Bansod, Snehal B.
Local bone transportation or bone transport is a distraction osteogenesis technique that was first introduced by Ilizarov 1–5 for treating long bone defects resulting from trauma, oncologic resection, and other severe congenital or acquired deformities. Patients who have congenital or surgical osseous defects have to undergo bone-grafting procedures, which are unpredictable, risky, and carry donor site morbidity.
Bone transport is a distraction osteogenesis technique that involves slow movement of a free segment of bone (transport segment) across an osseous defect that developed because of severe congenital deformity, trauma, or oncologic resection. After gradual advancement of the transport segment, new bone tissue forms behind the moving segment, thereby filling the defect with new bone.
According to Ilizarov 4–7, the techniques are divided into three groups on the basis of the number of distraction/compression sites:
These techniques, in turn, are more definitively defined on the basis of the type of force that is applied between the bone segments: compression or distraction.
It is used primarily in cases with small osseous defects of up to several millimeters, where healing of the two bone ends is abnormal, resulting in nonunion. In cases not requiring an increase in limb length, compression forces are applied, and the pathologic tissue undergoes reparative remodeling, which results in reparative callus formation and fusion of bone ends. This is termed as monofocal compression osteosynthesis (Fig. 1).
In contrast, if an increase in limb length was desired, distraction forces would be applied to separate the bone ends. As distraction continues, the pathologic tissues are gradually transformed into regenerate bone. This is termed as monofocal distraction osteosynthesis.
In cases involving defects that are several millimeters wide, and an increase in length is desired, the segments may initially be compressed to stimulate reparative callus formation, followed by distraction to increase limb length (compression–distraction osteosynthesis).
Bifocal distraction–compression osteosynthesis
Used for larger bone defect. This procedure involves one distraction and one compression site. During bifocal osteosynthesis, a free bone segment (transport segment or transport disk) is created from one of the residual segments. This transport disk is then moved from the residual bone segment through the defect toward the residual target bone segment. During movement of the transport disk, new bone (distraction regenerate) is formed between the residual host bone segment and the transport disk. Once the transport disk reaches the residual target bone segment, compressive forces are applied at the docking site. At this docking site, the compressive forces stimulate gradual fusion of the contacting bony margins into solid regenerate bone. Thus, this technique is called bifocal distraction–compression osteosynthesis (Fig. 2).
Trifocal distraction–compression osteosynthesis
In cases with large bone defects, two transport disks are created from both residual bone segments and simultaneously moved centripetally toward each other so that they meet in the center of the defect. This distraction technique is called trifocal distraction–compression osteosynthesis and is usually characterized by two simultaneously formed distraction regenerates (bifocal distraction osteosynthesis) that are subsequently compressed (monofocal compression osteosynthesis) at the docking site in the center of the defect (Fig. 3).
A bilateral ankylosis female patient (Figs 4 and 5) underwent interpositional arthroplasty procedure for bilateral ankylosis. A reverse L osteotomy was performed as illustrated in Fig. 6. A transport distraction device was placed bilaterally after performing a reverse L osteotomy, and wound closure was performed with the distraction device port placed outside (Fig. 7). A postoperative orthopantomogram (Fig. 8) was performed. The distraction was started after 1 week at a rate of 1 mm/day. The transport disk was advanced till the glenoid fossa and stopped after no further distraction was possible. The patient continued mouth-opening physiotherapy exercises during this period. After a consolidation phase of 2 months (Fig. 9), the distraction device was removed and the patient’s mouth opening was checked (Fig. 10). A postoperative three-dimensional computed tomography scan was performed after 6 months to check the position of the neocondyle formed (Figs 11 and 12). The patient was followed up for 2 years with no recurrence of ankylosis. The mouth opening was 40 mm after 2 years.
The temporomandibular joint (TMJ) is the articulation of the mandibular condyle with the glenoid fossa of the temporal bone. It is a diarthrodial joint with unique characteristics. Unlike the other articulation of the human musculoskeletal system, the surfaces of TMJ are covered by fibrocartilage, rather than hyaline cartilage. Various time-tested methods have been tried to reconstruct the TMJ and its articulation. However, all the previous methods had some limitation or had donor site morbidity as one of the complications 8–16.
Distraction osteogenesis is the process of slow bone expansion in which new bone is generated in an osteotomy gap in response to tension stresses placed across the bone gap. Distraction osteogenesis has been found to be a successful treatment alternative for patients with congenitally deficient mandible 17.
A unique feature of the distraction technique is that patients can open their mouth during the distraction process, which appears to induce functional remodeling of the new bone. One such secondary gain for patients with congenital micrognathia treated with distraction osteogenesis has been at the level of the TMJ: the condyle appears to be upright and increase in size and volume 17.
