Does Evoked Electromyography Detect the Injured Facial Nerve Recovery Earlier Than Clinical Assessments?

Abstract

The key element in managing postoperative facial nerve (FN) injuries is timely diagnosis and intervention as indicated. The purpose of this study was to measure and compare evoked electromyography (EEMG) and clinical assessment in terms of the recovery of the injured FN in operated temporomandibular joint ankylosis (TMJA) cases. The investigators designed a prospective cohort study in the primary operated TMJA patients. The primary predictor variable was the technique used to assess FN function, House-Brackmann Facial Nerve Grading System (HBFNGS) or EEMG. The primary outcome variable was time to FN recovery. The FN recovery was assessed in different time points (1 week, 1 month, 3 months, and 6 months). Age, gender, side (unilateral/bilateral), type of ankylosis (Sawhney's classification), and operating time were kept as covariates. Categorical variables were analyzed using Fisher's exact test. Multilevel survival analysis was performed considering the subject as cluster to perform Kaplan-Meier analysis and compute the hazards ratio using the Cox-regression method with adjustment for covariates. P <0.05 was set as statistically significant. The study sample composed of 43 (69 sides) TMJA cases who underwent surgery developed iatrogenic FN injury in 10 cases (14 sides [9 right; 5 left]). The incidence of FN injury was 20.3% (14/69). Sawhey's type III/type IV ankylosis and the operating time for more than 2 hours showed a statistically significant (p<0.05) increase in FN injury. The mean duration to detect FN recovery by EEMG was 9 days (95% confidence interval, 5 to 12 days), but the HBFNGS took 161 days (95% confidence interval, 141 to 181 days). The chance of early detection by EEMG was 18.6 times more than the chance by the HBFNGS (Cox-hazard ratio, 18.6). To conclude, EEMG is a noninvasive and reliable tool that detects FN recovery much earlier than the HBFNGS in the postoperative TMJA cases.