Pins and nails Flashcards
Which technique has become the principle way to hold long bones of the leg and to a lesser degree the humerus?
Intramedullary nails
What care must be taken when imaging intramedullary nail insertion?
Radiation dose that the surgeon is subjected to
What are pins also known as?
K-wires
Describe the design of a pin
Have sharp “trochar points” or occasionlly threaded, self tapping ends
How are pins inserted?
Driven into bone fragments by hand driven T-handles or on hand or even air powered drills
When are pins most commonly used?
In small bones (e.g. foot and hands)
Occassionally in upper limb long bones in small children
Why are pins generally used in pairs?
To minimise the rotatory element in the final pin/bone construct
When might pins be used in conjunction with flexible wire?
To achieve compression between 2 small bone surfaces (e.g. patella fracture)
What 2 ways is flexible wire used?
Cerclage (static)
Tension band 9dynamic)
How are flexible wires used as cerclage?
Encircles or crosses the fragments pushing them together (e.g. cracked long bone)
Why have nails replaced cerclage in most situations?
Do less damage to the blood supply if used properly
Are much more robust
Give an example of when cerclage is useful
Around cracked fragments of bone around endoprostheses - during hip reviison surgery sometimes deliberately crack femur to remove primary prosthesis - cerclage can be used to maintain a medullary cavity so that the new prosthesis can still be inserted
How do wires work as a tension band?
Utilises the power of surrounding muscles to produce compression at a fracture site (e.g. patellar, olecranon and medial malleolar fractures) - the more the muscles work the more stable the fracture will be
Why is tension banding a useful way of rehabilitating damaged joints?
Movement promotes stability and encourages joint nutrition and cartilage as well as bone recovery
Why when using cerclage wires is it important, where possible, to work beneath the periosteum?
To avoid damage to blood supply
Why are wires still used extensively in spinal surgery?
It can be threaded through restricted holes and its versatility can produce powerful fiation
What is the principal reason that wire has fallen out of routine use?
Its awkwardness is use and the need to twist it properly (over-twisting causes breakages)
Also surgeons find other techniques more elegant
How do intramedullary nails work?
Placed in the medullary canal and fucntion as a form of internal splint which stabilises long bone fractures with minimal damage to the surrounding soft tissues
What are the advantages of intramedullary nails?
Minimal damage to surrounding soft tissues
Uusally withstand axial and bending stresses
Can achieve rotatory control when combined with screws and playes
Can be mobilised early after surgery with weight bearing before bony union
What is the antegrade technique?
Nail is inserted into the bone from one end whilst not disturbing the fracture site ata all
What is essential when attempting antegrade technique?
X-ray image intensifier
What is the retrograde technique?
Fracture site is opened by soft tissue dissection and the fracture end delivered into the wound for reaming and insertion of the nail
What is reaming?
Widening of the intramedullary canalthrough paring off the inner surface of the bone
What are current developments in nail design centred around?
Whether to ream or use nails which are solid and thinner so they they can be inserted without damage to the inner blood supply
Which patient groups in particular benefit from early aggressive medullary fixation?
Elderly
Multiply injured people
Which 3 factors determine the effectiveness of a nail?
The material it is made of
How much of the nail is in contact with the bone
Dimensions and shape of the nail (and its wall thickness if ti is hollow_
What material are most nails made of?
Stainless steel
Why are most nails made of stainless steel?
Good strength and stiffness characteristics
Easy to handle during manufacturing
Well tolerated by body tissues
Why is titanium not a good material for nails?
More susceptible to weakening either if a hole is drilled across it or if it is accidentally abraded during insertion or locking
What is notch sensitivity?
If a material is accidentally abraded during insertion or locking
What is the working length of a nail?
The length of a nail that transmits load from one main fragment of a fractured bone to the other
Why is the working length of a nail important?
The stiffness of a nail in both rotation and bending is related inversely to its working length
How is a nail anchored to the bone in a multifragmentary shaft fracture?
Via cross-locking screws
How does working length affect the relative movement between the main bone fragments?
The longer the working length - the greater the relative movement between the main bone fragments
Why are nails which are inserted across a multifragmentary shaft fracture less able to resist bending and torsional forces?
Bone is gripped solely by the nails proximal and distal screws = LONGER working length (equal to the distance between top and bottom locking screws)
So less able to resist bending and torsional forces
Why are solid nails stronger than hollow nails of the same diameter?
More metal for their volume
How can the grip of hollow nails be optimised?
Chose a size which will grip the inside of a reamed bone, whatever its size, along a large length of its internal diameter
Curve nails roughly to conform to the shape of the bone for which they are designed
How can the bending stiffness of hollow nails be increased?
Increase thickness of walls
What is the advantage of having a somewhat flexible nail?
Has a little “give” on insertion making it easier to put in and will allow nail to deform slightly to conform to the natural shape of the bone
How is the stiffness related to the diameter of the nail?
Stiffness = proportional to the diameter raised to the fourth power
How is the bending strength related to the diameter of a nail?
varies with the third power of the diameter
How are the strength and stiffness of a nail related?
As nails get a bit stronger they get considerably more stiff
How can stiffness be reduced in a nail?
Using a longitudinal slot in the wall
What is the disadvantage of a longitudinal slot in the wall of a nail?
Loses some overall bending strength and especially torsional strength
Describe the typical design of most nails
Curved according to the shape of the bone
Slotted along their length
Wall thickness of 1.2mm
What are the 5 ideal indications for nailing?
Transverse and short oblique fractures of the tibial and femoral shafts
Comminuted fractures of tibia and femur (providing cross locking capabilities are available)
Pathological shaft fractures (esp in osteoporotic bone)
Delayed or non-union of the shafts of the femur or tibia
Selected open fractures
What are the contraindications to nailing?
Children (nail may damage growth plates)
When there is a fracture involving an adjacent joint
What are the 3 configurations nails can be used in?
Simple nail with no additions
With screws (situated obliquely or at right angles to the axis of the nail and passing through holes in the nail)
With plates
In what fractures are nails particularly used in association with plates?
To treat fractures of the proximal and distal femur
Why are simple nails good?
Maintains fairly accurate, but not necessary precise, anatomical alignment
Permits early weight bearing
Which 3 bones are simple nails mst commonly used in?
Femur
Tibia
Humerus
How can the effective working length of a nail be increased?
By adding cross screws
Why is using cross screws good?
Increases effective working length of a nail
Ensure good rotatory control (independent of the contact between nail and bone)
Increases the length of long bones which can be nailed
Why are the upper and lower ends of the femur problematic in fracture fixation?
Femur is constantly being bent under load because of the 135 degree offset of the femoral neck (creates an angle of about 7 degrees between the axis of the femur and the tibial plateau when the tibial plateau is orientated horizontally, parallel with the ground)
Which group are fractures of the femoral neck common?
Old age (particularly osteoporotic women)
How does an extracapsular femur fracture tend to sit?
Proximal fragment to keel over medially and the femur to shorten
What dictates the degree of displacement of an extracapsular femur fracture?
The degree of damage to the medial part of the upper femoral shaft
How is medial ffragmentation of the upper femur treated? Why?
Impractical to restore
Add extra support to lateral side with a plate
Nail the remaining proximal femoral neck
(fem neck is effectively rejoined to the shaft by a nail acting as a cantilever against the buttressed lateral femoral cortex)
What are the complications of nailing?
Centre around difficulty of insertion
- Reamers can get stuck or penetrate through outside of the bone
- Nail can be inserted in wrong position
- Rotatory misalignment is common
- Infection
