The Development of Cage Technology and Minimally Invasive Spine Surgery

The spinal implant market is experiencing a surge of interbody fusion devices, the most exciting new technology in decades. Industry commentators have projected up to 30% penetration of these device in the market by the year 2001. Minimally invasive techniques to accomplish spinal fusion will be of primary interest in the coming years, as the surgical community strives to reduce costs and improve clinical success. Bone graft materials and biologic bone growth enhancements will also play an important role in the future spine market, as the market evolves to meet the clinical demands of spinal fusion.

Difficulties in obtaining intervertebral fusions in the 1980's led to early investigations of a new breed of spinal implants and techniques. Spinal fusion cages, or interbody fusion devices were developed to increase immediate stability and promote reliable solid bony fusion. The apparent mechanical advantage to these devices is stabilization of the intervertebral space by placing the outer annulus in tension and the device in compression, creating motion segment stability through the soft tissues instead of relying on bony purchase. Cages have been under development for nearly a decade, with a dramatic increase in both research and development activities in just the last five or six years.

Since September 1996, two different fusion cages have been approved. Both devices are used in pairs and are approved for treatment of symptomatic degenerative disc disease by anterior (BAK only) or posterior interbody fusion of one or two levels in the lumbar spine from L2 to the sacrum. Reports submitted to the FDA describe fusion rates of 90.6% to 96%, which is better than traditional fusion methods which can be as low as 60%. Several other fusion implant designs are undergoing experimental, investigational, and clinical trials, and may gain FDA approval in the near future.

Video-assisted techniques were introduced to endoscopic methods nearly a decade ago, with the first anterior endoscopic lumbar discectomy reported in 1991. Since then, applications for spinal surgery have widened. Recent reports of laparoscopic methods for anterior interbody fusion using fusion cages have been encouraging. the main advantages to laparoscopy are improved visualization of vertebral structures, decreased blood loss and infection potential, smaller incisions and reduced scarring, reduced post-operative pain, shorter hospitalization, shorter rehabilitation time, and overall reduced medical costs. One disadvantage of minimally-invasive techniques in the spine is that new advanced technical skills must be acquired and frequently practiced for the surgeon to be effective. Surgeon training in video-assisted minimally-invasive techniques is therefore crucial for future development of thoroscopic, endoscopic, and laparoscopic spinal procedures for interbody fusion. Development of coordination instruments and implants is also necessary for successful application of the technique. As new innovations in video technology, instruments and surgical technique continue to evolve, minimally invasive applications in the spine may become preferable alternatives to a variety of open surgical procedures.

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