Preoperative and postoperative assessment of temporal and masseter muscle size with magnetic resonance imaging in patients undergoing unilateral temporomandibular joint surgery.

The aim of this study was to assess any change between the preoperative and postoperative sizes of temporal and masseter muscles with magnetic resonance imaging (MRI) in patients undergoing unilateral temporomandibular joint surgery. This study was designed and implemented retrospectively. For clinical evaluation, a visual analog scale (VAS) and maximum mouth opening (MMO) were used. In order to make a preoperative diagnosis and perform a 6-month control, muscle size was measured in millimeters (mm) on T1 axial sections in MRI. Statistical analyses were performed using the SPSS 23.0 software package. Numeric variables were compared between two dependent groups using the Wilcoxon signed rank test. Statistical significance was set at p < 0.05. Twelve patients who underwent unilateral discectomy plus dermis-fat grafting, with classical preauricular inverse L incision, were included in the study, and data for eleven female patients were evaluated. The difference in size between the operated and non-operated sides was found to be statistically insignificant at the preoperative stage for both masseter muscle (operated side m: 13.264 ± 1.822 mm; non-operated side m: 13.264 ± 2.315 mm; p = 0.929) and temporal muscle (operated side m: 20.345 ± 2.609 mm; non-operated side m: 20.582 ± 2.366 mm; p = 0.594). There was a significant size reduction in the masseter muscle on the operated side in the postoperative period (preop m: 13.264 ± 1.822 mm; postop m: 12.036 ± 1.728 mm; p = 0.018). Although there was also a size reduction in the operated side of the temporal muscle in the postoperative period, that difference did not reach statistical significance (preop m: 20.345 ± 2.609 mm; postop m: 19.445 ± 1.603 mm; p = 0.182). On the non-operated side, there were no significant postoperative changes in the sizes of either the masseter muscle (preop m: 13.264 ± 2.315 mm; postop m: 12.682 ± 2.059 mm; p = 0.248) or the temporal muscle (preop m: 20.582 ± 2.366; postop m: 19.891 ± 3.487 mm; p = 0.625). Considering the study findings as a whole, a size reduction was observed in the operated side of the masseter muscle after TMJ surgery. The etiology of this change may be surgical trauma to the temporal and masseter muscles, skeletal alteration resulting from condylar change secondary to discectomy, and patients restraining themselves from application of maximum bite force as a result of a self-protection mechanism due to postoperative pain.