Objective: To determine the referral patterns of the lumbar medial branches and the fifth lumbar dorsal ramus.

Hypothesis: The lumbar medial branch referral patterns created by minimum threshold electrical stimulation may differ from those obtained after zygapophysial joint (Z-joint) injections.

Summary of background data: Lumbar Z-joint referral patterns have been identified following provocative Z-joint injections. There are no reports of lumbar medial branch referral patterns.

Methods: The right L1 through L4 medial branch of the posterior primary ramus and the right L5 dorsal ramus in each of eight healthy volunteer males (n=40), without a history of back pain, were electrically stimulated under fluoroscopic imaging. All subjects were blinded to the level of stimulation, and each individual mapped out the referral area on a human line drawing at the time of each stimulus. The referral patterns after electrical stimulation and the stimulation thresholds were recorded. These referral patterns were compared to referral patterns recorded during provocative Z-joint injections by other authors.

Conclusion: All of the subjects’ mapped referral sites coincided with each other, creating a well defined composite drawing. These referral zones are different than those reported after injection of the lumbar Z-joint, which may have clinical and therapeutic implications. These referral maps may provide the clinician with additional insight when evaluating a patient with lumbar, flank, or gluteal pain of undetermined etiology.

Key words: Zygapophysial joint, facet joint, medial branch, lumbago, referral pattern