Accepted Manuscript Title: “Minimally-Invasive Posterior Lumbar Stabilization for Degenerative Low Back Pain and Sciatica. A review.” Author: G. Bonaldi C. Brembilla A. Cianfoni PII: DOI: Reference:

S0720-048X(14)00212-5 http://dx.doi.org/doi:10.1016/j.ejrad.2014.04.012 EURR 6748

To appear in:

European Journal of Radiology

Received date: Revised date: Accepted date:

9-2-2014 26-3-2014 18-4-2014

Please cite this article as: Bonaldi G, Brembilla C, Cianfoni A, “MinimallyInvasive Posterior Lumbar Stabilization for Degenerative Low Back Pain and Sciatica. A review.”, European Journal of Radiology (2014), http://dx.doi.org/10.1016/j.ejrad.2014.04.012 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

"Minimally-Invasive Posterior Lumbar Stabilization for Degenerative Low Back Pain and Sciatica. A review.”

Neuroradiology Dept. Ospedale Papa Giovanni XXIII Bergamo - Italy

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Name of the corresponding author: dr. Giuseppe Bonaldi

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*Neuroradiology of Neurocenter of Italian Switzerland Lugano, CH

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Bonaldi G.,Brembilla C., Cianfoni A.*

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e-mail address: [email protected]

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telephone #: +39 035 2674363 / fax #: +39 035 2674839

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"Minimally-Invasive Posterior Lumbar Stabilization for Degenerative Low Back Pain and Sciatica. A review.”

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ABSTRACT

The most diffused surgical techniques for stabilization of the painful degenerated and

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instable lumbar spine, represented by transpedicular screws and rods instrumentation with or without interbody cages or disk replacements, require widely open and/or

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difficult and poorly anatomical accesses. However, such surgical techniques and approaches, although still considered “standard of care”, are burdened by high costs,

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long recovery times and several potential complications. Hence the effort to open new minimally-invasive surgical approaches to eliminate painful abnormal motion.

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The surgical and radiological communities are exploring, since more than a decade, alternative, minimally-invasive or even percutaneous techniques to fuse and lock an

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instable lumbar segment. Another promising line of research is represented by the so-called dynamic stabilization (non-fusion or motion preservation back surgery),

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which aims to provide stabilization to the lumbar spinal units (SUs), while

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maintaining their mobility and function. Risk of potential complications of traditional fusion methods (infection, CSF leaks, harvest site pain, instrumentation failure) are reduced, particularly transitional disease (i.e. the biomechanical stresses imposed on the adjacent segments, resulting in delayed degenerative changes in adjacent facet joints and discs). Dynamic stabilization modifies the distribution of loads within the SU, moving them away from sensitive (painful) areas of the SU. Basic biomechanics of the SU will be discussed, to clarify the mode of action of the different posterior stabilization devices. Most devices are minimally invasive or percutaneous, thus accessible to radiologists’ interventional practice. Devices will be described, together with indications for patient selection, surgical approaches and possible complications.

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Key words: Dynamic fixation, Interspinous spacer, Minimally invasive surgery, Spinal surgery, Lumbar interspinous devices, Lumbar fusion, Degenerative disc disease, Low back

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pain.

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INTRODUCTION

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The last decades have seen a growing trend in use of minimally invasive techniques in spine surgery for the degenerated lumbar spine. Patients prefer such techniques

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because they reduce recovery times, yield less morbidity, and provide cosmetic benefits, and availability of Internet access to the medical consumer have increased

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the public demand for these procedures. Due to a low rate of complications, minimal soft tissue trauma, and reduced blood loss, more spine procedures are being

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performed in this manner, entailing shorter hospital stays, often on an outpatient

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basis. Also growing is the relevance of the epidemiology of low back pain (LBP) related the degenerative modifications of the lumbar spine, particularly in the aging population. LBP is a leading cause of chronic disability and psychological distress. In Europe, estimates of the lifetime prevalence of back pain range from 60% to 90% [1– 3]. Back pain can be a sign of degenerative segmental instability, defined as “an abnormal response to applied loads, characterized by motion in motion segments beyond normal constraints” by the American Academy of Orthopedic Surgeons [4– 6]. Motion in degenerated joints (i.e., beyond the normal limits of the joint itself) generates pain; eliminating abnormal motion seems to eliminate pain. Therefore, surgical spinal fusion (locking of two or more vertebrae as a single unit) with or without instrumentation has been the mainstay of surgical approaches for these forms of LBP. However, conventional fusion methods entail several potential complications (e.g., infection, cerebrospinal fluid leaks, harvest-site pain, instrumentation failure) . Page 3 of 44

Hence the effort to open new minimally-invasive surgical approaches to eliminate painful abnormal motion. Anatomically the most directly and easily accessible is the posterior one, and such corridor have been developed utilizing the interspinous space for X-STOP (see ahead) placement to treat lumbar stenosis in a minimally invasive

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fashion. The attention of biomechanics experts and spine surgeons has been focused mainly on the posterior structures of the spine, facets, and spinous processes, for two

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main reasons: (i) these structures are readily accessible by a minimally invasive

approach and (ii) actions upon them determined by different devices can profoundly

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modify the functional behavior of the SU.

Posterior structures of the spine can be utilized by the spine surgeon in an attempt to

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obtain fusion at the instable level/s while at the same time minimizing openness of access corridors, post-operative paravertebral and epidural scarring, amount and size

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of hardware, costs and so on. Highly instable situations may still require fusion, although fusion techniques may increase the biomechanical stresses imposed on the

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adjacent segments, resulting in overload and early degenerative changes in adjacent

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facet joints and disks [7–11]. These issues have led to attempts to develop new motion-preservation technologies for the surgical treatment of spinal instability,

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commonly referred to as “dynamic stabilization”. Dynamic stabilization has been defined as “a system that would alter favorably the movement and load transmission of a spinal motion segment, without the intention of fusion of the segment” [12]. Dynamic stabilization (or “soft stabilization”) is intended to restrict motion in the direction or plane that produces pain (“painful motion”), thereby allowing a full range of motion. Dynamic stabilization techniques introduce a more gradual, intermediate therapeutic step between abnormal movement of the spinal unit (SU) (instability) and total absence of movement (fusion). The most significant advances in dynamic stabilization techniques were made in the past 10–15 years. The combination of preservation of motion and minimal surgical invasiveness seems to be opening a new era in the surgery of symptomatic degenerative spine instability.

