The normal posture and shape of the spine are concepts that are difficult to define. It involves the relationship between various body parts, especially of the head and torso, compared with the median line of the body. When viewed from the side, in a normal upright position, the median line should run from the earlobe through the greater trochanter of the femur, past the front of the flexion/extensions of the stretched knee joint to finish just in front of the lateral malleolus. In this ideal situation, the body uses the least energy to maintain this posture, because very few muscle need to be tensed.
However, the variation in build and posture of the spine is so large that only profound shape abnormalities can be called pathological. The tilting of the pelvis, which has a direct relation to the size of the lumbar lordosis, plays an important role in achieving a ‘good posture.’
With abnormal back shapes, one has to make a distinction between supple shape deviations, which can be improved by exercise and posture therapy and disappear when lying down; and structural shape defects with a rigid component, which cannot be corrected by exercise and posture therapy and do not, or not completely, disappear when lying down.
Strictly speaking, posture is also important in sitting, lying and walking position, but normally in the physical-diagnostic examination, the posture is only related to the standing, upright position.