The surgical anatomy of lumbar medial branch neurotomy (facet denervation)

Objective. To demonstrate the validity of placing electrodes parallel to the target nerve in lumbar radiofrequency neurotomy. Design. Previous data on the anatomy of the lumbar dorsal rami were reviewed and a demonstration cadaver was prepared. Under direct vision, electrodes were placed on, and parallel to, the L4 medial branch and the L5 dorsal ramus. Photographs were taken to record the placement, and radiographs were taken to illustrate the orientation and location of the electrode in relation to bony landmarks. Results. In order to lie in contact with, and parallel to, the target nerve, electrodes need to be inserted obliquely from below, so that their active tip crosses the neck of the superior articular process. At typical lumbar levels, the tip should lie opposite the middle two quarters of the superior articular process. At the L5 level, it should lie opposite the middle and posterior thirds of the S1 superior articular process. Conclusion. If electrodes are placed parallel to the target nerve, the lesions made can be expected to encompass the target nerves. If electrodes are placed perpendicular to the nerve, the nerve may escape coagulation, or be only partially coagulated. Placing the electrode parallel to the nerve has a demonstrated anatomical basis, and has been vindicated clinically. Other techniques lack such a basis, and have not been vindicated clinically. Suboptimal techniques may underlie suboptimal outcomes from lumbar medial branch neurotomy.