Lanx has announced that a new study published ahead of print in Surgical Technology International that suggests that using the Aspen minimally invasive surgery MIS fusion system in conjunction with lumbar discectomy can help decrease the incidence of subsequent disc herniation, while providing a less invasive fusion procedure. All had previously undergone at least one micro-lumbar discectomy without fusion. There were no intraoperative complications and patients remained in the hospital for an average of one day. At a mean follow-up of 21 months, patients demonstrated functional improvement, with no clinical evidence of complications or reherniation.
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A large number of interspinous process devices IPD have been recently introduced to the lumbar spine market as an alternative to conventional decompressive surgery in managing symptomatic lumbar spinal pathology, especially in the older population. Despite the fact that they are composed of a wide range of different materials including titanium, polyetheretherketone, and elastomeric compounds, the aim of these devices is to unload spine, restoring foraminal height, and stabilize the spine by distracting the spinous processes.
Although the initial reports represented the IPD as a safe, effective, and minimally invasive surgical alternative for relief of neurological symptoms in patients with low back degenerative diseases, recent studies have demonstrated less impressive clinical results and higher rate of failure than initially reported.
The purpose of this paper is to provide a comprehensive overview on interspinous implants, their mechanisms of action, safety, cost, and effectiveness in the treatment of lumbar stenosis and degenerative disc diseases. The typical findings are radial fissures, prolapses, endplate damage, annular protrusion, internal disc disruption, disc space narrowing, hypertrophic ligaments, hypertrophic facet joints, and osteophytes [ 1 — 4 ].
These degenerative changes may cause instability in advanced stages of the disease [ 5 — 19 ]. The clinical endpoint of these degenerations is the compression of neural structures at the level of the neural foramina or of the spinal canal. Typically, patients complain about low back pain with or without pseudoradicular pain or dysesthesia. However, some investigators began to explore novel minimally invasive approaches to stabilize the lumbar spine. Although a growing number of different minimal invasive treatments have been introduced for the degenerative lumbar spine disease, the interspinous process devices are becoming an acceptable alternative for lumbar decompressive surgery [ 28 — 32 ].
However, interspinous devices are presented also as a viable option for treating a vast number of lumbar pathologies ranging from facet syndrome and discogenic low back pain to degenerative spinal stenosis, discopathy, and lumbar instability. The arising consequence is the need to understand the pathological and mechanical causes of each degenerative problem and determine the right treatment paradigm through a critical analysis of all available experimental and clinical biomechanical information [ 33 — 38 ].
Various authors suggest that advantages of IPD compared with standard surgical decompression techniques are the option of local anesthesia, preservation of bone and soft tissue, reduced risk of epidural scarring and cerebrospinal fluid leakage, with a shorter hospital stay and rehabilitation period, and reversibility of the surgical procedure that does not limit future surgical treatment options [ 39 — 46 ]. Currently, there are no long-term clinical trials for IPD: published clinical data are sparse and in the majority of cases consist of small, nonrandomized studies with short-term follow-up.
In this paper we provide an overview of the current notions of the biomechanical principles of the interspinous process devices, as well as in experimental and clinical studies. These considerations are applicable with different types of interspinous spinous devices with only few differences between the distinct categories.
The pathoanatomic feature of neurogenic intermittent claudication in lumbar degenerative diseases is the venous stasis in lumbar spine extension, causing neurologic symptoms as motor weakness in the lower extremities, pain, tingling, and sensory deficit, which make walking for a long distance impossible.
The first recommended indication for the implantation of an IPD was mild and moderate intermittent neurogenic claudication from spinal stenosis [ 36 ]. The key selection criteria were and are that patients symptoms must be relieved by flexion of the lumbar spine.
Flexion of the stenotic lumbar spine stretches the redundant ligamentum flavum and enlarges the neural foramina, thus relieving lower extremity symptoms. Recently, most of the devices have been marketed as treatments for discogenic low back pain: posterior elements distraction unloads posterior annulus modulating the mechanical stimuli to the nociceptive nerve endings of the sinuvertebral nerve.
A decisive index for the relief of the clinical signs and symptoms is the enlargement spinal canal area. In a magnetic resonance imaging cadaver study, Richards et al. Neural foramina area is increased after insertion of an interspinous device.
Lee et al. The interrelation between unloading of the discal structures and distraction of posterior lumbar elements is a much debated issue. Nevertheless, the biomechanical mechanism is not clear, because both compression and distraction cause a significant decrease in nucleus pressure; however, the compression results in a greater pressure decrease than distraction. It was theorized that reduction in pressure with distraction results from a void between both endplates [ 44 ].
