Distraction osteogenesis ("DO") was described in modern terms and refined in the late 1960s by a Soviet physician named Gavriel Ilizarov. He was able to lengthen the limbs of dwarfs up to eighteen inches with his external distraction appliances. Many of the principles established by Dr. Ilizarov are still in use today, though, except for the GenerOs family of devices, the

vast majority of devices to lengthen limbs remain external to the body. This means that pins must be drilled into the bones through the skin to hold the devices in position. The transcutaneous (protruding through the skin) pins painfully stretch and scar the patient. They are the source of most of the complications currently associated with DO.

Dr. Ilizarov showed repeatedly that DO occurs when an osteotomy, or bone cut, is created by the surgeon, and the bone ends are methodically pulled apart with the aid of a precision device.

There are three phases of DO: the Latency Phase, the Activation Phase, and the Consolidation Phase. During the Latency Phase the bone cut or osteotomy is held in its original position

while the body produces soft, immature bone tissue called a bone callus. The Latency Phase usually lasts about seven days.

Then the Activation Phase begins as the bone ends are distracted apart to expand the osteotomy site. If this is done within the vascular physiologic limits of one millimeter per day, then new bone is produced. If the distraction is too slow, then the bone ends fuse prematurely. If the distraction is too fast, then only fibrous tissue is produced rather than bone. The Activation Phase lasts approximately as long as the number of millimeters distracted in days. For example, a desired bone lengthening of 20 millimeters would require 20 days of distraction. The final phase is the Consolidation Phase. During this period the bone is held in position until calcification is noted across the distraction gap on radiographs (X-rays).

The Consolidation Phase usually lasts two to three times the length of the activation phase. Clinically, with the right device, any bone in the body should be amenable to distraction osteogenesis. OrthoNetx devices have been successfully used to lengthen jaws, tooth-bearing bone, arms and legs. Variations of the DO process can also be used to correct angulation of bone if necessary.