The seventh cervical vertebra is an appropriate landmark for thoracic kyphosis measures using distance from the wall.

Background: Hyperkyphosis is frequently found nowadays due to the change in current lifestyles and age-related system decline. A simple hyperkyphosis measurement can be made easily using the perpendicular distance from the landmark to the wall. However, the existing evidence applied two different landmarks [occiput and the seventh cervical vertebra (C7)] and the measurement using rulers was susceptible to error due to their misalignment.

Objective: To assess an appropriate landmark for thoracic kyphosis measurement using distance from the wall (KMD), by comparing between occiput and C7, as measured using rulers and verified using data from a specially developed machine, the so-called infrared-gun kyphosis wall distance tool (IG-KypDisT), and the Cobb angles.

Methods: Community-dwelling individuals with a risk of thoracic hyperkyphosis (age $\ge 10$ years, $n=43$) were cross-sectionally assessed for their thoracic hyperkyphosis using the perpendicular distance from the landmarks, occiput and C7, to the wall using rulers and IG-KypDisT. Then the Cobb angles of these participants were measured within seven days.

Results: The outcomes from both landmarks differed by approximately 0.8 cm ($p=$ 0.084). The outcomes derived from C7 were more reliable (ICCs>0.93, $p<$0.001), with greater concurrent validity with the radiologic data ($r=$ 0.738, $p<$0.001), with the overall variance predicted by the regression models for the Cobb angles being higher than that from the occiput (47-48% from C7 and 38-39% from occiput). The outcomes derived from rulers and IG-KypDisT showed no significant differences.

Conclusion: The present findings support the reliability and validity of KMD assessments at C7 using rulers as a simple standard measure of thoracic hyperkyphosis that can be used in various clinical, community, and research settings.