Lecture 3: Principles of Ortho Surgery 2 (Exam 1) Flashcards
How are external skeletal fixators versatile
Can be used for long bone fractures, corrective osteotomies, joint arthrodesis, & temporary joint immobilization
When are external skeletal fixators not used
- Not indicated for articular fractures
- Rarely used for pelvic & spinal fractures
What fixator is good for stabilization after a closed reduction of comminuted fractures
External skeletal fixators
What is the functional period for external fixators
- Varies depending on frame constructed
- Related to onset of pin loosening
How are linear external fixation framed classified
- Number of planes occupied by the frame
- Number of sides of limb from where the fixator protrudes
What are the common linear external fixator frames
- Unilateral-uniplanar (type Ia)
- Unilateral biplanar (type Ib)
- Bilateral uniplanar (Type II)
- Bilateral biplanar (Type III)
What the diff btw/ max type II frames & min type II frames
- Max frames are filled w/ full pins
- Min frames are constructed w/ min of 2 full pins
Label the following
Describe the Type III
- Type II + Ia (montage)
- Interconnected for strength
- Stiffest configuration
Describe half pin placement
Penetrates both cortices but only one skin surface
Describe full pin placement
Penetrate both cortices & skin surfaces
Label the following
Describe linkage devices (clamps)
- Join fixation pins to connecting bars & connecting bars to each
- Larger holes are for external connecting bars (Bottom arrow)
- Smaller holes in the bolts are for fixation pins (top arrow)
Label the following clamps
How can the strength & stiffness of external fixators be increased
- Predrill before inserting pos profile threaded pins
- Increase the pin #
- Increase the pin size
- Locate the pins near joints & near fracture
- Decrease distance btw/ bone & pin-clamp interface
- Increase connecting bar size or use augmentation plates
- Increase # & planes of connecting bars
- Tie IM pin into fixator frame
What is the max pin # & pin size that can be used for external fixators
- # - up to 4 pins
- Size - Up to 25% of bone diameter
How are fixation pins inserted
- Expose pin insertion site
- Center pin in bone
- Predrill pin hole
- Insert pin w/ low RPM power
- Release incision around pin to prevent skin tension
- Pin drilled into bone @ the point of greatest cross sectional diameter (trocar point exits far cortical surface 2 to 3 mm)
What are circular external fixators (rings) used for
- Stabilize fractures
- Compress nonunions or distract fractures
- Transport bone segments
- Dynamically correct bone angular & length deformities
What are ring fixators unique for & why
- For controlled distraction of bone segments
- Creates new bone formation in trailing pathways (distraction osteogenesis)
What do small diameter tensioned wires do
- Provide stability to bone segments
- Allows axial micromotion @ fracture site w/out compromising fixator stability
What is this
Circular external fixators
What are the types of intramedullary fixations
- Intramedullary pins (IM)
- Kirschner wires (“K” wires)
- Interlocking nail
What are IM pins used for
Diaphyseal fractures in the humerus, femur, tibia, ulna, & MC/MT bones
When should IM pins not be used
They are contraindicated for the radius b/c the insertion point of pin interferes w/ the carpus
What are the biomechanical advantages of IM pins
- Resistance to applied bending loads
- Equally resistant to bending loads applied from any direction b/c around & +/- centered in medullary canal
What are the biomechanical disadvantages of IM pins
- Poor resistance to axial (compressive) loads
- Poor resistance to rotational loads
- Lack of fixation (interlocking) w/ bone
What do IM pins req
Supplementation w/ other implants like cerclage wire or external fixator/plate to provide rotational & axial support
Label the two pins
What IM pin size should be used w/ cerclage wire
60 to 70% of the medullary canal width
What IM pin size should be used w/ external fixators
50 to 60% of the medullary canal width
What IM pin size should be used w/ a bone plate
40 to 50% of the medullary canal width
What are some concepts that should be noted when applying IM pins
- Span length of bone w/ IM pin
- Retrograde or normograde pin insertion in the humerus & femur
- Normograde pin insertion in the tibia
- Check the pin location w/ reference pin & by manipulating the joint
