Review of Interspinous Process Devices
Stephanie Hsu, BA, James Zucherman Md
Interspinous Process Device Introduction
Spinal stenosis is a narrowing of the spinal canal causing compression of neutral structures and/or their blood supply. The underlying pathologies include thickened lamina, hypertrophied ligamentum flavum, spondylolisthesis (slippage of one vertebra forward over the vertebra below), disc bulge, facet arthrosis and congenital narrowing of the spinal canal.
As the disc degenerates and dehydrates, the disc space collapses, leading to annular bulging and infolding of the ligamentum flavum. The facet joints assume a larger load, leading to facet arthrosis, osteophyte formation, and even facet cysts. These degenerative changes reduce the area of the canal for the passage of the nerves.
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In the subarticular zone, traversing nerve root is compressed. In the neuroforamen, compression of the exiting nerve root can occur. Spondylolisthesis contributes to further narrowing of the spinal canal and neuroforamen. Neurogenic claudication is a complex of symptoms resulting from lumbar spinal stenosis (narrowing of nerve passageways). The most significant symptoms include leg pain and numbness. Often, these symptoms are relieved by forward flexion of the spine.
Degenerative spine conditions, especially spinal stenosis, are becoming more common with the increasingly aging population.
Treatments include physical therapy and steroid epidural injections. For severe symptoms, surgical decompression include laminotomy, laminectomy, endoscopic decompression, or other minimally invasive decompressive techniques.
Interspinous process devices (IPD) have been developed to achieve indirect decompression by limiting lumbar extension of the abnormal joint and enlarging the spinal canal and neuroforamen. Candidates for IPD are individuals who get relief when they flex (sit and bend forward) and experience worsening of symptoms when their spine is extended (standing and walking).
The advantages of IPD compared to standard surgical decompression include the option of local anesthesia as well as the reduced risks of nerve injury, epidural fibrosis, and spinal fluid leakage. The IPD surgery is minimally invasive, and the bony structures and soft tissues are left intact.
Usually the hospital stay and rehabilitation are shorter. The IPD procedure is also reversible and allows further surgical treatment if necessary. For these reasons, IPD is especially attractive and suitable for patients with multiple comorbidities, though results are better in those under 70. By distracting the spinous processes and restricting extension, the IPD devices unload the facet joints and restore neuroforaminal and central canal size.
In a study, Guehring et al also showed that IPD devices lower intradiscal pressure.
Currently available IPD brands
Increasing number of interspinous process devices (IPD) have been introduced as an alternative to standard lumbar spine surgeries. There are now dynamic or static interspinous process devices, and interspinous process fusion devices.
Interspinous devices include:
X-Stop (Medtronic, US)
DIAM (Medtronic, US)
Superion (Vertiflex, US)
Coflex (Paradigm Spine, US)
Wallis (Zimmer Spine, US)
Viking (Sintea, Italy)
Ellipse (Sintea, Italy)
BacJac (Pioneer, US)
ExtenSure (NuVasive, US)
Promise (Biomech, Taiwan)
Rocker (Biomech, Taiwan)
Biolig (Cousin Biotech, France)
In-Space (Synthes, US) – Terminated
I-MAXX (Maxx Spine, Germany)
Flexus (Globus, US)
Spinos (Privelop, Germany)
Aperius (Medtronic, US)
Helifix (Alphatex Spine, US)
Interspinous fusion devices include:
Aspen (Lanx, Biomet)
BacFuse (Pioneer, US)
Stabilink (Southern Spine, US)
Spire (Medtronic, US)
BridgePoint (Alphatec Spine, US)
SP-Fix (Globus, US)
Posterior Fusion System (Lanx, US)
Axle (X-Spine, Bacterin, US)
Affix (NuVasive, US)
Aileron (Life Spine, US)
coflex-F (Paradigm Spine, US)
Inspan (Spine Frontier, US)
Interbridge Interspinous Posterior Fixation System (LDR Spine, Zimmer Biomet, US)
Minuteman (Spinal Simplicity, US)
PrimaLOK (OsteoMed, US)
Octave (Life Spine, US)
Zip Mis Interspinous Fusion System (Aurora Spine, US)
Neurological and Functional Outcome Measurements
There are different outcome scales to evaluate neurological and functional status of patients with neurogenic claudication. The most commonly used outcome measurements include:
1.) Zurich Claudication Questionnaire (ZCQ), also called the Brigham Spinal Stenosis
Questionnaire or Swiss Spinal Stenosis Questionnaire
The Zurich Claudication Questionnaire (ZCQ) has three subscales: symptom severity with a range of 1 to 5, physical function with a range of 1 to 4, and patient satisfaction with a range of 1 to 4. A satisfied patient has a satisfaction score of less than 2.5
2.) The Modified Roland Disability Questionnaire for Sciatica (MRDQ)
The Modified Roland Disability Questionnaire for sciatica (MRDQ) has 23 points, with higher scores indicating more disability.
