Artículo Especial

Mandibular distraction and the temporomandibular joint
Distracción mandibular y articulación temporomandibular

F. Monje Gil

Jefe de Servicio de Cirugía Oral Maxilofacial, Hospital Universitario Infanta Cristina

Correspondencia:
Florencio Monje Gil
Servicio de Cirugía Oral y Maxilofacial. Hospital Univ. Infanta Elena
Crtra. de Portugal s/n - 06001 Badajoz
E-mail: fmonje@oralmaxilofacial.com

The concept of distraction applied in the treatment of craniofacial abnormalities began in the year 1972¹ with the lengthening of the jaw of a dog. Later other experimental papers^2,3,4 have contributed to the understanding of the different biological aspects of this procedure. Clinical application in humans began with the work of McCarthy^5,6 to the extent that, due to him, this method began to be used systematically for certain craniofacial abnormalities.

The Temporomandibular Joint (TMJ) is composed of the mandibular condyle, joint disc, temporal fossa, capsule and ligaments. The mandibular condyle has a mechanical function but it also has a growth function, which is to a certain respect adaptive. It is of interest to bear in mind that for this, the mandibular condyle has joint cartilage which serves in addition as growth cartilage. This growth cartilage has various layers: articular, proliferative, fibrocartilaginous and calcified. This organization is visible until adolescence.

After this the clear division of the joint cartilage in this region is very difficult to appreciate. As well as condrocytes and other cellular components of the cartilage, we need to know that the matrix exists in this cartilage and intercellular substance. The matrix is made up of collagen fibers which are in turn synthesized in the chondrocyte. It provides great resistance to traction but little resistance to compression. The intercellular substance is made up of proteoglycans and water. It provides great resistance to the forces of compression. This, in short, is a very complex joint for different reasons: variety of the tissues that compose it, mechanical activity and growth. It is a very important articular disc for all the functions of the TMJ, [affecting] the relationship with mandibular movements and in certain cases, with occlusal factors. But on the other hand, the richness of the connective tissue contributes to a series of biological characteristics of the disc: regeneration, adaptability and remodeling. However, these characteristics are easy to define scientifically but separating these three factors clinically is very complicated.

Mandibular distraction is based on a series of biological principles: performing an osteotomy, preserving vascularization, adequate latency period, correct rhythm of distraction and correct consolidation period.⁷ However, many of the mechanical principles are still not known today which includes the relationship of the different forces generated by mandibular distraction and the TMJ. On the other hand, in various experimental works^8,9 the appearance of changes in joints, such as in the knee, in relation with the distraction of the bones near by, has been verified (cartilaginous fibrillation, loss of proteoglycans and cartilaginous necrosis). However, few works have studied the relationship between mandibular distraction, in the different planes of the space, and the TMJ.

What first has to be clarified is whether mandibular distraction, in the different planes of the space, really produces a variation in the position of the mandibular condyle. The essential work covering this aspect is by Samchukov¹⁰. A computer model is used in order to visualize the effect of distraction in the sagittal plane depending on if the distractor is placed parallel to the surface of the bone or parallel to the axis of distraction. If it is placed parallel to the axis of distraction there is no type of repercussion in the space on the position of the condyle. However, if it is placed parallel to the bone surface, for every mm of distraction there is a lateral displacement of the mandibular condyle of 0.25 mm. According to the same model, when distraction is carried out in the transverse dimension following a medial osteotomy of the mandible, there is an internal rotation of the mandibular condyle.

Mandibular distraction in the transverse dimension and the temporomandibular joint

