The purpose of this study is to analyse the changes in back muscle size and strength following use of Dysport®, and to establish whether there is any association between pain reduction and change in strength, in patients suffering from chronic low back pain.

Inclusion Criteria:

• Suffering from muscular low back pain (between L-1 and S-1 level).
• Symptoms of more than six months duration.
• No benefit from previous treatments.
• Patient must present with bilaterally more than 2 active trigger points (TrPs) in the region of the low back musculature.
• CT scan or MRI examination of the lumbar spine was performed within the past year.
• Absence of significant pathology, such as bone fracture, nerve damage or severe psychiatric condition.

Exclusion Criteria:

• Constant or persistent severe pain due to nerve root compression or fibromyalgia.
• The patient has received surgery on the spine.
• Other musculoskeletal disabilities e.g. myasthenia gravis, or disorders of the neuromuscular junction.
• Any serious pathology, such as cancer, systemic inflammatory disease, vertebral fractures, neurological signs, spinal infection.
• Epidural injection of local anaesthetics and steroids within 12 weeks proceeding inclusion.
• Trigger point injection of local anaesthetics and steroid within 8 weeks proceeding inclusion.
• Pain associated with urinary tract infections, or gynaecological disorders.
• Bleeding disturbances or currently using coumarin derivatives.