Table 1 : Guidelines for measuring external neck landmarks*.

Landmark
Thyromental distance (TMD)	Lower midline border of mandible in jaw occlusion and neck extended to thyroid notch
Hyoid to cricoid cartilage distance (HCD)	Hyoid bone to upper border of cricoid cartilage
Sternomental distance (SMD)	Mentum as per TMD to sternal notch
Thyroid cricoid distance (TCD)	Thyroid notch to lower border of cricoid cartilage
Thyroid width (TW)	Lateral borders of upper thyroid cartilage
Thyroid height (TH)	Thyroid notch to lower border of thyroid cartilage
Hyoid mental distance (HMD)	Mentum as per TMD extended to hyoid bone
Occiptial process to C7 distance (OCD)	Lowest point of occipital process to upper border of C7

*All measurements, with the exception of OCD, are taken with the head and neck in an
extended position. The OCD is taken with the neck in neutral position.