31: Interspinous Process Motion-Sparing Implant

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Procedure 31 Interspinous Process Motion-Sparing Implant

Christopher F. Wolf, Mark M. Mikhael, Arya Nick Shamie

Indications

image Lumbar stenosis at one or two levels

• Central stenosis
• Lateral recess stenosis
• Foraminal stenosis
• Facet hypertrophy and cyst formation

image Patient must report a resolution of symptoms when seated or flexed forward (i.e., “shopping cart” sign) when upright.

Indications Pitfalls

• Symptoms unresolved with lumbar flexion

• Axial back pain as the main complaint (versus buttock and/or leg pain)

• Osteoporosis with recent history of fragility fracture (severe osteoporosis)

• Spondylolisthesis greater than 25% on static or dynamic radiographs

• Significant scoliosis (greater than 25 degrees at the level of stenosis)

• Ankylosis of the involved segment

Indications Controversies

• “Mild to moderate” stenosis indication for ISP implantation refers to patients’ symptoms (able to walk at least 50 feet), not the MRI findings.

• Although studies show that claudication in patients with severe stenosis (on magnetic resonance imaging [MRI]) can be helped with ISP implants, some surgeons reserve this device for mild to moderate stenosis (on MRI) patients only.

• Three-level implantation of the device is not currently approved. Some surgeons have had success with treatment of three-level stenosis with ISP implantation.

Figures 31-3, 31-5, 31-6, and 31-8 © 2011 Medtronic Spine, LLC. Used with permission.

Examination/Imaging

image Standing anteroposterior (AP), lateral (neutral, extension [left] and flexion [right]) views (Figure 31-1)

• If patient has grade 2 spondylolisthesis on static or dynamic films, that condition is considered a contraindication to the interspinous process (ISP) procedure.

image MRI with axial, sagittal, and coronal imaging to assess disk herniation, canal stenosis, and Modic changes (Figure 31-2)

image

FIGURE 31-1

image

FIGURE 31-2

Treatment Options

• Nonsurgical management, that is, physical therapy, epidural steroid injections, and so forth

• Laminectomy without fusion or with fusion in setting of spondylolisthesis

• Anterior versus lateral interbody fusion alone with indirect decompression

• Disk arthroplasty

Surgical Anatomy

image Midline skin incision with bilateral fascial incision exposing the inferior and superior aspects of the spinous processes at the selected interspinous segment (Figure 31-3)

image Careful preservation of the supraspinous ligament

image Avoiding disruption of the facet joint anatomy

image

FIGURE 31-3

Positioning

image Lateral positioning on radiolucent table (Figure 31-4)

image Prone positioning on a Jackson table with a Wilson frame for maximal flexion at the index level

image

FIGURE 31-4

Positioning Pearls

• Radiolucent table

• Ensure patient positioning with hips and knees flexed to accentuate lumbar flexion; this position will splay the spinous processes, aiding in ease of insertion of the ISP device.

Positioning Pitfalls

• Inadequate imaging: Use AP and lateral fluoroscopy to confirm, before incision, that desired views can be obtained.

Positioning Equipment

• Bean bag with adequate padding for all bony prominences

• Secure patient with straps, especially for procedures done under conscious sedation/local anesthetic.

Positioning Controversies

• Appropriate lumbar flexion for lateral positioning

• Maximum flexion obtained with lateral decubitus versus prone positioning

Portals/Exposures

image Make a midline incision.

image Perform blunt subperiosteal dissection with Cobb elevator, avoiding excessive muscle injury.

image Avoid injury to the supraspinous ligament as well as the facet anatomy.

image Remove excessive spinous process osteophytes with rongeur.

Portals/Exposures Pearls

• If operating at the L4-5 level, avoid an incision directly over the prominent L4 spinous process, and deviate slightly more caudad to center on the interspinous space.

• Hypertrophic facet capsules need to be trimmed to position the implant as anterior as possible.

Portals/Exposures Pitfalls

• Ensure the patient is adequately secured to the bed with straps.

• If the facet capsule is hypertrophic, the implant will be placed too posteriorly, compromising its efficacy and increasing the risk of implant dislodgement.

Portals/Exposures Equipment

• Cobb elevator

• Large right-angled Gelpi retractor

Procedure

Step 1: Positioning

image The lateral position can be used in combination with conscious sedation and local anesthetic (see Figure 31-4).

image General anesthesia and prone positioning is also appropriate if a Wilson frame is used.

