43 Static Bending Compression Test Rigid spinal fixation is the current gold standard in the surgical management of lumbar spinal instability. However, it can result in many complications such as nonunion, screw loosening, screw fracture, and flat back syndrome.1,2 Rigid fixation also increases biomechanical stresses on segments adjacent to the fusion level.3 Clinically, the results of several long-term follow-up studies have suggested that spinal fusion might cause deterioration of the adjacent segment.4 For 2 decades, the dominant surgical justification for fusing the painful motion segment has been the concept of instability. Spinal instrumentation has been continuously developing from a rigid system to the more physiological, flexible, and so-called dynamic stabilization. Devices that have been developed for dynamic stabilization include artificial nucleus replacement, artificial disk replacement, and ligamentoplasty. Using ligaments across the pedicle screw system is thought to be the most effective method in dynamic stabilization because it allows for disk unloading and can correct sagittal plane imbalance of the spine. The Graf ligamentoplasty system restricted flexion and was modestly successful, but it increased the load over the posterior annulus.5,6 The Dynesys Dynamic Stabilization System (Zimmer Spine, Inc., Warsaw, IN) system reduced movement in both flexion and extension. However, the plastic cylinder of the Dynesys system is weak and it may prove difficult to unload the disk if the patient achieves a position of lordosis. This has resulted in a search for new material for flexible stabilization in spine surgery, or semirigid metallic dynamic stabilization. Nitinol is an alloy of nickel and titanium that belongs to a class of materials called shape memory alloys. The properties of nitinol alloys are high elasticity and high tensile force, which means they can be used for tension bands posteriorly in the spine surgery.7 Nitinol is biologically and mechanically compatible as an implant. The alloy has a particular propensity for temperature, being flexible at 10°C low and forms a shape at temperatures above body temperature.8–10 The BioFlex rod system has been developed by the author in our hospital. The system consists of a nitinol spring/straight rod and titanium screws. It is well suited for use in the posterior thoracolumbar spine. Currently, the BioFlex rod system is the only semirigid metallic device for dynamic stabilization with or without fusion available for clinical use in Korea. The BioFlex (Bio-Smart Ltd., Songnam-si, Korea) spring rod pedicle screw system is versatile and is indicated for a wide variety of posterior lumbar fusion and dynamic stabilization surgeries: Relative contraindications for use include:
BioFlex Spring Rod Pedicle Screw System
Indications and Contraindications
Advantage of System Components
Description of System Component
Indications and Contraindications
Low back pain from symptomatic degenerative disk disease
Spondylosis and spondylolisthesis in whole grade
Segmental instability
Following destabilizing decompression in a symptomatic canal or foraminal stenosis
Pseudarthrosis
Posterior lumbar interbody fusion and posterior fixation
Correction of degenerative kyphoscoliosis
Prevention of adjacent segment instability
Injury of ligament structures
Deformity correction, including postlaminectomy kyphosis and scoliosis
Trauma
Tumor
Developmentally inadequate pedicles
Active infection
Biomechanical Testing
Operative Techniques
Case Illustrations
DiscussionRelated posts:
Prosthetic Disk Nucleus Partial Disk Replacement: Pathobiological and Biomechanical Rationale for Design and Function
Complications of Lumbar Disk Arthroplasty
Tension Band System
Cervidisc Concept, Six Years Follow-Up and Introducing Cervidisc II: DISCOVERY
Rationale for Dynamic Stabilization
MAVERICK Total Disc Replacement
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