Chapter 2.2 Flashcards
What are the two types of fixation pins for external fixation?
Smooth and threaded
Which type of threaded pin is stronger and purchases bone more securely?
Positive threaded pins
What is the benefit of a positive threaded pin having a shaft diameter that is the same its whole length?
Reduces bending stress
What should be done to improve the quality of the pin–bone interface?
Predrilling a hole slightly smaller than shaft diameter
What is the range of diameters for positive threaded pins available from veterinary suppliers?
1 to 6 mm
What types of threaded pins are supplied with threads at one end?
Half pins
What types of threaded pins have threads in the center?
Full pins
Penatrating both cortices
What sizes are pin gripping clamps available in?
Mini, small, and large sizes
What type of thread profile is designed for cortical bone?
Finer thread
What type of thread profile is designed for cancellous bone?
Coarser thread
Are carbon fiber rods radiolucent?
Yes
Can acrylic be used as connecting bars?
Yes
Mechanical studies have shown that a ____ mm
diameter acrylic or epoxy bar has similar rigidity to a 3.175 mm stainless steel bar
19 mm
6 acrylic : 1 stainless steel bar
What type of injuries are external fixators most suited for?
Injuries below the elbow and stifle
External fixators are also used for complex femoral and humeral fractures, and for the spine.
What is one primary advantage of using external fixators?
They can often be applied in a closed fashion, preserving blood supply and fracture hematoma.
What is a hanging limb system used for?
Stretching contracted muscles and swollen soft tissues, and aligning joints above and below the fracture.
What imaging technique can improve pin placement accuracy?
Fluoroscopic imaging.
How should pins be placed in the soft tissue and avoid to minimize complications?
They should penetrate as little soft tissue as possible and avoid neurovascular structures.
What is a mechanical advantage of bilateral frames?
Bilateral frames provide more stability but penetrate more soft tissue.
What is one method to improve the mechanical performance of a frame without using full pins?
Placing two unilateral frames approximately 90º to each other (biplanar configuration).
What type of configuration is considered very rigid for severe fractures?
Triangular configurations (bilateral with a unilateral frame on the cranial aspect).
What is the minimum number of pins that must be purchased for each fragment?
A minimum of two pins
This is essential to ensure stability at the pin–bone interface.
How does using more pins affect the stress at the pin–bone interface?
Reduces stress
Using three or four pins is often considered for better stability.
What is the maximum diameter of pins in relation to the diameter of the bone?
No more than 25% of the diameter of the bone
This helps in maintaining the structural integrity of the bone.
What should be done if room is restricted in a fragment?
Use a pin of slightly smaller diameter
This allows for placement of three pins instead of two larger ones.
What is the advantage of angling pins to one another?
Adds a little to stability
However, parallel alignment of more threaded pins provides superior purchase.
How far should pins be positioned from the fragment ends?
At least two pin diameters from the fragment edge
This is particularly important if fissures are likely to be present.
Where should the pin gripping clamps be positioned?
As close to the bone as possible, without contact with the skin
This helps to stabilize the frame by shortening the pin length.
What should be considered when linear systems might not adapt well to a particular fracture?
Free form external fixators using acrylic or epoxy putty compounds
These allow for more flexibility in pin placement.
What is a primary advantage of free form external fixators?
Pins do not have to be in the same plane
This is beneficial for matching irregular bone shapes or spanning joints.
In what situations can external fixators be used?
As adjunct fixation for intramedullary pins, locked intramedullary nails, or plates
This is applicable in rare cases.
What is optimal for stabilization in a comminuted fracture of the mandible?
Three pins placed in each major segment of bone
This ensures adequate support and stability.
What is the minimum distance to allow between the skin and the pin gripping clamp?
At least 1 cm
This helps prevent skin irritation or damage.
What do locked intramedullary nails resist?
Bending, axial, and rotational forces
Locked intramedullary nails are secured with bone screws or locking bolts. The nails are stainless steel.
How are locked intramedullary nails aligned during insertion?
Using a drill jig that orients the drill guides
The drill jig passes on the outside of the limb.
Which types of fractures are locked intramedullary nails most effectively used to stabilize?
Middiaphyseal fractures of the humerus, femur, and tibia
What is a locked intramedullary nail made of?
Stainless steel
What diameters are locked intramedullary nails available in?
- 8.0 mm
- 6.0 mm
- 4.7 mm
- 4.0 mm
What locking screw diameters are compatible with the 8.0 mm nail?
- 4.5 mm
- 3.5 mm
What locking screw diameters are compatible with the 6.0 mm nail?
