Study Design:​ In vivo intradiscal pressure measurement in different postures in healthy individuals and in those with ongoing back problems.

Objectives:​ With the most recent technique, 1) to analyze the influence of degeneration on the intradiscal pressure, 2) to calculate the spinal load on the L4–L5 intervertebral discs, and 3) to assess the relation between the spinal load and movement of the intervertebral motion segment.

Summary of Background Data:​ Almost all the data on intradiscal pressure are from the studies by Nachemson. The results from these pioneering studies have formed the basis for current knowledge about the in vivo loading conditions of the human spine. Although performed already during the 1960s and 1970s with the technique available at that time, virtually no other similar studies have been performed to corroborate the findings.

Methods:​ The intradiscal pressure (vertical and horizontal) was measured using an advanced pressure sensor in 8 healthy volunteers and 28 patients with ongoing low back pain, sciatica, or both at L4–L5. Among other calculations, the actual loading conditions in various body positions were calculated in relation to the angle between the two vertebrae of the studied motion segments.

Results:​ The effect of respiration on intradiscal pressure was shown as a continuously periodic fluctuation in the healthy prone individual. The intradiscal pressure was significantly reduced according to the degree of disc degeneration as estimated by magnetic resonance imaging. There possibly was a difference between the vertical and horizontal pressures in the degenerated and nondegenerated discs because the nucleus pulposus was pressure-tropic property. The spinal load increased in the following order of body positions:​ prone, 144 N;​ lateral, 240 N;​ upright standing, 800 N;​ and upright sitting, 996N (P<​ 0.0001). In the standing and sitting body positions, the spinal load increased not only with forward bending, but also with backward bending. The spinal load was highly dependent on the angulation in the motion segment. The movements of the spine from a flexed to an extended position made the load of the spine change in a curvilinear fashion, fitting a squared equation in the standing body position. There was a correlation between the spinal load and the angle of the motion segment in the standing but not in the sitting body position.

Conclusions:​ The spinal load was highly dependent on the angle of the motion segment in normal discs in vivo.—The intradiscal pressure in degenerated discs was significantly reduced compared with that of normal discs. However, further studies on the effect of respiratory movement on intradiscal pressure, the difference between vertical and the horizontal pressures, and the difference in the spinal load between standing and the sitting body positions are necessary. The data obtained from the current study are fundamental to understanding the pathomechanisms and biomechanical problems of disc disease.