Bilateral TMJ Changes Secondary to Unilateral Condylar Hyperplasia

Background: Patients with unilateral condylar hyperplasia (UCH) may present with TMJ symptoms, rather than concerns or recognition of asymmetry. Localization of TMJ pain may be on the affected (long) side, unaffected side, or both. Flattening, severe erosion and internal derangement on the opposite side can be appreciated radiologically. This can be a red herring, shielding the true diagnosis of UCH from the contralateral side. We hypothesize that excessive growth of the ipsilateral condylar neck and head on the side of UCH results in an upward and backward force on the opposite side TMJ, with resultant symptoms and findings (condylar flattening, anterior disk displacement, eminence changes). The purpose of this paper is to highlight the bilateral TMJ findings in UCH, and address potential treatment strategies. Methods: This is a retrospective study involving radiologic and biographical data from subjects with TMJ UCH, as well as controls. Patient details and high quality Cone beam CT (CBCT) scans (1 mm slices or less) were analyzed. CT scans were digitized and morphometric points were placed using Planmeca software (Hoffman Estates, Illinois). Linear and volumetric measures were taken in reference to the eminence, TMJ space, condylar position, and neck lengths. Volumetric analysis of the condylar head and neck was done using Analyze 14.0 software (Overland Park, KS, USA). Results were assessed using univariate analysis (T-Wilcoxon test). Results: Forty patients were included (29 with UCH, 11 controls). The condylar head was flatter and erosive appearing on the contralateral UCH side compared to both ipsilateral side in the same subject, and compared to controls. Analysis between the affected and unaffected sides in patients with UCH showed a significant difference in condylar head and neck length ( P = .0019) and volume ( P = .0030); anterior glenoid space ( P = .035) and vertical height of condylar eminence ( P = .00044). The difference in ramus length was not significant ( P = .6533). Between the controls and the UCH patients, there was a significant difference in the variance in condylar head and neck length ( P = 1.98e-07) and volume between the 2 sides ( P = 1.94e-08) but not ramus length ( P = 1). The vertical height of the condylar eminence was smaller on the affected side than in the controls ( P = .0018) and the anterior glenoid space was significantly smaller on the unaffected side compared to the controls ( P = .0053). Conclusion: This study highlights TMJ morphological differences in patients with UCH. These differences in condylar and glenoid morphology are consistent and should be used to aid and underpin the diagnosis and direct treatment. Importantly, patients who present with TMJ pain and erosion on one side, should be assessed for opposite side UCH, as the underlying culprit.