Although the condyle head itself is not a growth site, the condyle responds to the functional loads placed on it. The greatest advantage of the distraction technique is that patients are allowed to open and close their mouths and masticate during the process of bone generation and expansion. This permits functional remodeling to occur, accounting for the positive effect of the distraction process on the mandibular condyle 17.The concept of transport distraction osteogenesis was developed by Costantino et al. 18 in 1990 in segmental mandibular regeneration in a canine model, which evolved and was later successfully used by Stucki-McCormick 19 in 1997 for neocondyle genesis. Other studies showed that the concept of functional remodeling can be used for the creation of a neocondyle using transport distraction osteogenesis 20–22.
Transport distraction osteogenesis is the technique of regenerating bone and soft tissue in discontinuity defect. An osteotomy is made 1.5 cm from the end of the distal stump of the bone adjacent to the discontinuity defect, creating a transport disc. Using a distraction device, the transport disc is advanced through the soft tissue discontinuity defect, creating new bone within the distraction gap, as the leading edge becomes enveloped by a fibrocartilagenous cap. This cap is surgically removed at the end of the distraction process to establish osseous continuity. Because the native mandible is used as the template for mandibular reconstruction, the neomandible has the same size and shape as the native mandible. The soft tissues are also recreated including a buccal and lingual sulcus, and attached and unattached gingiva. This allows for more ideal prosthetic reconstruction, including the placement of osseointegrated implants. These characteristics of the transport distraction technique have been used to recreate the mandibular articulation in the form of a neocondyle. Unlike mandibular reconstruction, the fibrocartilage cap of the leading edge of a transport disc is not removed. Rather, it acts as the new pseudodisc.
In this case, the maximum amount of bone regenerate after transportation was 22 mm. The amount of bone regenerate depends on the size of the surgical defect. For the success of transport distraction osteogenesis in condylar reconstruction, it is incumbent on the patient to actively participate in physical therapy because the secondary gain at the level of the mandibular condyle occurs primarily as a consequence of the patient opening wide and maintaining soft diet, especially during the period of neutral fixation when functional remodeling occurs. Physical therapy was continued for several months after distraction because the process of functional remodeling continues after the distraction device is removed.
Restoration of normal function and motion in patients with TMJ problems such as ankylosis, fractures have been difficult. TMJ ankylosis problems are associated with severe retrognathia, which makes it more difficult to treat. Therefore, when treating these patients, two parameters must be addressed: the ankylosis and mandibular growth. Until now, the standard treatment has been resection of the ankylosed condyle and its replacement with a free graft that provides the cartilage–bone interface and a growth site. Unfortunately, these procedures have unpredictable results as far as the growth pattern is concerned, and many of these patients have required multiple surgeries. The transport distraction osteogenesis procedure was found to have certain advantages over the previous techniques of costochondral grafting, such as the amount and the direction of mandibular growth and lengthening being more predictable because the surgeons can control distraction.
In addition to the skeletal manipulation and bone healing, the other major advantage is the ability to increase the soft tissue during the distraction process. These tissues do not simply become attenuated during distraction but rather undergo synthesis and regeneration. The advancement of the surrounding soft tissue produces a superior esthetic result. This case found that transport distraction fulfills the objective of predictability and effectiveness in TMJ reconstruction. It produces a cartilage–bone interface at the joint, which mimics a normal TMJ. The use of a bidirectional device allows correction in vertical and horizontal planes. The appropriate rate of callus lengthening creates well-vascularized bone in the distraction gap, which may be not subject to the process of graft incorporation and resorption. A second surgical site for bone grafting is not necessary, thus reducing the operating time, the risk of blood transfusion, and postoperative morbidity. The ease of applicability of transport distractor makes it a relatively simpler technique than grafting procedures.
Considering the above advantages, it could be said that this technique can also be applied in case of disorders such as idiopathic condylar resorption, degenerative TMJ disorders, and TMJ proplast-Teflon implant failures.
Summary and conclusion
Transport distraction osteogenesis has been used to reconstruct segmental defects. However, nonunion at the docking site and pseudoarthrosis covered with thick cartilage has been considered as a deficiency of the bone transport technique.
However, this case found this disadvantage favorable for TMJ reconstruction. Further research is needed to examine the long-term effects of neocondyle genesis.
The author thank Dr Vipin Thakker, ex-associate professor of the Government Dental College and Hospital, Mumbai, for helping him with publication of the paper.
Conflicts of interest
There are no conflicts of interest.
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