If used for permanent fixation pins and wires are usually chosen if very little load is going through the fracture site or they are adding to the stability of a plate or an external fixator. Typical uses for wires or pins are to fix finger fractures, hand fractures, shoulder fractures and wrists. K-wires are often used to assist with the fixation in fractures of the patella, elbow and ankle. A device known as an image intensifier is often used to insert the device under x-ray guidance, allowing insertion of the pin or wire through the skin without operation.

Larger than wires and able to be threaded, Steinmann pins are typically employed to apply traction skeletally for one of the long bones, mostly in the leg. They are driven through the bone and attached to a weight via a stirrup-like device which applies the traction to maintain bony alignment until sufficient callus has formed for the traction to be removed. Traction is used much less often now as this technique has been overtaken by more advanced methods of internal fixation which allows us to avoid the negative consequences of long term bed rest needed for traction.

Fixation Screws

Using bone screws is a basic technique of modern orthopaedic and trauma management, used either on their own or as part of another implant technique. Screws can be self tapping or need tapping beforehand. The force needed to pull a screw out of the bone is affected by various factors and the main determining factor is the density of the bone into which it is inserted. The total area of contact between the bone and the threads is also important and self tapping screws are typically used. Screws are inserted clockwise either straight in or along a path already drilled and once the screw head hits the cortical bone it generates tension with screws typically inserted at a force equivalent to 80 percent of the force which would strip them.

Bone is an active and dynamic body organ and can adapt to the stresses formed by the application of the screws, allowing a gradual reduction in fixation force with time. However, the fracture is usually healed before the fixation is likely to loosen. The two main kinds of screws available are cancellous and cortical bone screws, the denser bone of the cortex being fixed with cortical screws and the more honeycomb bone of the bone ends fixed with cancellous screws. The surface areas of contact between thread and bone are greater in cancellous screws, allowing cancellous screws to achieve purchase in less dense bone.

Pre-drilling or tapping is not generally needed in cancellous bone due to its porosity and ease of insertion. Lack of tapping is often better as the insertion of the screw compresses the bone and may increase the local density of the bone, making the screw purchase more secure. Positional screws are used to attach an implant device such as a plate to the bone by compressing between the bone and the plate. Typical insertion involves drilling a pilot hole with a matching bit for the screw size and an appropriate thread tap is used unless self tapping screws are to be inserted.

The lag technique uses small screws called lag screws to fix and compress across the line of a fracture, applying compression forces to maintain stability and alignment of long bones or reduction of fractures inside joints. The highest level of stability and compression is delivered by applying the screw directly across the fracture site. The rotation and bending forces which occur during normal post operative rehabilitation require additional stabilisation than lag screws, mostly using external fixators or plates.

In a percutaneous technique often used for hip fracture fixation, cannulated screws can be inserted along the previously inserted guide wire which has been located under the control of x-ray guidance, completing the fixation started by wiring. As surgeons always try to minimise the size of operations and the resulting damage to soft tissues and bone membranes, cannulated screws are typically used in limited open surgery. Screws are now typically self drilling and self tapping although they are much more expensive than normal screws.