Dorsal Median Band aka plica mediana dorsalis – Cause of the elusive midline placement

plicaOne 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.

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I encountered this several times in my own practice and often made modifications to paddles as illustrated here.

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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.

Omega Plate – ideal bone anchor

I use a cranial fixation dogbone bent like an Omega sign as an screw-on anchor for rigid fixation.  While midline spinous process straddling is my preferred paddle anchor there are cases when that is not possible.  For example, most cervical cases, especially retrograde do not have an adequate bony keel to anchor to.  Likewise if I use a unilateral laminotomy to place a paddle I have not exposed enough bone.  In these cases I anchor the Omega directly to the bone with 4mm screws.

Omega plate

See the Omega anchor technique illustrated here.

Lateralized Central Point of Stimulation

SpectraCP

The ability to lateralize the central point of stimulation is made possible through Anode Intensification.  This can direct current off midline which is useful for cases where patient demonstrate a non-anatomic midline.  It is also useful in patients with severe scoliosis.

Open trial for bypassing scar tissue

open trialPatients with previous laminectomies are very difficult to trial due to the extensive epidural scarring. While it is possible to go ventral to the cord and come back dorsal above the scar, this is seldom well tolerated by patients. I prefer to use an open trial technique where I perform a laminectomy immediately above the scar and bring the leads in from a tuoy needle below. That way I can close the wound and then pull the leads at a later date as a typical trial. If the patients goes perm I can insert the paddle at the new laminectomy site with little difficulty if done within a couple of weeks.

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SuturingSuture Training Videos

There are some great surgery training videos on YouTube.  I highly recommend these which illustrate basic suture technique, instrument tie, one-handed tie and two-handed tie.  Personally, the instrument tie is the easiest followed by one-handed tie.  A lot of surgery training programs say to learn the two-handed tie, but I think it is a waste of time since it is hardly ever used and IMO is harder than the one-handed tie.