The measurement of the height of the posterior disc as indirect sign of the intradiscal pressure showed an average from 0. In a cadaveric disc pressure study, Swanson et al. The exhaustive mechanism of the intradiscal pressure interaction with the neural structures is today not clarified. Axial loading MRI examination is seldom used to show the dynamical modification of a degenerative disc in the lumbar spine.
It is performed with the patient supine and gravity is typically simulated using a compressive system comprised of a vest worn by the patient over the shoulders and upper chest attached to a footplate against which the patient's feet are braced.
The examination is performed in a neutral position and after loading with axial and sagittal T2-weighted scans. The images are subsequently evaluated to identify load-induced changes. A dynamically degenerative modification of the lumbar spine has been observed when performing MRI under axial loading. Previously studies reported that disc bulging increases under loading conditions with consequent restrictions of the spinal canal area, irregular slipping, and abnormal movements of the articular facet joints, as well as increases in local scoliosis with asymmetric restrictions of the neuroforamen area [ 53 ].
Another indirect measure published is the distance between the spinous processes. The reported data [ 38 , 40 ] show the persistence of the distraction over a period of two years and four years. Nevertheless, major criticism against this index is the absence of a direct correlation between the interspinous distance and the clinical symptoms. Consequently, the interspinous distance should be used only as auxiliary indicator. Based on these data, a severely osteoporotic patient may be contraindicated for interspinous device, because a fracture of the spinous process might occur intraoperatively or postoperatively.
Surgeons should be aware that the insertion of an interspinous device requires personalized forces and caution, but osteopenia is not an absolute contraindication for the operation. Fuchs was the first to suggest that interspinous device can be implanted with unilateral medial or total facetectomy to stabilize the spine; however, there is no biomechanical paper to show the level of stability provided by IPD after unilateral facetectomy specially that biomechanical studies have documented the destabilizing effects of unilateral facetectomy [ 55 , 56 ].
Ploumis et al. Gonzalez-Blohm et al. They suggested that IPD may be a suitable device to provide immediate flexion-extension balance after a unilateral laminotomy. PLIF constructs with IPD and pedicle screws performed equivalently in flexion-extension and axial rotation, but the PLIF-bilateral pedicle screws construct was more resistant to lateral bending motions.
The authors requested further biomechanical and clinical evidence to strongly support the recommendation of a stand-alone interspinous fusion device or as supplemental fixation to expandable posterior interbody cages [ 58 ]. The first interspinous implant for the lumbar spine was developed in the s by Knowles. Owing to flaws in design, material, surgical technique, and applied indications, its use was abandoned. The first modern interspinous device, the Wallis system, was developed by Abbot Spine in and it was used primarily in patients with recurrent disc herniation [ 14 ].
This system was not initially marketed commercially while waiting for long-term follow-up results. In a reported prospective trial, the application of the first generation Wallis device improved outcome in patients who underwent a second discectomy.
Despite favorable results, Senegas thought that the device could be improved. A second generation of the Wallis device, slightly different in shape, and composed of polyetheretherketone PEEK , was used with other surgical procedures, to reduce pain severity in cases of moderate disc degeneration, central spinal stenosis, and significant lower back pain. The implant was fashioned out of silicone into the shape of a dumbbell to off-load the facet joints and decrease the intradiscal pressure.
But despite the promising in vitro results, no further clinical application was published to date and it is unclear whether the implant advanced much further than the laboratory settings. In the s, several other IDP devices displaying significant differences in design, materials, surgical techniques, and indications appeared in Europe and South America, for which there are ongoing trials of evaluation for a host of clinical indications.
Kaech et al. Caserta et al. The X-Stop device Medtronic, Tolochenaz, Switzerland was approved by the US Food and Drug Administration in for the treatment of neurogenic intermittent claudication secondary to lumbar stenosis [ 38 ]. Contemporary models of fusion interspinous devices have evolved from spinous process wiring with bone blocks and early device designs as the Wilson plate: the newer devices range from paired plates with teeth to U-shaped devices with wings that are attached to the spinous processes.
They are intended to be an alternative to pedicle screw and rod constructs and also to aid in the stabilization of the spine with interbody fusion.
Recently with greater focus on motion-preservation alternatives, interest in nonfusion interspinous devices has emerged. Interspinous fixation devices are placed under direct visualization or percutaneously using a C-arm and they can be categorized by design as static, dynamic, or fusion devices.
Despite the fact that they are composed of a wide range of different materials including titanium, polyetheretherketone, bone allograft, and elastomeric compounds, the intention of the implant is to maintain a constant degree of distraction between the spinous processes. In the latest years, the spine market saw few of the world's leading medtech companies abandon their position in the hotly contested sector, where they were, at best, a bit player.
