External skeletal fixation and fracture reduction

Question 1

External skeletal fixation

Answer 1

A means of stabilising fractures / osteotomies / joints using percutaneous pins or wires that penetrate bone cortices internally and are connected together externally to form a rigid frame.

There are different linear and circular external skeletal fixator systems available, which can also be combined in so-called hybrid constructs.

Question 2

Elements of a linear external fixator

Answer 2

Pin: connects the frame to the bone, either smooth or threaded

Connecting bar or rod: used to join a group of pins together to immobilise the fragments

Clamp: double (connects two connecting rods) or single (attaches a pin to the connecting rod)

Question 3

Negatively profiled (Ellis) pin

Answer 3

Thread cut out of pin - negative profile.

The thread/pin interface is the weak point on the Ellis pins - protect by inserting pin/thread interface into the medullary canal of the bone.

Threaded portion only engages one cortex (far) – poorer resistance to pullout.

Question 4

Positively profile (Imex) pins

Answer 4

Thread built on - positive profile - more expensive & no weak point.

Threaded portion engages both cortices – better resistance to pull out.

Question 5

Linear frame configurations

Answer 5

Unilateral (Ia): Half pin splintage - fixation pins pass through only one skin surface (both bone cortices). The connecting clamps and bars are placed on one side of the leg only.

Ib: Two unilateral frames (1a) applied in different planes.

Bilateral (II): Full pin splintage - fixation pins pass through both skin surfaces and both bone cortices. The connecting clamps and bars are used on both sides of the leg.

Bilateral/biplanar (III): a combination of half pin and full pin splintage - type I and type II splints are placed perpendicular to each other and are interconnected at both ends creating a 3-d frame.

Question 6

Application of ESF

Answer 6

Type 2 frames are prohibited on the humerus and femur by the thoracic wall/abdomen

Safe corridors for pin placement are reported for each bone and must be respected

Prior to pin insertion, a 1-2cm skin incision is made and a small soft tissue tunnel is dissected all the way to the bone cortex. A drill sleeve must be used to protect the soft tissues

Aim for 4 pins per fragment (3 minimum)

All pins should engage 2 cortices

Pins should be 20% of the bone diameter

External skeletal fixation is inherently a bridging form of fixation

It is therefore most commonly utilised for comminuted (non-reconstructable) fractures

Reconstructible, compressible fractures should generally be reconstructed and compressed - not possible with ESF

Question 7

Methods to increase the strength of the ESF

Answer 7

1. Frame configuration - bilateral biplanar stronger than bilateral which is stronger than unilateral.
2. Bar - using a double bar doubles the resistance to compression
3. Placing the bar as close to the bone as possible increases resistance to compression
4. Pins - Mechanical studies have shown that a maximum of 4 pins per fragment is ideal.
5. Use pins no bigger than a 1/5th of the diameter of the bone to reduce the chance of iatrogenic fracture
6. Space the pins out over the length of the bone
7. Place the central pins as close to the fracture as possible

Question 8

Management of ESF

Answer 8

Absorbent non-adherent dressings are initially applied around the pin tracts

Rubber caps can be placed on sharp pin ends

The frame can be bandaged for protection

The pin tracts are only cleaned if they are excessively exudative, otherwise they should not be disturbed

Question 9

Circular ESF

Answer 9

Uses small wires instead of pins, which are fastened to rings.

This makes the system suitable for the application on small bones or to very small fracture fragments close to the joints.

Other important applications for circular ESF’s are limb lengthening and correction of angular limb deformities.

Question 10

Advantages of ESF

Answer 10

Inexpensive

Easy?

Can be applied minimally invasively

Minimal inventory and instrumentation

Adjustable

Does not require skin closure

Question 11

Disadvantages of ESF

Answer 11

Bulky

Challenging post-op management

Owner/patient compliance

Pin tract infections

Loosening and loss of pins

Difficult to maintain for prolonged periods

Question 12

Direct fracture reduction

Answer 12

reducing a fracture via manipulating the fractured bone ends

Question 13

Indirect fracture reduction

Answer 13

reducing a fracture via manipulating the fragments away from the fracture

Question 14

Open fracture reduction

Answer 14

reducing a fracture via an open surgical approach, often with direct techniques

Question 15

Closed fracture reduction

Answer 15

reducing a fracture without opening the fracture site

Question 16

Open but don’t touch fracture reduction

Answer 16

open approach to the fracture but efforts are made not to expose or handle the fracture ends or small fragments

Question 17

When and how to use closed fracture reduction

Answer 17

For recent fractures, stable fractures and fractures easily palpable - especially with lower limb fractures.

Suggested methods to assist closed reduction include traction, counter-traction and manipulation or bending.

Reduction can be assisted by using the animals weight for 10-30 minutes prior to attempts to reduce the fracture – this is achieved by applying a tie around the affected extremity and hoisting the leg up to a drip stand so the anaesthetised animal is just suspended in the air.

Question 18

How and when to do and open fracture reduction

Answer 18

Most fractures will require open reduction.

This can be assisted by the use of levers (Hohman Retractors) and bone holding forceps.

Traction, counter-traction and manipulation will also be necessary to overcome dynamic muscle contraction.

Muscle relaxants are occasionally useful but generally the affected muscle is swollen and inflamed and full ‘chemical’ relaxation may not be achievable.

Transverse fractures can be reduced by a manoeuvre called “Toggling” - a process whereby the bone is bent to 180°, then the fracture ends are opposed and the bone is straightened

Fracture distractors are available but rarely used.

Enough bone needs to be exposed for placement of the distractor, which is screwed on to the bone, and then a knurled nut is used to winch the fragments apart.

Distractors may be useful in heavy muscled giant breeds especially with upper limb bone or chronic fractures.

Question 19

Pros of open reduction

Answer 19

Better visualisation of fragments

Easier to manipulate and reduce

Easier to maintain reduction

Question 20

Pros of closed reduction

Answer 20

Avoids strippin of soft tissues from bone

Maintains periosteal blood supply

Preserves a fracture clot