- Use additional fixation to control rotation & axial loading
What is the normograde placement of IM pins
- Insert pin to enter the bone proximally in craniolateral trochanteric fossa
- Direct the pin caudally & glide along the caudal cortex & seat it in the caudocentral aspect of condyle
Describe retrograde placement of IM pins
- Insert pin in the marrow cavity @ fracture surface
- Force the shaft of the pin against caudomedial cortex & drive the pin proximally
- Reduce the fracture & drive the pin distally (seat it in the caudocentral aspect of femoral condyle)
What are Steinmann pins or Kirschner wires
- Used as crossed pins (wires) or placed in triangulated pattern in metaphyseal & physeal fractures in young animals
- K wires are also used as IM pins in very small animals
When are interlocking nails used
- Placement of interlocking nails in the femur
- I-Loc biomedtrix
Describe interlocking nails
- Stabilize simple & comminuted mid-diaphyseal femoral fractures
- Effective IM fixation to bridge non reducible fractures
What do interlocking nails provide resistance to
- Bending
- Rotation
- Axial loading forces
How are IM pins secured
- By proximal & distal transfixing screws
- Engage the bone to the nail
- Provide axial, bending, & torsional stability
What are some concepts that need to be considered when applying interlocking nails
- Use largest nail that fits in the bone
- Span the length of the bone w/ nail
- Ream medullary canal w/ steinmann pin or use reamers
- Insert nails in a normograde fashion
- Position nail screw holes 2 cm away from the fracture
- Secure nail w/ 4 screws or fixation bolts for optimal fixation
Describe orthopedic wire
- Used as cerclage wire or hemicerclage wire
- Used in combo w/ other ortho implants
- Supplements axial, rotational, & bending support of fractures
What is cerclage wire
Ortho wire placed around the circumference of bone
What is hemicerclage wire or interfragmentary wire
Wire place through predrilled holes in bone
What does cerclage wire combined w/ K-wires do
- Prevents wire slipping where bone diameter changes
- Secures the cerclage wires @ oblique angle to long axis of bone
What are some cerclage wire distinctions
- Most used implant in vet ortho
- Most misused implant
What does misuse of cerclage wire cause
A significant % of post op complication in vet px
What does cerclage wire do
- Provides stability to anatomically reconstructed long oblique or spiral fractures
- Hold multi fragments in position
What must happen for cerclage wire to fxn as a stabilizer
Wire must compress between fracture surfaces to prevents fragments from moving or collapsing under wt. bearing loads
What are the 3 criteria for cerclage wire
- Length of fracture is 2 - 3 diameter of marrow cavity
- Max of two fracture lines (no more than two main segments & one large butterfly fragment)
- Fracture is anatomically reduced
If cerclage wire criteria is met what will be the benefit
The wire will provide additional stability by generating compression btw/ fragments to hold in place during healing
T/F: Cerclage wire doesn’t have to be supported by additional implants
False it is always supported by additional implants
What occurs if >2 or 3 bone segments present or if fracture lines are not sufficient in length & cerclage wire is being used
Cerclage wire is only used to to hold fragments in position b/c it can not generate compression needed to resist wgt. bearing loads
What is the most common reason for failure of cerclage wire fails
Trying to gain stability w/ cerclage wire in multifragmented fracture
What are concepts should be remembered when applying cerclage wire
- Only anatomically reconstructed long oblique or spiral fractures (18g wire in Lg dogs & 22 or 20 g wire in cats and sm dogs)
- Place 2 to 3 cerclage wires per fracture line
- Place wires perpendicular to long axis of bone
- Space the wires 1/2 to 1 bone diameter apart & @ least 0.5 cm (5mm) from fracture
- Support the cerclage wire w/ IM pin, interlocking nails, ESF, or plate
What are the steps for application of cerclage wire
- Twist the wire ends by hand
- Use needle holders to twist & tighten the wire by pulling & twisting
- Tighten & cut the wire 3 mm from start of twist (leave @ least 3 full twists)
Describe avulsion fractures
- Where groups of muscle originate or insert in bone
- Greater trochanter olecranon & the supraglenoid tuberosity of the scapula