The first experimental investigation was published by Harper and cols.¹¹ The Macaca Mulatta was used as a model. An osteotomy was carried out on the mandibular midline. Between the seventh and fourteenth day after the osteotomy, distraction was carried out at a rate of 0.5 mm twice a day for seven to ten days. Histological analysis was carried out in the different areas of the mandibular condyles. The changes in the anterolateral and posteromedial areas of these condyles were very minor and affected fundamentally the distribution of collagen fibers. However, the appearance of more severe histological changes occurred in the anteromedial and posterolateral areas where reabsorption within the cartilaginous area could be appreciated together with the appearance of severe disorganization in the orientation of the bundles of collagen fibers. Nevertheless, no erosions were discernable on the condyle surface. These changes were attributable to the pressure on theses areas of the condyles by certain areas of the temporal fossa. However, the authors concluded that these were adaptation and reactive changes due to compression forces which were tolerated better when the daily distraction rate was distributed in various phases. The following experimental investigation which studied the relationship between distraction in the transverse dimension and the TMJ was by Stelnicki.¹² In this study the dog was used as an experimental model. This was a very complex work as during the distraction different movements were combined, the essential one being distraction in the transverse dimension. A latency period of five days was applied and a rhythm of distraction of 1 mm per day. The consolidation period was 8 weeks. The parameter studied was the morphologic-macroscopic analysis of the fossa and mandibular condyle. In the different groups studied condylar erosion to larger or smaller extent was appreciated. Therefore, this study demonstrated that distraction in the transverse dimension, under the conditions set out in the investigation, produces severe degenerative changes which do not disappear at the end of the 8 week consolidation period. Obviously the authors recognize that all these changes are produced by the forces of compression applied on the mandibular condyle. However, what is lacking in the study is the absence of a correct histopathological study which explores in depth the fine structure of these changes, and in which the effect on soft tissues such as the disc and the joint capsule is observed.

The only existing clinical paper that relates distraction in the transverse dimension and the TMJ is by Kewitt and Van Sickels.¹³ The results obtained regarding mandibular distraction in the transverse dimension were analyzed in 23 patients. A latency period of 5 days was applied together with a daily rate of distraction of 0.75 mm divided into three expansion periods a day. As well as studying other factors such as neurosensory function, periodontal and dental structures, the appearance of symptoms related with the TMJ was studied from a clinical point of view. Of the 15 patients that were suitable for this study, 7 had preoperative symptoms of the TMJ, 5 of which showed improvement in these symptoms, and two did not show any type of change after surgery. However, these patients were later given, following distraction in the transverse dimension, other orthodontic treatment with single or bimaxillary surgery, and it was not possible to know what was attributable to the distraction, the orthodontic treatment or orthognathic surgery.

Mandibular distraction in the sagittal plane and the temporomandibular joint

The previous experimental study in this field had been published by Ellis.¹⁴ The Macaca Mulatta was used as an experimental model. A bilateral sagittal osteotomy was carried out. In one group rigid fixation was used and in the other group intermaxillary fixation was used. In the group with rigid fixation a posterior displacement of the condyle was observed, which caused the posterior side of the condyle to be pushed against the posterior wall of the glenoid fossa of the temporal bone. Histological analysis revealed a reabsorption of the posterior surface of the condyle and the anterior surface of the post-glenoid spine. The author admits that these changes, in human clinical, can lead to degenerative changes and ankylosis, although he acknowledges that they may become part of a series of remodeling changes. Therefore, this study could be the antecedent of the experimental works which study the relationship between mandibular distraction in the sagittal plane and the TMJ.

The first work was in fact by McCormick.¹⁵ The dog was used as an experimental model. Activation was begun 10 days after surgery, and the rhythm of distraction was 1mm per day. In one group 20 mm was reached and in another 10 mm. The analysis of results was done using a computed axial tomography. The flattening of the posterior wall was greater in the condyles of the 20 mm distraction group. There was no evidence of necrosis or degeneration. There were minimal changes in the temporal fossa. In addition to this there were changes in the condyle on the contralateral side of the distraction. The authors considered that these were all reversible and transitory changes.

The article by Karaharju-Suvanto and cols¹⁶ is very interesting. Growing sheep were used as experimental models. A latency period of 5 days was observed after the osteotomy. The distraction rhythm was from 0.5 to 1 mm per day. A histological method was used and the repercussions of this [type of] distraction was studied in different groups of animals: at 4.5, 20 and 52 weeks. In the first group thinner cartilage could be appreciated together with an increase in osteoblastic activity. Changes were observed in the contralateral condyle but they were much smaller. In the second group the changes in the condyle on the same side were very small, and in the third group the changes in the condyle on the same side were nearly the same as those in the control group. The authors came to a series of conclusions. The first was that, as growing animals were used, these were remodeling and reversible changes and degeneration changes were never observed. The second conclusion was that the contralateral joint was minimally affected.

