DISTRACTION OSTEOGENESIS

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Distraction osteogenesis, also called callus distraction,callotasis and osteodistraction is a surgical process used to reconstruct skeletal deformities and lengthen the long bones of the body. A corticotomy is used to fracture the bone into two segments, and the two bone ends of the bone are gradually moved apart during the distraction phase, allowing new bone to form in the gap.When the desired or possible length is reached, a consolidation phase follows in which the bone is allowed to keep healing. Distraction osteogenesis has the benefit of simultaneously increasing bone length and the volume of surrounding soft tissues.

Although distraction technology has been used mainly in the field of orthopedics, early results in rats and humans indicated that the process can be applied to correct deformities of the jaw. These techniques are now utilised extensively by maxillofacial surgeons for the correction of micrognathia, midface, and fronto-orbital hypoplasia in patients with craniofacial deformities.
In 1905, Alessandro Codivilla introduced surgical practices for lengthening of the lower limbs.Early techniques had a high number of complications, particularly during healing, and often resulted in a failure to achieve the goal of the surgery

In 1934 the New York Hospital For Joint Disease worked on an early method developed by Ilizarov. The major item that the US team of surgeons developed was the metal frame the leg was placed in to hold it perfectly in place till the cut made in the bone was healed over.

The breakthrough came with a technique introduced by Russian orthopedic surgeon Gavril Ilizarov. Ilizarov developed a procedure based on the biology of the bone and on the ability of the surrounding soft-tissues to regenerate under tension; the technique involved an external fixator, the Ilizarov apparatus, structured as a modular ring. Although the types of complications remained the same (infection, the most common complication occurring particularly along the pin tracks, pain, nerve and soft tissue irritation the Ilizarov technique reduced the frequency and severity of the complications. The Ilizarov technique made the surgery safer,and allowed the goal of lengthening the limb to be achieved.

Difficulties arising during distraction osteogenesis

Difficulties that may arise during distraction osteogenesis are commonly classified in medical scientific literature according to the standard introduced by professor Dror Paley in a 1990 article.Paley distinguished among problems (defined as “a difficulty that arises during the distraction or fixation period that is fully resolved by the end of the treatment period by non operative means”), obstacles, and complications.

        

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Techniques
Using exclusively an external fixator

The most common is the Ilizarov surgery with the Ilizarov external fixator. Other external fixators are Wagner, Orthofix and Judet. Dr. Helong Bai (8th Hospital in Chongqing, China) developed the technique "Micro-wound" with a different apparatus.
[edit] Ilizarov surgery
Main article: Ilizarov apparatus
Ilizarov.jpg

Ilizarov surgery, developed by Gavriel Ilizarov, a Russian orthopedic surgeon, in 1951, is the oldest and most common method of distraction osteogenesis. It often brings complications while some new methods have a much lower rate of complications.

The process involves the following:

* Shattered bones and devascularised ones are removed from the patient, leaving a gap;
* The healthy part of the upper bone is broken into two segments with an external saw;
* The leg is then fitted with the Ilizarov frame that pierces through the skin, muscles, and bone;
* Screws attached to the middle bone are turned 1 millimetre (mm) per day, so that new bone tissues that are formed in the growth zone are gradually pulled apart to increase the gap (One millimetre has been found to be the optimal bone distraction rate. Lengthening too fast overstretches the soft tissues, resulting not only in pain, but also in the inability of the bone to fill up the gap; too slow, and the bone hardens before the full lengthening process is complete.);
* After the gap is closed, the patient continues to wear the frame until the new bone solidifies; the waiting period is usually 120 days before the leg can be used.

Ilizarov surgery is extremely painful, uncomfortable, infection-prone, and often causes unsightly scars. Frames used to be made of stainless steel rings weighing up to 7 kilogram (kg), but newer models are made of Carbon fiber reinforced plastic, which though lighter, are equally cumbersome.

Derivative devices provide physicians better control over the bone axis and angle during elongation, such as the Taylor Spacial Frame (TSF) which is computer assisted. The downside of these developments are their relative complexity and resulting longer learning curve.

For decades, the Ilizarov procedure was the best chance for shattered bones to be restored, and crooked ones straightened. Breakthroughs in distraction osteogenesis in the 1990s, however, have resulted in less painful (albeit more expensive) alternatives, such as unilateral rails.

        

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Maxillofacial Distraction Osteogenesis

Correcting the majority of congenital craniofacial defects, as well as some facial injuries resulting from trauma, requires making bones longer. Distraction osteogenesis is an effective way to grow new bone, but it is much more difficult to accomplish in the face than in other areas of the body. Bones must often be moved in three dimensions, as opposed to just one, as in a limb, and scarring must be kept to a minimum. Researchers are attempting to improve the distraction devices used in the face. Until recently, the mechanisms were external and only operated along straight lines. Now, maxillofacial surgeons can use curvilinear devices capable of moving bone in three dimensions.

These new devices still need to be improved. They depend on patient caretakers reliably turning a screw. The next goal is to create devices that will move bone continuously, not in daily increments of 1 mm. These continuously moving devices would cause less pain, wouldn’t require daily patient compliance, and might promote faster bone growth. At the moment, researchers are testing a continuously moving device in animal models, and they have found that the device’s components are durable, that its user interface works, and that it is tolerated by the body. When the position sensor in the device is perfected, the device will be ready to use in people.

In distraction osteogenesis procedures involving the face, it is critical that bone movements be carefully planned before a device is implanted. No existing device is capable of changing its trajectory mid-course, and small skeletal changes lead to large changes in the structure of the face. Recently researchers have developed state-of-the-art software capable of simulating the entire process of distraction osteogenesis. The 3-D planning tool uses data from CT scans to create a segmented model of the patient’s skull, and it then calculates the vector of movement required to achieve desirable bone positioning. Outcome CT scans can be overlaid on the original model to assess the effectiveness of the procedure. In the future, researchers hope that the distraction devices used in maxillofacial procedures will continue to improve, along with the corresponding software

        

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