- Contraction of muscle group generates tension pulls bony insertion or origin from anatomic location
- Best way to resist tension is use of tension band
What is the purpose of a tension band
Convert distractive tensile forces into compressive forces
What is the mechanical principle of tension band wiring
Tightening wire exerts force that conteracts muscle contraction & compresses fracture surface
What are some concepts to remember when applying tension band wires
- Use 2 K wires or small steinmann pins
- Place wires parallel to each other & perpendicular to fracture
- Seat wires in opposite cortex
- Place hole for wire the same distance below the fracture as the pins are above the fracture
- Tighten the wire in direct contact w/ bone
When is using bone plates & screws ideal
- For complex or stable fractures
- When prolonged healing is anticipated
- When optimal postoperative limb fxn is desirable
What are plates used for
- Compression
- Neutralization
- Bridging w/ or w/out an IM pin
What type of fractures are compression plates are used on
Transverse
What type of fracture are neutralization plates used on
To support long oblique fractures reconstructed w/ lag screws
What fractures are bridging plates w/ IM pins used on
To span a nonreducible fracture
Label the bone screws
Describe a neutralization plate
Protects reconstructed bone from torsional, bending, & shear forces
Describe bridging plates
- Serves as splint for spatial alignment of bone during healing
- Plate & screws carry ALL applied loads during early post op period which results in greater stress on bone screws than w/ compression or neutralization plates where applied loads are shared w/ bone
Describe a buttress plate
Functions to prevent collapse of adjacent articular surface
Describe a locking plate (screws secured in bone & plate)
- Alignment must be correct before securing a plate (locking screws will hold bone in position)
- If using a combo of standard screws & locking screws the plate should conform to the bone & standard screws should be applied first to pull bone to the plate
What are some concepts to remember when applying bone plates
- Select the appropriate plate size
- Select a plate that spans the bone length for diaphyseal fractures
- Accurately contour the plate (not locking the plates)
- Place a min of 3 screws/6 secure cortices above & below the fracture
- Use longer & stronger plates for bridging plates (our augment w/ an IM pin for a plate rod)
Describe lag screws
- Compress the fracture line btw/ 2 bony fragments
- Inserted through a plate hole or directly into bone outside of the bone plate
- For shorter oblique fractures use bisect angle
What is the optimal position of a lag screw
Perpendicular to fracture line
What is a bisect angle
- Lag screw placed btw/ line 90 deg to fix the surface & 90 degrees to long axis of bone
- Prevents the slipping of fragments
Where can the holes be placed in the bone for lag screws
- In the near cortex (glide hole)
- In the far cortex (thread hole)
Define a glide hole
Hole equal in diameter to outside diameter or thread diameter of the screw
Define a thread hole
Hole equal in diameter to the inner core diameter or shaft of the screw
What are the steps of placing lag screws
- Drill a glide hole in a near bone segment (drill bit w/ the diameter of the outside screw thread)
- Insert the sleeve through the glide hole until far bone segment engaged (drill thread hole w/ drill bit the same diameter as the core of the screw)
- Use a countersink to cut bevels into the cortical bone @ the entrance of the glide hole to increase the contact area btw/ the bone & the screw
- Determine the length of the screw inserted w/ a depth gauge
- Use tap to cut threads for the screw in the far bone segment
- Insert the screw & tighten to create interfragmentary compression
What are some concepts to remember apply lag screws
- Reduce & secure fx before lag screws
- To get optimal compression place the screw perpendicular to the fx
- If you drill near the cortex drill a bit equal to the screw thread diameter
- If you drill in the far cortex drill a bit equal to screw core diameter
- W/ partially threaded screws the threads should not cross fx
How are partially threaded cancellous bone screws inserted
- Drill near & far cortices as threaded hole
- Measure the depth of the hole
- Tap holes
- insert the screw to compress the fracture (the threads should NOT cross the fracture line)
