Small animal fracture repair Flashcards
What are orthogonal radiographs?
Radiographs taken at right angle to each other
What is a fracture score
Numerical value given to fracture to determine how difficult fracture repair will be based on biological & non-biological factors
The higher the score the more demanding the fracture will be to repair
What are patient factors to consider when fracture scoring
weight of animal
- heavier = higher score
age
- younger = lower score
boisterousness & ability to manage cage rest
concurrent illnesses
What are fracture factors to consider when fracture scoring
type of fracture
- does it allow compression plating or require external fixator?
open or closed?
associated with soft tissue injuries
single or one of several fractures?
What are owner factors to consider when fracture scoring
will they comply with post-op instructions?
finances
What are surgeon factors to consider when fracture scoring
are they able to manage this fracture?
is the correct equipment available?
what are the normal forces on a long bone due to weight bearing and muscle contraction
Bending
Torsion
Tension
Axial compression
Name the forces acting on this bone
- axial compression
- tension
- bending (when weight bearing, leg placed at angle to ground or asymmetrical muscle contraction)
- torsion (when body changes direction with leg planted on ground)
why is it important to consider tension & compression aspects of the long bone in certain fracture types?
All diaphyseal bones are asymmetrically loaded when weight bearing
The mandible is also asymmetrically loaded during mastication
Which side should a plate be applied to?
Tension side as it will not be broken by tensile forces but will be by successive compressions
What are the tension aspects of the femur, tibia, radius, humerus & mandible
What are the consequences of axial compression on fractures?
good if fracture is transverse (at right angle to long bone) or if fracture interdigitates
if not the compression of a comminuted (multiple fragments) or oblique fracture causes fracture to collapse or shear
What are the consequences of tension on fractures?
tension produced by ligaments or tendons pulling on one of the bone fragments causes fracture to be distracted & needs to be overcome with lag screwing or tension bands
What are the consequences of torsion on fractures?
results in rotation of fracture site
requires management with plates, external fixator or interlocking nail
What are the consequences of bending on fractures?
occurs due to asymmetrical nature of bone loading
pin in centre of medullary cavity is best suited at counteracting this force
When does primary bone healing occur
when there is bone to bone healing
requires intimate contact of bone ends (preferably under compression)
- requires application of bone plate & extensive dissection & manipulation of soft tissue
When does secondary bone healing occur
When there is intervening callus formation
Doesn’t require accurate reduction of fracture
What is strain in bone healing
teh change in length over the original length of the fracture
if there is a small gap & much movement then strain is high & fracture fails to heal as tissue ruptures
to reduce strain the gap can be widened
- bone ends resorb or
- fracture becomes progressively stiffer by formation of granulation tissue, callus & bone
What is the purpose of post-operative radiographs after fracture repair
used to assess:
- alignment of fracture
- positioning of implants
- encroachment of implants into joints or soft tissues or bridging of growth plates in young animals
In what situations should radiographic assessment be made after a fracture repair?
prior to removal of implants
if progression is not as anticipated
there is evidence of sepsis
What are common options for fracture repairs
intramedullary pin & cerclage wire
plating (+/- compression)
intramedullary nail
external fixator
pin & tension band
combination
Describe the intramedullary pin
good at counteracting bending forces as it lies in centre of bone
poor at axial compression unless bone column reinstated
- generally reformed with aid of cerclage wires
increase in pin diameter results in disproportionate increase in strength
cerclage wires draw fragments to their normal position & fix them relying on circular cross-section of bone to produce stability
if fracture is transverse (at right angle to long axis of bone) then rotation is possible
- doesn’t occur with oblique fracture
- to prevent rotation plate can be used in addition to pin (plate rod combination) or external fixator
Describe the normograde placement of an IM pin
pin is placed from proximal end of proximal fragment
small skin incision is made & pin seated into bone
once pin is positioned in medullary cavity & advanced to just proximal to fracture site, the fracture is reduced
then pin is pushed into distal fragment
Describe retrograde placement of an IM pin
Pin enters proximal fragment distally (from fracture site)
leaves proximal bone fragment & small wound is made in skin & pin is pushed through
Pin then redirected and driven into distal fragment & fracture is reduced
What kind of repair has been done here
Tibial fracture repaired by IM pin & multiple cerclage wires
What is the function of an external fixator in a transverse fracture?
