during the placement of implants
- minimal disturbance of fracture hematoma, periosteum, and blood supply
What is minimally invasive osteosynthesis? What is used for guidance?
implants are placed through incisions distant to the fracture —> fracture not approached, closed reduction
intra-operative fluoroscopy - guides implant placement and confirms fracture reduction and alignment
What is the goal of biological osteosynthesis?
return limb alignment and length to normal without disruption of fracture
What considerations are included when determining implant selection?
- fracture type and location - articular vs. metaphyseal vs. diaphyseal, comminuted vs. simple
- bone affected - forces acting on bone
- patient factors - age, comorbidities, environment, size/weight
- surgeon preference and experience
What are examples of primary and secondary implants?
PRIMARY - bone plates, interlocking nails, external skeletal fixators
SECONDARY - Kirschner wires, cerclage wire, interfragmentary screws (provide additional rigidity)
What are the 2 most common types of bone plates?
- STAINLESS STEEL - 316L iron-carbon alloy, very stiff, fails by bending
- TITANIUM - less stiff, better fatigue resistance, less reactive, expensive —> bendable, so good for growing bones
What is a dynamic compression plate (DCP)?
plate that can be used for compression, neutralization, or bridging with screw holes designed to allow screw placement that promotes compression of fracture ends
- flat surface = friction between plate and bone creates stability
How do limited contact compression plates (LC-DCPs) compare to DCPs?
decreased plate to bone contact allows for improved cortical perfusion, reduced stress concentration at screw holes, and contouring
- can also be used for compression, neutralization, or bridging
How does the structure of limited contact DCPs compare to DCPs?
contoured underside allows for stress to be more evenly distributed across the plate and less disruption of periosteal vascularity
How are locking compression plates used?
combination of holes accommodate conventional screws and locking head screws, acting as an internal fixator eliminated the need for perfect contouring
- compression, neutralization, bridging
What is the purpose of using locking plates with locking head screws?
locks in to prevent the need for plate-bone contact for stable repair = more stability with fewer screws
When are locking plates most commonly used?
minimally invasive plate osteosynthesis (MIPO)
- can use both locking and cortical screws
How do locking plates compare to conventional plates?
greater forces are required to cause pull-out screws making them better for osteoporotic bone, soft bones, and comminuted fractures
What are 3 types of locking plates?
- string of pearls - easier to contour to the curvature of bones
- fixin plates
- polyaxial locking plate (PAX)
What are string of pearls plates? What screws are used?
locking plate with added stability and limited contact on bone, making it easier to contour in any direction
unicortical screws provide almost the same stability as bicortical screws
(neutralization, bridging)
What are reconstruction plates? How do they compare to DCPs?
plates with deep notching between holes, which allows for contouring in an additional plane
- not as strong as DCP
- able to be used in areas that require complex plate contouring, like the mandible
What are veterinary cuttable plates (VCPs)? How do they compare to DCPs?
versatile plates able to be but to any length
- relatively weak compared to DCP
- can be stacked to increase stiffness
- does not provide compression
What is the goal to using screws to repair fractures? What size diameters are used compared to the bone? What provides maximal stability?
achieve as much contact with bone with sufficiently stable implant of minimal size
screw diameter should not exceed 40% of bone diameter when used in diaphysis
screws should engage the near (cis) and far (trans) cortex of the bone
What do the core and outer diameters of screws determine?
CORE = bending strength
OUTER = pull out strength
When are cancellous and cortical screws used?
CANCELLOUS - metaphyseal and epiphyseal bone of younger animals and soft bone, since they’re harder to pull out
CORTICAL - dense, cortical bone
How do the diameters, thread, and pitch compare in cancellous and cortical screws?
CANCELLOUS - high outer:core diameter ratio, deep thread, large pitch
CORTICAL - low outer:core diameter ratio, shallow thread, decreased pitch
What are self-tapping screws?
screws with fluted tips, which do not require tapping - pre-cutting the thread pattern into the bone following drilling
What are locking screws? How are they placed?
self-tapping, largest core diameter screw that is stronger and cortical screws and contains a threaded head that locked into the threaded locking plates
perpendicular through holes in the locking plate (CANNOT USE OTHER PLATES)
How do screws work in conventional plates?
