Chapter 33 Interspinous Spacers

More than 2 million physician-related visits yearly can be attributed to symptoms of lumbar spinal stenosis. Accordingly, spinal stenosis is perhaps the most common reason for low back surgery in patients older than 50 years [1–3]. As life expectancy increases and our population continues to age, the prevalence of symptomatic lumbar spinal stenosis is expected to climb [4].

Spinal stenosis can be classified as congenital or degenerative (acquired). The acquired form is more common and often results from natural spinal degeneration but can also occur because of scoliosis, segmental instability, or neoplastic processes. Common symptoms associated with degenerative lumbar spinal stenosis in patients older than 50 years include intermittent claudication with pain in the back and legs. Symptoms are typically aggravated with either standing or walking. Patients who suffer from classic lumbar stenosis often walk in a flexed manner. Anatomically, we know that this position results in an increased area of the spinal canal. These postural changes are a compensatory action trying to correct a decreased central canal and foraminal volume.

Until the last decade, patients who suffer from spinal stenosis have been limited to a choice between conservative nonsurgical therapies and formal decompressive surgery. Conservative treatment typically has consisted of activity modification, physical therapy, nonsteroidal anti-inflammatory medications, and corticosteroid injections.

Surgical indications for treatment of lumbar spinal stenosis have not been clearly defined in the literature [5]. A decompressive laminectomy with or without fusion has been the surgical treatment of choice by most surgeons for those patients in whom conservative management of lumbar spinal stenosis has failed and who present with a poor quality of life secondary to pain and or limitations in walking tolerance. Johnsson and associates [6] compared patients with lumbar spinal stenosis who were treated surgically and nonsurgically. The group who underwent surgery reported 60% improvement, versus 30% in the nonsurgical group. A similar study by Atlas and colleagues [7] reported success rates of 55% and 28% for surgical and nonsurgical treatments, respectively, at 1 year [7]. In rare cases, such as acute cauda equina syndrome or progressive neurologic weakness, surgical indications are more clear-cut.

Complications associated with decompressive lumbar surgery beyond worsening pain and disability have included postoperative hematoma formation, neurologic deficits, wound healing problems, and even death [8–14]. A review of the pertinent literature has identified several medical comorbidities and risk factors that may increase risks of decompressive surgery. These include diabetes, obesity, cardiac disease, chronic obstructive pulmonary disease, rheumatoid disease, depression, smoking, and long duration of symptoms [15–19]. Furthermore, results of decompressive surgery vary from study to study, in that 30% to 70% of patients report significant improvement in overall symptoms [20]. Some deterioration of surgical results has also been shown to occur over time [21].

Development of the interspinous spacer represents an alternative treatment for some patients with spinal stenosis for whom conservative management has failed. The potential benefits of interspinous process implantation is that it can be performed with use of local anesthesia with sedation, involves relatively short operating time, and can often be performed in an outpatient setting. Because the development of advancing spinal stenosis typically occurs in the sixth decade of life and later, the overall risk profile for the interspinous spacer procedure may arguably be more favorable for a select group patients, considering in that this age group, chronic medical comorbidities and risk factors are common.

At the time of this publication, a handful of interspinous spacers are available for implantation. The X-STOP Interspinous Process Decompression System (Kyphon, Sunnyvale, CA) is a device approved by the U.S. Food and Drug Administration (FDA) for implantation at one or two levels in patients with neurogenic claudication due to lumbar spinal stenosis. Prospective data from investigational device exemption (IDE) studies have shown the X-STOP device to be superior to conservative nonsurgical care for selected patients [22]. Studies have also shown that the implant may reduce pressure on the facet joints and improve overall canal dimensions [23,24].

The Wallis Normalization System (Abbott Spine, Austin, TX) and the Device for Intervertebral Assisted Motion (DIAM) (Medtronic Sofamor Danek, Memphis, TN) are currently under clinical investigation as nonfusion devices to treat spinal stenosis and other degenerative spinal conditions. Although different in overall design, both devices are implanted between the spinous processes and have shown favorable results in their “infancy” [25–27].

The Coflex Interspinous Spacer (Paradigm Spine, New York, NY) is another interspinous spacer with origins in France in the mid 1990s. The device has been used in Europe and is currently undergoing clinical trials in the United States. This is a U-shaped implant that is placed between the spinous processes and is designed to improve the cross-sectional diameter of the spinal canal [28].

The SUPERION Interspinous Spacer (VertiFlex, Inc., San Clemente, CA) was developed as another minimally invasive device to treat neurogenic claudication. This implant is composed of titanium alloy and is delivered by way of a small portal through the supraspinous ligament. Biomechanical studies have shown improvements in foraminal height, width, and area following implantation of this device [29].

A host of other interspinous spacers are currently in development.

Indications and contraindications

The current indications for interspinous spacer implantation vary slightly with the available devices. The main indication is symptomatic lumbar spinal stenosis at one or two levels as defined by history and physical examination with diagnostic confirmation (by magnetic resonance imaging or computed tomography) of moderate disease. Candidates should have a documented history of pain that is alleviated by flexion.

