Pin Types:

There are 3 types of pins in external fixation applications.

1. K Wire:

They are straight wires with pointed sharp ends. It is generally used with bilateral fixation by entering from one side of the extremity and removing it from the other side. In general, thin diameters are preferred and used by stretching to increase its strength.

The type with a round stop bead placed in the middle of the K Wires is called the Olive K Wire. It is used to pulling the fragment to which it is applied. It is especially used for the reduction and fixation of fractures close to the joint.

2. Schanz Screw / Half Pin:

They are long pins with a pointed and sharp tip and a threaded part. It is placed on one side. However, the threaded part should hold both cortexes of the bone to which it is applied. Single cortex placement is insufficient.

Since there is no stretching in these, diameters as thick as possible are preferred for sufficient strength.

Diameters between 20% and 25% of the bone diameter to which it will be applied are suitable.

Schanz screws thicker than 30% of the bone diameter can cause bone fracture. It should be avoided.

3. Transfix Pin:

They are pins with a pointed-sharp tip and a threaded part in the middle. These pins are also used for bilateral fixation by entering from one side of the extremity and removing from the other side. However, since stretching is not done, thick diameters are preferred in terms of sufficient bearing strength. The principles of thickness are the same as for schanz screws.

It is mostly used in the proximal metaphysis of the tibia and calcaneus.

Pin Placement Principals:

At least 2 pins must be placed in each fragment. Single pin does not provide stability.

A maximum of 4 pins should be placed on each fragment. Placement of more than four pins does not contribute positively to fixation biomechanics.

Proximal pins should be placed further from the fracture line. Distal pins may be slightly closer to the fracture line.

The approximate bone dimensions of each size animal and the recommended pin diameters and rod diameters are presented in the table:

Pins that are too close together are biomechanically ineffective. There must be at least 10 mm distance between two pins.

Pins should not be placed too close to the fracture line. There should be a distance of at least 10 mm from the fracture line.

Pins should not be too close to the joint line. Care should be taken to keep it outside the joint capsule. It should be at least 10 mm away from the joint line.

(The distance expressed as 10 mm here is an average value. It increases as the bone gets thicker. It may decrease as the bone gets thinner.)

In the application of the external fixator surgical technique, first the fracture line is reduced and the extremity orientation is corrected. This is usually achieved by pulling or suspending the extremity. If the fracture line is open, reduction is achieved and protected with appropriate surgical instruments.

It should be checked and confirmed in both the Anteroposterior (AP) and Lateral (Lat) planes that the fracture line is reduced and the orientation is correct. X-Ray or Scopy device is required for this step.

The type and framework of the fixator to be used in the fixation should be decided in advance and the planning should be done accordingly.

In the first row, the most proximal and most distal pins sholud be placed and fixed. Stability is ensured by sending the pins in between.

If the threaded pins are sharp, they can be apply directly. If it is a blunt tip, it is necessary to drill the bone with the drill tip first. In this case, the drill bit diameter to be used should be 30% smaller than the pin diameter on average. In both cases, for threaded pins, a skin incision should be made first and the pin should be sent by preventing damage to the skin with a suitable surgical tool. Otherwise, the risk of damage to the skin and surrounding soft tissues of the schanz screw threads is quite high.

Schanz screws should preferably be sent with a hand drill. However, if the application will be made with motor tools, it must be used with low speed. Otherwise, it may cause heat necrosis due to heating in the bone. It is strongly recommended that the second cortex be placed slowly with the handpiece, even in motorized application.

Straight wires can be place directly from the skin without making any incisions.

There is no harm in sending flat wires with motorized devices, provided that they are at low speed.

As the carrier rods of the fixator move away from the skin, the stability power decreases. If it's too close, it can damage the skin. It should be detected by placing 1-2 finger distance between them.

As the length of the carrier rod increases, the stability power increases. But it is meaningless if it is more than the bone length.

Stability increases as the carrier rod thickness increases. A rod with a diameter suitable for the detected bone and extremity size should be used.