The role of three-dimensional computed tomography in the evaluation of temporomandibular joint ankylosis.

AIMS: The aim of the study was to evaluate the role of three-dimensional computed tomography (3D-CT) in the assessment of temporomandibular joint (TMJ) ankylosis and its importance in treatment planning. The objectives of study were to measure and assess the mediolateral extent of ankylosis mass in 3D-CT and to compare the extent with intraoperative assessment. The study was also aimed to measure the coronoid process elongation in 3D-CT and its significance in treatment planning.
MATERIALS AND METHODS: This prospective study included 3D-CT evaluation of 11 patients with TMJ ankylosis during the period of February 2006-October 2007.
RESULTS: The 3D-CT assessment provided the length of the coronoid process and the relation of vital structures including maxillary artery to the ankylosed mass. Measurement of ankylosed mass also aids in preoperative measurement of the graft required to reconstruct the defect following removal of the ankylosed mass.
CONCLUSION: Our study concludes that 3D-CT is a useful tool in the diagnosis and treatment planning of TMJ ankylosis.

Imaging is a key stone for delivery of craniofacial health care. Recent developments have led to many diverse technologies and approaches. Oral and maxillofacial surgeons have been provided with many radiographic projections and many specialized radiographic techniques. The surgeon usually chooses a radiographic examination that will result in greatest diagnostic yield with least amount of radiation exposure to patient.

The temporomandibular joint (TMJ) ankylosis is an extremely disabling affliction that causes problems in mastication, deglutition, speech, appearance, and hygiene. In growing patients, deformities of the mandible and maxilla may occur together with malocclusion. The effective treatment of TMJ ankylosis requires detailed preoperative evaluation of the type and extent of the deformity.

The conventional radiography had played a major role in TMJ ankylosis till last few decades. The techniques used for TMJ imaging[1] include plain radiography, panoramic radiography, tomograms, conventional computed tomography (CT), arthrography, three-dimensional CT (3D-CT), magnetic resonance imaging, ultrasonography, arthroscopy, kinesiology, and radionuclide imaging. The standard mandibular series offers only two-dimensional view of the joint. The conventional radiographs often necessitate multiple views of the joint and lead to more radiation exposure to the patient. They have a disadvantage of poor structural resolution from superimposition of adjacent anatomic structures and geometric error. Extension of ankylosis is not clearly visualized in most of the conventional radiographic techniques.

Recently, 3D-CT constructed from the two-dimensional image of CT scan to simulate the soft tissue or bony structure of the real target was proposed. With 3D-CT image, the size and extent of the defect are clearly observable. The entire scan procedure lasts about a minute and motion artifacts are minimized. With the evolution of radiographic technology, 3D-CT has become an important radio diagnostic method in TMJ ankylosis. Due to the increasing use of the 3D-CT and its importance in the diagnosis, we review new developments in 3D imaging and its visualization and convergence of the data with its clinical application in diagnosis and treatment planning of TMJ ankylosis.

Materials and Methods

This prospective study included 3D-CT evaluations of 11 patients with TMJ ankylosis during the period of February 2006–October 2007. The patients of both sexes, of age group ranging from 8 to 25 years, with unilateral ankylosis, with no previous history of surgery, and willing to undergo 3D-CT were included in the study. Patients enrolled in the study were subjected to detailed case history and clinical examination. The following parameters were observed and recorded: Cause of the ankylosis, the amount of mouth opening, and the presence of deviation of midline. The amount of mouth opening was recorded by measuring interincisal distance between upper and lower incisors using slide callipers on maximum mouth opening.

Following this, all patients underwent 3D-CT scan using Siemens 64-slice CT machine. Scan was performed using the following parameters: section thickness, 1.0 mm; spiral gap, 1.0; window width, 2000 HU; window level, 600 HU; voltage, 120 kV; and electric current, 100 mA.

The CT images were reformatted into 3D-CT using Syngo CT. 3D software. The medial extension of ankylosis mass and the length of coronoid process on the involved side were measured.

