Three Dimensional Morphological Grading of the Ankylosed TMJ for Surgical Planning: A Retrospective Observational Study

Introduction: Temporomandibular Joint (TMJ) ankylosis remains an enigma in craniofacial surgery due to the challenges encountered while restoring mouth opening, facial form and airway to normalcy. Though TMJ ankylosis is a relatively simple diagnosis to make, the specific surgical plan depends on the nature and extent of the fusion of the mandible with the cranial base.

Aim: To classify the pattern of bone deformity found in TMJ ankylosis using three Dimensional (3D) Computed Tomography (CT) imaging and its role in determining the type of procedures required for effective gap arthroplasty.

Materials and Methods: This retrospective study was done to evaluate the 3D CT reconstructed images of 66 consecutive patients having 82 ankylosed joints treated from January 2007 to December 2019 with a standardised protocol. A grading system was used with the following criteria: coronoid hyperplasia, sigmoid notch to skull-base fusion and loss of residual joint space. The gap arthroplasty required for each grade of ankylosis was also analysed. The complete data in the present study was tabulated in Microsoft Excel sheet and frequency (n) analysis was done for all variables.

Results: Out of 66 patients (82 ankylotic joints) 37 males and 29 females), age range 2.5-51 years, average age 18.2 years) 27% of the total joints surveyed belonged to grade 1 type of ankylosis. None of these joints had complete bony fusion (absence of the radiolucent zone between the cranium and condyle). A 10% of the joints had moderate ankylosis (grade 2). None of them revealed complete bony fusion (absence of the radiolucent zone) or fusion of the sigmoid with the cranial base. Grade 3 ankylosis was the most widely seen pattern of ankylosis (63% of the present study subjects) and 92% had a history of childhood onset. A 90% of the joints in this group had ipsilateral coronoid hyperplasia. A 48% of the joints with severe ankylosis (grade 3) showed bony fusion with the cranial base, with loss or absence of the radiolucent zone {Fusion Line (FL)} between the cranial base and the condyle.

Conclusion: The extent and severity of TMJ ankylosis needs to be ascertained prior to planning TM Joint ankylosis surgery. A 3D CT assessment and subsequent radiologic grading provides a reliable guide for ankylosis release.