One of the most common questions I get in training physicians in SCS is how to deal with the difficult midline placement. We’ve all seen case where the lead or paddle flows nicely into the epidural space but then suddenly darts left or right.
The cause is an elusive band of tissue called the Dorsal Median Band aka plica mediana dorsalis between the dorsal dura and the underside of the lamina. This band of tissue has been implicated in the administration of epidural anesthesia whereby patients get unilateral coverage specifically. This has been described in early radiology literature. Y. Eugene Mironer, MD describes use of this band as a midline anchor for percutaneous electrodes.
Many times this band is removed when the laminectomy is performed. However, when the paddle is advanced beyond the laminectomy site, midline placement can be very difficult. The lateralization of the paddle can be further exacerbated by the triangulated shape of the thoracic lamina.
I encountered this several times in my own practice and often made modifications to paddles as illustrated here.
While this is a helpful modification, modern day paddles with their tight contact spacing prohibit this type of alteration.
The three primary vendors Boston Scientific, Medtronic and St. Jude Medical offer dissectors to help in paddle placement. The first two manufacture blunt peel-pack hockey stick style elevators, while St. Jude reps typically carry 1cm Aesculap malleable brain retractor blades. All three are effective at clearing the epidural space, however I recommend sharp dissection of this band to avoid cord compression.
When I encounter the Dorsal Median Band, my preferred technique is to perform a second laminectomy above the initial one. I then undercut the two sites and occassionally dissect with a Penfield #3 to dissect the epidural space. Inevitably this technique is much quicker than repeated attempts at blunt dissection and multiple passes which are a potential source of cord trauma.