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HISTORICAL NOTES

In 1937 Williams [13–14] first recognized the principle of distraction in his conservative treatment of lumbosacral disabilities, by maintaining a posture of

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flexion to correct the intervertebral subluxation and the narrowing of the foramina. In his anatomo-pathological studies he emphasized the role of intervertebral disc

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degeneration in priming lumbar and radicular pain. He also showed radiographic

evidence of the widening of the intervertebral foramen in flexion of the lumbar spine.

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In 1943 Breck and Basom [15] introduced the surgical concept of maintaining a fixed distraction in flexion of the lumbar spine, through the use of interspinous bone

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blocks. The Authors proposed a surgical arthrodesis in flexion of the interspinous space by means of a bone graft, defined by the Authors themselves as “mortised

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interspinous bone block”, harvested from tibia or iliac crest, with the aim to relieve zygapophysial overload and to widen the neural foramina. This paper opened the way

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to surgery of the interspinous space.

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Knowles in 1954 first designed and patented a metallic device for use as an interspinous distractor, with the aim of a minimally invasive approach to the

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degenerated lumbar spine. Knowles’ basic concept was that unloading the lumbar structures could reverse the degenerative process and prime regeneration. Knowles approach was not accepted by the surgical community until the eighties, when interspinous prostheses were proposed by French Authors, Sénégas [16] in 1988 and Bronsard in 1989. Bronsard’s proposal was that of a prosthesis implanted between the vertebral spinous processes with locking suspension. It consists of a flat, semi-elastic braid and one or more small pads made of the same material as the braid. In the patent description is stated that “The invention is used in particular for straightening the vertebrae in order to combat lordosis”. Bronsard first introduced the concept of using elastic material, acting as a shock absorber. Sénégas, such as Knowles, was convinced that his “titanium interspinous blocker” could reverse degeneration of the spinal unit. Extended clinical experience was

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developed in the nineties, and in 2000 Sénégas released the final version of the device, still in use nowadays and made of polyetheretherketone (PEEK) (see ahead) [17-18]. In the same year more devices were developed based on the elastic principle of shock

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absorbing, the DIAM (see ahead) in particular could gain a wide success in the

opinion and use of spine surgeons. But the real diffusion of interspinous devices was

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due to the invention of Zuchermann [19], an innovative device really minimally

invasive and the first one totally respecting local anatomy, with regard in particular

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for the supraspinous ligament (see ahead for description of the device).

The final step in the evolution of such devices is represented by the percutaneous

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ones, among them the first having been the Aperius produced by Kyphon (now Medtronic). The device is made of titanium, while the second one, the InSpace

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proposed by Synthes, is made of PEEK.

More recently we observed a return to the origins, with the appearance on the market

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of interspinous spacers giving, at the same time of a distraction of the space and

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modification of loads in the spinal unit, the possibility of a associating a rigid

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arthrodesis (posterior fusion).

BASIC BIOMECHANICS

The basic functional SU is the smallest physiological unit of motion of the spine. It is therefore termed a “motion segment”. It consists of two adjacent vertebrae, the disk, and all the connecting ligaments. Individual motion segments contribute to the total motion of the spine. In flexion and extension, muscles apply a bending moment to the SU. During flexion of the lumbar spine, the total motion obtained (modification of posture from neutral to flexion) is the sum of the modifications obtained at the level of each single component of the SU, i.e., a decrease of the anterior disk height and a widening of interspinous space (angle between the spinous processes, which are stretched and moved apart). The supraspinous ligament is the structure limiting

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flexion more effectively. The opposite happens in extension, with an increase in the anterior disk height and closing of the interspinous space. The neutral zone (NZ) is the position of the SU in which a small bending moment can result in a large movement (i.e., a large change in the angles between the two

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vertebrae). In a normal SU, the center of the NZ corresponds to the middle position between flexion and extension. A small moment is required to start flexion (or

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extension). However, with a progressive increase in the movement it becomes

increasingly harder to obtain new flexion (or extension). The NZ is a measure of the

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laxity of the SU, and it widens in the presence of instability. Pathological widening of the NZ allows exaggerated movements, which in turn require a large amount of

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energy for return to the neutral state. Dynamic devices aim to reduce the NZ. The instantaneous center of rotation (ICR) corresponds to the point at which, if load

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is applied, no bending occurs. It is defined as “instantaneous” because it can change at every instant during different types of movements. Predicting the ICR in structures

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as complex as the SU is difficult. The ICR changes with different movements and

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these changes become more unpredictable in the presence of instability. More often, in a healthy SU, in the standing, inactive position, the ICR is located posterior to the

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center of the disk, just above the inferior endplate (corresponding approximately to the center of gravity). It moves in flexion–extension, and the variability is considerable. There are no simple rules to predict the effect of stabilization devices on the ICR, but one is notable: the ICR moves toward an increase of stiffness. When an interspinous spacer is deployed, biomechanics are not modified during flexion (if the supraspinous process is preserved surgically). During extension, the biomechanics are not modified until the spacer is under compression. When the spacer undergoes compression, the anterior annulus is stretched, and an additional increase in the anterior height of the disk is obtained. To allow and compensate for this, the facets move opposite to the normal direction, opening instead of closing. That is, the movement, which is no longer obtainable at the expense of the interspinous space (decrease of the angle in extension) is now obtained at the level of

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different, elastic structures. An immediate consequence is that back pain induced in extension by pressure originating in the facets or posterior annulus of the lumbar spine may be relieved by unloading of the facets or posterior annulus generated by interspinous decompression . At the same time, posterior stabilization devices can

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have a primary role in modifying the loads of specific regions of the disk.

Rigid, inelastic tension bands can be added to the posterior construct, tying the upper

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and lower spinous processes to the interspinous device, thus giving an additional

moment to resist bending. In the normal/uninstrumented condition, the ICR in flexion

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moves anteriorly, whereas the action of the tension band keeps the ICR more posterior, thereby limiting its shifting. This action results in a reduction of

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compression forces on the anterior annulus and a reduction of tension on the posterior annulus and facets (Fig. 1). Conversely, the rigid interspinous spacer in extension

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moves the ICR posteriorly behind the facets (i.e., toward the increase in stiffness determined by the device), thereby modifying the loads on the different parts of the

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SU: the load on the facets and posterior annulus is reduced instead of increased

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(tension instead of compression) (Fig. 2).

In a cadaveric study on the effects of an interspinous implant on disk pressures,

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Swanson and colleagues reported that the pressures of the posterior annulus and nucleus pulposus were reduced by 63% and 41%, respectively, during extension, and by 38% and 20%, respectively, in the neutral, standing position [20].

