Does the Surgical Approach Influence Masseter Muscle Contractility in Patients With Unilateral Mandibular Condylar Fractures?

BACKGROUND

Surface electromyography provides an objective, noninvasive method for assessing masseter muscle function and postoperative recovery following open reduction and internal fixation (ORIF) of mandibular condylar fractures.

PURPOSE: The purpose of the study was to compare masseter muscle power and contractility following ORIF of unilateral mandibular condylar fractures using the transparotid (TP) and transmasseteric anterior parotid (TMAP) approaches.

STUDY DESIGN, SETTING, SAMPLE: This retrospective cohort study included adult subjects who underwent ORIF for unilateral condylar fractures using TP or TMAP approaches between January 2021 and December 2022. Subjects with pretraumatic temporomandibular joint disorders, additional surgical approaches, or incomplete surface electromyography data were excluded. Twenty-two subjects were analyzed (11 per group).

PREDICTOR VARIABLE: The predictor variable was surgical approach (TP vs TMAP).

MAIN OUTCOME VARIABLES: The primary outcome variables were maximum amplitude and mean power. The amplitude is the maximum peak of the negative phase to the maximum peak of positive phase in electromyography. Power is defined as the sum of action potentials produced in the muscle.

COVARIATES: The covariates were age, sex, and fracture patterns.

ANALYSES: Longitudinal changes were analyzed using repeated measures analysis of variance. Operated and contralateral sides were compared using paired t-tests. Kaplan-Meier survival analysis assessed time to ≥80% recovery (P < .05).

RESULTS

The mean age was 32.8 ± 11.2 years in the TP group and 27.8 ± 8.5 years in the TMAP group (P = .3), with male predominance (86.3%, n = 19). Repeated-measures analysis of variance demonstrated a significant effect of time on both amplitude and power within group (P < .001), with no significant time × approach interaction. Kaplan-Meier analysis showed that all subjects achieved ≥80% recovery by the earliest postoperative interval (7-10 days), with no difference between approaches (P = .4). At 3 months, a small but significant reduction in mean power persisted on the operated side in the TMAP group (P = .024).

CONCLUSION AND RELEVANCE: Regardless of the approach used, the masseter muscle achieved ≥80% functional recovery within 7-10 days. Recovery is primarily time-dependent, allowing the choice of surgical approach to be guided by fracture characteristics and surgeon expertise.