External fixation is a surgical treatment used to set bone fractures in which a cast would not allow proper alignment of the fracture. In this kind of reduction, holes are drilled into uninjured areas of bones around the fracture and special bolts or wires are screwed into the holes. Outside the body, a rod or a curved piece of metal with special joints joins the bolts to make a rigid support. External fixation is usually used when internal fixation is contraindicated often to treat open fractures, or as a temporary solution.
There are two main kinds of external fixators. One is known as mono-lateral fixation where the metal external structure is on one side of the limb. The other is circular fixation and in this case the metal structure is circular or an arch and surrounds the limb. Installation of the external fixator is performed in an operating room, normally under general anesthesia. Removal of the external frame and bolts can be done with no anesthesia in an office visit.
Circular fixation external fixators are often used for fractures of long bones that are weight bearing such as the femur and tibia. It is known that bearing weight through a fracture by walking on it, for example, with the added support of the external fixator frame actually helps fractures to heal. The benefit of weight bearing is due to a phenomenon known as Wolff's law. Wolff's law teaches that load on the fracture site under normal weight bearing promotes healing and avoids atrophy of the fracture site.
Circular fixation external fixators typically include two or more spaced apart rings. The rings surround the limb, for example the leg. Bone engaging pins are mounted onto the rings and extend inwardly through soft tissue including skin and muscle and engage the bone near the fracture site. The pins may engage only the outer cortical bone or engage cancellous bone as well and may extend entirely through the bone. The rings are spaced apart from each other by distractors in the form of externally threaded rods and internally threaded nuts.
These external fixators perform generally satisfactory, but are time consuming for the surgeon to assemble onto the patient. The threaded rods are very long and the threaded moving of the nuts along the rods requires many rotations of the nuts for each rod. Further there are three or more rods for each fixator. Also three or more rings may need to be adjusted. Further to obtain a tactile feel for distracting of the bone, nuts and rods with fine threads are preferred. All this threading of the nuts is very time consuming. This time consuming threading makes the surgery in which external fixators are installed slow and expensive and exposes the patient to risks associated with longer surgical procedures. Therefore, it would be advantageous to provide an improved external fixator.