DESIGN RATIONALE OF DIFFERENT DEVICES AND GENERAL SURGICAL PRINCIPLES

Dynamic Posterior Stabilization Devices

Dynamic stabilization devices aim to provide stabilization while maintaining the mobility and function of the SUs by favoring realignment, preventing extremes of flexion and extension, and unloading through modification of the distribution of loads

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and painful areas within the SU. They relieve stress peaks across the degenerated structures, particularly facets and the anterior and posterior annulus. Dynamic posterior stabilization devices fall into two main categories of design: interspinous spacers and pedicle screw based systems. Interspinous spacers may or

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may not be provided with tension bands, which are passed around the upper and

purpose of securing the device and limiting flexion/rotation.

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lower spinous processes and then tied to the interspinous component, with the double

Rigid, non-deformable interspinous spacers have a constant effect on the distraction

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of the spinous processes. Alternatively low-rigidity, deformable spacers act more as shock absorbers, with a consequently more physiological action on range of motion

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of the SU together with an increase in bone compliance.

The interspinous process decompression system X-STOP (Medtronic) was proposed

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by Zucherman and colleagues [19] in the late 1990s for treatment of the symptoms of intermittent neurogenic claudication (INC) due to segmental spinal stenosis [21–23].

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X-STOP (Fig. 3) consists of an oval spacer positioned between the two spinous

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processes at the symptomatic level. The lateral wing is then attached to prevent the implant from migrating anteriorly or laterally out of position. Anterior migration and

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posterior migration are also limited, respectively, by the lamina and the supraspinous ligament (the latter not being violated). The central pivot was rigid and made of titanium in the first version. Now it is semi-rigid thanks to a layer of PEEK external to the metal. It is deployed through a small posterior surgical approach. It is intended to prevent extension of the stenotic levels, yet allowing flexion, axial rotation, and lateral bending [24]. Leaving the supraspinous ligament in place and intact has the double effect of not only preventing posterior migration of the device but also of not modifying the behavior of the SU in flexion. Biomechanical studies have shown that the implant significantly reduces intradiskal pressure and facet load, as well as preventing narrowing of the spinal canal and neural foramens [20, 25, 26]. It is an alternative therapy to conservative treatment and

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decompressive surgery for patients suffering from INC. Its safety and effectiveness have been confirmed in a randomized, controlled trial [19, 27, 28]. Similar devices on the European market which have not yet been approved in the USA are available. Among them:

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• Superion™ (VertiFlex); • Aperius™ (Medtronic);

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• In-Space™ (Synthes); • Flexus™ (Globus Medical);

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• BacJac™ (Pioneer Surgical Technology);

• Prow™ (Non-Linear Technology Spine)

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and others.

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• Falena™ (Mikai, Italy);

Superion and Aperius are rigid, being made of titanium, and both are deployed

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through a percutaneous approach. In-Space, Flexus, BacJac and Falena, similar to the

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X-STOP, are made of PEEK in the part of the device in contact with bone. Polyetheretherketone (PEEK) is a semi-crystalline thermoplastic that exhibits

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strength, stiffness, resilience, and biocompatibility, which is ideal for use in orthopedic surgery. It allows stress to be distributed more evenly on the surrounding bony structures, limiting an overload that could lead to acute fracture or chronic bone porosity and resorption. They are deployed percutaneously or through mini-open surgical access (like X-STOP).

The Prow is made of ultra-high-molecular-weight polyethylene (UHMWPE), a material used extensively for over 40 years in total joint replacements. Similar to PEEK, it has an elasticity modulus close to that of bone, granting support to adjacent bone with a lessened chance of subsidence. Wallis™ (Abbot Spine) [16–18] and the DIAM™ (Medtronic) [29,30] are doubleaction devices in which the interspinous spacer is secured with two tension bands wrapped around the upper and lower adjacent spinous processes. The bands also give support to the supraspinous ligament in limiting flexion of the SU (hence the doublePage 10 of 44

action of the devices; more intense for Wallis and less for DIAM, whose surgical insertion does not entail sectioning of the supraspinous ligament). The spacer of Wallis is made of PEEK. The core of DIAM is made of silicone, whereas the outer mesh and tether are made of polyethylene terephthalate (polyester). Silicone is more

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resilient and compressible, and is preloaded by compression before insertion. This permits posterior tensioning of the ligaments and disk, allowing a type of

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ligamentotaxis (particularly of the posterior annulus fibrosus).

Similar to DIAM is IntraSpine™ (Cousin Biotech, France), which is made of the

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same silicone covered with a polyester textile. The silicone core has a shape based on a different concept compared with other interspinous devices. The central core fitting

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the interspinous space has an anterior part, designed to suit the interlaminar space. This kind of “nose”, covered with a layer of silicone to avoid fibrosis in the yellow

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ligament area, gives the device a more anterior (ventral) point of action directly between the laminae, with a consequently more efficient action on the ICR (similar to

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that of the PercuDyn system, see ahead).

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The Coflex™ (Paradigm Spine) is a U-shaped titanium device, inserted surgically between the spinous processes. This entails removal of all interspinous and

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supraspinous ligaments. Compared to dynamic devices, it is more rigid and, because of its shape, has more contact surface with bone. This could be an advantage over other interspinous/interlaminar decompression devices, thereby reducing the risk of delayed bone subsidence (see below in the “Complications” paragraph). Screw-based posterior stabilization devices fall in a different category of design. Most of them, like Dynesys™ (Zimmer Spine) or Stabilimax NZ™ (Applied Spine Technologies), are not minimally invasive. They require an open surgical approach similar to the one used for instrumented fusions. Dynesys is built in analogy with the posterior screws and rod instrumentation systems. However, the spacers are made of flexible plastic tubes (polyurethane) surrounding a thin nylon-like cord (polyethylene). After implantation the system creates a dynamic push–pull relationship that stabilizes the affected joints without

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fusion. The device was developed and has been used in Europe since 1994, with mixed results [31,32]. Clearance for the Dynesys system by the Food and Drug Administration (FDA) in the USA is limited to use as an adjunct to spinal fusion of the thoracic, lumbar and sacral spine for degenerative spondylolisthesis with

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neurological impairment, and for a prior failed spinal fusion (pseudoarthrosis).

Clinical trials are ongoing for use of Dynesys as a stand-alone device in the absence

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of spinal fusion.

Stabilimax NZ features dual concentric springs combined with a ball-and-socket joint

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to enhance spinal stability and to increase the resistance of the passive spinal system around the device, while permitting controlled motion in flexion and extension.

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Stabilimax NZ is inserted by pedicle screws in exactly the same way as fusion devices. However, a bone graft is not placed to promote bone growth for fusion.

