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.

Lateral paddle migration – salvaged with percutaneous lead

This 59 year old woman with midthoracic dextroscoliosis underwent a paddle placement by outside physician at the target level after a successful trial.  Several weeks post-op the patient experienced loss of coverage on the left side (inside of curve).  This is a common complication in placement of the paddle.  Leads tend to migrate to the outside of the curve so implantation should be performed on the medial side.  Furthermore there is significant rotatory deformity as you can see from the spinous process position.

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While I love the Artisan paddle, this lateral migration is more common given its narrow width.

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As you can see, this paddle placement violates my preference for anchoring immediately below the paddle at the crotch of the tails.

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I was able to salvage this implant with a percutaneous lead placed on the inside of the curve in about 15 minutes (much easier than a paddle revision).

Retained percutaneous lead – fractured

Retained lead Lat1 Retained lead Lat2  Retained lead AP1

This case came from a very experienced trialing physician who could not remove the previously placed St. Jude trial lead.  He called me when the lead broke three inches from skin insertion after attempting to pull it out in the post-op clinic.  He tried numerous positions with the patient flexing and extending, but the lead would not withdraw.  I instructed him to pull the lead as much as he could then thorough prep the insertion point and cut the lead with sterile scissors.  Then the presumably sterile remainder would withdraw into the wound and the tract would close.  The patient was kept on antibiotics and taken to the operating room on week later for retrieval and permanent implantation.

Retained lead AP2

The lead was harvested from a skin incision over the remaining tail and withdrawn.  The lead was pinched in the lateral portion of the interlaminar space adjacent to the facet.  A Penta paddle was placed at the previous target level and patient tolerated the procedure well.

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