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Novel spine technology supported by material evolution: extensive data seem to support solid outcome for Alphatec Spine's new orthopedic technology using Invibio's PEEK polymer.

The constant search for improved materials is one of the axioms in orthopedic implant manufacturing. As is the case with many other companies, product development professionals at Carlsbad, CA-based Alphatec Spine, Inc. continually work to find innovative solutions to age-old orthopedic problems. In September, the company gained 510(k) clearance from the FDA for its Novel Cervical Interbody implant. Alphatec, a developer of spinal fusion technology, is among one of a few companies in the medical device industry to achieve regulatory approval for a polyetheretherketone (PEEK)-based cervical interbody fusion (IBF) device. Used to treat cervical disc damage, the Novel Cervical Interbody spacer is implanted surgically during an anterior cervical discectomy and fusion (ACDF) procedure. The IBF-designated device is manufactured with PEEK- OPTIMA polymer developed by Invibio, a West Conshohocken, PA-based provider of high-performance biomaterials used in varied medical device applications. One of the reasons Alphatec chose the material is that it is highly radiolucent and provides improved visualization to guide implant placement and optimize post-operative assessment of surrounding tissue and fusion progress.

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"The Novel Cervical Interbody System, especially when used in conjunction with Alphatec's Trestle Anterior Cervical Plating System and other existing products, offers surgeons a complete anterior solution for cervical spine that is far superior to and unlike anything available to this point," said Constantine Toumbis, MD, PhD, a neurosurgeon specializing in spine surgery. Dr. Toumbis was involved in the development of the Novel Cervical Interbody implant.

PEEK-OPTIMA has been used in numerous regulatory-approved spinal devices since it was introduced in 1999, and since then has gathered a proven history of long-term implantation. Key capabilities and benefits of the polymer for spinal fusion applications include: controlled imaging for implant placement verification and post-operative assessment; bone-like modulus encourages load sharing, minimizes stress shielding and stimulates bone healing and growth; high compressive strength to meet load requirements; and excellent creep resistance to maintain implant shape and specifications. Additionally, PEEK-OPTIMA withstands repeat sterilization via conventional processes without adverse affect on mechanical properties, performance or biocompatibility. (Editor's note: For more information on sterilization in orthopedics, read this issue's feature article on page 40.)

The PEEK-OPTIMA-based Novel Cervical Interbody device is the most recent product in Alphatec's portfolio of solutions for the cervical spine. Alphatec used its rigorous New Product Development (NPD) process to successfully launch the new interbody system in fewer than nine months, from concept to market. The eight-phase NPD process ensures that the final product design meets the surgeons' needs and has been fully validated to meet the intended clinical use. Offered in three sizes, the device is designed to receive a maximum amount of grafting material and optimize endplate contact. System features include enhanced imaging capabilities, 7-degree lordotic angle, multiple footprint options to accommodate anatomical variances, a large contact area to resist subsidence, a large graft area for orthobiologic material, a range of sizes, and heights from 5-12 mm. The Novel Cervical Interbody system complements existing Alphatec products, including the Trestle Anterior Cervical Plating System and the Solanas Posterior Cervical Fusion System.

Interbody fusion technologies, including ACDF (used to treat a bulging, herniated or otherwise damaged disc in the cervical region) and other surgical procedures, have proven successful in treating many degenerative spinal conditions. The total interbody market in the United States is estimated at more than $930 million this year and forecasted to approach $1 billion by 2010. In 2008, cervical interbody procedures in the United States are estimated to account for 49% of all interbody procedures performed.

Alternative to Bone

New surgical approaches and techniques continue to evolve, spurred in part by innovative medical device companies such as Alphatec. Focused on the design, development, manufacturing and marketing of products for the surgical treatment of the spine disorders, Alphatec is recognized for its "surgeon's culture," emphasizing collaboration with spinal surgeons to conceptualize, design, co-develop and rapidly deliver customized solutions to meet critical surgeon/patient needs.

