Wednesday, June 3, 2009
Fixing Fractures - Part Two
If the fracture is only experiencing a small level of force across its site then fixation pins or wires can be sufficient or can add appropriately to the fixation already provided by a fixator or plate. Fractures of the upper arm and shoulder, wrist, fingers and hands are the most commonly fixed with this method. Tension band wiring is used for fractures of the elbow, knee-cap and ankle, with k-wiring sometimes used to add to stability. By using a percutaneous technique a pin can be inserted through the skin using x-ray guidance with an image intensifier.
Steinmann pins, often threaded and thicker than K-wires, have been routinely employed to engage and maintain skeletal traction predominantly in the bones of the leg. The pin is inserted through the bone and this is attached to a traction cord via a stirrup device, holding the bone in the correct position until enough healing callus has formed to allow removal. Modern techniques of fixing fractures sooner and more accurately have meant that the application of traction for long periods, with the risks of bed rest, can now be avoided.
Bone 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 adapts to the tension and the force applied by the screws decreases gradually with time, however the time for this to occur to loosen the compression is typically longer than the time needed for fracture healing. Cortical and cancellous screws are the two types available, with cortical screws used for the denser bone of the long bones and cancellous screws for the less dense bone of bone ends. Cortical screws have less and cancellous screws more surface area for purchase on the bone. Cancellous screws are used in the softer bone and cortical screws in harder 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.
A degree of compression can be produced by inserting lag screws across the line of a fracture to increase alignment and stability of a long bone fracture and to produce and maintain reduction of a fracture across a joint. To provide the greatest degree of stability requires the screw to be placed at right angles to the line of the break. It is unlikely that lag screws will give sufficient stability alone so they are often supplemented with added stability from an external fixator or a plate.
Cannulated screws are often used to fix hip fractures and can be inserted percutaneously without needing a full open operative technique, inserting the screw along the track already identified by a guide wire and performed under x-ray control for positional control. To limit the potential damage to the soft tissues and the size of the operation, cannulated screws are employed in operations with limited open surgery. Modern screws are self tapping and self drilling as they are inserted and are much more costly than normal screws which are not cannulated.
Steinmann pins, often threaded and thicker than K-wires, have been routinely employed to engage and maintain skeletal traction predominantly in the bones of the leg. The pin is inserted through the bone and this is attached to a traction cord via a stirrup device, holding the bone in the correct position until enough healing callus has formed to allow removal. Modern techniques of fixing fractures sooner and more accurately have meant that the application of traction for long periods, with the risks of bed rest, can now be avoided.
Bone 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 adapts to the tension and the force applied by the screws decreases gradually with time, however the time for this to occur to loosen the compression is typically longer than the time needed for fracture healing. Cortical and cancellous screws are the two types available, with cortical screws used for the denser bone of the long bones and cancellous screws for the less dense bone of bone ends. Cortical screws have less and cancellous screws more surface area for purchase on the bone. Cancellous screws are used in the softer bone and cortical screws in harder 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.
A degree of compression can be produced by inserting lag screws across the line of a fracture to increase alignment and stability of a long bone fracture and to produce and maintain reduction of a fracture across a joint. To provide the greatest degree of stability requires the screw to be placed at right angles to the line of the break. It is unlikely that lag screws will give sufficient stability alone so they are often supplemented with added stability from an external fixator or a plate.
Cannulated screws are often used to fix hip fractures and can be inserted percutaneously without needing a full open operative technique, inserting the screw along the track already identified by a guide wire and performed under x-ray control for positional control. To limit the potential damage to the soft tissues and the size of the operation, cannulated screws are employed in operations with limited open surgery. Modern screws are self tapping and self drilling as they are inserted and are much more costly than normal screws which are not cannulated.
About the Author:
Jonathan Blood Smyth, editor of the Physiotherapy Site, writes articles about Physiotherapy, back pain, orthopaedic conditions, neck pain, injury management and physiotherapists in Glasgow. Jonathan is a superintendant physiotherapist at an NHS hospital in the South-West of the UK.
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