BBI Contributing Editor
NEW YORK – The Global Symposium on Motion Preservation was held at the New York Marriott Marquis in May, sponsored by the Spine Arthroplasty Society (North Palm Beach, Florida). It was organized to provide a venue on the benefits of non-fusion technology as a means for spinal stabilization. The society provides a forum for the review of new techniques that may provide a significant change in the treatment and resolution of degenerative disc disease. Presentations focused on non-fusion techniques and minimally invasive technology for total disc replacement, nucleus replacement, dynamic stabilization, motion preservation technologies, facet joint replacement as well as annulus and nucleus repair and regeneration. There were 1,600 attendees at the symposium, many coming from other countries.
Spinal fusion surgery (arthrodesis) is commonly performed for restoring function and relieving pain associated with degenerative disc disease and low back pain conditions. It entails removing the disc and creating a solid bony mass using an alternative bone source. A principal drawback is that it results in motion restrictions, a condition that worsens as discs adjacent to the fused vertebrae also degenerate.
About 30% of fusion patients will suffer degeneration of one or more additional discs within a decade after surgery. This limitation has led to the emergence of a host of new spinal product companies that are developing non-fusion devices which offer the promise of significant improvement in pain reduction along with near full range-of-motion. According to Standard and Poors (New York), the spinal market represents $2.4 billion and is experiencing a growth rate of more than 20% annually.
More than 5 million Americans suffer with chronic back pain, making it the leading cause of lost workdays. About 10% of all patients that present with back pain undergo some form of surgical intervention. While there are varying causes of lower back pain, an estimated 75% of these cases are associated with degenerative disc disease. An estimated 1.1 million spine surgeries are performed in the U.S. each year, which include about 500,000 patients who undergo spinal fusion procedures.
Lumbar and cervical artificial discs
Many spinal product companies are developing disc and nucleus replacement devices. The Charité artificial disc from DePuy Spine (Raynham, Massachusetts), a subsidiary of Johnson & Johnson (New Brunswick, New Jersey), is the first and only disc replacement product currently marketed in the U.S. It received clearance from the FDA in October 2004 as an alternative to lumbar spinal fusion.
Synthes Spine (West Chester, Pennsylvania), a subsidiary of Synthes-Stratec (Oberdorf, Switzerland), is developing the ProDisc lumbar total disc and the ProDisc-C cervical total disc. The discs are comprised of two alloy endplates and a polyethylene core. They utilize modular designs to enable surgeons to customize the devices to each patient.
Cervitech (Rockaway, New Jersey) has initiated clinical trials in the U.S. for its PCM (porous coated motion) artificial cervical disc. The device is being marketed in Europe. It is a two-part cobalt chrome and UHMWPE total disc replacement that is designed to allow translational motion in an arc consistent with the natural motion of the cervical spine segment. Its press-fit osteoconductive endplate surfaces are intended to enhance fixation of both halves to the respective vertebrae. The large, anatomically designed cobalt chrome endplates are shaped to maximize loading in the more dense lateral vertebral surfaces.
Nexgen Spine (Whippany, New Jersey) is developing a total disc prostheses for both the lumbar and cervical spine that are constructed of elastomeric polycarbonate polyurethanes having multidurometer designs (i.e., polymers of differing hardness) that closely reproduce the mechanical properties of the natural disc and provide shock absorption.
Stryker Spine (Allendale, New Jersey), a subsidiary of Stryker (Kalamazoo, Michigan), is conducting clinical trials in the U.S. of its FlexiCore artificial lumbar spinal disc. It is a metal-on-metal cobalt chrome device that is inserted as a single unit with a ball-and-socket joint linking the upper and lower portions. The domed baseplate surfaces are shaped to approximate the concavities of the vertebral body endplates, and are coated with titanium plasma spray to enhance bony ingrowth for fixation.
Dr. Thomas Errico, associate professor of orthopaedics and neurosurgery at New York University’s Hospital for Joint Diseases (New York), is the inventor and a clinical investigator of the FlexiCore disc. He also is developing CerviCore, a cervical artificial disc.
Pearsalls Ltd. (Taunton, UK) is developing the Neodisc artificial cervical disc, a composite of an elastomeric core encapsulated by a textile structure. It is designed to mimic the biomechanical properties of a natural disc. Results of clinical trials at the Royal Orthopaedic Hospital (Birmingham, UK) were presented at the symposium by Dr. Andre Jackowski, a co-inventor of the device.