Contraindications to surgery are as follows:

More than two levels of moderate stenosis

Severe stenosis at any given level

Spondylolisthesis of severity greater than grade I

Advanced deformity at the proposed level(s) of implantation

Advanced osteoporosis

History of previous decompression surgery at the targeted levels

Some devices, including the X-STOP, cannot be implanted at L5-S1. Caution should also be exercised in the implantation of such devices in patients with known history of allergy to metals.

Procedures and technique

The SUPERION Interspinous Spacer will be used for the purposes of describing the implantation technique for lumbar spinal stenosis (Fig. 33-1):

1. The patient’s written informed consent is obtained.

2. The patient is placed in the prone position on a radiolucent surgical table. The legs should be slightly flexed. All bony prominences should be well padded.

3. Following the introduction of intravenous sedation by the anesthesia staff, the skin is anesthetized with a local injection.

4. Biplanar fluoroscopic images are obtained to confirm the correct level for implantation.

5. A 12- to 15-mm incision is made directly over the midline (Fig. 33-2).

6. The first of two dilators is inserted and is advanced through the supraspinous ligament at the affected level (Fig. 33-3). Fluoroscopic confirmation of the position should be obtained (Fig. 33-4).

7. A second, larger dilator is advanced over the initial dilator, with utilization of depth markers imprinted on the instruments (Fig. 33-5).

8. A cannula is placed over the dilators and is advanced through the supraspinous ligament (Fig. 33-6). A handle and mallet can be used to further advance the cannula if needed.

8. An optional reamer can is now be placed down the cannula to further prepare the interspinous space (Fig. 33-7). The larger dilator is then removed.

9. The interspinous gauge is placed down the cannula (Fig. 33-8). Fluoroscopic imaging should be obtained to confirm the correct depth.

10. The interspinous gauge should be opened until resistance is detected (Fig. 33-9).

11. An implant of the correct size, as measured by the interspinous gauge, is placed between the posterior spinous processes (Fig. 33-10). As the device is placed, anteroposterior fluoroscopic images should be obtained to confirm its depth and placement.

12. The T-handled inserter is then rotated to deploy the superior and inferior projections. Final anteroposterior and lateral fluoroscopic images should be obtained (Fig. 33-11).

Figure 33–1 SUPERION Interspinous Spacer (VertiFlex, Inc., San Clemente, CA).

Figure 33–2 Midline incision.

Figure 33–3 Insertion of the smaller dilator through the supraspinous ligament.

Figure 33–4 Anteroposterior (A) and lateral (B) views confirming placement of the dilator.

Figure 33–5 Insertion of the larger dilator.

Figure 33–6 Insertion of the working cannula.

Figure 33–7 Intraoperative picture showing the insertion of the optional reamer into the cannula (A) and reamer itself (B).

Figure 33–8 Placement of the interspinous gauge into the cannula.

Figure 33–9 Schematic drawing of the interspinous gauge between the posterior spinous processes in closed (A), open positions (B) and open position which is confirmed by fluoroscopic lateral view (C).

Figure 33–10 Implant placed between the posterior spinous processes.

Figure 33–11 Final anteroposterior (A) and lateral (B) fluoroscopic radiographs confirming placement of the implant.

CASE STUDY 33.1 Spinal Stenosis at the L5-S1 Level Treated by Superion Interspinous Spacer

A 59-year-old woman presented with an 8-month history of low back and severe left leg pain with moderate weakness that had not been relieved with more than 6 months of nonsurgical management. Baseline radiographs (Fig. 33-12) and magnetic resonance imaging confirmed a diagnosis of spinal stenosis at the L5-S1 level.

Figure 33–12 Case Study 33.1: Preoperative radiographs of the lumbar spine.

The patient provided informed consent to participate in the clinical evaluation of the SUPERION Interspinous Spacer, and before the operation, she completed Zurich Claudication Questionnaire, Oswestry Disability Index, Visual Analog Scale, and SF-12v2 Health Survey. The patient elected surgical intervention using the SUPERION device at the L5-S1 level.

The patient was placed in the prone position on an operating table capable of C-arm fluoroscopy. With the patient under general anesthesia, a 2-cm midline incision was made at the L5-S1 level. The L5-S1 interspinous space was sequentially dilated to accommodate the SUPERION cannula, and the interspinous space was prepared with use of an interspinous reamer. The interspinous space was measured and a 13-mm SUPERION device was implanted between the L5-S1 spinous processes (Fig. 33-13), with a total surgical time of 20 minutes and an estimated blood loss of less than 50 mL.

Figure 33–13 Case Study 33.1: Postoperative radiographs showing placement of the SUPERION Interspinous Spacer (VertiFlex, Inc., San Clemente, CA) at L5-S1.

Radiographs obtained at the 1-year follow-up visit verify that the SUPERION device has maintained distraction of the L5-S1 space, and there were no reported complications. Clinical outcome scores were significantly improved from baseline through 1 year postoperatively as follows: Zurich Claudication Questionnaire Symptoms score from 3.7 to 1.0 and Zurich Claudication Questionnaire Physical Function score from 3.20 to 1.20, with a 1-year patient satisfaction score of 1.00; Oswestry Disability Index score from 68.9 to 8.9; Visual Analog Scale Back pain score from 2.3 to 0.2, and Visual Analog Scale Leg pain score from 9.7 to 0.1.