commonly prescribed as conservative treatment of low back pain. These devices could affect the distribution of loads among passive and active lumbar subsystems. However, with only one study in this field proposed by Nachemson et al (1983), their biomechanical action such as the reduction of the intradiscal pressure (IDP) remains unknown and controversial. The goal of this study was to investigate the IDP change induced by a rigid lumbar orthosis from a new non-invasive measurement method. Method.– From the comparison of two radiographs EOS (Biospace, Paris) with and without a lumbar orthosis, the displacements and rotations of each vertebra were calculated and implemented in a patient-specific finite element modelling. The IDP measurements along each lumbar disc were extracted with a precision of 2.5 Pa. Twenty patients were tested in standing or sitting posture with a semi-rigid lumbar orthosis Lordactiv (Ormihl-Danet, Villeurbanne) in two conditions: with or without a curved rigid lumbar part. Result.– A curved rigid lumbar part was necessary to obtain significant IDP distribution change along the anteroposterior direction. Interestingly, an IDP decrease appeared in somepatients until–50 Pa.However, the IDP change appeared very posture, disc level and patient-dependent ranging from –50 to +8 Pa. Discussion.– An IDP distribution change reveals a different load sharing between posterior elements and intervertebral discs whereas decompression only could be explained by a decrease muscle activity. Especially, the intradiscal elasticity (age-dependent) and the lumbar back adipose tissue thickness are the main variables correlated with the interindividual differences. Conclusion.– These results demonstrated that wearing a rigid lumbar orthosis can significantly influence the stress-strain values in diseased discs, provided that the patient is kept an sufficient elasticity.