An external fixator can be thought of as a cage or frame that is attached to the bone with special bone screws or wires. The fixator remains on the outside of the limb while the screws or wires pass through the skin into the bone. By anchoring this cage-like device to the leg and using the pull-apart method, bone lengthening is achieved.
Limb lengthening surgery works on the principle of bone regeneration (osteogenesis) as bones are pulled apart. With external fixation, a customized apparatus that encircles the leg is surgically attached to the limb.
To perform a lengthening, the surgeon cuts the bone into two segments. Each of the two segments of the bone is then attached to the fixator with special bone screws or wires. For a circular fixator, each segment is attached to a separate ring. For rail fixators, each bone segment is attached to an individual pin clamp. Adjustments are then made to the fixator to perform the limb lengthening.
Circular fixators can have special rods, called struts, placed in between the rings. These struts allow the bone to be lengthened, rotated, and/or angulated in any direction. The advantage of this type of external fixator is that it is very versatile. It can be used to correct both limb length and bone deformity simultaneously. The disadvantage of this frame is that it is bulky, which makes it more bothersome to wear. Rail-type fixators are less bulky but have less versatility in terms of combining gradual correction of deformity and leg length. Either type of fixator, however, can be used to perform limb lengthening.
The bone is surgically separated, and the frame extends when the device’s struts are lengthened, which is done several times a day. Bone lengthening usually begins about five to seven days after surgery, and the process can take up to a year or more. Until lengthening is complete and the bone is given a chance to harden, the fixator remains attached. After the external fixator is removed, a cast or brace may be required for some time.
Fixation pins are continuously connected to the bone, which may result in pin tract infections and possible pin breakages. Nerve or vascular damage following insertion of the pins and soft tissue tethering around the wires or pins is also possible. Some patients suffer from bone weakening while in the fixator. Additionally, there may be permanent loss of range of motion in the nearby joints. Patients can greatly reduce the risk of permanent joint damage by following the physical therapy prescribed post-surgery.
While the incisions used to apply an external fixator are very small, there are often six or eight of them spread out over the limb. This may be less cosmetically appealing to some patients compared to the incisions used in placing an intramedullary lengthening device.
Additionally, having a frame attached to the outside of your limb can be bothersome. Your clothing may need to be altered to accommodate for the increased size of the limb. The fixator can bump into or scratch the other limb. Sitting and lying down with the external device attached to your limb may also require an adjustment period.
After the surgery attaching the device, patients generally spend a week or longer in the hospital. Frequent surgeon visits to adjust the pins are critical, and physical therapy is required to maintain a normal range of motion. Special care is necessary to clean and protect the pins or screws to prevent infection.