Long-term evaluation of the stability of reconstructed condyles by transport distraction osteogenesis


This retrospective longitudinal study evaluated the long-term stability of reconstructed condyles by transport distraction osteogenesis of the mandibular ramus in patients with unilateral temporomandibular joint (TMJ) ankylosis. 7 patients were followed up for 16–92 months (mean 39.4 months). The mean age of the patients at the time of distraction was 22.9 years (range 7–44 years). Maximal mouth opening and panoramic radiographs were recorded preoperatively, at the time of device removal and several years after removal of distraction device. At follow-up, cone beam CT images of the TMJ were obtained to confirm the changes of the reconstructed condyle. Absolute height (Co–Inc) and relative height (Co–Inc/Co–Go) of the reconstructed condyle and the asymmetric difference ratio (AR) were examined to assess the changes of condylar height and mandibular symmetry. The mean maximal mouth opening was stable during the period of follow-up. The mean absolute height and relative height of the reconstructed condyle decreased significantly ( P < 0.05). Although no significant difference was found, the mandibular asymmetry difference ratio increased by 16.7%. These results suggested that the heights of reconstructed condyles were not stable in the long-term, and the mandible tended to be asymmetrical.

Temporomandibular joint (TMJ) ankylosis may be defined as ‘an inability to open the mouth due to either a fibrous or bony union between the head of the condyle and the glenoid fossa’. It may cause impaired speech, eating difficulties, facial disfigurement, airway compromise and psychological stress. It is usually caused by trauma with associated condylar fracture. Corrective surgery is usually the treatment of choice. When arthroplasty is performed, it is often accompanied by condylar reconstruction to restore the ramus height and jaw occlusion.

Recently, ramus transport distraction osteogenesis has been utilized to reconstruct condyles. Few studies have reported the long-term outcomes of this operation and the sample sizes in these studies have been small. The object of this study was to examine the long-term stability of reconstructed condyles and changes in the mandibular symmetry of patients with unilateral TMJ ankylosis.

Patients and methods

Patients with unilateral TMJ ankylosis treated by arthroplasty and transport distraction osteogenesis between 2002 and 2009 were included in this study. Patients with recurrent ankylosis and those with systemic diseases that influenced bone physiology were excluded.

For each patient, the ankylotic bone mass was resected through an extended preauricular approach and the resultant gap was larger than 1.5 cm. In the operation, the passive maximal mouth opening was more than 35 mm, which was achieved by placing a mouth-gag in the molar region. The temporal muscle myofascial flap was inserted into the gap by folding it downwards into the fossa. It was sutured with the anterolateral edge of the residual articular disc. The distraction device was attached and the direction of distraction was adjusted in order to transport the segment to the glenoid fossa.

After removal of the device, an L-shape osteotomy was performed. The distraction device was installed in the correct site after the mobility of the segment was tested by activating the distraction device. Figure 1 A shows the distraction device installed in the appropriate site.

Fig. 1
Operative procedures.

After a latency period of 5–6 days, distraction of 1 mm per day was divided into 3 times. When the distance between the transport segment and skull base reached 2 mm, the distraction was stopped so that no pressure was created on the flap. During the consolidation period, physical therapy was applied. After a consolidation period of 3–4 months, the distraction device was removed. Figure 1 B demonstrates the regenerate bone formed in the distraction gap. The transported segment was remodelled to form a neocondyle.

Outcome assessment

Maximal mouth opening was recorded and standardized panoramic radiographs were taken preoperatively, at the time of device removal, and at follow-up for each patient. Cone beam CT images were also obtained at follow-up.

