This study will examine the accuracy of an ultrasound-guided L5 dorsal ramus block technique.

The lumbar facet joints have been implicated as a causal factor in 15 to 40% of patients suffering from chronic low back pain. Because physical examination and medical imaging have limited value in determining the source of pain, diagnostic blocks play an important role in the management of this common condition. Blocks of the L5 dorsal ramus (DR) are used to diagnosed pain originating from the L5-S1 facet joint, which is one of the most commonly implicated levels in patients with low back pain. Fluoroscopic guidance, which uses x-rays, is currently the standard imaging modality used to perform this block. Recently, ultrasound guidance has seen increasing use because of its greater accessibility and lack of ionizing radiation. Although USG has been shown to provide a high level of accuracy at other levels, the greater anatomical complexity found at the L5-S1 has hindered the development of a satisfactory L5 DR block technique. In this study the investigators will use fluoroscopic control to examine the accuracy of a novel ultrasound-guided approach to this block.

Inclusion Criteria:

-Any consenting patient over 18 years of age with axial low back pain who requires a diagnostic L5 dorsal ramus block.

Exclusion Criteria:

• Inability to consent
• Iodine or lidocaine allergy,
• Pregnancy,
• Coagulopathy (as defined by an INR over 1.4, platelets under 100,000, or a documented bleeding disorder)
• Inability to visualize lumbosacral anatomy during an ultrasound pre- scan

Patients suffering from chronic low back pain thought to involve the L5 dorsal ramus