Spine Research With Roentgen Stereophotogrammetric Analysis

For patients in whom a spinal fusion is indicated, the posterior lumbar interbody fusion (PLIF) may be recommended to restore stability to the affected spinal segment1. Pioneered by a Dr.Cloward in the 1940s to treat painful intervertebral discs damaged by degeneration, PLIF involves removal of the entire nuclear portion of the disc and subsequent replacement with multiple blocks of transplanted bone. The purpose of the fusion is to eliminate or reduce the amount of the motion at the affected site, and, therefore, the source of pain.

Four major intervertebral cages have been approved by the Food and Drug Administration (FDA) for use in humans: the Brantigan Interbody fusion Cage, the Ray Threaded Fusion Cage, the Bagby and Kuslich cage, and, most recently, the Trabecular Metal™ Cage. Comprised of 98 percent tantalum and 2 percent vitreous carbon, Trabecular Metal™ has the highest coefficient of friction of any implant material on the market, allowing for optimal initial implant-bone fit. Furthermore, the unique porous structure of Trabecular Metal™ provides significantly more space for tissue ingrowth to occur, facilitating a more cohesive implant-bone interface as well as long-term stability of the implant.

Long-term follow up data on the efficacy of the Brantigan Interbody fusion cage, Ray Threaded Fusion cage, and Bagby and Kuslich cages are limited, with the most rigorous studies (i.e. controlled prospective studies) typically providing outcomes approximately 2 years post-surgery. Overall, these studies show that, while existing intervertebral cages have made significant advances in terms of addressing the disadvantages associated with traditional bone grafting/fixation techniques, problems continue to persist. Through comprehensive and accurate clinical evaluation of the Trabecular Metal™ intervertebral cage, the Research Team hopes to document advances in the PLIF technique, thereby informing current research as well as clinical practice.

The primary goal of the proposed research is to gather data on the clinical efficacy of the Trabecular Metal™ Posterior Lumbar Interbody Fusion (PLIF) cage with pedicle screw instrumentation for the treatment of one-level lumbar spine fusions. Based on this pilot data, we hope to establish a level of acceptable clinical performance for the Trabecular Metal™ cage, a benchmark against which subsequent investigations can be compared.

Direct surgical exploration is considered the most reliable method for accurately determining fusion success, both from a structural and functional perspective, following spinal fusion surgery. Unfortunately, this method is highly invasive, costly and seldom used. Furthermore, surgical exploration does not provide any longitudinal information as to the stability of the implant, including the monitoring of any occurrence of migration.

In contrast, Roentgen Stereophotogrammetric Analysis(RSA)can detect the presence or absence of mobility between intervertebral segments (i.e. functional stability of the fusion) with a high degree of accuracy. RSA is a radiographic technique that uses small tantalum balls implanted into the patient's bone to measure micromotion (<1 mm) at the bone - implant interface, something which is not possible to do reliably using regular x-ray techniques. RSA provides a method for detecting inferior implant designs or cement formulations using only a small number of patients before release of these products into large clinical trials.

RSA has been in use for several decades,and its safety is well documented.A computerized, digital RSA system has recently been installed and calibrated at our center. Its measurement capabilities have been rigorously validated, and it is currently being used to assess a new knee implant design. Expansion of the system to include spine RSA can be easily accomplished.