Degenerative Lumbar Spinal Stenosis (LSS) is an extremely common condition affecting more than 102 million people each year. It is a narrowing of the spinal canal in the lower back. It causes pain and even disorders of the lower limbs. When the symptoms get worse and the individual feels functional discomfort despite medical treatment, surgical intervention is recommended. Two surgical options are available: Rigid Stabilization Devices as conventional fusion with or without cage, or dynamic stabilization system as B-DYN device, this system is called "dynamic" because it allows the stabilization of the operated part while preserving a certain mobility.

The main objective of this study is to evaluate the efficacy and tolerance of B-Dyn versus conventional bolted fusion (with or without cage) in the treatment of degenerative lumbar stenosis (DLS) on the degree of postoperative functional incapacity. So the investigator's hypothesis is that the use of the B-DYN device in the treatment of DLS could lead to the maintenance of functional disability related to low back pain (maintenance of walking and mobility).

Another important point to be demonstrated in this study is the preservation of the mobility of the stage overlying the assembly performed by B-Dyn. Indeed, the continued degeneration of segments adjacent to lumbar vertebral fusions is a concern for surgeons For B-Dyn, which is a dynamic stabilization, the combination of rigid and flexible parts allows the mobility of the overlying stage to be preserved and could also lead to a decrease in adjacent syndrome in the long-term compared to the use of conventional fusion.

The duration of patient follow-up is 60 months. The inclusion period is 56 months to recruit the necessary number of subjects for the study (a total of 216 patients is expected).

The Lumbar Spinal Stenosis: LSS is an extremely common pathology that affects more than 102 million people worldwide every year.

It is most often linked to the combination of a disk space narrowing (loss of height and bulging within the canal), a hypertrophy of the yellow ligament and of the joint capsules and also a bone overgrowth by the posterior vertebral joints. This may be associated with Grade I spondylolisthesis.

This pathology often extends over several levels, frequently two (L5S1, L4L5 or L4L5, L3L4) sometimes more. A relatively homogeneous group of patients falls within the group of stenosis, from S1 to L2, without significant deviation (scoliosis or cyphosis type).

A wide variety of different surgical techniques are used to treat patients with LSS and patients who have symptoms despite well-conducted medical treatment. Decompressive laminectomy may prove to be insufficient when several levels are affected and also due to the fears of instability induced by the gesture itself (the joint hypertrophy responsible for nerve root compression is also a stabilizing element). Therefore, the scientific community usually associates a gesture of stabilization with the gesture of decompression.

The choice of stabilizing means is discussed without any conclusive answer provided by any controlled study. This question accounts for the subject of this study.

Two alternatives are discussed:

• The current gold standard is to practice rigid stabilization through bolted fusion, with or without inter somatic cage, despite the fact that it causes an excessive rigidification of the mobile segment, therefore responsible for the acceleration of the degeneration of the upper level.
• Soft stabilization system with pedicular screwing B-Dyn type. It stabilizes the arthrodesis while maintaining some mobility. This partial preservation of mobility could slow down or prevent the upper level's degradation.

Based on the judgment from the dynamic profile images, the devices, some of which are approved in the USA claim to favor fusion while providing no information on the mobility of the upper level in their studies.

The aim of this randomized and prospective comparative study would not only be to establish the non-inferiority of the procedure under study, versus conventional fusion (with or without cage) on the degree of functional disability after surgery, but also to demonstrate the significantly higher preservation of the upper level's mobility when assembling.

First inclusion : May 2020

Inclusion period : 56 months

Follow up of the last patient: December 2029

Analysis and results: June 2030

Inclusion Criteria:

Disease related criteria:

1. Stenosis on 1, 2 or 3 disc levels (grade B or C or D according to Schizas classification or central stenosis of grade A according to Schizas classification with a lateral stenosis (postero-lateral overhang or disc protrusion)) on MRI (lumbar spine MRI )
2. Spondylolisthesis grade 1 or no the upper surgical (treated) level
3. Neurological impairment or neurogenic claudication on one or both legs (VAS score > 30)
4. Subjects who have failed well-managed medical treatment that has not resulted in long-lasting symptom relief (duration of symptoms > 3 months);
5. Subjects with no contraindication to fusion or the application of B-Dyn®.

Population-related criteria

1. Subjects of both sexes, 40 years of age and older
2. Subjects who have given free, informed and written consent to participate in the study;
3. Subjects who are able to respond to questionnaires and who can communicate in the language of the study country ;
4. Subjects affiliated to a social security scheme or entitled to a social security scheme.

Exclusion Criteria:

Disease related criteria:

1. Spondylolisthesis of grade > 1 on the upper surgical (treated) level
2. Intervention required on more than 3 disc levels
3. Degenerative Scoliosis (Cobb angle > 20°);
4. Stenosis located only on the L5-S1 level
5. History of instrumented lumbar surgery (cage, rod, etc.) on the upper or lower level, except in the case of instrumentation of the lower level with an intra-spinous device.
6. Stenosis not caused by from degenerative changes.
7. Isolated disc herniation
8. Other specific vertebral damage (for example: ankylosing spondylitis, cancer or neurological disorders)
9. History of vertebral compression fractures at the instrumented level
10. History of osteoporotic fractures
11. Psychological disorders (e.g. dementia ….etc) or drug addiction that lead to an inability to participate in the study
12. Chronic infection

Population related criteria:

1. Withdrawal of consent;
2. Pregnant or Breastfeeding woman
3. Participation in a clinical trial in the 3 months prior to the initial visit;
4. Predicted unavailability during study. Patient deprived of liberty or under guardianship.

Medical Device related criteria:

1. Allergy to any of the components of the medical device.

The patient will be blinded from the randomizing arm. As the procedure is performed under general anaesthesia, the patient will not be informed whether or not the B-Dyn® device has been implanted as a result of the procedure. The primary endpoint (the ODI being a reported outcome patient) will therefore be assessed blind to the randomizing arm. Other secondary endpoints such as quality of life or pain intensity will also be assessed blindly from the randomizing arm (patient assessment). Blinding of the surgeon is not possible. The device cannot be blinded from the surgeon's view.