- tightening the screw generates friction between the bone and the plate, which is necessary for stability
- loading of the limb results in forces shared between the plate and the bone
How do screws in locking plates work?
tightened screws lock the screw into the plate, creating a construct that converts shear and bending stress into compressive forces at the bone-screw interface
What are lag screws? What happens when they are tightened?
screws placed perpendicular across an oblique or sagittal fracture end with the glide hole drilled into the cis cortex, cause the trans cortex to be drilled into the core
pulls the trans cortex closer to the cis cortex, causing compression across the fracture
When are lag screws used?
- articular fractures
- oblique fractures
can be placed through conventional plate holes
How are position screws used? How do they compare to lag screws?
screw is placed across a fracture line to hold fragments in place without providing compression
weaker repair compared to lag screws
- able to be placed through conventional plate holes
Where on the bone are plates placed?
on the side of most tension
How are conventional plates placed? What is required for stable repair?
precisely contoured to match the normal shape of the bone surface with maximal contact to prevent distraction of fracture ends during screw placement
screw purchase of at least 6 cortices above and below fracture —> 3 screws
How are locking plates placed? What is required for stable repair?
minimal to no contouring required
screw purchase of at least 4 cortices above and below fracture —> 2 screws
What affects a plate’s function?
how it is placed on the bone in relation to the fracture
- compression
- neutralization
- buttress
- bridging
When are compression plates most commonly placed? What does this allow?
transverse or nearly transverse fractures where compression is applied by the spherical gliding principle
compression of bone at the fracture site
What is compression mode? How are screws loaded?
plate applied to achieve compression across the fracture - commonly used for transverse fractures because it does not cause shearing
eccentrically loaded to apply compression by the spherical gliding principle
What carries most of the load in compression mode? What does this allow?
mostly the bone
promotes primary bone healing
What is neutralization mode? How does the plate act?
plates used in addition to primarily placed lag or positional screws
protects against shearing, bending, and rotational forces that would otherwise damage the interfragmentary repair achieved by the screws
DCP plate in neutralization mode:
spiral convoluted fracture with wire for stabilization
What is bridging mode? What bears the load?
plate spans fractured area which cannot be anatomically reconstructed - comminuted area is bridged by the plate
plate - no load sharing at fracture with screw holes left empty —> micro-motion promotes secondary bone healing
What plate/screw combination is used in bridging mode? When is it most commonly used?
longer plate with fewer screws
biological osteosynthesis, MIPO
When is buttress mode used? What screws are used?
metaphyseal fractures to prevent collapse of the adjacent articular surface
lag screws —> most holes should be filled
What is subject to load in buttress mode?
plate —> axial forces do not help with fracture compression and do not promote load sharing by the bone
(supports cortex and resists displacement)
What is required for stable repair with locking plates? How do they compare to cortical screws?
screw purchase of at least 4 cortices above and below fracture —> 2 screws
- have increased core diameter = increased bending resistance
- converts shear stress in axial loading to compression forces at screw-bone interface
What are the 3 principles of locking plate placement?
- 2 screw minimum per segment (4 cortices)
- 3rd screw at each section increases torsional stability
- addition of more than 3 screws has little advantage
How does the size of the fracture gap alter locking plate placement?
small (1 mm) = screws omitted from 1-2 holes adjacent to fracture
larger (> 6 mm) = screws places as close to fracture site as possible, which decreases working length
What is an interlocking nail? When is it used?
internal fixation that combines benefits of an intramedullary rod and a plate —> has a removable jig to guide placement of screws
- diaphyseal comminuted fracture biological osteosynthesis
- NOT used for fractures of the radius
Interlocking nail:
What are the major risks of internal fixation?
- implant failure: loosening, breakage, migration
- osteomyelitis
- impingement of nerves common in femoral IM pins
- osteopenia secondary to implates that are too strong
- delayed, nonunion, malunion
What are the most common causes of implant loosening with DCP/LC-DCP and locking plates?
axial load exceeding friction causing sequential pull out
axial load exceeding compression force causing implants to fail all together
What is the most common cause of implant bending/breaking?
axial forces cause cycling of the implant depending on material and working length
- more holes left open = decreased strength of the plate
