Background and objectives: Unilateral condylar hyperplasia (UCH) is a growth disorder affecting the mandible, with an unknown pathophysiology and aetiology. Micro-computed tomography (microCT) has been established as an accurate and non-destructive tool to determine the three-dimensional architectural parametres and the physical properties of bone. The purpose of this study is to visualize the three-dimensional bone microstructure of resected mandibular condyles of patients with UCH.

Methods: This study prospectively included 17 patients with a clinical presentation of progressive mandibular asymmetry and a true positive SPECT scan. All patients underwent condylectomy to arrest further progression. The resected condyles were scanned with a microCT (18 μm resolution). Rectangular volumes of interest were selected in four quadrants (lateral-medial and superior-inferior) of the trabecular bone of each condyle. Bone architectural parameters (volume fraction, trabecular number, thickness and separation, degree of mineralization, degree of structural anisotrophy) were calculated with routine morphometric software.

Results: Eight of the 17 resected condyles (47%) showed clear destruction of the subchondral cortical bone layer. The bone architectural parameters of the trabecular structure showed large variation and marked structural heterogeneity. When comparing the present results with the literature the trabecular structure in mandibular condyles of UCH patients show higher bone volume fraction (25.1 ± 7.2%) and increased trabecular thickness (0.17 ± 0.04 mm) and trabecular separation (0.60 ± 0.22 mm) and increased structural anisotropy (1.84 ± 0.34) and showed lower degree of mineralization (695.9 ± 41.60 mg HA/ccm) and comparable trabecular number (1.69 ± 0.36 mm ⁻¹ ).

Conclusion: The present microCT findings in UCH patients demonstrate a marked difference in both cortical and trabecular bone structure of the condyle compared to the known architecture of non-affected mandibular condyles.