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[Clinical study of three-dimensional reconstruction of computed tomography in diagnosis of condylar fractures].

OBJECTIVE
To explore a method of getting good three-dimensional (3D) reconstruction images of temporomandibular joint (TMJ) by computed tomography (CT), and evaluate diagnosis value of 3DCT in condylar fractures.


METHODS
Of the 14 patients studied, 12 were male and 2 were female with age ranging from 4 to 37 years old. 4 were old fractures and the other 10 were fresh fractures. All patients' orthopanotomograms were taken first, and then were scanned with CT. The scanning conditions were 300-345 mAS and 120kV, and the scanning methods included cross-sectional (11/14), coronal-sectional (2/14) and spiral (1/14) (pitch: 1, thickness of layers: 2.5 mm) scanning. Scanning scopes: The cross-sectional and spiral scanning were from 1 cm above the Frankfort horizontal plane to the middle of the mandibular ramus or Menton; The coronal-sectional scanning was from the mastoid process to the anterior point of the mandibular ramus or Pogonion. The thickness of the scanning layers was 2.5 mm (12/14) or 5 mm (2/14). Finally, 3D reconstructed images were obtained by shaded surface display (SSD). The cross-sectional images were obtained by being removed the cervical vertebra, the styloid process, the occipital bone and part of the mastoid process with Subtract Manual Irroi before reconstruction to avoid interference with the observation of TMJ and skull basis.


RESULTS
1. The best 3D CT reconstructed images were obtained by 2.5 mm-thin-layer cross-sectional scanning by being removed parts of the adjacent structures, and the bone lines were clear and smooth without adjacent bone structures shading TMJ. The quality of images taken spirally was similar to those taken cross-sectionally. While the coronal scanning neglected some important anatomic symbols which might be valuable to diagnose condylar displacement. 2. Of the 14 patients, 7 were unilateral condylar fractures and 7 were bilateral (21 sides altogether), among which 18 sides were high fractures of condyles and 3 were fractures of condylar neck. High oblique line fractures and comminuted fractures had major condylar rotation displacement which moved forward, downward and inside, whereas, vertical fractures only had minor displacement. Inward rotation displacement occurred in medial bent fractures. 10 of 14 patients (15 sides) had been conducted operation, and the same situations as seen from 3DCT reconstructed images were found.


CONCLUSION
3DCT images can display condylar fractures accurately and directly, and are very useful for surgeons to select treating methods of condylar fractures.