Kinematic, Kinetic and Surface Electromyography Analysis Following Zygomatic Fracture Reconstruction

Abstract

The surgical indications of zygomatic fracture include aesthetic and functional impairment. No standard method exists for assessing the functional outcome nowadays, and traditional methods are subjective and inadequately quantitative for comprehensive analyses. This study was conducted to obtain a clinically applicable, reliable, quantitative, and noninvasive system for measuring the jaw function through kinematic, kinetic, and surface electromyography (sEMG) analysis. Because we previously established a model based on a healthy population, we applied the proposed system to patients with zygomatic fracture for this study. The study group comprised 20 young adults (18 male, 2 female) with simple zygomatic fracture. Twelve of them received open reduction and plate fixation (surgical group) and the other eight did not (nonsurgical group). We used a jaw motion analyzer to detect jaw movement, a sEMG instrument to evaluate the activity of the bilateral temporalis and masseter muscle, and an occlusal bite force system to measure the bite force. We compared jaw function over the affected side and sound side, and among the surgical group, nonsurgical group, and healthy population. In the surgical group, no functional difference was observed over the affected side and sound side 2 months after operation. However, the sEMG analysis revealed that the temporalis and masseter muscle and bite force exhibited less function over the affected side than over the sound side 3 months after the injury occurred in non-surgical group. Compared with the healthy population, the surgical group exhibited a shorter condylar path, narrower maximal mouth opening, less sEMG activity over masseter muscle, and less bite force over the affected side at 1 month after operation; however, their condition improved and did not differ from the control group at 2 months after operation. By contrast, the nonsurgical group continued to exhibit poorer jaw movement, less sEMG activity, and less bite force compared with the healthy population even 3 months after injury. Furthermore, the bite force was significantly lower in the nonsurgical group than in the surgical group at post-operative 3 month. (p = .002). We obtained a clinically applicable, quantitative, reliable, and noninvasive system for evaluating jaw and mastication function with biofeedback characteristics. For patients with a simple zygomatic fracture, the degree of jaw movement, sEMG activity, and bite force could return to normal by the second month after open reduction, stable fixation, and early rehabilitation.

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