The medial extension of ankylosis was determined as follows. In the transverse plane, a reference paramedian line was drawn to pass through the nasal septum and the center of the occipital foramen. Another horizontal line perpendicular to the vertical line and tangent to the condyle was constructed [Figure 1]. The distance from the midline to the medial pole was measured as d1 and d2 on the normal and ankylosed sides, respectively. The lateral poles were projected on the horizontal line and their distance from the midline was measured as D1 and D2, on normal and ankylosed sides, respectively. The difference between D1 and d1 denotes normal condylar width on the unaffected side. The difference between D2 and d2 gives the size of ankylosed mass.

Figure 1

Method to determine width of ankylosis mass

The length of the coronoid was measured by drawing a line passing tangent to the mandibular incisura.

A group of three maxillofacial surgeons were randomly allocated cases for surgical management. All these data were recorded and given to the operating surgeon. The scores are given by the surgeon postoperatively for each case, according to the usefulness evaluation Proforma. The surgeon evaluates the usefulness of 3D-CT, considering the following perspectives: treatment planning, surgical approach, extent of difficulty, and anticipatory complications. Scores of the usefulness evaluation Proforma are as follows:

0 - 3D-CT data were little or not useful

1 - Informative

2 - Useful

3 - Very useful.

These scores were tabulated and discussed. Our study was to correlate the preoperative clinical and radiological findings of joint ankylosis with those found at surgery and to evaluate the usefulness of 3D-CT in the diagnosis and treatment planning of TMJ ankylosis.

Results

This study was conducted on 11 patients who reported to the Department of Oral and Maxillofacial Surgery and were diagnosed as unilateral TMJ ankylosis. They underwent clinical examination, routine radiographic examination, and in addition, 3D-CT examination. The following data [Table 1] were collected and recorded.

Table 1

Patient Clinical data: Ankylosis mass, coronoid length and surgeons score

In our study, trauma was the major etiologic factor for TMJ ankylosis, accounting for 8 out of 11 patients. In our study on unilateral TMJ ankylosis, left side was more commonly involved accounting for 63.63% of the cases reported. Mouth opening ranged from 2 to 8 mm. The mean inter-incisal mouth opening was around 4.72 mm. 3D-CT confirmed the mandibular angle prominence and accentuation of the antegonial notch, together with reduced vertical height of the ramus. The mediolateral width of ankylosed mass ranged from 20.9 to 23.6 mm. The coronoid process length ranged from 19.2 to 27.6 mm. In two of our cases, 3D-CT measurements showed elongation of coronoid process and coronoid process was seen above the zygomatic arch in 3-D CT. The elongated coronoid process was confirmed at surgery and coronoidectomy was performed.

Discussion

Temporomandibular disorders (TMD) constitute a complex set of specific entities with a reported prevalence of 5–12%. Toyama et al.[2] stress that imaging diagnosis is essential in differentiating and evaluating restricted mouth opening. Ankylosis[1] causes pain and difficulties with speech, eating, and oral hygiene, which have a great impact on the patient. TMJ ankylosis in childhood[3] can impair mandibular growth and function, producing a severe facial deformity leading to “bird face.” According to Sawhney,[1] longstanding, early-onset ankylosis in childhood results in marked facial asymmetry, whereas the bony changes are minimal when the problem occurs during adolescence or the patient had early treatment.

Ankylosis[4] is commonly associated with trauma (13–100%), local or systemic infection (0–53%), or systemic diseases such as ankylosing spondylitis, rheumatoid arthritis, or psoriasis. In our study, trauma (72.72%) was most common etiology. This was similar to the data of Schobel et al. and Behcet et al. The preoperative mouth opening ranged from 2 to 8 mm. The mean value of mouth opening was 4.36 mm.