The following study was by Zou and cols.¹⁷ They used the goat as an experimental model and they aimed to investigate the repercussion on the TMJ of different levels of distraction. After a latency period of 7 days, a distraction rate was applied in one group of 1 mm per day (0.5 mm every 12 hours). In the other group distraction was 2 mm per day (1 mm every 12 hours). Histological analysis revealed that in the first group the changes could be considered remodeling and adaptive changes, and that these were centered on the posterosuperior portion of the mandibular condyle. However, in the group that underwent the largest amount of distraction per day, there were clear signs of degeneration. For these authors the changes were not necessarily due to the amount lengthened, but to the daily distraction rhythm. Therefore, the "speed" of the distraction has a series of negative effects, not only regarding callus ossification but also the adaptation changes of the TMJ.

The study by Thurmuller and cols¹⁸ used the minipig as an experimental model. There was no latency period and the distractor was activated, depending on the group, at a rate of 1, 2 or 4 mm per day until 12 mm was reached. A radiographic study was carried out together with a very interesting morphological study (analysis of condylar size and form, condylar surface area and characteristics of the joint disc). The results at 20, 60 and 90 days were also studied. The final results showed that, when compared with the control group, the groups in which the daily rate was 2 to 4 mm, the condyle was smaller with increased convexity, although erosion was not observed. When distraction was between 2 and 4 mm per day, the joint disc was thinner at its more medial portion, and macroscopical alterations could be appreciated in the whole of the joint disc on the same side of the distraction. Although these changes were very obvious in the groups which underwent the largest rate of distraction, the authors were not able to establish if this was due to remodelation or if it was due to a clearly degenerative phenomenon.

In the study by Muhonen and cols^19,20 the rabbit was used as an experimental model. The aim was to investigate using PET how radiotherapy and therapies using the hyperbaric [oxygenation] chamber affect the TMJ of animals who are subjected to mandibular distraction. The control group showed mandibular distraction led to increased detection in the TMJ using PET, when homolateral distraction of the mandible was used. This was taken to signify that these adaptation or remodeling changes were characteristic of the TMJ itself. Radiotherapy led to reduced detection of the tracer. However, when these animals were treated in the hyperbaric [oxygenation] chamber, there was an increase again.

The first clinical study was by McCormick²¹ who analyzed using a CT scan the results in 10 patients who had undergone a distraction of 0.5 mm every 12 hours during a stabilization period of 8 weeks. The patients analyzed had unilateral distraction and the results showed an increase in the volume of the condyle on the distracted [side]. The latter was more erect and the temporal fossa had not been affected by the change.

This same group²² in the year 1997, investigated the therapeutic consequences that sagittal mandibular distraction had on the TMJ. This was based on the "bone transport" concept. By virtue of this concept, certain types of mandibular anomalies, either congenital or traumatic could be solved by transporting a fragment of mandible towards the temporal fossa. There are other works^23-25 supporting this therapeutic procedure. The opinion of this group is opposed by other authors such as Eppley²⁵ who support primary reconstruction of the TMJ in congenital defect cases, postresection defects arising from ankylosis or traumatic defects, by means of a costochondral graft following the classical technique. Depending on the functional and aesthetic results, the mandible with the graft can subsequently be lengthened.

As a consequence of examining the published literature, the following can be concluded:

• Mandibular distraction in the sagittal or transverse dimension leads to changes in the position of the condyles.

• Distraction in the transverse plane leads to considerable changes in the joints that can be remodeling, reactive and/or clearly degenerative changes.

• Age is very important. When distraction is carried out in growing individuals, it would appear that the changes that take place are transitory and less important.

• The daily rhythm of distraction is more important than the total amount of the distraction.

• From a clinical point of view there should be a protocol regarding the use of distraction in TMJ reconstruction.

• There are very few scientific studies that establish from a clinical point of view, the repercussions of mandibular distraction on the TMJ and the protocol that should be established in this sense for treating this pathology.

References

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