small -treatment options for fractures Flashcards
what are the 5 most common options for SA fracture repair?
- Intramedullary pin and cerclage wire
- Plating ( +/- compression)
- Intramedullary nail
- External fixator
- Pin and tension band
Various combinations of these including a pin and plate (plate rod combination) and an IM pin with tied in external fixator
what force is the intrameddulary pin good at counteracting?
what force is it poor at counteracting?
what is used with the intermedallary pin?
Excellent at counteracting bending forces as it lies in the centre of the bone but poor at axial compression unless the bone column is reinstated.
With this form of fixation the bone column is generally reformed with the aid of cerclage wires
what is the relationship between intermeduallary pin diameter and strenght?
disproportionate - small increase in diametre = big increase in strength
what is the purpose of cerclage wires?
Cerclage wires draw fragments to their normal position and then fix them relying on the circular cross-section of the bone to produce stability
what can occur with transvers fractures and intermeddalry pins, how is this counteracted?
If a fracture is transverse i.e. at right angles to the long axis of the bone then rotation is possible. This does not occur with an oblique fracture.
To prevent this rotation a plate can be used in addition to the pin (plate rod combination) or an external fixator employed
how are IM pins placed using the normograde method?
normograde:
- pin placed from proximal end of the proximal fragment
- via a skin incision
-Once the pin is positioned in the medullary cavity and advanced to just proximal to the fracture site the fracture is reduced. Then the pin is pushed into the distal fragment.
This is more difficult than retrograde pinning but allows accurate placement of the pin proximally avoiding the sciatic nerve in the femur or entering the stifle in the tibial repair.
what are the two methods to place IM pins?
normograde and retrograde
how are IM pins placed using the retrograde method?
- The pin enters the proximal fragment distally i.e. from the fracture site
- It leaves the proximal bone fragment and a small wound is made in the skin and the pin pushed through.
- The pin is grasped by the Jacob’s chick pulled proximally till it is positioned just proximal to the fracture site
- The fracture is reduced and pin driven into the distal fragment
This is easier than normograde pinning but suffers from loss of control as to where the proximal part of the pin lies
what is the issue with retrograde IM pin placement in the cat?
can damage the siatic nerve
what is the issue with retrograde Im pin placement in the tibia?
can enter the stifle
what is the benefit of placing an external fixator with an IM pin?
the IM interlocking nail is not used often in vet med.
what are the two disadvantages with this method and what is the one advantage?
Dis:
This requires special jigs to ensure the screws enters the nail
They are strong and excellent at preventing rotation and bending
Ad:
They can only be used in straight bones such as the tibia and femur
what is an external fixator?
This is a means of repairing a fracture with a series of pins placed through
the skin and connected to a connecting bar.
The pins are attached to the bar with clamps or epoxyresin
These pins may be threaded or the triangulation of the pins prevents them pulling out
why is the external fixator good for fracture repair?
This is very versatile and type of fracture repair and counteracts all the forces
applied to a fracture particularly if combined with an IM pin (biplanar ones are stronger)
They are particularly useful for open fractures where open wound management
may be required
what are the 5 disadvantages of external fixators?
- The pins are prone to infection.
- They may be discharge especially where the pins pass through large muscle masses.
- They require frequent examinations and may require re-application of loose pins
- They may require staging down. ie removing a few pins to change the load bearing from the fixator to the bone.
- Several follow up radiographs may be necessary
what type of fixation does a comminuted fracture need?
plate fixation
what forces does plate fixation prtect against?
Protect against axial and rotational forces but are less good at preventing bending as they are not positioned along the central axis of the bone. This is particularly true when the far or trans cortex is incomplete and the plate is exposed to cyclical loading
what is the difference between locking and non-locking plate fixators?
The non locking are the older type and require the plate to adhere to the screws by friction. This also applies to the plate and bone
In the locking plate there is a thread in the plate where the screw engages as as well as in the bone. The diameter of the screw that engages in the plate is generally greater than that which engages the bone.
special guides are required to align the screw with the thread of the plate
what is a buttress plate like?
A buttress plate has a strong central section that bridges a comminuted section of the fracture. In this arrangement the plate takes all the load
what is a neutralisation plate like?
A neutralisation plate allows reconstruction of the fracture acting as an scaffold and taking some of the load, the rest being taken by the reconstructed bone
what does a compression plate do?
The compression plate compresses the fracture by making use of eccentrically placed screws in an oval screw hole. The screw starts its flight at the top of the slope and when tightened it moves down the slope and shifts the one fragment towards the fracture hence compressing it. When used this way the bone
takes all of the load.
what can cause plate failure?
cyclical loading of bending forces can cause the plate to fail
the humerus, femur and tibia this bending tendency can be managed with an IM pin, a rod plate combination
what are avulsion or tension fractures?
These are a special set of fractures that are produced by distractive forces generated internally.
distractive forces eg - quadriceps on tibial tuberosity or triceps on olecranon or gluteal muscles on the greater trochanter
As a result they are exposed to distractive forces during healing
what can be done about avulsionor tension fractures?
With larger fragments they can be repaired by placing a screw and compressing it using a lagging technique
Alternatively distractive forces can be converted into compressive forms using a tension band
describe how a lag screw works?
- With a lag screw compression can be applied to the fracture
- The near hole is over drilled to have the same diameter as the thread so it doesn’t grip - glide hole
- When the screw is tightened it pulls the far fragment against the near
- This is used to produced rigid fixation and will counteract the distractive forces
how does a tension band work?
- The fracture is reduced i.e. aligned and then two pins are used to fix it in position.
- A figure of 8 of wire is applied opposite the distractive force and the two arms are tightened.
- With the wire tightened and pulling in the opposite direction to the distractive force the end result or resultant (Pythagoras’ parallelogram of forces) is a compressive force applied to the fracture
what is different about avian bones?
- Pneumatised(air filled) bone with periosteal blood supply that must be preserved during fracture repair
- Avian bone is brittle and more prone to splintering
- Avian bone heals primarily from the endosteum
- Healing is rapid
where do the primary wing feathers and tail feathers originate?
Primary wing feathers originate in the periosteum of the ulna and the tail feathers in the pygostyle
what type of frature in birds has a poor prognosis?
Fractures involving the joint or within 10mm of such carry a poor prognosis
what type of stabalistion can be applied to avian bones?
Due to the thin and brittle bones IM pins and external fixators are used rather than plates
