Implants Used with Internal Fixation - Pins and Wires Flashcards by Chloe Tredinnick

What are the 2 ways in which internal fixation can be applied?

Open reduction and internal fixation
Minimally invasive percutaneous plate osteosynthesis

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What is the aim of internal fixation?

To treat fractures by rigidly holding the fracture fragments together using implants with the aim to provide reliable, predictable bone healing

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Are pins and wires mainly used as primary or auxillary implants?

Auxillary

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What are pins and k wires made from?

316L stainless steel

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What is the difference between pins and k-wires?

Diameter

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Smooth stainless-steel pins are available in many sizes with a variety of tips, what are they?

Trocar – most common (3 sharp sides)

Chisel (2 sharp sides)

Threaded either at the end or at the centre.

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What size do steinmann pins come in?

(1.5mm – 6.5mm)

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Are steinmann pins or kirschner wires more elastic?

Kirschner wires (Kwire)

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What size are K wires?

< 2mm (0.7 – 1.6mm diameter)

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Advantages of IM pins (7)

The most rigid implant in resisting bending

Relatively easy to put in place

Can be applied using minimally invasive methods

Affordable

Versatile

Easy to remove when needed

Little inventory required (an IM pin can be applied by hand with a Jakob’s chuck or with an electric drill).

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Disadvantages of IM pins

Do not neutralize all forces acting on a fracture ( compression, rotation, shear, tension)

Dissemination of infection during open fractures, by seeding contaminants proximally and distally within the medullary cavity (low risk).

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Indications for use of IM pins? (combination..)

In combination with
-bone plates (plate-rod construct)
- ESF
- Cerclage wire
- Stand alone

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What configuration is used for IM pin can be left long and be connected with the ESF?

Tied in

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As the IM pin is placed in the centre of the weight bearing axis, the addition of an IM pin is particularly recommended when?

A non-load sharing situation of a comminuted fracture scenario.

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When ate IM pins used In combination with cerclage wire?

Only for very selected long oblique fractures.

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What are the 2 scenarios IM pins can be used alone?

Metacarpal, metatarsal bones - The surrounding bones counteract some of the mechanical disadvantages.

Very young animals or very small animals - The fast healing counteracts some of the disadvantages. In these cases, it is also often preferable to combine the IM pin with an ESF.

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Which of these statements about selecting pins and their sizes is correct?

Selection is based on radiographs.

Cats have straight bones which allow potentially smaller pins.

Too large a pin can result in interference with medullary blood supply and so delay the union.

When using an IM pin in combination with a plate or ESF, the pin should fill approximately 60-70% of the medullary cavity.

When using an IM pin to repair a mid-shaft fracture in combination with cerclage wires, the pin should fill 30-40% of the medullary cavity at its narrowest point.

Always start with a larger pin.

Selection is based on radiographs.

Too large a pin can result in interference with medullary blood supply and so delay the union.

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Cats have straight bones - what pin does this allow for?

Potentially larger

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When using an IM pin in combination with a plate or ESF, the pin should fill approximately ?% of the canal width.

30-40%

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When using an IM pin to repair a mid-shaft fracture in combination with cerclage wires, the pin should fill ? of the medullary cavity at its narrowest point.

60-70%

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What size pin to start with?

Small as poss and increase.

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What is the advantage of using IM Pin using hand chuck to place?

get a better ‘feeling’ for where the pin is going.

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Inserting IM pin with hand chuck:
- How does the pin start?
- What happens once entry point selected?

Start with only a small amount of pin penetrating from the hand chuck.
Rotate the pin back and forth once the entry point is selected.

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What are the 2 ways an IM pin can be placed?

Normograde
Retrograde

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An IM pin should be seated well - where?

Metaphyseal bone

For most bones and fracture scenarios, a which insertion is recommended.

Normograde

How is an IM pin placed in a retrograde fashion in the femur? CARE- why?

Pins can also be placed in a retrograde fashion in the femur, being driven from the fracture site up the proximal bone segment. This must be done with the hip in extension to avoid damage to the sciatic nerve as it exits the bone. The fracture is then reduced, and the pin is then advanced back down across the fracture site and into the distal fragment.

How do you know when the pin has reached distal region? (normograde femur?)

Resistance is felt

During normograde placement: What reduces the risk of inadvertent penetration of the distal cortex at the level of the stifle?

Distraction can be assisted by removing the sharp tip of the pin as it passes through the fracture site.

What size intramedullary pin is recommended when combined with a plate for the stabilisation of long bone fractures?

