Pins, Wires, & External Fixation Flashcards
What are intramedullary pins? When are they most comonly used? When is their use contraindicated?
Steinmann pins placed in the medullary cavity of bone
fractures of the humerus, femur, tibia, ulna, metatarsal, and metacarpal
radius - insertion point interferes with carpus and violates the joint
What are intramedullary (Steinmann) pins made out of?
316L stainless steel cylindrical rods with a trochar or chisel point
What are 3 advantages to the use of intramedullary (Steinmann) pins?
- resistant to bending loads from any directions
- less expensive, inventory, and surgical exposure
- less tissue trauma and vascular damage
What are 4 disadvantages to the use of intramedullary (Steinmann) pins?
- not designed to maintain bone length
- resists bending forces only
- proximal pin migration
- limited application
How are the diameters of intramedullary pins determined? How are pins placed?
- ensure 60-70% of the medullary cavity will be filled and pair the pin with a cerclage wire
- can use a smaller diameter when paired with an external fixator (50-60%) or bone plate (40-50%)
select 2 pins of the same length, one acting as a guide to aim the second pin
What needs to be avoided when placing intramedullary pins? In what directions are pins placed?
must not penetrate joint surface, end of pin is cut or left long and tied to an external fixator
- NORMOGRADE = toward fracture (femur, tibia, humerus)
- RETROGRADE = away from fracture (femur, humerus)
What are Kirshner wires?
small, smooth Steinmann pins with trochar points
- more bendable
- threaded to avoid movement
Is this intramedullary pin placed correctly?
no - pin is through the proximal joint
How is an intramedullary pin applied normograde? What is a pro and con to this application?
- start the pin at one end of the bone and drive it into the medullary canal toward the fracture site
- reduce the fracture and drive it into the metaphyseal bone
PRO - less fracture manipulation
CON - difficult to identify correct entry point
How is an intramedullary pin applied retrograde?
- expose fracture and place pin in the medullary canal of the proximal segment
- drive pin until it exits the proximal segment
- replace chuck on proximal portion of the pin and withdraw to the fracture segment
- reduce fracture and drive pin into the metaphyseal bone
When is the use of cross pins indicated? What do they do?
simple fractures close to the joint - physeal, metaphyseal
engages the near and far cortexes to counteract rotational and bending forces
What is the cause of seroma development post-op following placement of pins? How are they resolved?
forms at the pin end due to irritation of the pin moving in soft tissue
- removal once the fracture heals and bone union occurs
- non-healed fracture = another surgery
What are interlocking nails? What does it do? Where are they most commonly placed?
nails inserted into the medullary canal and locked into place with screws or cross-locking bolts placed through the fracture segments and nail
resist all forces - bending (nail), axial/rotational (locking bone screws)
mid-diaphyseal humeral, femoral, or tibial fractures
When is the placement of interlocking nails contraindicated?
within the radium - violates the joint
How are screws placed on the distal and proximal ends for interlocking nails?
> 2 cm from the fracture line
- DISTAL: trocar or blunt
- PROXIMAL: internally threaded hole, 2 alignment tabs
What are fatigue fractures?
fractures at screw hole sites when an inadequate-sized nail is used or when the nail hole is adjacent to the fracture line
What is orthopedic wire? How are they used?
malleable form of stainless steel with a larger diameter, making it have higher tensile strength
NEVER used as sole method of fracture fixation, except for interfragmentary fractures —> used with IM pins, external fixators, and plates
What are 2 reasons to use full cerclage wire?
- long oblique or spiral fractures in which the fracture line is at least 2 times the diameter of the diaphysis at the fracture line (must be reduced)
- multiple (>4) fragments held in position
What is the golden rule for the placement of full cerclage wire? What sizes are used?
at least 0.5 cm from the fracture ends and 1 cm apart
- large dogs ~20 kg = 18 gauge
- small dogs and cats = 20-22 gauge
How are full cerclage wires placed?
- use a wire passer to pass wire around the bone - always place at least 2 full wires
- ensure it is placed perpendicular to the bone
- use a wire tightener to twist the wire under tension preload
- cut the wire leaving 2-3 twists
What is avoided when placing cerclage wires?
5 twists and bending over
- can weaken and loosen wire, allowing it to slide on bone and disrupt blood supply
When are hemicerclage wires used? How are they placed?
limited indications - short oblique diaphyseal fractures —> counteracts rotation in one direction
- hole is drilled in the proximal and distal fracture segments
- wire is paced through the holes and around the IM pin, then tightened
(holes tend to weaken bone)
When are skewer pins used? How are they placed? What action does it have?
short oblique fractures —> incorporates cerclage wire and K-wire
- K-wire is placed on the line that bisects the perpendiculars of the long axis of the bone and fracture
- cerclage wire is placed around the K-wire and tightened
compresses the fracture
When are tension bands placed? What is their purpose?
avulsion fractures at the origin and insertion of muscles on bone —> greater trochanter/tuberosity, olecranon, supraglenoid tuberosity, patella, lateral malleolus
converts distractive tensile forces into compressive forces
How are tension bands placed?