According to the method described by Kambylafkas et al., the outlines of the condyle and the ascending ramus of both sides were traced using Photoshop software. Line L 1 and line L 2 were drawn and the Co point, Inc point, and Go point were localized. The absolute height (Co–Inc) and ramus height (Co–Go) were measured ( Fig. 2 ). All parameters were measured by two experienced maxillofacial surgeons and were reduced to actual size using the standard height bar on the right edge of the panoramic radiographs. The intra-examiner variation was assessed by asking these two examiners to re-examine the radiographs. The inter-examiner reliability was assessed by intraclass correlation coefficients (ICCs). The relative height of each condyle was calculated using the following formula: Co–Inc/Co–Go. The asymmetry difference ratio (AR) was calculated using the formula: % difference = ( C A )/( C + A )/2 × 100% where C is controlled side ramus height, and A is affected side ramus height.

Fig. 2
Methods of measurement. L 1 is a line tangent to most prominent points of the posterior margin of the ramus. L 2 is a line tangent to the most prominent points of the inferior border mandible. Co is the most superior point on the condylar head. Inc is the deepest point between processus coronoideus and processus condylaris. The absolute condylar height (Co–Inc) and the total height of ramus (Co–Go) were measured.

Data were analysed for statistical significance using paired t -tests. A P -value of <0.05 was considered to be significant. Statistical analyses were conducted using SPSS 18.0 software (SPSS Inc., Chicago, IL, USA).


7 patients were included in this study. The duration of follow-up was more than 1 year (range 16–92 months; mean 39.4 months). This sample comprised 2 females and 5 males. Their mean age was 22.9 years (range 7–44 years) at the time of distraction. The mean maximal mouth opening was 4.1 mm (range 0.0–8.0 cm) preoperatively, 35.3 mm (range 25–40 mm) during the operation, and 31.4 mm (range 23–37 mm) at follow-up. The intra-examiner repeatability was tested by paired t -test. For examiner A, two times’ measurements: Std. = 1.19 mm, Sig. = 0.277 > 0.05. For examiner B, two times’ measurements: Std. = 1.18 mm, Sig. = 0.422 > 0.05. ICC results showed the measurements examined by these two examiners agreed extremely well (ICCs = 0.99). From the time of device removal to follow-up, the mean absolute height of the reconstructed condyle reduced by 6 mm (from 10.5 mm to 4.5 mm); the mean relative height decreased by 11.7% (from 19.4% to 7.7%); and the mandibular asymmetry difference ratio increased by 16.7% (from 25.1% to 41.8%). Table 1 shows the measurements and details for each patient.

Table 1
Measurement results and details of patients.
Patient Gender Age (years) Affected side Follow-up duration (months) Phase 1 MMO (mm) Phase 2 MMO (mm) Phase 4 MMO (mm) Phase 3 Co–IncA (mm) Phase 4 Co–IncA (mm) Phase 3 RH (%) Phase 4 RH (%) Phase 3 AR (%) Phase 4 AR (%)
1 Female 7 Left TMJ 92 5.0 35.0 31.0 7.3 0.0 17.3 0.0 38.5 74.8
2 Male 35 Right TMJ 20.5 0.0 40.0 31.0 10.7 2.6 19.2 6.5 22.4 38.3
3 Female 7 Right TMJ 16 8.0 35.0 23.0 9.3 7.9 18.1 15.0 15.0 17.6
4 Male 44 Right TMJ 41 2.0 25.0 30.0 7.0 5.8 11.6 10.4 17.9 15.3
5 Male 19 Right TMJ 24 8.0 35.0 37.0 17.0 5.6 22.5 8.3 4.5 25.4
6 Male 33 Left TMJ 25 4.0 37.0 33.0 9.7 9.3 15.2 13.4 22.5 20.0
7 Male 15 Right TMJ 57 2.0 40.0 35.0 12.8 0.0 31.7 0.0 54.9 100.9
Mean 22.9 39.4 4.1 35.3 31.4 10.5 4.5 19.4 7.7 25.1 41.8
Std. 3.1 5.1 4.5 3.5 3.7 6.4 6.0 16.6 33.2
Sig. 0.113 0.021 0.030 0.061
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Jan 24, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Long-term evaluation of the stability of reconstructed condyles by transport distraction osteogenesis
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