Spinal Cord Stimulators: Typical Positioning and Postsurgical Complications Elcin Zan, M.D. Kubra N. Kurt, M.S. Paul J. Christo, M.D. David M. Yousem, M.D., M.B.A. The Johns Hopkins Medical Institution, Baltimore, MD

DISCLOSURE OF INTEREST In accord with policies of The Johns Hopkins University, none of the authors has any financial interest in any manufacturer of these devices

Background Spinal cord stimulators (SCS) offer pain reduction/control for selected patients who have failed previous methods for treating their discomfort

Purpose The expected positioning (based on pain location) and types of electrodes, placement pc vs surgical paddle and potential complications

Methodology IRB approval A 5 year retrospective search for RIS "epidural stimulator", "epidural electrode", "epidural wire” spinal procedures (CT, myelogram, and plain radiographs) 24 patients /36 SCS

Results 16 F/8 M implantation via PC or laminectomy 25% (9/36) trial/temporary 69% (25/36) permanent 6% (2/36) no clinical data (temporarily vs permanently)

Types of electrodes 4 contact paddle (10/36; 27.8%) 6 contact paddle (4/36; 11.1%) 8 contact paddle (12/36; 33.3%) 16 contact paddle (10/36; 27.8%) Configuration single, dual (4x2, 8x2) or triple (5-6-5) parallel columns of contacts

The distance between the electrodes and the posterior bony central canal ; 1.3 mm-10.4 mm (mean 4 mm, SD 2.054) All but four electrodes (11.1%, 4/36 ); posterior 1/3 of the spinal canal within the posterior epidural space

SCS electrode implantation level (C3-L2) Number of SCSs implanted at that level Lead entry level (T1-L3) Number of leads inserted at that level Cervical6% (2/36)Cervical3% (1/36) Thoracic T8-T11 78% (28/36) 56% (20/36) Thoracic T9-L1 83%(30/36) 64% (23/36) Thoracolumbar/ Lumbar 16% (6/36)Lumbar14%(5/36)

Pain due to injury/ complex regional pain syndrome (sports injury, fell in bath tub, crush, motor vehicle accident, heavy lifting) 6 Postlaminectomy syndrome5 Failed back surgery syndrome4 Chronic intractable pain as a consequence of degenerative disc disease 4 Post stroke pain2 Neuromuscular scoliosis1 Degenerative scoliosis1 Bilateral thoracic outlet syndrome1

Outcomes & complications Pain relief from EMR: 71% (17/24) partial pain relief (15 permanent and 2 trials ) 17% (4/24) complete pain relief (3 permanent and 1 trial ) 4.2% (1/24) no benefit *2 patients; no clinical data

Displaced electrode significantly off midline Atypical positioning of the electrode; out of posterior 1/3 of the spinal canal Electrode fracture/ retained material Lead migration TC based on 36 images 39% 8.3% (3/36)11.1% (4/36)5.5% (2/36) 13.8% (5/36) IPG displacementIPG failureIPG revision Battery failure TC based on 24 EMR 50% 4.1% (1/24)8.3% (2/24)25% (6/24) 12.5% (3/24) Inflammation/ cellulitis at the implantation site Arachnoditis/ arachnoid adhesion Fever of unknown origin IC based on 24 EMR 29% 12.5% (3/24)8.3% (2/24) CSF leakage and failure of healing Irritation/discomfor t at the implantation site Local epidural hematoma Long term incisional pain Other 25%8.3% (2/24) 4.1% (1/24)

Conclusion The typical location of the electrode and the possible complications of SCS therapy should be familiar to radiologists who work in practice settings where this option is afforded to patients