Anatomy · functional reading
Intradiscal pressure
Intradiscal pressure is the pressure inside the nucleus of the intervertebral disc. It varies with body position, the loads carried and the movements performed.
Scientific basis
The first in vivo measurements were carried out by Alf Nachemson beginning in the 1960s. They showed higher pressure in sitting than in standing and long served as a reference in ergonomics.
The measurements by Wilke et al. (1999), taken in one volunteer with a sensor implanted in the L4-L5 disc, qualify this result. In particular, they report similar values in standing (about 0.5 MPa) and in relaxed sitting without a backrest (about 0.46 MPa), a slightly higher value in actively upright sitting (about 0.55 MPa), and a markedly lower value lying down.
The comparison between sitting and standing therefore depends heavily on how a person sits. In both cases, bending the trunk forward and carrying loads markedly increase the pressure.
Blue Portance / SBNFA™ reading
In the SBNFA™, intradiscal pressure is not read as an isolated value. Attention also goes to: how long the same pressure is maintained; its distribution within the disc; its variability over time.
The Nachemson–Wilke debate clearly illustrates the SBNFA™ reading: it is not sitting as such that determines disc stress, but the way the pelvis and spine organize themselves — and the possibility of varying that organization.
The hypothesis that a pelvis–femur relationship close to 90° is associated with reduced disc stress belongs to the SBNFA™ reading; it is consistent with some data on seat inclination but has not been measured directly.
Contribution to the analysis of sitting
A seat can be analyzed according to the pelvic orientation it promotes, the resulting lumbar curve, and the possibility of varying these parameters. An instantaneous pressure value is not enough to characterize a seat.
Not to be confused with
Intervertebral disc, the anatomical structure; contact pressure (interface pressure), measured between the body and the seat surface; spinal load, the overall force transmitted through the spine.
Related terms
Sources and scope
- Nachemson (1981): disc pressure measurements (Spine)
- Wilke et al. (1999): new in vivo measurements of intradiscal pressure in daily life (Spine)
Established measurement data, but obtained from very small samples (a single subject in Wilke et al.). The link between intradiscal pressure and pain is not direct.
