Fracture stabilization devices
What they are good at
The available devices include: Casts, pins, wires, screws, plates, intramedullary nails, and external fixators. Each can be thought of as being better at resisting (or applying) certain kinds of forces. It is often helpful to think of the kind of force that caused the fracture (described above) and then trying to determine which devices can best be used to “reverse” or counteract those forces.
Casts: Casts are best at applying bending forces and thus are best used to apply the opposite bending force after reduction of a fracture caused by bending loads.
Casts can, by judicious placement of the “molds” be used to try to “reverse” the deformity of a shear fracture – but they are often unsuccessful, losing reduction as swelling goes down.
Casts can also try to use applied bending loads to produce tension on one bone broken in compression when the compressed bone is paired with another unbroken bone as here in the radius (failed in compression)/ulna intact. Pushing the wrist into ulnar deviation causes the ligaments on the radiocarpal side to pull the compressed radius out to length (called ligamentotaxis. Again this is often not terribly successful. In addition extreme flexion/ulnar deviation positioning tends to result in significant post cast stiffness and dysfunction.
Pins: Pins are best at resisting shearing loads and thus are often used to best advantage to fix “sheared off” fragments. They do this best when they are inserted through dense cancellous bone and do not function well in hollow cylinders of cortical bone or osteoporotic metaphysis.
This is demonstrated here by the 16-penny nails used to “pin” this soup can and this two by four, both of which have oblique “shear fractures through them.