Deciding that they did not want to invest any additional resources in attempting to grow its small share of the market, Abbott Spine agreed to be acquired by Zimmer Holdings Inc. Francis Medical Technologies was acquired by Medtronic. We listed the most important devices that are still on the market Table 1.
The X-Stop interspinous process decompression system is an interspinous spacer developed to treat patients with neurogenic intermittent claudication. X-Stop is the only IDP device with class I data and a prospective randomized control trial supporting its safety and efficacy compared to the nonoperative treatment. It is indicated for treatment of patients aged 50 or older suffering from pain or cramping in the legs neurogenic intermittent claudication secondary to a confirmed diagnosis of lumbar spinal stenosis.
The X-Stop may be implanted at one or two lumbar levels. The U. Food and Drug Administration approval of X-Stop interspinous decompression system was based on laboratory, mechanical, and cadaver studies and also a multicenter, prospective randomized controlled clinical study [ 38 ].
Intraoperative image shows the X-Stop interspinous device implanted cranially to a posterior fixation with pedicle screws, to avoid the topping off phenomenon. Surgical technique used was as follows: patients are placed on an operative table in a prone or right lateral decubitus position. The intervertebral level to be treated is identified by fluoroscopy. Because the implant was designed to be placed without removing any bony or soft tissues, the technique may be performed under local anesthesia.
It is of paramount importance to keep the supraspinous ligament intact. Paraspinal muscles are elevated off the spinous processes and medial lamina bilaterally using electrocautery. Occasionally, hypertrophied facets that block entry into the anterior interspinous space are trimmed partially to enable anterior placement of the implant. A small curve dilator is inserted across the interspinous ligament; after the correct level is verified by fluoroscopy, the small dilator is removed and the larger curve dilator is inserted.
After removing the latter dilator, the sizing distractor is inserted and the interspinous space is distracted until the supraspinous ligament becomes taught. The correct implant size is indicated on the sizing instrument and the appropriately sized X-Stop implant is inserted between the spinous process.
The oval spacer separates the spinous processes and limits extension at the implanted level. The oval spacer distributes the load along the concave shape of the spinous processes. The screw hole for the universal wing on the left side is visualized and the screw is engaged. The two wings are approximated towards the midline and the screw is secured. The two lateral wings prevent migration anteriorly or laterally, and the supraspinous ligament prevents the implant from migrating posteriorly.
This device was originally developed in France by Dr. It is a titanium device with a U-shaped body and two wings on each side Figure 3.
This implant is designed to permit flexion of the spine, thus restricting mobility in extension and rotation. The Coflex is FDA approved as an adjunct to fusion but is not approved as a stand-alone spacer. Although it was initially developed as a motion-preserving alternative used to treat various lumbar degenerative disorders, long-term studies from Europe suggested that the subset of patients with spinal stenosis and Grade I spondylolisthesis experienced the most significant improvement.
Surgical technique used was as follows: the patient is placed in prone position with slightly lumbar flexion. The interspinous ligament is removed and its bony attachments are resected.
Posterior fixation using an interspinous device for the treatment of degenerative spine disease
It is generally accepted that spinal fusion , in conjunction with decompression, produces better clinical outcomes in patients with degenerative spondylolisthesis , and that the use of instrumented fixation achieves greater fusion rates beyond that of onlay alone. Historically, pedicle screws or facet screws have been the choice for vertebral fixation. Each of these, however, presents certain risks to the patient, since screw placement is in close proximity to nerve roots and vasculature. Furthermore, C-arm fluoroscopy is required to ensure proper screw placement, exposing the patient and surgical team to high levels of radiation. Differing from interspinous process decompression systems, this device is designed for fixation and fusion. Wilson and Andrews frames Mizuho OSI flex the spine forward, increasing the interspinous process space, which may result in placement of an oversized implant. This would have a number of potentially deleterious effects.
TLIF with Unilateral Pedicle Screws and Aspen™ Spinous Process Fixation System
A year-old Caucasian female homemaker and avid golfer presents with low back pain and right buttock pain that radiates into the lateral aspect of her shin. Sitting worsens pain and lying down helps to relieve pain. Past medical history is significant for a major car accident at age She has had no prior spine surgery. She is 5'2" tall and weighs pounds. The patient has not undergone bone density study. Non-operative treatment includes selective nerve root blocks, epidural steroid injections and physical therapy.
New data show Aspen MIS fusion reduces risk of recurrent disc herniation