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PercuDyn™ (Interventional Spine) (Fig. 4) is a screw-based posterior stabilization device. Two screws are inserted with a totally percutaneous, fluoroscopy-guided

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approach through the pedicles into the vertebral body. The polycarbonate- urethane-

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resilient heads provide support to the inferior articular facets of the upper vertebra, thereby limiting their range of motion in extension. This device can be used if a

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spinous process is not present (L5–S1 or post-laminectomy). Moreover, the device might be better at treating diskogenic pain. The spacer is mounted more anteriorly with respect to a true interspinous device. Consequently, it exerts a more efficient action in moving the ICR outside the disk, forcing the segment into flexion into a neutral position and keeping the posterior annulus as distracted as possible. Thus, on a theoretical, biomechanical basis, it should decrease intradiskal pressure, reduce annular compression, and preserve posterior disk height in a more efficient way than more posteriorly applied devices [33]. Trials are being conducted to evaluate the safety and efficacy of several of the devices described above (Flexus, Prow, In-Space, Superion, Wallis, DIAM, Aperius, Coflex, Stabilimax NZ).

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In addition to the above-described technologies, other dynamic stabilization devices are in various stages of development. In addition, some companies are developing technologies that would allow a combination of posterior dynamic stabilization

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devices and total disk replacement as an alternative to spinal fusion.

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Posterior Interspinous fixation (arthrodesis)

These devices, developed more recently, allow a rigid stabilization of the posterior

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elements of the SU, by means of the association of a synthetic device and the deposition during surgery of autologous bone, bone from bank or bone substitutes,

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with the aim to eventually obtain a real, stable arthrodesis at the level of the interspinous space. These devices are therefore not dynamic in their action.

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These newer devices range from paired plates with teeth to U-shaped devices with wings that are rigidly attached to the spinous process, by means of variably

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engineered zip or locking systems. Thus, interspinous fixation (fusion) devices

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contrast with interspinous distraction devices (spacers), which are used alone for decompression and are typically not fixed to the spinous process. 

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Interspinous fixation devices are placed under direct visualization (mini-open surgery), while screw and rod systems may be placed either under direct visualization or percutaneously.

Posterior interspinous fusion has several advantages over the pedicle screw fixation in terms of skin incision, muscle dissection, less intraoperative estimated blood loss, less hardware and shorter operative times. While biomechanical studies indicate that interspinous fixation devices may be similar to pedicle screw-rod constructs in limiting the range of flexion-extension, they may be less effective than bilateral pedicle screw-rod fixation for limiting axial rotation and lateral bending. They are being evaluated as alternatives to pedicle screw-and-rod constructs in combination with interbody fusion. However, they might also be used to distract the spinous processes and decrease lordosis. Thus, interspinous fixation devices might be used

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off-label without interbody fusion as decompression (distraction) devices in patients with spinal stenosis (stand-alone use). However, the success of long-term clinical outcomes, and/or even the need of this type of fixation after specific decompression techniques, are still controversial. Some

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surgeons advocate the use of the interspinous spacer device as a backup for minimal decompression surgeries such as laminectomies, while others suggest limiting their

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application to supplemental fixation (that is, posterior fixation to interbody cages). Furthermore, interspinous spacers implantation after unilateral decompression has

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shown satisfactory clinical outcomes in patients suffering from mild to moderate central and unilateral stenosis, where the decompression before interspinous device

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implantation was performed to avoid insufficient nerve root release by indirect decompression of the interspinous spacer [34].

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A biomechanical study shows that the interspinous spacer may be a suitable device to provide immediate flexion-extension balance after a unilateral laminectomy, but the

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bilateral pedicle screw system (BPSS) provides greater immediate stability in lateral

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bending and axial rotation motions. Both PLIF constructs performed equivalently in flexion-extension and axial rotation, but the PLIF-BPSS construct is more resistant to

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lateral bending motions. The Authors suggest that further biomechanical and clinical evidence is required to strongly support the recommendation of a stand-alone interspinous fusion device or as supplemental fixation to expandable posterior interbody cages [35].

The following interspinous fixation devices have received clearance to market by the U.S. Food and Drug Administration (FDA). This may not be an exhaustive list. • Affix™ (NuVasive)

• Aileron™ (Life Spine) • Aspen™ (Lanx) • Axle™ (X-Spine) • BacFuse™ (Pioneer Surgical) • BridgePoint™ (Alphatec) Page 14 of 44

• Inspan™ (Spine Frontier) • PrimaLOK™ (OsteoMed) • Octave™ (Life Spine) • Romeo2™ (Spineart)

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• Spire™ (Medtronic) • SP-Fix™ (Globus)

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• ZIP MIS Interspinous Fusion Implant™ (Aurora Spine, Carlsbad, CA)

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The Aspen™ (Lanx Broomfield Colorado) , a titanium alloy device, is made of two

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lateral plates attached to the spinous processes, with a central space to be filled with biologic material for final arthrodesis. Similar to the Aspen are the ZIP MIS Interspinous Fusion Implant (Aurora Spine, Carlsbad, CA) and the Romeo2™

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(Spineart, Switzerland).

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Posterior Facet Screw Fixation

The concept of lumbar spine facet fixation has existed since 1948, with King’s

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description [36] of a novel method of internal fixation in the lumbosacral spine as an alternative to immobilization in plaster; in his operation short screws are placed horizontally directly across the facet joint. This was modified by Boucher in 1959 (“true transfacet” technique) [37] by using longer screws and slightly altered placement, i.e. two screws (for each level, one per side), traversing the facets more vertically from medial to lateral (Fig. 5 A). Magerl [38 ] described the “translaminar transfacet” technique in 1984. Screws are significantly longer because the entry point is at the base of the contralateral spinous process (Fig. 5 B). This increases the effective working length of the screw on both sides of the facet joint thus increasing strength of the fixation The translaminar transfacet technique was thought by most surgeons to be of greater biomechanical efficacy, and therefore it achieved the greatest popularity. This is despite the fact that it is more technically demanding and Page 15 of 44

arguably more dangerous than the “true” transfacet technique. The danger of the latter results from the required long passage of crossing screws through the lamina before they traverse the facet joint. Despite the longevity of facet fixation as a method for spine immobilization, its use

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was largely usurped by pedicle screw fixation. Pedicle screws were believed to

increase the stability and stiffness of the construct and do not require the presence of

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intact dorsal elements, as does the translaminar approach for facet screws.

However, facet screw fixation techniques provide an attractive option in alternative to

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the classical screws-and-rods approach, minimizing soft tissue trauma and retaining the normal anatomy of the facets. This method of fixation avoids injury to the

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adjacent facet above the fused segment, which may decrease the incidence of adjacent segment disease. Although there have been concerns regarding the

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biomechanical stability of transfacet fixation, recent biomechanical studies have demonstrated that both short-term and long-term cycling of motion segments

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instrumented with bilateral facet fixation have equivalent biomechanical performance

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to standard pedicle screw instrumentation [39]. Biomechanical studies have demonstrated significant stability in flexion, extension, and rotation [40].

