Cauda equina syndrome after unilateral medial branch blocks of the lower lumbar zygapophyseal joints.

Medial branch blockade of the lumbar facet joints is widely performed and generally accepted as a safe intervention. We present a case of neurological damage following a medial branch blockade with local anesthetic and steroid. A patient suffering from chronic low back pain radiating to the buttocks and thighs underwent nine medial branch blockades over a few years. Three months after successful back surgery to remove a herniated L 2-3 disk, the pain recurred, and left L 3-4 , L 4-5, and L 5 -S 1  medial branch blocks were performed under fluoroscopy. Immediately following the procedure, the patient developed paraparesis in both legs, loss of pinprick but preserved fine touch sensation, proprioception, and sphincter sensory and motor function. MRI showed ischemic lesions of the cauda equina. Direct needle trauma was discounted as a cause, due to the bilateral neurological deficit, plus the lack of pain during the procedure. Particulate steroid preparations can form aggregates, which may embolize and block small terminal arteries, causing neurological damage. Although the patient received nine sets of injections uneventfully during the previous 36 months, this procedure took place 3 months following spinal surgery. This rare, but catastrophic case of cauda equina syndrome occurred following L 3-4 , L 4-5 , and L 5 -S 1  medial branch blockades 3 months after spinal surgery, which is believed to be caused by accidental intra-arterial injection of particulate methylprednisolone, with consequent aggregates causing blockage and ensuing ischemia. Therefore we suggest particulate steroid preparations should not be used in axial spinal injection.