Vertebron (Stratford, Connecticut) is developing both cervical and lumbar artificial discs and anticipates initiating clinical trials in early 2006 and 2007, respectively. The cervical motion preservation device is designed to allow for offset, independent screw placement to accommodate adjacent level procedures. The lumbar motion preservation device will be offered in both an unconstrained and semi-constrained version to allow for intra-op and post-op flexibility. Porous titanium endplate surfaces permit bony ingrowth for added implant stability of these devices.
The company currently markets pedicle screws, a semi-constrained cervical plate and, via distributors, structural allografts and demineralized bone matrices.
LDR Spine (Austin, Texas), a subsidiary of LDR Medical (Troyes, France), markets outside the U.S. a line of fusion and non-fusion products. Its Mobidisc artificial lumbar disc and Mobi-C artificial cervical disc are sold internationally and have been used in clinical trials in more than 400 patients.
Dynamic Spine (Mahtomedi, Minnesota) is a development-stage company founded by Dr. Glenn Buttermann that is developing an intervertebral prosthetic disc (IPD) and specialized instrumentation. The IPD consists of fixation components that are implanted within the vertebral body adjacent to the disc and a compressible (spring) component implanted within the intact annulus that acts to restore disc height and to absorb shock. A system of specialized instrumentation is used to implant and adjust the device intraoperatively, to accommodate to the patient’s size and anatomy, and to restore the biomechanics and stability of the motion segment. A poster presentation at the symposium provided results of lumbar disc loading in animal trials.
Theken Disc (Akron, Ohio) featured the eDisc, a microelectronic module which uses wireless telemetry data collection to assist a surgeon in its placement and for postoperative patient management. The eDisc is being developed to restore the kinematics of the natural disc as well as its nonlinear elasticity. It utilizes a proprietary elastomeric polymer that is tailored to endure the harsh motions and loads of the lumbar spine.
Globus Medical (Phoenixville, Pennsylvania) has initiated a clinical trial for its Secure-C cervical artificial disc under a recently granted IDE by the FDA. More than 15 centers will participate in this trial.
Posterior dynamic stabilization devices
There are two types of posterior dynamic stabilization devices, interspinous spacers and pedicle screw-based systems.
The Dynesys system from Zimmer Spine (Edina, Minnesota), a subsidiary of Zimmer (Warsaw, Indiana), is an alternative to spinal fusion. It uses flexible materials to stabilize the affected lumbar region while preserving the natural anatomy of the spine. The Dynesys system has been marketed in Europe for several years but is not yet approved for sale in the U.S. It is being evaluated in clinical trials for treating spinal stenosis.
St. Francis Medical Technologies (Alameda, California) is developing the X-Stop non-fusion implant for patients suffering with degenerative lumbar spinal stenosis and Grade 1 spondylolisthesis. It is being clinically evaluated under an investigational device exemption (IDE) from the FDA.
Impliant (Milford, Connecticut) is developing posterior motion-preserving spinal implants. Its TOPS System is a mobile posterior implant that is designed to treat spine-related leg and back pain. It stabilizes but does not fuse the affected vertebral level to alleviate pain stemming from degenerative facet arthrosis, spondylolisthesis and spinal stenosis.
Surgeons perform a decompression and place four pedicle screws to connect the TOPS device, thereby enabling patients to return to near-normal twisting, turning and bending activities. The TOPS System is comprised of titanium plates and an articulating polyurethane construct.
Applied Spine Technologies (New Haven, Connecticut) is developing the M-Brace, a posterior dynamic stabilization device designed to support the spine while preserving motion and flexibility. It was developed in the laboratory of professor Manohar Panjabi, of the departments of orthopedics and rehabilitation, and mechanical engineering at Yale University (New Haven, Connecticut).
The M-Brace utilizes pedicle screw vertebral anchors and attaches them to a mechanism with flexible joints. The device support varies as the spine moves, with maximum support in the center of the range of motion. It offers the advantages over current spinal fixation products of a less invasive and less traumatic procedure, maintenance of normal spine motion and disc function, and the potential to prevent or slow adjacent segment disease.
The company plans to enter clinical trials in the U.S. and Europe early next year.
Archus Orthopedics (Redmond, Washington) recently reported completion of the first clinical trials in Europe of its Total Facet Arthroplasty System (TFAS), a spinal implant designed to treat spinal stenosis. It replaces the degenerative facet joints with a prosthetic joint implant intended to restore stability and normal motion to the spine, eliminating the need for fusion. Traditionally, patients with spinal stenosis undergo decompression laminectomy surgery, which is often accompanied by spinal fusion. The TFAS device received the CE mark in March, but is not yet being sold in Europe.
Facet Solutions (Logan, Utah) is developing a system of implants and instrumentation to allow a spine surgeon to perform facet joint arthroplasty. The company plans to soon begin trials in the U.S. and in foreign countries.