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Translaminar facet screws significantly increase the stiffness of spinal motion segments [41].

The technique is simple and effective [42]. Screws are cannulated, and positioning is percutaneous, totally image-guided. The precise length of the device is adjustable in situ allowing for precise placement of the screw tip. At that stage, if further facet compression is desirable, a ratchet-gun mechanism allows the surgeon to compress the facets without danger of advancing the screw tip. A double helical thread design along with the ability for axial compression increases the biomechanical stability of the bone-implant interface.  The following facet fixation devices have received clearance to market by the Food and Drug Administration. This may not be an exhaustive list. • ANCHOR FS Facet Fixation System™ (Medtronic)

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• BONE-LOK™ Percutaneous Transfacet Device (Triage Medical)? • Capture Facet Fixation System™ (Spineology) • FacetGun Max Facet Fixation System™ (Amedica) • PrimaLOK FF™ (Osteomed) • ZYFUSE Facet Fixation System™ (Globus Medical)

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• Zygafix Facet Fusion System™ (X-Spine)

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• ILLICO Facet Fixation System™ (Alphatec Spine)

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Clinical studies have reported a high success rate with minimal complications [43-

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46].

Facet Dowels

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Percutaneous facet fusion is a minimally-invasive technique used to eliminate unwanted motion between z ygapophyseal joints of the lumbar spine. This minimally-

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invasive approach achieves its effects by encouraging the growth of new bone tissue

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that fixes, or fuses, the targeted joints in a single permanent position. In this way, the procedure can help relieve pain coming directly from the joints themselves. From a

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diagnostic point of view, such surgery, although minimally-invasive, is usually performed after a period of anesthetic blocks of the joints, steroid injections, even RF ablation of the dorsal nerve; all this procedures must confirm origin of pain from zygapophyseal joints, although not treatable in a more conservative manner. The procedure, when performed as a standalone surgery, can address minor facet joint instability, potentially eliminating the need for more extensive surgical treatments. This is particularly true in patients, such as the elderly population, whose daily activities do not entail a large amount of motion of the lumbar spine, also owing to age-related weakness of muscles, that produce a relatively minor amount of unwanted spinal motion in the unstable facet joints. Moreover, a stand-alone use of facet dowels might be indicated in limited-motion SUs, such as in presence of advanced degenerative disk disease (DDD) at the same level. When performed along Page 17 of 44

with an anterior interbody fusion, it can promote long-term spinal stability by increasing the effectiveness of the main procedure. Percutaneous facet fusion is an approved surgical procedure in the U.S. Percutaneous facet fusion comes in two basic forms. In the first version, dowels made

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of bone or from the bone of a cadaver donor are inserted in the facet cavity (Fig. 6). Bone is demineralized to expose the native bone morphogenetic proteins in the graft.

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Gradually, these inserted dowels will trigger a healing response that produces bone growth and fuses the joint shut. In the short-term, placement of these dowels also

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disengages the joint, reduces the pressure on nerves running through the joint and stops the joint from bearing any weight.

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Examples are the Threaded Facet Dowel™ by Synthes (a surface-demineralized cortical allograft bone), the OsteoLock and BacFast™ (produced by Biologics

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Bacterin) made of demineralized cortical bone, or the TrueFuse™ (Orthopedic Development Corporation), made of allograft (donated cortical bone derived from

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both the femur and tibia).

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A variant of percutaneous facet fusion is represented by use of a facet spacer locked with two cannulated screws, one for facet (Facet Wedge™ – Synthes). This spacer is

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intended to lock the joint as an aid to fusion through immobilization of the facet joints, with or without bone graft, at single or multiple levels, from L1 to S1. It can be inserted with a minimal invasive technique either to augment other fusion techniques or as a stand-alone device for cases without low-grade segmental instability.

PATIENT SELECTION

Indications to use of posterior interspinous fusion, facet dowels and posterior facet screw fixation are mostly those of other, more invasive technique for spinal fusion widely used to treat LBP coming from degenerative modifications of the SU with a medium to high degree of spinal instability, and have already been previously discussed.

Page 18 of 44

Rigid or semi-rigid interspinous devices such as the X-STOP, Aperius or In-Space were developed originally for the treatment of INC symptoms due to segmental spinal stenosis [21–23]. INC symptoms are pain and discomfort radiating to the buttocks, thigh, and lower

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limbs during standing and walking. This is exacerbated by lumbar extension and

relieved by flexion. Standing narrows the neural foramina and canal area, resulting in

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the impingement of nerve roots, whereas flexing (such as when sitting or riding a

bicycle) increases the cross-sectional area of the spinal canal, thereby relieving this

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impingement. In extension, the implant significantly increases the canal area, subarticular diameter, canal diameter and area/width of the foramen [20, 47, 48]. The

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final effect is that the implant prevents narrowing of the spinal canal and foramina in extension, thereby reducing or eliminating compression of the nerve root. Figure 7

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illustrates widening of the spinal canal after insertion of an interspinous device (see legend).

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This indication for implantation of an interspinous device has been validated by a

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randomized, controlled, prospective, multicenter trial comparing patients treated with X-STOP with patients treated by non-surgical means [19,27,28]. However, the

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indications for control of axial pain are poorly defined and left to the surgeon’s personal opinions and experience. Reliable data are lacking but hopefully ongoing trials will provide the necessary evidence for appropriate choices. Most studies are focused on moderate degenerative lumbar stenosis at one or two levels or treatment of mild-to-moderate DDD of the lumbar spine. The most frequent indications are early disk degeneration (“black disk”, which is an incorrect, non-radiological definition that is widely used in surgical communities), contained disk herniations, mild segmental instability (postoperative or not), and facet syndrome (with hypertrophy, osteophytosis, cysts, incongruity). The indications proposed by Sénégas for the Wallis system [16-18] are significant loss of disk material after surgery, a degenerative disk adjacent to a fused segment, and an isolated Modic 1lesion [49]

Page 19 of 44

thought to be the cause of chronic LBP. Another indication is providing a cushioning mechanism to SU adjacent to fused levels. The principles of biomechanics should direct surgical strategy. Rigid or semi-rigid interspinous components limit extension, moving the ICR and loads away from the

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facets and posterior annulus. The tension bands limit flexion and rotation, adding stability and helping to restore the alignment of the metamers. Changes in the

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location of the ICR change the deformation of local areas of tissue, moving the distribution of the loads. In the case illustrated in Figure 8, the pain source is

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presumably the anterior inflammatory osteochondrosis. The surgical strategy should rely more on limitation of flexion (i.e., on the tension band to reduce the anterior disk

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load). The interspinous spacer partially limits the load on the anterior disk, however, forcing the facets to open instead of closing in extension (as previously discussed).

