Comparison of the Effectiveness of Ultrasound-guided Versus Radioguided Medial Lumbar Bundle Branch Block

In adults with chronic low back pain, the investigators will compare the effectiveness of the medial bundle branch block on three lumbar levels (L3-L4, L4-L5 and L5-S1) performed either by radiographic guidance or by ultrasound approach according to a transverse approach.

The objective of this study will be to evaluate the benefit of these both procedures on pain, on the practice of daily activities and the incidence of adverse events in order to show whether the two modalities are equivalent.

"Lumbar facet syndrome" is a source of spinal distress affecting up to 45% of patients with chronic low back pain due to inflammation, degenerative or arthritic changes, overloading of the posterior or posterior lumbar facet joints.

First-line treatment for the relief of chronic low back pain of zygapophyseal joint origin includes bed rest, oral pain relievers / anti-inflammatory drugs, and physiotherapy. If unsuccessful, intra-articular injections and medial bundle branch block (BBM) provide diagnosis and are an alternative to neurotomy (radiofrequency or cryoneurolysis).

The BBM targets the medial branches of the posterior twigs, that is, it blocks the nociceptors and the muscles of the dermatome undertaken by targeting the medial branches of the dorsal vertebral branch supplying a facet above and below the vertebrae which ensure sensory innervation of the facet joint. The current standard technique is radiography requiring three punctures (transverse-axial plane) and the ultrasound technique is also described in this plan and also requires three puncture points. The investigatorswould like to compare this promising new technique to the standard radiographic technique since it would avoid irradiation and is easier to handle.

For this study, the investigatorswill compare the BBM on three lumbar levels (L3-L4, L4-L5 and L5-S1) performed under radiography versus ultrasound according to a transverse approach.

To compare the equivalence of this two modalities the investigators will evaluate :

* the benefit of the procedure on pain (via the visual analogue scale (VAS) collected before then at 1 week and at 1 month after the infiltrations)
* the evolution of the possibility of carrying out daily activities (via the Duke's activity status index (DASI) scale, collected at the same intervals as the VAS)
* the limits of daily activities (via the Oswestry Disability Index (ODI), collected at the same time intervals)
* the incidence of adverse events

A screening for anxiety and depressive disorders will be also performed before infiltration by the Hospital Anxiety and depression scale (HADS) comprising 14 items.

Eligibility Criteria:
Inclusion Criteria:

* Chronic Low-back pain for at least 3 months, without response to a conservative treatment of minimum 4 weeks
* No signs of dissociated pain, radiculitis, neurological diseases (including stroke, 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