[Predicting the difficulty of laryngoscopy using the distance between the lower border of the mandible and the thyroid notch].

We examined the relationship between the degree of difficulty in visualization of the larynx and the distance from the lower border of the mandible to the thyroid notch (M-T distance). Patients were examined and the M-T distance was measured with their neck fully extended during preoperative period. Difficulty of laryngoscopy was graded as reported previously. Five hundred sixty one patients were assessed, and those with obvious neck and head pathology were excluded. There were 440 cases (78.4%) in grade 1, 116 cases (20.7%) in grade 2 and only 5 cases (0.9%) in grade 3. There were no grade 4 cases. The M-T distance was 5.4 +/- 0.6 cm in grade 1, 4.6 +/- 0.7 cm in grade 2 and 3.6 +/- 0.7 cm in grade 3. These were significantly different with each other (P < 0.05). If the M-T distance is 4.5 cm or less, the difficulty in visualization of laryngoscope increases. Therefore, in the case in which the M-T distance is 4.5 cm or less, we recommend further examination and preparation for difficult laryngoscopy.