History of Distraction

The first clinical application of bone distraction was described in 1905 by Codivilla, who performed a bone distraction of the lower leg. The distractor was fixed with plaster at the upper and lower leg, providing only minor stability, and severe soft tissue problems such as necrosis occurred. Various experimental studies followed regarding the rate and distance of distraction and the effects of the periosteum and soft tissue on the distraction process. In 1927, Rosenthal reported the first distraction of the mandible. He treated a patient with a mandibular retrognathism by bone distraction and fixation of the distractor along the teeth. In 1952, Anderson used cortical bone pins for the fixation of the distractor, as described by Coleman et al. in 1967. This was a milestone in the technique of bone distraction because it enabled rigid fixation of the bone fragments.

The real father of bone distraction was a Russian orthopedic surgeon named Ilizarov, who popularized the technique more than 30 years before it became recognized in the West. In the late 1980s, he published in the United States for the first time his research and clinical results on bone distraction, prompting a wave of developments in bone distraction techniques worldwide.

Principle of Bone Distraction

The aim of bone distraction is to obtain new bone tissue and gain bone length by slow distraction of the callus. The basic principle of bone distraction is the process of bone fracture healing. Osteotomy can be performed by two methods. In the original method, as described by Ilizarov, a corticotomy is performed in which only the cortex of the bone is separated and the cancellus stays untouched. Another method, which is more often used in head and neck surgery, is to split the cortex and the cancellus of the bone to facilitate the process of distraction. With this technique, the forces needed to distract the bone are significantly lower, allowing use of smaller distractors that can be placed under the skin or the mucosa.

After the osteotomy and a latent period of 5 to 7 days, the bones on both sides of the osteotomy line are slowly pulled apart to stretch the fracture cleft and the newly formed callus. A latent period between the osteotomy and the start of the distraction process allows callus formation and soft tissue healing. Higher activity of the osteoblasts and blood vessel growth within the osteotomy line and the callus can be achieved. Various experimental and clinical studies have reported a latent period ranging from 0 to 14 days between the osteotomy and the start of the distraction, depending on the individual situation. In the field of head and neck surgery, an average waiting period of 5 to 7 days is advisable. However, patient age, bone size, and soft tissue coverage may influence the latent period.

Distraction must take place slowly to achieve new bone formation within the callus. An average distraction rate of 1 to 1.5 mm/day provides the best clinical results. At a lower rate of 0.5 mm/day or less, early ossification takes place, whereas at a higher rate of 2 mm/day or more, no bone formation occurs. Another important fact is the frequency of distraction. The ideal situation is a continuous distraction of callus, but because this is difficult, repeated distraction once or twice each day (1-1.5 mm/day total) seems to be useful.

Numerous experimental and clinical studies have investigated the effects of bone distraction and the progress of bone formation during distraction. It has been shown that the gap between the distracted bone edges is first occupied by fibrous tissue. As distraction proceeds, the fibrous tissue becomes longitudinally oriented in the direction of distraction. Early bone formation starts from the cut bone edges and advances along the fibrous tissue. Bone is formed predominantly by intermembranous ossification. Histological observations showed a gradual change from an amorphous matrix to a fibrous matrix and then to an osseous-like tissue. Bone columns crystallize along longitudinally oriented collagen bundles, expanding circumferentially to surrounding bundles. While the distraction gap increases, the bone columns increase in length and diameter, whereas the fibrous interzone remains constant at a few millimeters. Clinical and animal experimental data have shown that distraction osteogenesis provides unlimited new bone formation that remodels at a daily rate ranging from 200 to 400 μm. Most of the experimental data were obtained from orthopedic studies, and only limited information about the indications for maxillofacial surgery is available.

Various methods have been described for fixation of the distractor. The easiest method of fixation is to use bone pins that are placed in the bone near the osteotomy line and through the skin. The pins are fixed externally to the distractor, which can be slowly expanded. The external distractors are easy to fix and very stable, but most of them are rather bulky, and the transcutaneous pins can cause scars. These factors encouraged the development of smaller devices that can be placed intraorally. Today, minidistractors and microdistractors are currently used; they are small enough to be placed completely subcutaneously or under the mucosa. Only the screw for the activator of the distractor is visible.

Another distractor for the midface is the halo frame. The frame is fixed at the skull by screws and attached to the midface.

An important aspect of all distractors is their stability and stiffness. Experimental studies have shown that mobility during the process of distraction can cause micromovements, resulting in impaired bone formation. Distractor size is therefore limited by physical stability and rigidity.