30-40% of medullary canal diameter

IM normograde humerus pin: What can be done prior to advancing into the distal fragment to reduce the risk of penetration of the cortex as the pin is advanced in the distal fragment?

The sharp tip of the pin can be removed

When intramedullary pins are inserted into the humerus it is advised that pins be angled where to increase bone purchase and length of the pin used.

toward or inserted into the medial aspect of the humeral condyle

Which of the following forces are most resisted by intramedullary pins? Rotation Shear Tension Bending

Bending

Does this apply to IM pin of the femur or humerus: Apply whilst holding limb in extension ad adduction?

Femur

Does this apply to IM pin of the femur or humerus: Drill initially perpendicular to the bone surface then redirect

Humerus

Does this apply to IM pin of the femur or humerus: Retrograde with an increased risk to enter joint

Humerus

Does this apply to IM pin of the femur or humerus: Insert from trochanteric fossa

Femur

Femur IM pin: A) Where is it inserted from? B) Normo or retrograde preferred?

A) Trochanteric fossa B) Normo

Why is retrograde IM femur pins contraindicated in cats?

High risk of sciatic nerve irritation/damage

How is the leg positioned for IM pin placement in the femur?

Apply while holding the leg in extension and adduction, this helps to avoid the sciatic nerve

Humerus IM pin: A) Normo or retro? B) What angle is the pin placed? C) Where is the pin aimed?

A) Normo B) Drill initially perpendicular to the bone surface then redirect C) Aim caudally, medially and distally towards the medial epicondylar crest

What is the risk of retrograde placement with the humerus?

Enter shoulder joint

Where is the entry point for humerus IM pin?

Entry point on lateral slope of the ridge of the greater tubercle near its base

How is the length produced/pin length finalised for humerus and femur IM pin placement?

Cut as short as poss or tie in

Ulna IM pin placement: A) Which part of ulnar bone is v hard? B) Normo or retograde easier? C) CARE with IM pins why?

A) Proximal B) Retro C) Difficult to get adequate size

For olecranon fractures must use at least a pin and..?

tension band, preferably plate

Tibia IM pin placement: A) Which direction? B) Where is the pin inserted?

A) Normograde B) Insert pin from the medial side of the proximal tibia at a point halfway between tibial tuberosity and medial collateral ligament.

How are IM pins placed in metacarpal/metatarsal

Retrograde or normograde via a carefully drilled or burred dorsal slot.

Whilst placing an IM pin, you should watch the # site to prevent?

Fissures

AVOID penetration of which cortex?

Distal

Use a bolt cutter to cut the pin as short as possible above the bone What length?

<5mm

What happens is the pin is left too long? (4)

- Seroma - Damage other structures - Post op pain - Redcued stability

How do you prep/cut the pin to ensure it is as short a possible.

Seat the pin to the proper depth and then withdraw it about 1-2cm. Cut the pin as close as possible and then impact it with a punch and mallet.

When can a cerclage wire be used permanently?

Long oblique fractures when used in combination with another method of fixation such as an intramedullary pin or plate.

What are the possible uses of cerclages wires? (2)

Temporary Permanent

How long should end of cerclage wire be cut before twisting?

1.5-2cm

Cerclage wires must be twisted symmetrically - why?

An incorrectly twisted knot does not hold under load.

Other than twisting - what are the 2 other ways to secure a cerclage wire?

Single + double loop

When applying cerclage wire which of the following statements is correct? - For short oblique fractures one cerclage wire will often be sufficient. - Cerclage wire is best secured with two twist knots. - Cerclage wire can be used when the length of an oblique fracture is at least twice the diameter of the bone and a minimum of two cerclage wires should be applied. - Cerclage wire is an appropriate method of fixation when striving for secondary bone healing.

Cerclage wire can be used when the length of an oblique fracture is at least twice the diameter of the bone and a minimum of two cerclage wires should be applied.

What change in the wire significantly increases the tensile strength of the wire?

increase in radius

Tensile strength formula?

Tensile strength = π x radius^2

What wire is placed through predrilled holes in bone.?

Hemicerclage/interfragmentary wire

What wire is placed around the circumference of the bone?

Cerclage wire

What often CAUSES complications with wire placement?

Wire too thin Inappropriate wire Failure to tighten Insufficient cerclage.

Cerclage wires; true or false: Can be used alone in some instances

FALSE Should only be used with other implants, never alone.

Cerclage wires; What is the MAXIMUM number of # fragments?

Cerclage wires: How long can the # line be compared to diameter of marrow cavity?

Length of fracture line should be two to three times the diameter of the marrow cavity.

At least how many cerclage wires should be used?

