Are Paraspinous Intramuscular Injections of Botulinum Toxin A (BoNT-A) Efficient in the Treatment of Chronic Low-back Pain (LBP)?

Inclusion Criteria: * LBP defined as a pain located between the thoracic lumbar hinge and the gluteal sulcus, where pain had evolved over a period of 6 months despite well conducted medical treatment, self-assessed lumbar pain intensity over 50 millimeters long on a visual analogue scale of 100 millimeters (0=no pain; 100=maximal pain), * having been on sick leave for 60 or more days in the year preceding the inclusion (in order to include patients with high consequences of chronic low-back pain on their work), * same long-term chronic pain treatment for at least 6 weeks Exclusion Criteria: * age under 18 or over 55 years (to avoid secondary causes of low back pain, like spinal tumor), * ongoing pregnancy or breast-feeding, * a neuromuscular pathology (myasthenia gravis, amyotrophic lateral sclerosis, myopathy, polymyositis), aminoglycoside treatment at the time of inclusion, * skin infection at injection points, * diabetes and alcoholism (in order to avoid other etiologies of chronic pain), * a history of injecting BoNT-A A, * anticoagulation treatment, sciatica, * suspected spinal inflammatory disorder (spondylitis, inflammatory rheumatism, tumoral pathology), * a failed back surgery syndrome (when surgery failed to relieve low-back pain), - incapacity to stand, cardiorespiratory deficiency which does not allow the isokinetic exploration of the spinal muscles, * cognitive disorders limiting patient participation, * conflicts of interest owing to existing pain (unconsolidated work accident, ongoing damage compensation). * Spine infection, tumour or trauma had been specifically excluded by an MRI done by all patients before the inclusion in the present study. * No patient was allowed to take opiates during the time of the study, * facet joint injections were also not permitted during the study period.