Randomized study assessing the accuracy of cervical facet joint nerve (medial branch) blocks using different injectate volumes.

Background: Neck pain is a frequent cause of disability, with facet joint arthropathy accounting for a large percentage of cases. The diagnosis of cervical facet joint pain is usually made with diagnostic blocks of the nerves that innervate them. Yet, medial branch blocks are associated with a high false-positive rate. One hypothesized cause of inaccurate diagnostic blocks is inadvertent extravasation of injectate into adjacent pain-generating structures. The objective of this study was to evaluate the accuracy of medial branch blocks by using different injectate volumes.

Methods: Twenty-four patients received cervical medial branch blocks, using either 0.5 or 0.25 ml of bupivacaine mixed with contrast. One half of the patients in each group were suballocated to receive the blocks in the prone position and the other half through a lateral approach. Participants then underwent computed tomography of the cervical spine to evaluate accuracy and patterns of aberrant contrast spread.

Results: Sixteen instances of aberrant spread were observed in nine patients receiving blocks using 0.5 ml versus seven occurrences in six patients in the 0.25 ml group (P = 0.07). Aberrant spread was most commonly observed (57%) when an injection at C3 engulfed the third occipital nerve. Among the 86 nerve blocks, foraminal spread occurred in five instances using 0.5 ml and in two cases with 0.25 ml. The six "missed" nerves were equally divided between treatment groups. No significant difference in any outcome measure was observed between the prone and lateral positions.

Conclusions: Reducing the volume during cervical medial branch blocks may improve precision and accuracy.