At least 2

How far apart should cerclage wires be placed?

About half a bone diameter

With what bone type should a k wire as a skewer pin be considered do to possibility of cerclage wires slipping?

Conical bone

What force must cerclage wires generate between # surfaces to prevent movement/collapse?

Compression

What diameter cerclage for cats and small dogs?

22 gauge (0.8mm)

What diameter cerclage for medium dogs?

20 gauge (1mm)

What diameter cerclage for large dogs >20kg?

18 gauge (1.2mm)

Securing cerclage wires with twist knot: A) What is the principle? B) What instrument is needed?

A) The two strands of wire wrap around each other. B) Use wire pliers.

Twist knots (securing cerclage wires) A) How to generate equal tension and good knot security? B) How many twist knots to secure

A) Pull away from bone whilst twisting B) Only one to two twists required to secure the knot, usually leave three, but not longer.

Twist knots (securing cerclage wires) A) How are they left for maximum security? B) What happens is there is insufficient soft tissue coverage?

A) For maximum stability leave perpendicular to bone. B) If there is really insufficient soft tissue coverage, continue to pull and twist further and bend over flat on the bone (but bending weakens cerclage).

Single/double loop knots securing cerclage wires: A) What is needed at one end? B) What device is needed?

A) Small loop at one end B) Tightening device

When are tension band wires used?(2)

- Stabilise avulsion # - Osteotomies; where tensile forces are present

Typical sites for tension band wires? (4)

Olecranon Tibial tuberosity Calcaneus Malleoli

When placing tension band wire in the tibia, how far should the K wire be advanced?

To engage and just penetrate caudal cortex

Which way is the tunnel made for tension band wire of the tibia?

Medio-lateral

How many twist knots when securing tension band wire?

Where are the wires trimmed with tension band wire?

Level of 3rd-4th twist

Which of the following best describes the function of the two K wires that are placed as part of a pin and tension band construct? - To anchor the tension band - To convert a distraction force into a compressive force - To counter rotational forces - To counteract the tension of the attaching soft tissues

To counter rotational forces

For a tension band wire (TBW) - what is done?

construct (usually two) K-wires are combined with a figure of eight cerclage wire.

For a tension band wire (TBW) What forces are counteracted and what are they converted into?

This construct counteracts active distractive forces and converts them into compressive forces.

Indications for TBW? (2)

Avulsion fractures Osteotomies at relevant locations, e.g. tibial tuberosity transposition.

Match the anatomic structures with the avulsed fragment on which they pull. Supraglenoid tubercle of the scapula

Bicep

Match the anatomic structures with the avulsed fragment on which they pull. Olecronon

Tricep

Match the anatomic structures with the avulsed fragment on which they pull. Styloid processes of radius and ulna; malleoli

Collateral lig

Match the anatomic structures with the avulsed fragment on which they pull. Greater trochanter of the femur

Gluteals

Match the anatomic structures with the avulsed fragment on which they pull. Patella; tibial tuberosity

Patellar tendon

TBW: application: A) How many K wires? B) Where are K wires placed? C) Where are K wires seated?

A) 2 B) Place parallel to each other and perpendicular to the fracture/osteotomy to allow compression of the fracture site as the cerclage wire is tightened. C) in the opposite cortex.

TBW: application: A) Where is a hole placed? (include where and direction)

Place a hole in transverse direction for the orthopaedic wire the same distance below the fracture as the pins are inserted above.

TBW: application: A) How are the K wires placed in holes? B) How are k wires positioned at the end?

A) Place two pieces of K-wire in figure-of-eight and tighten them into two twists on either side. B) Bent down and buried in soft tissue.

Using a figure of 8 with k wires in TBW; what are the two benefits of this?

- Symmetrical tension - Most stable construct

Interlocking nails What forces are resisted? (2)

Torsion Compression

Interlocking nails neutralises forces that what cannot?

IM pins

Generally with interlocking nails: What are placed?

2 bolts proximally 2 bolts distally

When can cross pins be used? (2)

- Simple salter Harris - Metaphyseal #

Cross ins must penetrate what?

Trans-cortex

What are used for crossed dynamic pins? (3)

Rush pins small Steinmann pins K-wires.

What is the benefit of Rush pins over Steinmann(2)

More flexible An oblique tip for sliding in the medullary cavity and a hook at the other end

Crossed Dynamic Pins: A) How many points of contact with the bone to ensure # stable? B) What is # stability due to?

A) 3 B) Elasticity

Stability of crossed dynamic pins compared to parallel/cross pins?

LESS - use not encouraged