Prevents rotation & offers some resistance to axial compression
What kind of repair has been done here
Transverse humeral fracture repaired with IM pin & external fixator
Describe the intramedullary interlocking nail
requires special jigs to ensure screws enter nail
prevent rotation and bending
can only be used in straight bones (e.g., tibia and femur)
not used commonly
Describe the external fixator
repairs fracture with series of pins placed through skin & connected to connecting bar
pins attached to bar with clamps or epoxyresin
versatile repair & counteracts all forces applied to fracture (esp. if in combination with IM pin)
good for open fractures where open wound management may be required
What are some complications of external fixators
pins prone to infection
may be discharge (esp. when pins pass through large muscle mass)
require frequent examination & may require re-application of loose pins
may require staging down (removing few pins to change load bearing from fixator to bone)
several follow up radiographs may be necessary
Describe plate fixation
allow reconstruction of comminuted (multi-fragmented fractures
protect against axial and rotational forces (less good at bending as not positioned along central axis)
can be locking or non-locking
Describe locking vs non-locking plate fixation
non-locking:
- require plate to adhere to screws & bone by friction
locking:
- has thread in plate where screws engage as well as in bone
- diameter of screws in plate greater than screws in bone
- special guides required to align screw with thread of plate
What is a buttress plate
has strong central section that bridges a comminuted section of fracture
plate takes all the load
what is a neutrilisation plate
allows reconstruction of the fracture & acts as a scaffold, taking some of the load, the rest is taken by the reconstructed bone
what is a compression plate
compresses fracture by making use of eccentrically placed screws in oval screw hole
screw starts at top of slope & when tightened moves down slope & shifts the one fragment towards the fracture (hence compressing it)
the bone takes all the load
What is cyclical loading
Repeated application of stress on plate over time, which can lead to fatigue & eventual failure if load is unevenly distributed or exceeds plate’s threshold
What is the primary cause of plate failure & how can it be mitigated in the humerus, femur & tibia?
Trans cortex is incomplete, which, combined with absence of section of ulna, exposes plate to cyclical loading & failure.
In humerus, femur & tibia, this bending tendency can be managed using:
- IM pin
- Rod plate combination
What are avulsion or tension fractures & give examples?
fractures produced by distractive forced generated internally
as a result they are exposed to distractive forces during healing
larger fragments can be repaired by placing screw & compressing it using lagging technique
alternatively distractive forces can be converted into compressive forces using a tension band
examples:
- tibial tuberosity distracted by quadriceps
- olecranon distracted by triceps
- greater trochanter by gluteal muscles (image)
Describe lag screws
with lag screw compression can be applied to fracture
near hole is over drilled to have same diameter as thread so it doesn’t grip
when screw is tightened it pulls far fragment against near
used to produce rigid fixation & counteract distractive forces
Describe tension bands
fracture is reduced (aligned & then 2 pins used to fix it in position)
figure of 8 wire is applied opposite distractive force & 2 arms are tightened
with wire tightened & pulling in opposite direction to distractive force it results in compressive force applied to fracture
What are some things to consider when dealing with avian fractures
pneumatised bone with periosteal blood supply must be preserved during fracture repair
avian bone is brittle & more prone to splintering
avian bone heals primarily from endosteum
healing is rapid
anatomical abnormalities due to flight adaptations
- e.g. keep, coracoids & synsacrum
primary wing feathers originate in periosteum of ulna & tail feathers in pygostyle
fractures involving joint or within 10mm have poor prognosis
due to thin & brittle bones, IM pins & external fixators are used rather than plates
What is going on here
humeral fracture repaired with IM pin tied into uniplanar external fixator
clamps replaced with epoxyresin to reduce weight of device
