Distraction osteogenesis (synonym: callus distraction) is a surgical procedure whose literal translation already explains the procedure: new bone formation by pulling apart. Following the biological healing processes after fractures (broken bones), the new production of bone substance in the fracture gap is achieved by removing the bone fragments from each other. After an accidental bone fracture, the soft tissues surrounding the fracture gap react with new bone and vessel formation, provided that the bone fragments are not fixed one hundred percent in their original position to each other, but a narrow gap remains. This is referred to as secondary bone healing, since new bone substance must first be formed to bridge the gap. In the fracture gap, so-called callus (synonyms: bone callus; fracture callus; fracture callus) is formed by osteoblasts (bone-producing cells). This is transformed into mineralized bone within a few weeks and is then visible radiographically.
Indications (areas of application)
Distraction osteogenesis is used in various surgical specialties. Dental implantology resorts to the callus distraction procedure when there is insufficient alveolar bone (the bone portion of the jaws where the roots of the teeth were formerly anchored, as opposed to the base of the jaw on which the alveolar bone is supported) to place a sufficiently sized implant. It is used for alveolar augmentation prior to implant placement (increasing the amount of jawbone that formerly supported teeth before an implant is placed).
Contraindications
These can be derived from the complications mentioned above:
- If oral hygiene cannot be improved preoperatively (before surgery), a high risk of infection must be expected
- Low patient compliance (patient does not adhere to the necessary behavioral measures), e.g., in the case of alcohol abuse
- Poorly adjusted diabetes
- Immunodeficiency (severely weakened immune defenses), for example, during therapy with immunosuppressants
- Heavy smokers have a greatly increased risk of infection
- With bisphosphonate therapy and radiotherapy, revascularization (new formation of blood vessels) takes place only with difficulty
Before surgery
- In advance, the patient is informed about alternative surgical techniques as well as risks and complications. Planning is based on preoperative radiographs and taking into account any risk parameters that may be present in the patient’s medical history (anamnesis).
The surgical procedure
For distraction osteogenesis, surgery takes advantage of the principle of secondary bone healing. A fracture gap surgically created by osteotomy (surgical transection of bone or excision of a piece of bone) is stimulated to form callus or bone. In addition, a controlled traction force is applied to the artificially created gap by means of a special device attached to the bone fragments (bone fragments on both sides of the gap), the so-called distractor, so that the fracture surfaces are distracted (moved away from each other, pulled apart) in a controlled manner by approximately 0.8 mm to 10 mm daily. With this precisely measured daily distraction distance, the gap is continuously bridged with new callus, so that a steady lengthening of the bone in question is achieved. The procedure is divided into two surgical interventions at intervals of approximately 12 weeks and the intervening phase of new bone formation:
1st phase: osteotomy and placement of the distractor.
- Local anesthesia (local anesthesia).
- Incision: the mucosa over the bone part to be mobilized is detached from the bone surface only on the alveolar process (part of the jaw where the tooth compartments = alveoli are located) and buccally (towards the cheek). The oral (facing the oral cavity) mucosa must supply the bone fragment to be moved via its blood vessels.
- Osteotomy (surgical cutting of bone or the excision of a piece of bone) of the bone fragment (surgical creation of an artificial fracture gap) to be moved, the oral pedicle on the mucosa must not be affected.
- Fixing (attaching) the distractor with pins or screws to the fragment to be moved and to the jaw, which remains stable, across the separation site.
- Saliva-proof wound closure by sutures
2nd phase: resting phase
For 5 to 7 days, wound healing is allowed to proceed without activating the distractor. In the resting phase, callus formation by the osteoblasts and revascularization (new vessel formation) begin. 3rd phase: Callus distraction
The distractor is activated twice daily via a set screw protruding from the mucosa so that the fracture surfaces are distracted 0.8 mm to 1 mm per day. If less is activated, premature ossification occurs; if too much is set, the osteoblasts cannot form enough callus to bridge the gap. Distraction continues until the alveolar bone has gained sufficient height. 4th phase: Retention phase:
Approximately 12 weeks are estimated for stabilization of the distraction results and formation of the bone structures. 5th phase: surgical removal of the distractor
After radiographic control of the healing process, the distractor is exposed and removed, again under local anesthesia, and the wound is closed with sutures to make it saliva-proof. In any case, planned implant placement should be performed at intervals of one to two weeks to minimize the risk of infection.
After surgery
- Rest: after the surgical procedures, the patient should take care of the surgical area by eating soft food. While this restriction extends only for a few days after the second operation, after the first operation, if possible, too hard and chewing food should be avoided until well into the retention phase.
- Oral hygiene: appropriate instructions should be implemented consistently, such as thorough tooth cleaning with the surgical area excluded, instead disinfecting rinses e.g. with chlorhexidine digluconate.
- Post-bleeding: blood circulation-promoting activities must refrain (sports, caffeinated beverages, alcohol).
Possible complications
- Infections (inflammation of soft tissue and/or bone) via the distractor entry sites.
- Exceptional pain
- Nerve irritation
- Soft tissue irritations
- Infections due to postoperative (after surgery) reduced oral hygiene.
- Wound healing disorders in the presence of risk factors such as smoking (tobacco use), diabetes mellitus, weakened immune defenses, bisphosphonate therapy, radiotherapy and many others.