- fragment is reduced
- a hole is drilled in the cortex abone as below the fracture line
- 2 K-wires are driven perpendicular to the fracture line and parallel to each other to maintain reduction
- both sides of the wire are tightened equally so they are in direct contact with the bone
- bend and twist the K-wire
How is cerclage wire placed?
wire is placed circumferentially around the bone column and twisted —> compresses across the fracture line
How are external skeletal fixators used? When is their use contraindicated?
used to stabilize bone segments with percutaneous wires/pins for closed/open fractures, limb deformities, temporary joint immobilization, and arthrodesis
articular fractures
How are external skeletal fixators classified?
based on the number of places occupied by the frame and the number of sides of the limb from where the fixator protrudes
- Ia = single rod with screws coming from one angle
- Ib = two rods with screws coming from 2 angles
- II = pin from one rod connected to another
What 3 devices make up external skeletal fixators?
- fixation pins - hold the major fragments
- external connectors - support (stainless steel, carbon composite, titanium)
- linkage devices - attach pins and connectors
In what 2 ways is the strength/stiffness of external skeletal fixators increased?
- increased pin diameter - do not exceed 25-30% of bone diameter
- increased number of fixation pins up to 4 pins in the proximal and distal major fragments
What are some other ways to increase the strength/stiffness of external skeletal fixators?
- locate pins near the joints and fracture
- decrease the distance between the bone and pin-clamp interface
- increase the connecting bar size and number of planes of the bar
- tie intramedullary pin into the fixator frame
- successively stronger and stiffer type I to III
What are the 4 types of external fixator pins?
- half - end-threaded to penetrate both cortices, but only 1 skin surface
- full - centrally threaded to penetrate both cortices and skin surfaces
- negative - core diameter of the threaded section is smaller than the diameter of the smooth section
- positive - core diameter is consistent between smooth and threaded regions
What are the minimum amount of pins needed for each fracture fragments?
minimum 2 pins (4 total) per fragment with 3 pins optimal (6 total)
When are unilateral-uniplanar (Type Ia) external fixators used?
- radial fractures - cranial and medial surfaces
- tibial fractures - medial surface
- femur/humerus fractures - lateral surfaces
What are the 2 uses of unilateral-biplanar (Type Ib) external fixators?
- radius - craniomedial and craniolateral
- tibia - cranial and medial
What are the maximal and minimal amount of pins used in bilateral-uniplanar (Type II) external fixators? When are they used?
- MAXIMAL = filled with full amount of pins
- MINIMAL = 2 full pins
radius and tibial frontal planes only —> cannot be used on femur and humerus
What is the structure of bilateral-biplanar (Type III) external fixators? When are they used?
type II frame in the frontal plane and type Ia frame in the midsaggital plane
only in very large dogs with low fracture assessment scores on the radius and tibia
When are external fixators used with an intramedullary pin? How can the fixation be increased without increasing pin numbers?
complicated humeral and femoral fractures - IM pin + type Ia or IIb
add more external bars or an augmentation plate
What is the two-stage technique of placing acrylic splints?
pin placement and fracture reduction assessed before hardening of the acrylic
What are 3 advantages to using external fixators and acrylic frames?
- can connect pins in various planes, which is helpful for mandibular fractures
- lightweight = good for use in toy breeds, cats, and exotics
- eliminates need for fixation clamps
What post-op care is required for external fixators? When is it able to be removed?
- sterile gauzes are opened, crumpled, and placed around and between fixation pins and the limb is wrapped with elastic bandage
- pin-skin interface is cleaned and bandage is changed everyday until 1 week post-op if little to no d/c is noted
once the bone has healed —> under sedation, pin-gripper is loosened, and fixation pins are removed
What are 4 indications for circular/ring fixators?
- compress or distract fractures/nonunions
- dynamically correct bone angular and length deformities
- transport bone segments
- complicated fractures of the tibia and radius
What is the structure of ring fixators? When is the diameter altered?
2 rings placed on each side of the fracture with the most proximal and distal rings places at metaphyseal locations and inner rings placed close to the fracture side + 4 pairs of wires
increased to decrease axial stiffness (affects wire length)
What are 6 external fixator complications?
- pins or wires loosening or breaking
- delayed, nonunion, or malunion fractures due to loosening of the fixator
- pin tract infection
- osteomyelitis
- loss of joint motion
- nerve or vascular damage —> AVOID PINS IN DIAPHYSIS OF HUMERUS BLINDLY
What are some advantages to external fixator placement?
- variety of construct options
- can be placed with minimal disruption of the fracture fragments with percutaneous pin placement
- implants are able to be removed following fracture healing and can be done in stages to slowing increase loading on the bone (Wolff’s Law)
- useful for treatment of grad II and III open fractures
- cost is relatively low compares to some internal fixation devices
- less invasive than plate fixation
- allows better access to wounds than external coaptation
What are some disadvantages of external fixator placement?
- frequent rechecks required ($$) for bandage changes and evaluation
- morbidity associated with skin-pin interface
- pin loosening, implant failure
- external hardware poses risk to the fracture repait to people/objects —> requires high level of compliance!
- additional procedures required for destabilization and implant removal
Altering external fixator rigidity:
