| Though most interbody fusion cages are made of titanium, a new material is quickly gaining popularity with surgeons. Polyether-etherketone (PEEK) is a hard radiolucent plastic that is used in conjunction with carbon fiber reinforcement or as pure PEEK. Most manufacturers who use PEEK use radio marker dots so the surgeon can see where the implant meets the vertebral body endplate. Zimmer Spine, Surgicraft, SCIENT’X, and Depuy Spine have all developed lines of interbody fusion devices using PEEK technology.
Zimmer Spine offers the BAK® Vista® Radiolucent Interbody Fusion System. The BAK Vista System is constructed of radiolucent, carbon-fiber reinforced PEEK-OPTIMA® polymer. PEEK-OPTIMA is a product of Invibio, a provider of biocompatible, implantable grade PEEK plastics. Specifically, Invibio's PEEK-OPTIMA polymer is used in the development of implantable medical devices having blood or tissue contact for more than 30 days. PEEK-OPTIMA has an elasticity modulus of 3.6Gpa, which is very close to that of cortical bone. This means that PEEK-OPTIMA optimizes the load transfer between the cage and the adjacent vertebral bodies and reduces the affects of stress shielding on the graft material. This promotes better bone fusion. In addition to spinal cages, PEEK-OPTIMA has been used in suture anchors, spiked washers, surgical screws, femoral implants, and more.
Zimmer’s BAK Vista System is the only approved radiolucent stand-alone implant that provides clear and confident fusion assessment with the proven reliability of the BAK threaded cage design. Due to the system’s PEEK-OPTIMA construction, the BAK Vista allows for unobstructed radiologic visualization and a compressive strength that surpasses average daily load requirements. The design’s carbon-fiber reinforcement contributes to the cage’s overall compression strength and its internal rib design supports stability and long-term usage. Also, the BAK Vista System is based on the same design as the original BAK implant, providing assurance that the system is tried and true.
A second manufacturer that uses Invibio’s PEEK-OPTIMA polymer is Surgicraft. Surgicraft offers STALIF™, a stand-alone anterior lumbar fusion cage. STALIF is the natural evolution of the Hartshill Horseshoe, which has over 10 years clinical success as a stand-alone implant. The radiolucent STALIF cage has a larger medial lateral width to prevent implant sinkage. The larger medial lateral width ensures that the cage sits on the cortical bone at the edge of the vertebral body, rather than on the softer cancellous bone at the core. This results in less sinkage and loss of height and spinal alignment. Also, marking struts offer x-ray imaging for positioning during surgery and for post operative assessments through CT or MRI scans.
SCIENT'X offers the CC interbody fusion cage, which is made of pure PEEK-OPTIMA. Gold wire markers embedded in the matrix enable radiological verification. CC interbody cages facilitate arthrodesis either by an anterior or posterior approach. The shape of CC cages ensures interbody space preservation, thus avoiding collapse of the vertebral end plates. Stabilization is ensured through neutralization of the axial compression forces and through conservation of the interbody space, restoring normal spinal curvature. Also, lordotic-profiled CC cages in association with the posterior assembly facilitates the recovery of lordosis.
Depuy Spine offers the OCELOT™ Stackable Cage System, which provides anterior column support for single or multilevel corpectomies or total vertebrectomies from T1 to L5. OCELOT cages are constructed of PEEK Carbon Fiber Polymer. The cages are stacked to a desired height, accommodating various patient needs. The cages become biomechanically inert over time as the body heals from the procedure. OCELOT cages are available in four footprints: large, medium, small, and extra-small, accommodating both thoracic and lumbar vertebrae. Each footprint comes in 9mm, 12mm, and 24mm, allowing the surgeon to create a construct up to 120mm tall in 3mm increments. The superior and inferior surfaces of each cage have ridges that provide for an interlocking interface and resist pullout, migration, and rotation. The Carbon Fiber Reinforced Polymer material is radiolucent on x-rays, but tantalum marker beads allow radiographic location and orientation.
All the products listed here are manufactured from PEEK because of its similar stiffness to bone and its radiolucency. These characteristics have made PEEK a hot biomaterial for implantable medical devices.
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