Preoperative evaluation usually consists of history, and physical and radiographic examination. Radiography[25] is an essential diagnostic tool for TMJ ankylosis. Patient positioning is crucial in panoramic imaging of the condyles. If the head is inclined posteriorly, the image of the condyle appears flattened and can simulate the presence of an osteophyte. Conversely, if the head is inclined anteriorly, the condyle may appear sclerotic. This often necessitates multiple view, hence more radiation exposure to the patient. Ahlqvist et al.'s[6] study revealed that thin bone separating the glenoid fossa from the middle cranial fossa and the external auditory canal/middle ear have an inclination to imaging planes used in TMJ radiography, making them highly susceptible to projection artifacts. Sanders et al.[1] reported that conventional radiography underestimated the extent of the bony ankylosis that is found at the time of operation. CT is accurate in two dimensions. However, the surgeon has to construct a three-dimensional image in his mind similar to the shape and form of the deformity. Multislice CT[7] represents a potential advancement in CT and allows obtaining thinner slices and high image quality in less acquisition time. This leads the way for development of faster and accurate three-dimensional imaging. The introduction of spiral CT[8] is another major advancement in CT scanning, particularly considering the reduction in acquisition time and improvements in two-dimensional and three-dimensional reconstructions.

In our study, the 3D-CT provided excellent visualization of the osseous components of the condylar process of the mandible and the glenoid process of temporal bone, as demonstrated by Kursunoglu et al.[9] In cranial morphometry where anatomical measurements are made using images, quantification and accuracy are the principal concerns. In our study, the measurement of coronoid length helped in the diagnosis of coronoid elongation in two of our cases. The 3D-CT images clearly demonstrated hyperplastic coronoid process and joint surfaces, as reported by Akan and Mehreliyeva.[10] This was confirmed in surgery and coronoidectomy was performed to achieve satisfactory mouth opening. The measurement of ankylosis mass helped in estimation of amounts of autogenous and alloplastic material required for gap arthroplasty prior to surgery.

Detailed knowledge of the deformity and three-dimensional view of ankylosis mass resulted in accurate and expeditious procedures. 3D-CT not only revealed the relationship of ankylosis mass with adjacent vital structures, but also provided detailed view of condylar head, glenoid fossa, sphenoid, and temporal bone. Metwalli[5] in his study measured the distance between the internal carotid artery, the internal jugular vein, the maxillary artery, and the medial pole of the mandibular condyle, and found that this distance decreased on the ankylosed side compared with the normal. Concern about the possible risk of damage to any of these structures compromises the exposure necessary for adequate resection of the ankylosed segment and is often the most common cause of subsequent re-ankylosis. However, identification of these structures and prior measurement of width of ankylosis mass on the 3D-CT reformatted images helped in the resection of ankylosis mass without causing any damage to these vital structures, and therefore providing a good gap between the mandibular stump and the base of the skull. Hence, the incidence of recurrence decreased remarkably irrespective of whether the gap was reconstructed with a graft or not.

Conclusions

The effective treatment of TMJ ankylosis required detailed preoperative evaluation of the type and extent of the deformity. Since recurrence is the major hurdle in the management of TMJ ankylosis, precise surgical treatment planning is necessary to reduce the incidence of recurrence. Plain and panoramic radiography does not provide adequate information of the ankylosed mass and its relation with adjacent structures. The length of the coronoid process and the relation of vital structures including maxillary artery to the ankylosed mass also need to be analyzed before treatment planning, which is possible on a 3D-CT examination. The 3D-CT images not only help in planning of surgical approaches, but also guide in anticipatory complications.

The importance of 3D-CT images in quantitative and qualitative analysis of the craniofacial complex is clearly recognized. 3D reformatted images can clearly demonstrate hyperplastic coronoid process and joint surfaces. Measurement of ankylosed mass also aids in preoperative measurement of the graft required to reconstruct the defect following removal of the ankylosed mass. Detailed knowledge of the ankylosis resulted in accurate and precise surgical procedures. Our study concludes that 3D-CT is a useful tool in the diagnosis and treatment planning of TMJ ankylosis.