The Need for Routine Assessment of Masseter Function After Masseteric Nerve Harvest With the Borschel Method, Elena Pescarini, MD1,2; Catriona Neville, BSc1; Tamsin Gwynn, BSc1; et al Karen Young, BSc1; Lekha Chandrasekharan, FRCR, DNB(Radiodiagnosis)3; Charles Nduka, MA(Oxon), MD, FRCSEng, FRCS(Plast)1; Ruben Yap Kannan, MB, MRCSEd, PhD, FRCS(Plast), Dip(Otol)HNS1 Author Affiliations Article Information 1Facial Palsy Unit, Queen Victoria Hospital, East Grinstead, United Kingdom 2Department of Plastic Surgery, University of Padova, Padova, Italy 3Department of Radiology, Queen Victoria Hospital, East Grinstead, United Kingdom JAMA Facial Plast Surg. Published online July 18, 2019. doi:10.1001/jamafacial.2019.0568 The masseteric nerve is increasingly used for nerve transfers to reanimate facial movements, and imaging studies have shown a postoperative reduction in masseteric muscle bulk, but this finding has not been correlated clinically.1 Testing this nerve transfer approach with reference to a specific technique (the Borschel method), we sought to determine whether routine postoperative assessment of the masseter muscle with magnetic resonance imaging (MRI) or electromyography (EMG) is necessary in all cases or if specific indications should prompt assessment. Methods In this retrospective case series, 18 patients underwent facial reanimation procedures using a masseteric nerve transfer from 2016 to 2018 in Queen Victoria Hospital. The Queen Victoria Hospital Quality and Governance Team approved this study. Written informed consent was obtained from all patients. Exclusion criteria included pre-existing trismus, masseteric atrophy/injury, and subzygomatic masseteric nerve harvest.2 Postoperative masseteric function was ascertained clinically and contrast-enhanced MRI scans were performed, with EMG used when MRI was not possible. Magnetic resonance imaging reference points were the mandibular notch for the deep masseter muscle and the anterosuperior nasal spine for its superficial aspect, with width reduction being quantitatively assessed using the Student t test. Statistical analysis comparing clinical and MRI/EMG assessments were performed from April 2019 to May 2019 using positive predictive value (PPV) tests and the Pearson χ2 test, with P < .05 values considered significant. The null hypothesis was that there was significant correlation between clinical findings and MRI/EMG findings. Results A total of 18 patients (10 males and 8 females) with a mean (SD) age of 40 (14) years (range, 14-61 years) were included in the study. The Borschel technique3 was used for nerve harvest, with a mean surgery-to-imaging interval of 12.5 months (range, 3-26 months) and no reports of postoperative adverse events (in spite of 2 previous temporalis transfers in 2 patients). Overall, reduced masseter muscle bulk was noted clinically in 2 patients (11%), whereas subclinical masseteric atrophy was noted on either MRI or EMG in 9 patients (50%). Atrophy was detected on MRI in only 7 (39%) patients. In these patients, the mean (SD) width of the harvested vs the unharvested sides of the superficial masseter was 13.8 (3.3) mm vs 18.3 (1.5) mm, with a statistically significant reduction in width (P = .03; 95% CI, 0.4-8.5). The mean (SD) width of the harvested vs unharvested sides of the deep masseter was 8.1 (2.8) mm vs 10.9 (3.9) mm, and there was no significant reduction in width (P = .22; 95% CI, −1.98 to 7.48) (Figure 1). Clinical reduction in masseter muscle bulk only correlated with EMG findings when EMG values were less than 50%. The null hypothesis was rejected with a χ2 value of 6.64 (P = .01), indicating an absence of correlation between postoperative clinical masseteric function and MRI/EMG results (Figure 2). The PPV for MRI in this cohort was 18.2% (95% CI, 12.08%-26.07%). Discussion Although first described in 1978,4 the use of the masseteric nerve as a donor in facial reanimation has only expanded in the last decade.5 Brenner et al6 found that the main stem of the masseteric nerve is at the level of the zygomatic arch in one-third of cases, with this incidence dropping to approximately 10% further distally. Based on this, techniques such as the Borschel3 and subzygomatic triangle2 have been described, with the Borschel technique being a relatively distal harvest. In the present study, 11% of patients had a reduction in muscle bulk that was found on clinical assessment, which was consistent with results of an anatomical study.5 Atrophy detected on MRI suggested that the superficial masseter was more likely than the deep masseter to be affected with the Borschel method of nerve harvest. Given the low risk of masseteric paralysis associated with the Borschel technique,3 our experience in the present study shows that there is no need for routine postoperative MRI/EMG tests after this procedure, unless clinical indications are present (eg, reduced masseter bulk) or as part of the preoperative assessment for subsequent temporalis transfers. Back to top Article Information Accepted for Publication: May 16, 2019. Corresponding Author: Elena Pescarini, MD, Department of Plastic Surgery, University of Padova, Via Giustiniani 2, Padova 35128, Italy (elena.pescarini@gmail.com). Published Online: July 18, 2019. doi:10.1001/jamafacial.2019.0568 Author Contributions: Dr Kannan had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. Study concept and design: Neville, Nduka, Kannan. Acquisition, analysis, or interpretation of data: Pescarini, Neville, Gwynn, Young, Chandrasekharan. Drafting of the manuscript: Kannan. Critical revision of the manuscript for important intellectual content: Pescarini, Neville, Gwynn, Young, Chandrasekharan, Nduka. Statistical analysis: Kannan. Administrative, technical, or material support: Neville, Gwynn, Young. Study supervision: Pescarini, Gwynn, Nduka, Kannan. Other—radiology details: Chandrasekharan. Conflict of Interest Disclosures: None reported. References References 1. 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