The current standard technique is radiography requiring three uni- or bilateral punctures (transverse-axial plane). The ultrasound technique is also described mainly in this plan but a new "caudal-cranial" ultrasound-guided technique was described by Chang et al in 2018 in which the major axis is used to conduct the needle to the desired area. The investigators would like to confirm that this new technique in a single puncture is also possible under ultrasound.

The convex probe is first positioned in the median longitudinal plane opposite the spinous processes of the lower lumbar vertebrae L4 and L5 with the coordinate system on the cranial side and the side opposite the mark on the sacrum side. The latter is visualized as a hyperechogenic continuous line. The probe is then moved away from the midline, the probe is slightly inclined in an oblique paramedian position looking towards the midline, and gradually slid towards laterality in order to reveal successively, the plane of the laminar interlines of the L3, L4 and L5 vertebrae, then the plane of the facelet spacing of these same vertebrae at the junction of the upper and lower articular processes, finally the plane of their transverse processes

Inclusion Criteria:

• chronic low back pain compatible with facet lumbar syndrome with chronic pain of at least 3 months
• who have not responded to conservative treatment after at least 4 weeks
• patients without signs of dissociated pain, radiculitis, neurological diseases including stroke and Parkinson's disease, spinal instability or deformities such as scoliosis, ankylosing spondylitis, history of lumbar surgery, fracture or lumbar tumor

Exclusion Criteria:

• Pregnant or breastfeeding women
• Allergy to injected products (Depomedrol or Linisol)
• Psychiatric disorders hindering understanding of the protocol
• Local or systemic infection
• Coagulation disorder
• Obese with a BMI> 35 kg / m²