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For this reason, almost all devices with a tension band are double-action devices, coupling bands and an interspinous spacer. Such systems tend to add stability to the

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vertebral segment, while simultaneously limiting the extremes of flexion and

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extension (i.e., reducing the NZ that was widened by the pathologic conditions) and restoring a range of motion that is as physiological as possible. Such systems increase

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resistance to compression and stretch, not (or only partially) affecting rotation and lateral bending.

As disk degeneration progresses, there is sprouting of vessels accompanied by nociceptive fibers from the outer toward the inner disk. This sprouting becomes painful owing to the presence of nodules of granulation tissue (sometimes evident on MRI as nodular zones of high signal) usually in the posterior annulus [50]. In some cases, as in Fig. 9, the origin of pain could be presumed to be from the hyperintensity zone (HIZ) in the posterior annulus. In such situations, the aim is to move the load away from the posterior annulus by means of the action on the ICR of a rigid posterior interspinous device. The action of the device could, in theory, reverse the wrong load condition on the annulus, favoring its regeneration and rehydration of the nucleus.

Page 20 of 44

Among the advantages of motion preservation that must be considered is the positive effect that normal load and motion have in maintaining all joints in good health, thereby providing ideal nutrition for the articular components. This is true for intervertebral disks, which are not vascularized and consequently rely for nutrition

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and oxygenation on osmotic diffusion from the surrounding tissues (particularly

through the permeability of the cartilage endplates). Nutrients are pumped into the

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disk, and movement plays a major part in this process. When treating diskogenic

pain, disk degeneration must be limited to Pfirrmann grades 1 to 4 [51], and diffused

degeneration of the endplates are acceptable).

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Modic changes should be excluded (though small spots of limited Modic

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Rigid or semi-rigid interspinous spacers may help reduce minimal degrees (grade 1.0 on a scale of 1 to 4) of degenerative spondilolisthesis Fig. 10 due to spondylotic facet

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deformation (but not a true olysthesis due to lysis, see ahead). Degenerative retrolisthesis with diskopathy, reduction in the height of the posterior

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annulus, and possible associated Baastrup syndrome (“kissing” spinous processes

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with progressive, painful interspinous degenerative alterations) are good indications

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for both a dynamic interspinous spacer, or minimally-invasive posterior fusion.

CONTRAINDICATIONS AND COMPLICATIONS

There are several contraindications to the use of interspinous implants (Table) [52]. An osteoporotic condition must be considered to be a contraindication because of the risk of fractures consequent to the pressures generated against bony surfaces. Barbagallo et al. [53] analyzed complications in a series of 69 patients. At a mean follow-up of 23 months, 8 complications (11.5%) were recorded: 4 device dislocations and 4 fractures of spinous processes. A prospective observational study [54] found a high prevalence of fractures of spinous processes in 38 patients (50 implants) after implantation of interspinous stand-alone devices. A fracture was not identifiable on plain radiographs, but postoperative computed tomography identified

Page 21 of 44

non-displaced spinous process factures in 11 patients (28.9% of patients, 22% of levels). Direct interview of patients as well as review of medical records indicated that 5 fractures were associated with mild-to-moderate lumbar back pain, and 6 fractures were asymptomatic. Three of the 11 patients underwent device removal and

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laminectomy for persistent pain. Fractures in the other 3 patients had healed by 1 year.

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In a recent study [55], feasibility and efficacy of cement augmentation of the

posterior vertebral arch (spinoplasty) before Aperius implantation in preventing

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perioperative and post-implant fractures of spinous processes was assessed. Spinoplasty seemed effective in preventing delayed fractures of the posterior arch

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after placement of interspinous spacers in patients at risk for fragility fractures.

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CONCLUSION

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Although back pain from degenerative changes of the lumbar spine is a huge medical

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and socio-economic problem, indications for surgery, as for different types of treatment, remain poorly defined. Spine degeneration comes with advancing age in

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almost every individual, and their prevalence is also very high in the general population in earlier stages of life. However, on the other side, the main issue is that diagnostic techniques cannot be reliably used to identify the exact source of pain, and our understanding of pain etiology is poor. When we consider such limitations and lack of diagnostic certainty, low-invasiveness becomes mandatory in spine surgery for degenerative diseases. Minimally invasive surgical approaches and implants should be used to avoid or delay more aggressive procedures, and their use as “intermediate” solutions is justified as long as iatrogenic trauma during implantation is minimal. From a speculative and prospective viewpoint, early correction of low grades of instability by minimally invasive devices, could not only stop or delay, but even reverse degeneration of the components of the SU. Moreover, they are cheaper and safer than instrumented fusion procedures, and do not preclude further

Page 22 of 44

therapeutic options. Nevertheless, many questions are yet to be answered. Further studies are required to determine the optimal design of implants. Radiologists are the best trained for the correct use and application of percutaneous or minimally invasive (often radiograph-guided) surgical methods and devices. Several of these surgical

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methods and devices have been proposed and developed by radiologists. Orthopedic surgeons and neurosurgeons share a long tradition of invasive treatments of the

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degenerative spine. These “two worlds” are getting closer, and an open and unbiased

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cooperation of these communities should represent good news for our patients.

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REFERENCES

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of chronic nonspecific low back pain. Eur Spine J 2006;15:S192–S300

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back pain. Eur Spine J 2006;15:S136–S168

3. Palmer KT, Walsh K, Bendall H, et al. Back pain in Britain: comparison of two prevalence surveys at an interval of 10 years. Brit Med J 2000;320:1577–1578

4. Paris SV. Physical signs of instability. Spine 1985;10: 277–279

5. Pope MH, Panjabi MM. Biomechanical definition of spine instability. Spine 1985;10:255–256

6. American Academy of Orthopaedic Surgeons. A glossary of spinal terminology. American Academy of Orthopedic Surgeons. Chicago; 1981

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7. Park P, Garton HJ, Gala VC, et al. Adjacent segment disease after lumbar or lumbosacral fusion: review of the literature. Spine 2004;29:1938–1944

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8. Schlegel JD, Smith JA, Schleusener RL. Lumbar motion segment pathology

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adjacent to thoracolumbar, lumbar and lumbosacral fusions. Spine 1996;21:970–981