- 3.5 mm
- 2.7 mm
What locking screw diameter is used with the 4.7 and 4.0 mm nails?
2.0 mm
How many holes does a standard locked intramedullary nail have?
Two holes proximal and two holes distal
What is the distance between holes in the 8.0 mm and 6.0 mm systems?
11 or 22 mm apart
What is the distance between holes in the 4.7 and 4.0 mm systems?
11 mm apart
What additional configurations are available for locked intramedullary nails?
- One hole proximal and two holes distal
- Two holes proximal and one hole distal
What feature does a locking bolt have to increase bending strength?
A short length of thread immediately below its head
What equipment is used to prepare the medullary canal for nail insertion?
Reamers that match the size of the selected nail
What is the first step after inserting the nail into position?
Remove the insertion tool and attach the drill jig
What is the purpose of scoring the bone surface with a trocar?
To help prevent migration of the drill bit
What must be done before tapping a hole for a bone screw?
Place a tap guide
How do locked intramedullary nails resist bending forces?
Due to their large diameter and central location
What mode are locked intramedullary nails usually placed in?
Bridging mode
What is a potential risk when placing only one locking screw or bolt?
Fragment may rotate around that point
What is the recommended size for the nail used in a fracture?
The largest size that will fit into the bone
In what manner must the nail be passed during insertion?
Normograde
What should be done first during the locking process?
Lock the distal fragment first
What should be done after locking the distal fragment?
Correct rotation and lock the proximal fragment
How should the connection between the extension and nail be during drilling?
IM nail
Very secure
When are locked intramedullary nails typically removed?
If they break, a nonunion develops, or if they become infected
What must be avoided to ensure proper hole drilling for screws with an intrmedullary nail?
IM nail
Drill must pass through the hole in the nail
What can happen if the nail is eccentrically located in the medullary canal?
IM nail
The point of contact of the drill bit may be sloped
What helps prevent drill drift during insertion?
IM nail
Scoring the bone surface and using sharp drill bits
What percentage of the diameter of the medullary canal should an intramedullar pin be to resist bending?
70% of the diameter of the medullary canal
BUT will not prevent collapse or rotation of a fracture unlike IM nail.
What are intramedullary pins commonly referred to as?
Steinmann pins
Intramedullary pins are often used in orthopedic procedures.
What is the typical diameter range for intramedullary pins?
2.0 to 5.0 mm
These pins are made of stainless steel.
What is the most common point style for intramedullary pins?
Three-faced trocar
Other point styles include bayonet and diamond points.
What lengths are intramedullary pins usually supplied in?
230 mm or 300 mm
Pins can also have a negative profile thread cut into one end.
What does K-wire refer to?
Small diameter stainless steel pins
K-wires typically range from 0.8 to 2.0 mm in diameter.
What is the typical length range for K-wires?
150 mm to 300 mm
The length depends on the application, such as small fragment work or circular fixators.
What is the primary application of intramedullary pins?
To align and support shaft fractures
They are placed within the medullary cavity.
What is considered the optimal size for an intramedullary pin relative to the medullary canal?
Approximately 70% of the diameter
This size helps resist bending forces experienced by a fracture.
True or False: Intramedullary pins prevent collapse or rotation of a fracture.
False
They do not prevent collapse or rotation; adjunct fixation is often necessary.
What methods can be used for adjunct fixation with intramedullary pins?
- Cerclage wiring
- Hemicerclage wiring
- External fixator
These methods help counter axial and rotational forces.
What does a ‘tie-in’ configuration refer to?
An intramedullary pin left protruding from the patient and incorporated into a fixator
This is applicable if it does not interfere with adjacent joint motion.
What is the effect of stacking pins in the medullary cavity?
Improves bending strength
Stacking pins adds little to axial or rotational stability.
What is the purpose of using crossed pins with intramedullary pins?
To maintain the position of small end fragments
They are driven from either side of the small fragment to cross the fracture.
What is a common indication for using K-wires?
Repair of physeal fractures
Physeal fractures have the advantage of healing quickly. Example: cross pins.
What should be avoided when passing wire during surgery?
Kinking the wire
Kinking makes it difficult to straighten and tighten the wire.
What is the advantage of using an intramedullary pin with a plate in buttress mode?
Reduces bending stress
The pin fills part of the medullary cavity.
What is the approximate diameter of an intramedullary pin that reduces bending stress effectively?
50% of the medullary diameter
This reduces bending stress in unsupported plate models. Kept in mind that 70% is optimal.
What material is orthopedic wire made from?
316L stainless steel
This material is malleable and comes in various diameters.
What is the range of diameters for orthopedic wire?