The prospect for combining non-fusion products (such as a disc nucleus replacement and a posterior dynamic stabilization device) appears to be gaining adherents and was the subject of The BBI Newsletter’s limited survey among 15 spinal surgeons and leading spinal product companies. A majority of surgeons interviewed responded favorably to the future potential of posterior non-fusion solutions with most showing great enthusiasm.
Among the marketers of spinal products, the prevailing view was one of caution, expressing the need for clinical trials to substantiate the benefits (flexibility and longevity) of posterior dynamic devices. These devices were seen as having the potential to capture a segment of the patient population that would currently be candidates for spinal fusion.
Nucleus replacements under development
Many companies are developing products for replacing only the nucleus (nucleus pulposus) of a herniated disc, rather than the entire disc. Ultimately, the results of clinical trials will determine the efficacy of any of these nucleus replacements.
Raymedica (Minneapolis) presented short- and long-term follow-up clinical trial results for its PDN–SOLO prosthetic disc nucleus. The device is composed of a hydrogel core in a flexible, inelastic, woven polyethylene jacket. The hydrogel undergoes a cyclic swelling and shrinking, depending on the load. The PDN-SOLO is being marketed outside the U.S. It is currently being redesigned.
Disc Dynamics (Eden Prairie, Minnesota) presented one-year follow-up results for its Dascor Disc Arthroplasty System, a nucleus replacement technology for the lumbar spine that recently received CE-mark approval. The company was formed as a spinoff from Advanced BioSurfaces (Minnetonka, Minnesota) to develop curable polymer technology for spinal applications.
The Dascor device is delivered under controlled pressure via an injection pump and cures in situ. The polyurethane polymer fills the void left by removal of the nuclear material. The Dascor device offers an alternative to spinal fusion by preserving disc anatomy and restoring stability and motion to the spine. An IDE has been filed with the FDA for the Dascor device.
Stryker Howmedica Osteonics (Rutherford, New Jersey), another subsidiary of Stryker, is developing the Aquarelle Hydrogel Nucleus. It is composed of a polyvinyl alcohol material. Biomechanical testing indicates that it has a performance similar to the intact nucleus. Some implants have been implanted in humans in Europe, and baboon studies have been initiated in the U.S.
Replication Medical (Cranbury, New Jersey) is clinically testing its NeuDisc spinal disc nucleus replacement material. It is composed of a biomimetic phase-separated hydrogel designed to mimic the structure and physical properties of soft tissue. Multiblock copolymers are organized into clusters that link the polymer chains into a 3-D network similar to that found in native connective tissues and that possesses the mechanical properties of the nucleus pulposus. The hydrogel is inserted through a cannula and, after implantation, swells up in about 12 hours. Clinical trials are under way in Europe.
CryoLife (Kennesaw, Georgia) is testing BioDisc, a protein hydrogel that is injected into the nuclear cavity in fluid form and rapidly hardens into a pliable support solid in the disc space. BioDisc has the same composition as CryoLife’s BioGlue surgical adhesive. It is prepared at the time of use by mixing bovine serum albumin with glutaraldehyde which serves as a cross-linking agent. CryoLife will soon be selling BioDisc in the UK and plans to initiate clinical trials in the U.S. in order to gain marketing approval in this country.
Synthes Spine is developing polymer-based hydrogels as injectable nucleus replacement materials. The hydrogels are liquid at room temperature and solidify inside the disc at body temperature.
Spine Wave (Shelton, Connecticut) is developing NuCore, an injectable protein-based material for replacement or augmentation of a degenerated disc. It is comprised of a binary formula of a chemical cross-linker and a protein copolymer solution that cures rapidly when injected into the disc nuclear space, forming a durable and adhesive hydrogel. The bolus of cured NuCore material is larger than the surgical entry site and forms a mechanical barrier to extrusion.
Clinical trials are under way in Europe for use of NuCore in microdiscectomy. The company plans to initiate a trial in the U.S. later this year for the use of NuCore to treat degenerative disc disease.
TranS1 (Wilmington, North Carolina) plans to start pilot studies this year on percutaneous nucleus replacement (PNR) and percutaneous disc reconstruction (PDR) devices for preserving motion in the lumbar spine. In January, the company launched its Axial Lumbar Interbody Fusion (AxiaLIF) System, which provides the least invasive approach to lumbar fusion with greatly reduced recovery time.
Using AxiaLIF, the lumbar spine is accessed through a percutaneous opening in the sacral bone, thereby avoiding the need for cutting through muscles and ligaments. This approach allows patients to be discharged from the hospital the day after surgery.