When Alphatec designers sought to define the cutting-edge properties and capabilities that would define the next generation of their innovative Novel product line, they turned to Invibio's PEEK-OPTIMA polymer.

With record numbers of baby boomers approaching retirement age, the volume of spinal surgeries is likely to increase. During the last decade, as spinal surgeons recognized the value of its radiolucent properties to visualizing post surgical fusion, use of PEEK polymer-based devices to aid cervical and lumber interbody fusion has increased dramatically. Almost all medical device companies operating in today's global spinal fusion market currently offer or are in the process of developing PEEK-based cages, vertebral body replacement devices and/or spacers. More than two million devices manufactured with PEEK-OPTIMA polymer have been implanted in patients to date. Lumbar spinal fusion was an early adopter of implantable PEEK-OPTIMA, where it is widely used in place of titanium as the predominate material for cages and spacers. The polymer's radiolucent properties, compatibility with magnetic resonance imaging and bone-like modulus contributed to its acceptance in lumbar spinal fusion. More recently, the versatile polymer has been increasingly used in cervical spinal fusion devices, as evidenced by Alphatec's Novel Cervical Interbody device and others. The increasing interest in implantable PEEK-OPTIMA is driven by several factors. In addition to the material and physical properties of the polymer, it also avoids the limitations associated with autograft harvest (a procedure to harvest bone graft material from the patient), and the supply and quality issues associated with allograft bone. In contrast to bone, there is an assured, consistent, and completely traceable supply of the polymer. Studies also suggests that PEEK-based devices offer lower complication rates compared to autograff.

Data Supports PEEK Clinical Fusion Efficacy

A substantial body of published clinical data (including the studies that follow) supports PEEK's efficacy in cervical fusion.

* Study #1: A comparison of changes over time in cervical foraminal height after tricortical iliac graft or polyetheretherketone cage placement following anterior discectomy. This retrospective study was undertaken to evaluate and compare cervical foraminal height changes after anterior cervical discectomy and fusion following the placement of a tricortical graft or a PEEK cage.

Methods: Thirty patients underwent anterior cervical microdiscectomy and free bone graft (FBG) insertion at 46 levels via the Smith-Robinson technique; the FBG was harvested from the right iliac crest. Another 35 patients underwent the same procedure, with fusion provided by the insertion of PEEK intervertebral cages at 41 levels. Fusion status and the C2-7 Cobb angle, interspace height, and foraminal height changes were observed on anterior, lateral, and oblique radiographs obtained at the 18-month follow-up examination. There were no differences between the groups with regard to clinical recovery, fusion status, and Cobb angle.

Results and Discussion: During the first post-operative month, significant interspace height reduction was observed in the FBG group; the mean heights ([+ or -] standard deviation) of the foramina were 8.2 [+ or -] 2.7 mm preoperatively, 10.8 [+ or -] 2.6 mm on postoperative day two, and 8.2 [+ or -] 1.5 after 18 months of follow-up for this group. In the PEEK cage group, the mean heights ([+ or -] standard deviation) of the foramina were 8.4 [+ or -] 2.8 mm preoperatively, 10.3 [+ or -] 1.1 mm on postoperative day 2, and 9.6 [+ or -] 1.2 after 18 months of follow-up. In the PEEK cage group, the foraminal height increase was significantly preserved at six-, 12- and 18-month follow-up. At the 18-month follow-up examination, there were no differences between the groups with regard to clinical recovery, fusion status and Cobb angle.

Conclusions: Foraminal height increase and nerve root decompression was sufficient in both groups. This study suggests that PEEK cages may provide sufficient preservation of foraminal height even one and a half years after the operation.

* Study #2: Solis cage (PEEK) for anterior cervical fusion to evaluate preliminary radiological results specific to fusion and subsidence. Study 2 was a retrospective radiological review of the first 15 consecutive cases of single-level anterior cervical interbody fusion using the PEEK-based Solis cage for cervical spondylotic radiculopathy or myelopathy utilizing anteroposterior and lateral radiographs taken immediately post surgery and again at three-, six-, 12-, and 24-month intervals. The post-surgical follow-up range was 12 to 35 months (average 18 months).