0.5 to 1.5 mm (24–16 gauge)
Larger diameters offer higher bending and tensile strength.
What is the effect of using a larger diameter wire?
Higher yield bending and tensile strength
Allows for greater initial tension and resistance to load.
What happens if the orthopedic wire is marked by instruments?
It reduces the wire’s ability to resist cycling loads
Proper handling is crucial to maintain wire integrity.
What must be ensured when placing the wire on the bone?
Intimate contact with the bone surface
The periosteum must be elevated to prevent necrosis.
What is a critical factor that can cause wires to fail?
Reduction in the effective diameter of the bone
Even small reductions (< 1% of bone diameter) can lead to loosening.
What is a full cerclage wire used for?
To wrap completely around the bone and compress fragments
Ideal for long oblique fractures.
What is the ideal configuration for using cerclage wires?
Long oblique or spiral fracture with length at least twice the diameter of the bone
This configuration helps in effective compression.
How far apart should cerclage wires be spaced?
Between half and the entire bone diameter apart
This spacing helps to compress effectively while preserving soft-tissue attachments.
What technique uses a K-wire to improve cerclage wire effectiveness?
Skewer pin technique
Redirects the action of the cerclage wire to prevent shearing of fragments.
What should cerclage wires not be used as?
The sole means of fracture repair
They should be used in conjunction with an intramedullary pin or other fixation methods.
What are the three common methods for tightening cerclage wires?
A. Twist knot
B. Single loop knot
C. Double loop knot
Each method has different tension and load resistance properties.
What is the primary purpose of cerclage wires?
To ensure intimate contact between proximal and distal fragments
This counters axially aligned compressive and rotational forces.
What must be maintained when bending over the wire tightener after tightening?
Tension in the crank
This ensures the free end folds back on itself securely.
What is a hemicerclage wire?
Wire passed through holes in fragments and wrapped around the bone
It adds little mechanical stability but can improve alignment.
For what type of fractures are interfragmentary wires most commonly used?
Simple fracture configurations in flat, non-weight-bearing bones
Primarily for mandibular and maxillary fractures.
What is the tension band wire technique used for?
To stabilize avulsion fragments
It opposes tensile forces from ligaments or tendons.
What type of knot is most commonly used with interfragmentary wires?
Twist knot
It allows simultaneous tightening and securing.
What is the initial tension achieved by a double loop cerclage knot?
300–500 N
Double loop knots are preferred for their strength.
What is the advantage of using a double loop knot over a single loop knot?
Twice as tight and strong
It has two strands and two arms to unbend.
What is the purpose of tension band wire in stabilizing avulsion fragments?
To counter tensile forces and convert them to compressive forces across the fracture line
This technique uses the pull of ligaments or tendons to stabilize fragments.
How many pins or K-wires are recommended for stabilizing avulsion fragments?
Two or more pins or K-wires
They are preferred over a single pin or screw to counter rotational forces.
What is the orientation of the pins when using tension band wire?
Perpendicular to the fracture plane
This orientation helps in effectively utilizing the resultant compressive forces.
What is the advantage of a lag screw in fracture stabilization?
It compresses the fragment to its bed
This can help counter rotational forces if there is interdigitation.
What is a disadvantage of using a lag screw for small fragments?
It may predispose the fragment to fracture due to pressure and tension
The size of the gliding hole and the screw head’s pressure are contributing factors.
Where is the transverse hole for the wire usually located in relation to the fracture line?
Approximately the same distance below the fracture line as the pins are above it
This positioning can be adjusted based on anatomy and exposure.
What pattern is created when passing the tension band wire?
A figure-of-eight pattern
This pattern directs the upper portion of the wire opposite to the pull of the ligament or tendon.
What type of knots are commonly used for tension band wires?
Twist knots
Loop style knots can also be used in some situations.
What should be done with the ends of the pins or K-wires after tightening the tension band wire?
Bend the ends away from the bone and cut them with 2–3 mm of bent arm
This helps embed the ends in the soft tissues around the fragment.
What limits the amount of static tension generated by a tension band wire?
The bending strength of the pins or K-wires
The size of the wire also plays a role in determining static tension.
Static tension refers to a type of tension band wiring where the forces applied to a fracture site remain relatively constant throughout the range of motion, unlike dynamic tension bands where forces increase with movement.
Fill in the blank: Tension band wires help to maintain tension more effectively if the wire is in direct contact with _______.
bone
Direct contact ensures effective tension maintenance.
What is the primary purpose of a tension band wire?
To counter dynamic forces in the ligament or tendon
Generating large static forces may not be crucial.