3.) The Visual Analog Scale (VAS)
In VAS, pain is evaluated on a 100 mm scale, ranging from 0 mm of “no pain” to 100 mm of “the worst pain imaginable.”
4.) The Oswestry Disability Index (ODI)
In the Oswestry Disability Index (ODI), 0 points indicates no disability and 100 points indicates the worst possible disability.
5.) Short Form (36) Health Survey (SF-36)
The Short Form (36) Health Survey (SF-36) is a patient reported questionnaire that includes eight scaled scores. Each scale is transformed into a 0-100 scale. The lower the score, the greater the disability: zero indicates maximum disability, while 100 indicates no disability. The eight scaled score sections include: vitality, physical functioning, bodily pain, general health perceptions, physical role functioning, emotional role functioning, social role functioning, and mental health.
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Literature Review
As of July 2016, 560 references regarding interspinous process devices were found through electronic database searches. In this review, 12 studies were chosen for evaluation based on the following criteria: randomized controlled trials and prospective studies. Review and meta-analysis were performed for these studies on treatment of lumbar spinal stenosis using interspinous process devices, standard surgical decompression, and other therapies.
Zucherman et al (2005) compared X-Stop to conservative treatment with epidural steroid injections. Their results from randomized, multicenter trials showed that for patients with neurogenic claudication, X-Stop led to a greater improvement of symptoms and function than epidural steroid blocks and conservative treatment. The ratio of success was almost 5 times greater than non-surgical treatment. Anderson et al (2006) compared X-Stop with conservative treatment in patients with degenerative spondylolisthesis. Both Zucherman et al and Anderson et al studies showed ZCQ improvement by 23.2 (SD 18.5-27.8).
Interspinous process devices have been compared to decompressive laminectomies for lumbar spinal stenosis in randomized studies. In a prospective case control study of 60 patients, Richter et al (2009) compared one group of patients who underwent Coflex interspinous process device procedure with surgical decompression with another group of patients who only underwent surgical decompression. Both cohorts demonstrated clinical improvement in VAS, ODI, and MRDQ. There were no statistically significant differences between the two groups at six weeks and at one year follow-up. Strömqvist et al (2013) compared X-Stop to decompressive laminectomies in one or two level lumbar spinal stenosis.
In their study, 100 patients with neurogenic claudication were relieved by flexion. Evaluation at six, 12, and 24 months showed no significant differences between decompressive laminectomies and X-Stop in ZCQ scores, VAS, and SF-36. However, X-Stop surgeries took less time (62 minutes) than laminectomies (98 minutes). There was also less blood loss with X-Stop surgeries: 54 mL as opposed to 262 mL in laminectomies. Reoperation rate was 26% for X-Stop and 6% for laminectomies. Lønne at al (2015) also compared the X-Stop to decompressive laminectomies. There were no significant differences in ZCQ and patient-reported scores. X-Stop surgery reoperation was 25% as compared to 5% for laminectomies. Prospective cohort studies by Bhadra et al (2008), Brussee et al (2008), Kuchta, et al (2009), and Galarza et al (2010) showed improvement after IPD procedures.
The spinous processes are tension-bearing structures. Placement of interspinous devices can convert the spinous processes to compression-loading structures. Osteoporotic or osteopenic spinous processes are susceptible to fractures or bone erosion. Other complications include device malposition or dislocation. However, there are numerous types of IPD devices manufactured in the world. It is very difficult to compare the rates of clinical success, failures, and complications between different brands.
The Advantages of Interspinous Process Devices (IPD)
One of the most important advantages of IPD is the safety of this minimally invasive procedure compared to surgical bony decompression. Though the results from any procedure are expected to not be as good as in younger healthier patients, IPD, because of its safety, is especially suitable for frail elderly patients with multiple medical comorbidities.
The IPD procedure is reversible and leaves bony structures and soft tissues intact. The device can be removed easily and other surgical treatment can be performed with the original anatomy essentially intact. The IPD procedure significantly reduces risk of nerve injury.
Since the procedure does not involve entering the spinal canal, it does not lead to epidural fibrosis or spinal fluid leakage. With the IPD procedure, iatrogenic instability does not occur as it may following bony decompression. Most IPD surgeries can also be performed under local anesthesia and usually, the hospital stay and rehabilitation are shortened.
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