9. Aota Y, Kumano K, Hirabayashi S. Postfusion instability at the adjacent segments

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after rigid pedicle screw fixation for degenerative lumbar spinal disorders. J Spinal

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Disord 1995;8:464–473

10. Etebar S, Cahill DW. Risk factors for adjacent segment failure following lumbar

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fixation with rigid instrumentation for degenerativeinstability. J Neurosurg

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1999;90:163–169

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11. Kumar MN, Jacquot F, Hall H. Long-term follow-up of functional outcomes and radiographic changes at adjacent levels following lumbar spine fusion for

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degenerative disc disease. Eur Spine J 2001;10: 309–313

12. Sengupta DK. Dynamic stabilization devices in the treatment of low back pain. Orthop Clin North Am 2004;35:43–56

13. Williams PC. Lesions of the Lumbosacral Spine. Part 1. Acute Traumatic Destruction of the Lumbosacral Intervertebral Disc. J Bone and Joint Surg 1937;19: 343-363

14. Williams PC. Lesions of the Lumbosacral Spine. Part II. Chronic Traumatic (Postural) Destruction of the Lumbosacral Intervertebral Disc. J Bone and Joint Surg 1937;19: 690-703

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15. Breck LW, Basom WC. The Flexion Treatment for Low-Back Pain. Indications, Outline of Conservative Management, and a New Spine-Fusion Procedure. J Bone

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and Joint Surg 1943;25: 58-64

16. Sénégas J, Etchevers JP, Baulny D, et al. Widening of the lumbar vertebral canal

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as an alternative to laminectomy, in the treatment of lumbar stenosis. Fr J Orthop

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Surg 1988;2:93–99

17. Sénégas J. Surgery of the intervertebral ligaments, alternative to arthrodesis in the

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treatment of degenerative instabilities. Acta Orthop Belg 1991;57(Suppl. 1):221–226

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[In French]

18. Sénégas J. Mechanical supplementation by non rigid fixation in degenerative

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2):164–169

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intervertebral lumbar segments: the Wallis system. Eur Spine J 2002;11(Suppl.

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19. Zucherman JF, Hsu KY, Hartjen CA, et al. A prospective randomized multicenter study for the treatment of lumbar spinal stenosis with the X-Stop interspinous implant: 1-year results. Eur Spine J 2004;13:22–31

20. Swanson KE, Lindsey DP, Hsu KY, et al. The effects of an interspinous implant on intervertebral disc pressures. Spine 2003;28:26–32

21. Katz JN, Harris MB. Lumbar spinal stenosis. N Engl J Med 2008;358:818–825

22. Arbit E, Pannullo S. Lumbar stenosis: a clinical review. Clin Orthop 2001;384:137–143

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23. Blau JN, Logue V. The natural history of intermittent claudication of the cauda equina. A long term follow-up study. Brain 1978;101(2):211-22

24. Lindsey DP, Swanson KE, Fuchs P, et al. The effects of an interspinous implant

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on the kinematics of the instrumented and adjacent levels in the lumbar spine. Spine

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2003;28:2192–2197

25. Wiseman C, Lindsey DP, Fredrick AD, et al. The effect of an interspinous

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process implant on facet loading during extension. Spine 2005;30:903–907

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26. Richards JC, Majumdar S, Lindsey DP, et al. The treatment mechanism of an interspinous process implant for lumbar neurogenic intermittent claudication. Spine

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2005;30:744–749

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27. Zucherman JF, Hsu KY, Hartjen CA, et al. A multicenter, prospective,

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randomized trial evaluating the X STOP interspinous process decompression system for the treatment of neurogenic intermittent claudication. Two-year follow-up results.

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Spine 2005;30:1351–1358

28. Kondrashov DG, Hannibal M, Hsu KY, et al. Interspinous process decompression with the X-STOP device for lumbar spinal stenosis. A 4-Year follow-up study. J Spinal Disord Tech 2006;19:323– 327

29. Taylor J. Nonfusion technologies of the posterior column: a new posterior shock absorber. Presented at the International Symposium on Intervertebral Disc Replacement and Non-Fusion Technology. Munich, May 3–5, 2001

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30. Taylor J, Ritland S. Technical and anatomical considerations for the placement of a posterior interspinous stabilizer. In: Mayer HM (ed) Minimally invasive spine surgery. Berlin: Springer, 2006:466–475

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31. Stoll TM, Gilles Dubois G, Schwarzenbach O. The dynamic neutralization system for the spine: A multi-center study of a novel non-fusion system. Eur Spine J

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2002;11(Suppl. 2):S170-S178

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32. Grob D, Benini A, Junge A, et al. Clinical experience with the Dynesys semirigid fixation system for the lumbar spine: surgical and patient-oriented outcome in 50

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cases after an average of 2 years. Spine 2005;30:324–331

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33. Palmer S, Mahar A, Oka R. Biomechanical and radiographic analysis of a novel, minimally invasive, extension-limiting device for the lumbar spine. Neurosurg Focus

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2007;22:1–6

34. Ploumis A, Christodoulou P, Kapoutsis D, et al. Surgical treatment of lumbar

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spinal stenosis with microdecompression and interspinous distraction device insertion. A case series. J Orthop Surg 2012;7:35

35. Gonzalez-Blohm SA, Doulgeris JJ, Aghayev K, et al. Biomechanical analysis of an interspinous fusion device as a stand-alone and as supplemental fixation to posterior expandable interbody cages in the lumbar spine. J Neurosurg Spine 2013 Nov 29 [Epub ahead of print]

36. King D. Internal fixation for lumbosacral fusion. J Bone Joint Surg 1948;30A: 560-565

37. Boucher HH. A method of spinal fusion. J Bone J Surg Br 1959;41-B:248–259

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38. Magerl F. Stabilization of the lower thoracic and lumbar spine with external skeletal fixation. Clin Orthop 1984;189:125–41

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39. Ferrara LA, Secor JL, Jin BH, et al. A biomechanical comparison of facet screw fixation and pedicle screw fixation: effects of short-term and long-term repetitive

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cycling. Spine 2003;28:1226–1234

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40. Vanden Berghe L, Mehdian H, Lee AJ, et al. Stability of the lumbar spine and

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method of instrumentation. Acta Orthop Belgica 1993;59:175-180

41. Heggeness MHO, Esses SI. Translaminar facet joint screw fixation for lumbar

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and lumbosacral fusion: a clinical and biomechanical study. Spine 1991;16(6

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Suppl):S266-9

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42. Mahar A, Kim C, Oka R, et al. Biomechanical Comparison of a Novel Percutaneous Transfacet Device and a Traditional Posterior System for Single Level

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Fusion. J Spinal Disord Tech 2006; 19(8):591-4