Step 1 Pearls

• In patients with high anesthetic risk, the lateral position can be used in combination with conscious sedation and ample local anesthetic, avoiding general anesthesia.

Step 2: Incision

image Make a midline skin incision with bilateral fascial incision exposing the inferior and superior aspects of the spinous processes at the selected interspinous segment (Figure 31-5).

image

FIGURE 31-5

Step 2 Pearls

• If operating at the L4-5 level, avoid an incision directly over the prominent L4 spinous process, and deviate slightly more caudad to center on the interspinous space.

Step 2 Pitfalls

• An incision too cephalad, making implant insertion more difficult

Step 3: Preparing Interspace

image Develop the interspinous space with the small and large dilators, and confirm the position on a radiograph (Figure 31-6).

image Gradually increase the space by dilation using the sizer until it is noted, clinically, that the interspinous ligament is taut (sometimes a “vacuum disk” is noted radiographically at the posterior aspect of the disk space, confirming a disk space distraction) (Figure 31-7).

image

FIGURE 31-6

image

FIGURE 31-7

Step 3 Pearls

• All implants have specific dilators for their respective system. It is important to become familiar with them before the procedure.

Step 3 Pitfalls

• Ensure, radiographically, the correct level, as well as that the dilators and sizers for the interspace are positioned sufficiently anteriorly, just posterior to the spinolaminar junction.

• Avoid overdilating, because this may lead to fracture of the spinous processes or rupture of the interspinous/supraspinous ligaments.

Step 4: Implantation

image Select the appropriate implant size based on the sizing trials.

image Each implant has unique fixation methods that should be clearly understood by the surgeon before the procedure (Figure 31-8).

image

FIGURE 31-8

Step 4 Pearls

• When sizing, the interspace tension in the supraspinous ligament should be developed until the sizing device has two-finger resistance; oversizing the implant should be avoided.

Step 4 Pitfalls

• Do not overstuff the interspace with too large an implant, because this may stress the spinous processes and result in a delayed fracture caused by superphysiologic forces on the spinous processes.

Postoperative Care and Expected Outcomes

image The patient can mobilize postoperatively with adequate analgesia.

image A 2-week follow-up should be done for wound evaluation as well as standing AP and lateral radiographs to ensure maintained implant positioning.

Postoperative Pearls

• Most patients state that their preoperative claudication pain is relieved immediately after surgery.

• Inadequate preoperative symptom relief should be evaluated with further imaging and may potentially require additional therapy, including physical therapy and at-time epidural steroid injections.

• If patient continues complaining of axial low back pain, they should be reminded that the surgery was to address their buttock and leg pain; once the leg and buttock pain is relieved, the patient may start complaining of the remaining low back pain.

Postoperative Pitfalls

• Although rare, any neurologic change occurring abruptly postoperatively should signal immediate evaluation by the surgeon, because dislodgement, fracture, disk herniation, and infection are a concern.

Evidence

Christie S, Song J, Fessler R. Dynamic interspinous process technology. Spine. 2005;30(Suppl 16):S73-S78.

This article is an overview of interspinous technology.

Kabir SM, Gupta SR, Casey AT. Lumbar interspinous spacers: a systematic review of clinical and biomechanical evidence. Spine. 2010;35:E1499-E1506.

This is a review of the biomechanical and clinical evidence related to interspinous spacer technology.

Kim D, Albert T. Interspinous process spacers. J Am Acad Orthop Surg. 2007;15:200-207.

This article is an overview of interspinous technology.

Siddiqui M, Nicol M, Karadimas E, et al. The positional magnetic resonance imaging changes in the lumbar spine following insertion of a novel interspinous process distraction device. Spine. 2005;30:2677-2682.

This article reports the MRI changes before and after interspinous process implantation.

Weiner BK. Interspinous process decompression system device affords superior outcomes and equal safety to non-operative therapy. Spine. 2005;30:2846-2847.

The article highlights the clinical advantages of the interspinous spacer over nonoperative therapy.

Zucherman JF, Hsu KY, Hartjen CA, et al. A multicenter, prospective, randomized trial evaluating the X STOP interspinous process decompression system for the treatment of neurogenic intermittent claudication: two-year follow up results. Spine. 2005;30:1351-1358.

This a Level I research paper evaluating the 2-year results of interspinous process spacer implantation for neurogenic intermittent claudication.

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