Methods: Anteroposterior and lateral radiographs were obtained immediately post surgery and at subsequent intervals of three, six, 12 and 24 months to measure anterior disc height (ADH), posterior disc height (PDH), interbody height ratio, distance between the posterior margin of the cage and the posterior wall of the vertebral body, and interbody angle. Trabecular continuity, bone bridging across disc space, and sclerosis at the vertebral end plates on both sides were evaluated to assess fusion. Time for fusion, subsidence, segmental sagittal alignment of the operated segment, and presence/absence of migration of the cage were the assessment parameters. Data analyzed using the MannWhitney non-parametric test.

Results and Discussion: Fusion was evident at three to six months post-surgery in all cases except one (93.33% fusion rate at six months); as of the last follow-up, fusion was maintained in all cases. Significantly greater than their respective pre-operative values, immediate postoperative ADH and PDH values measured immediately post operation were maintained through follow-up; when the follow-up radiographs were compared with the immediate postoperative X-rays significant subsidence was noted. No migration or extrusion of the cage was found as of the last follow up.

Conclusions: High fusion rate, low subsidence, stability, and facilitation of radiological assessment are attributable to the physical properties of the PEEK material as well as cage design.

* Study #3: Treatment of multilevel cervical fusion using PEEK cages to replace plate function. Plate and screw fixation usually is necessary to maintain spinal curvature and increase graft fusion rate in multilevel cervical discectomy, but complications, including screw breakage, screw pullout, esophagus perforation, and cord or nerve root injury can result. This study investigated the use of PEEK cages to replace plate function in multilevel cervical fusion.

Methods: A total of 180 consecutive cases of multi-level cervical degenerative disease studied were grouped as follows: Group A (60) patients underwent anterior discectomy and PEEK fusion; Group B (50) patients underwent anterior discectomy, autogenous iliac crest graft (AICG) fusion and plate fixation; Group C (70) patients underwent anterior discectomy and AICG only. X-rays of the cervical spine were taken every three months until fusion was complete, and the lateral X-ray view was used to measure spinal curvature. Graft complications were evaluated by radiographic findings (graft collapse, nonunion, dislodged graft). Functional/working status evaluated by Prolo scale; blood loss and operation time were recorded.

Results and Discussion: Total complication rates were 3.3% (Group A), 16% (Group B), and 54.3% (Group C); however, only 37.1% of patients (13/35) with graft complications had clinical symptoms (severe neck pain, radicular pain, or neurologic deficits). The fusion rate was higher and the time to fusion sooner in Groups A and B than Group C, p < 0.001 ([x.sup.2] test), demonstrating that the PEEK cage performed statistically better than did the plating group specific to total complications, p < 0.05. The major graft complications in Group C (AICG without plating) were graft collapse and nonunion; screw pullout and screw breakage were the main causes of plating complication. Minimum blood loss occurred in Group A, p < 0.05. Spinal lordosis increased by a mean of 4.61 [+ or -] 2.93 mm and 1.68 [+ or -] 5.02 mm in Groups A and B, respectively, whereas in Group C, spinal kyphosis increased by a mean of -2.09 [+ or -] 4.77 mm. Group A demonstrated a statistically better Prolo scale than did Group C, p < 0.0001.

Conclusions: Both the PEEK cage without plating (Author's note: The FDA has not approved interbody devices to be used without supplemental fixation) and AICG with plating are good methods for interbody fusion in multilevel cervical degenerative diseases. Both approaches increase spinal lordosis and graft fusion rate and result in fewer surgical complications. However, having demonstrated the lowest complication rate and the least amount of blood loss, the PEEK cage is preferred for multilevel fusion.