43. Montesano PX, Magerl F, Jacobs RR, et al. Translaminar facet joint screws. Orthopedics 1988;11:1393-1397

44. Jacobs RR, Montesano PX, Jackson RP. Enhancement of lumbar spine fusion by use of translaminar facet joint screws. Spine 1989;14:12-15

45. Humke T, Grob D, Dvorak J, et al. Translaminar screw fixation of the lumbar lumbosacral spine. A five-year follow-up. Spine 1998;23:1180-1184

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46. Grob D, Humke T. Translaminar screw fixation in the lumbar spine: technique, indications, results. Eur Spine J 1998;3:178-186

47. Siddiqui M, Nicol M, Karadimas E, et al. The positional magnetic resonance

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imaging changes in the lumbar spine following insertion of a novel interspinous

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process distraction device. Spine 2005;30:2677–2682

48. Siddiqui M, Karadimas E, Nicol M. Influence of X-Stop on neural foramina and

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spinal canal area in spinal stenosis. Spine 2006;31:2958–2962

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49. Modic MT, Steinberg PM, Ross JS, et al. Degenerative disk disease: assessment of changes in vertebral body marrow with MR imaging. Radiology 1988;166 (1 Pt

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1):193–199

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50. Aprill C, Bogduk N. High intensity zone: a diagnostic sign of painful lumbar disc

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on magnetic resonance imaging. Brit J Radiol 1992;65:361–369

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51. Pfirrmann CW, Metzdorf A, Zanetti M, et al. Magnetic resonance classification of lumbar intervertebral disc degeneration. Spine 2001;26:1873–8

52. Rolfe KW, Zucherman JF, Kondrashov DG, et al. Scoliosis and interspinous decompression with the X-STOP: prospective minimum 1-year outcomes in lumbar spinal stenosis. Spine J 2010;10:972–978

53. Barbagallo GM, Olindo G, Corbino L, Albanese V. Analysis of complications in patients treated with the X-Stop Interspinous Process Decompression System: proposal for a novel anatomic scoring system for patient selection and review of the literature. Neurosurgery 2009;65(1):111-119; discussion 119-20

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54. Kim DH, Tantorski M, Shaw J, et al. Occult spinous process fractures associated with interspinous process spacers. Spine 2011;36:E1080–E1085

55. Bonaldi G, Bertolini G, Marrocu A, et al. Posterior vertebral arch cement

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augmentation (spinoplasty) to prevent fracture of spinous processes after interspinous

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us

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spacer implant. Am J Neuroradiol 2012;33:522–528

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FIGURE LEGENDS

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Figure 1

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A tension band gives an additional moment resisting bending, thus reducing compression on the anterior annulus and tension on posterior annulus and facets. The

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ICR (green circle) is pulled dorsally.

Figure 2

The rigid interspinous spacer moves the ICR posteriorly, modifying the loads on the different parts of the S.U. (see text).

Figure 3 In A an image of the X-Stop, depicting the lateral wings, the central spacer, and the tissue expander that pierces the interspinous ligament. In B the device deployed in the interspinous ligament, with the wings limiting lateral migration. Page 30 of 44

Figure 4 The screw-based PercuDyn system. Titanium screws are anchored in the S1 pedicles

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(A), while the polycarbonate-urethane heads of the screws support and cushion the inferior facet complex of the upper L5 metamer (B-C-D), limiting its extension and

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unloading the disc.

Figure 5

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Posterior facet screw fixation. In A the “true transfacet” technique, as proposed by Boucher in 1959, entailing use of two screws (for each level, one per side), traversing

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the facets vertically from medial to lateral. In B the “translaminar transfacet” technique as proposed by Magerl in 1984. Compared to Boucher’s proposal, screws

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spinous process.

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are significantly longer because the entry point is at the base of the contralateral

Figure 6

Picture outlining facet dowels entering the zygapophyseal synovial cavities. The latter are first prepared with drill and reamers to expose the subcondrale cancellous bone, thus favoring subsequent fusion of the joints. An oversized dowel is then either screwed in (as in picture depicting threaded dowels) or impacted into the joint, thereby ensuring a tight press fit that will fix the dowel in place.

Figure 7 In A pre-operative sagittal MR showing segmental L4-L5 stenosis due to posterior annulus bulging (arrow) and enfolding of the yellow ligament (arrowhead). In B, after deployment of a rigid interspinous device, annulus and yellow ligament are Page 31 of 44

stretched, with reopening of the periradicular CSF space (arrows) e relief of cauda equine compression.

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Figure 8

T1-weighted (A) and T2-weighted (B) images of a L4-L5 disc space, depicting an

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anterior, partially inflammatory (mixed Modic 1 and 2 with prevalence of the

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edematous, grade 1 aspect ) osteocondrosis, affecting endplates and surrounding cancellous bone. A posterior, median bulging of the annulus fibrosus is associated. A

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double-action interspinous device is indicated: a tension band will limit flexion and anterior disk load, while the interspinous component will partially unload the

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posterior part of the disk.

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Figure 9

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Sagittal (A) and axial (B) views of a hyperintensity zones (HIZ) in the posterior

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aspect of the lumbar disc, representing tears and granulation tissue (arrows). Note in B (axial view) the T2-hyperintense crescent delaminating the hypointense fibers of the posterior annulus.

Figure 10 A / B

In A, the rigid, percutaneous Aperius interspinous spacer reduces the degenerative spondilolisthesis and increases the height of the posterior aspect of the disc space. In B (differente patient), a post-operative CT control clearly shows widening of the sagittal diameter of the spinal canal, together with an increase of the posterior height of the disc.

Page 32 of 44

   

 

 

 

 

 

TABLE 

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(1) Allergy to titanium or titanium alloys (or any component of the implant); 

(2) Spinal anatomy or disease that would prevent implantation of the device or cause the device 

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to be unstable in situ, such as: 

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a)  fracture  b)  significant scoliosis with a Cobb angle >25° 

c)  degenerative spondylolisthesis greater than grade 1.0 on a scale of 1 to 4 

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(3) Ankylosed segment at the affected level(s); 

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d)  true spondilolisthesis due to isthmic lysis (because the action of the device would widen and  aggravate the lysis and not modify the degree of the olysthesis) 

(4) Cauda equina syndrome (defined as neural compression causing neurogenic dysfunction of 

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the bowel or bladder); 

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(5) Active systemic infection or infection localized to implantation site;  (6) A diagnosis of severe osteoporosis, defined as bone mineral density (from dual‐energy X‐ray 

 

 

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absorptiometry or a comparable study) in the spine or hip that is >2.5 standard deviations below  the mean of normal adult values. 

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