Interspinous Spacers

Published on 12/03/2015 by admin

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Chapter 33 Interspinous Spacers

John H. Shim, MD, MBA, FACS, Jason S. Mazza, MSc, OPA-C, Daniel H. Kim, MD, FACS

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.