In our study, we hypothesized that sternum-mental angle (SMA) was a totally new preoperative predictor of difficult laryngeal exposure (DLE). The main objective of this study was to evaluate the diagnostic utility of SMA in predicting DLE in patients undergoing suspension microlaryngeal surgery, and we also searched for risk factors among the selected parameters.

A total of 95 patients with vocal cord dysfunction who underwent microlaryngeal surgery were collected. According to the Cormack–Lehane classification method, the patients were divided into non-DLE group (n=73) and DLE group (n=22). Preoperative assessments included age, sex, body mass index (BMI), Modified Mallampati's index (MMI), neck circumference (NC), thyroid-mental distance at neutral position (TMD-NP), TMD at full extension position (TMD-FE), sternum-mental distance at neutral position (SMD-NP), SMD at full extension position (SMD-FE), SMA at neutral position (SMA-NP) and SMA at full extension position (SMA-FE). SMA was defined as the angle between the horizontal line and the line from upper border of the manubrium sterni to mental prominence, and SMA's ability to predict difficult laryngoscopy was compared with that of established predictors.

The DLE incidence of the enrolled patients was 23%. Univariate analysis showed that patients in DLE group presented significantly smaller SMA values. SMA-NP less than 13 provided 68.2% sensitivity and 83.6% specificity and SMA-FE less than 22.5 provided 86.4% sensitivity and 80.8% specificity for the detection of DLE. SMA-FE (≤22.5) exhibited the largest area under the curve (AUC: 0.868; 95% CI: 0.784–0.952), confirming its better predictive ability. Binary multivariate logistic regression analyses identified four risk factors including MMI, TMD-FE, TMD-NP which were independently associated with DLE.

SMA is a new and simple predictor with a higher level of efficacy, and could help otorhinolaryngologist plan for managements in patients with DLE.