Published Literature Highlights Advantages

In its review of published literature specific to PEEK cages and spacers in cervical spine fusion applications, Spinal News International reported that PEEK cages offer a clinical advantage over autogenous iliac bone graft (AIBG) alone or AIGB with plate and screw stabilization across all endpoints measured: (1)

* Improved spinal alignment and geometry

* Reduced hospital stays and decreased blood loss

* Decreased complication rates

* Good/excellent functional outcomes

* Improved patient satisfaction

* Excellent fusion rates

Market Reflects Record Volumes of Aging Spines

The global orthopedic implant market, including spine, continues its rapid evolution. In the United States, spinal implants and instrumentation product sales totaled $4.1 billion in 2007. (2) Expected to rise by 8.9% annually, overall US demand for orthopedic implants is predicted to reach $22 billion by 2012. (2)

Over the course of the next two decades, an average of 10,000 baby boomers per day will reach retirement age in the United States. (3) As many of them will discover, most spinal conditions are not caused by injury or other trauma, but by age. Occurring naturally over time, degenerative conditions (including degenerative disc disease, spondylolisthesis and spinal stenosis) are the most common cause of neck and back pain. Beginning in early adulthood, the gradual and progressive process of spinal deterioration, combined with everyday wear and tear, can erode the structural integrity of vertebrae, discs, cartilage and joints, hindering flexibility and limiting functionality. Its load bearing capacity thus compromised, the spine is more susceptible to injury. More than 66% of Americans will experience cervical pain at some time in their lives, and for many, it will not be fleeting. (4) According to the International Association for the Study of Pain, more than 33% of patients with neck pain develop persistent or recurrent symptoms lasting longer than six months. The impact can be significant; some 25% to 30% of the US population report activity limitations resulting from cervical spinal conditions.

Advances in spinal implant technology and allied surgical techniques are forecast to combine with a rise in chronic back conditions to spur US market growth; implants used in spinal fusion and motion preservation surgeries, especially procedures for the repair of vertebrae and degenerative discs, will account for the largest market share and most promising growth opportunities. Patient outcome advantages following implantation of fusion cages, artificial discs and other devices (as compared to drug and physical therapies) will make surgery the preferred option for a variety of spinal deficiencies.

Fusion is the predominant surgical approach in the treatment of degenerative disc disease in the United States. Broadly accepted as a high-performing and versatile alternative to metallic, ceramic, bone and other biomaterials across the spinal fusion community, use of PEEK will enable new and emerging spinal fusion devices and technologies.

PEEK and other innovative biomaterials will continue to play an important role in enabling non-fusion applications designed to promote healing and support natural anatomical movement, through motion preservation and dynamic stabilization.

References:

(1.) "PEEK Cages and Spacers in Cervical Spinal Fusion Applications: A Review of Published Literature," Spinal News International, September 2007

(2.) "Orthopedic Implants to 2012," Freedonia, July 2008

(3.) "Social Security Deluge?" Ed Feulner, Washington Times, July 13, 2007

(4.) "Impact of Neck and Arm Pain on Overall Health Status," Scott D. Daffner, MD; Alan S. Hilibrand, MD; Brett S. Hanscom, MS; Brian T. Brislin, MD; Alexander R. Vaccaro, MD; Todd J. Albert, MD; Spine 28(17): 2030-2035, 2003.

Marc Jarman-Smith, PhD

Invibio, Inc.

Marcus Jarman-Smith, PhD, is a senior project manager with Invibio. His background is in biological, biochemical engineering and product development. His current focus is the interaction and integration of biomaterials for medical devices.
TABLE 1: PEEK-OPTIMA Comparison to Bone for Cervical Fusion

 PEEK-OPTIMA Allograft Autograft

Consistent quality
 and properties [check]
Assured,
 reliable supply [check]
Modulus similar
 to bone [check] [check] [check]
Easily made
 into device [check]
Clinical evidence
 of performance [check] [check] [check]

Graphic courtesy of Invibio.
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Author:Jarman-Smith, Marcus
Publication:Orthopedic Design & Technology
Article Type:Case study
Geographic Code:1USA
Date:Nov 1, 2008
Words:2652
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