After reaching the intended bone length, the distractor (or plate fixation) must stay in place for many weeks until mineralization and ossification of the newly formed callus has been completed and sufficient bone strength has been attained. The length of this period depends on individual factors such as the location of the osteotomy, the bone length gained, and the age of the patient. A retention period of 8 to 12 weeks seems to be sufficient for the facial skeleton. Some surgeons remove the distractor and use plates to provide stabilization for the consolidation period.

Principle of Bone Distraction

The aim of bone distraction is to obtain new bone tissue and gain bone length by slow distraction of the callus. The basic principle of bone distraction is the process of bone fracture healing. Osteotomy can be performed by two methods. In the original method, as described by Ilizarov, a corticotomy is performed in which only the cortex of the bone is separated and the cancellus stays untouched. Another method, which is more often used in head and neck surgery, is to split the cortex and the cancellus of the bone to facilitate the process of distraction. With this technique, the forces needed to distract the bone are significantly lower, allowing use of smaller distractors that can be placed under the skin or the mucosa.

After the osteotomy and a latent period of 5 to 7 days, the bones on both sides of the osteotomy line are slowly pulled apart to stretch the fracture cleft and the newly formed callus. A latent period between the osteotomy and the start of the distraction process allows callus formation and soft tissue healing. Higher activity of the osteoblasts and blood vessel growth within the osteotomy line and the callus can be achieved. Various experimental and clinical studies have reported a latent period ranging from 0 to 14 days between the osteotomy and the start of the distraction, depending on the individual situation. In the field of head and neck surgery, an average waiting period of 5 to 7 days is advisable. However, patient age, bone size, and soft tissue coverage may influence the latent period.

Distraction must take place slowly to achieve new bone formation within the callus. An average distraction rate of 1 to 1.5 mm/day provides the best clinical results. At a lower rate of 0.5 mm/day or less, early ossification takes place, whereas at a higher rate of 2 mm/day or more, no bone formation occurs. Another important fact is the frequency of distraction. The ideal situation is a continuous distraction of callus, but because this is difficult, repeated distraction once or twice each day (1-1.5 mm/day total) seems to be useful.

Numerous experimental and clinical studies have investigated the effects of bone distraction and the progress of bone formation during distraction. It has been shown that the gap between the distracted bone edges is first occupied by fibrous tissue. As distraction proceeds, the fibrous tissue becomes longitudinally oriented in the direction of distraction. Early bone formation starts from the cut bone edges and advances along the fibrous tissue. Bone is formed predominantly by intermembranous ossification. Histological observations showed a gradual change from an amorphous matrix to a fibrous matrix and then to an osseous-like tissue. Bone columns crystallize along longitudinally oriented collagen bundles, expanding circumferentially to surrounding bundles. While the distraction gap increases, the bone columns increase in length and diameter, whereas the fibrous interzone remains constant at a few millimeters. Clinical and animal experimental data have shown that distraction osteogenesis provides unlimited new bone formation that remodels at a daily rate ranging from 200 to 400 μm. Most of the experimental data were obtained from orthopedic studies, and only limited information about the indications for maxillofacial surgery is available.

Various methods have been described for fixation of the distractor. The easiest method of fixation is to use bone pins that are placed in the bone near the osteotomy line and through the skin. The pins are fixed externally to the distractor, which can be slowly expanded. The external distractors are easy to fix and very stable, but most of them are rather bulky, and the transcutaneous pins can cause scars. These factors encouraged the development of smaller devices that can be placed intraorally. Today, minidistractors and microdistractors are currently used; they are small enough to be placed completely subcutaneously or under the mucosa. Only the screw for the activator of the distractor is visible.

Another distractor for the midface is the halo frame. The frame is fixed at the skull by screws and attached to the midface.

An important aspect of all distractors is their stability and stiffness. Experimental studies have shown that mobility during the process of distraction can cause micromovements, resulting in impaired bone formation. Distractor size is therefore limited by physical stability and rigidity.

After reaching the intended bone length, the distractor (or plate fixation) must stay in place for many weeks until mineralization and ossification of the newly formed callus has been completed and sufficient bone strength has been attained. The length of this period depends on individual factors such as the location of the osteotomy, the bone length gained, and the age of the patient. A retention period of 8 to 12 weeks seems to be sufficient for the facial skeleton. Some surgeons remove the distractor and use plates to provide stabilization for the consolidation period.

Indications and Techniques for Bone Distraction

Congenital malformations of the mandible originally were the most common indications for distraction. McCarthy et al. first described the use of a miniaturized distractor as an extraoral device to lengthen the malformed mandible. Soon, smaller distractors were developed that were placed completely intraorally to avoid scars and hide the distractors. Currently, distraction of the mandible can be classified as distraction of the horizontal mandible ramus, the vertical mandible ramus, the mandible symphysis, or the alveolus.