BBI Contributing Writer

SAN DIEGO, California Neurosurgeons, neuroradiologists and other neurological specialists from around the globe gathered here in late April for the annual meeting of the American Association of Neurological Surgeons (AANS; Rolling Meadows, Illinois). The conference featured a review of years of experience with cerebral aneurysm embolization and updates in techniques for navigation of skull-based surgery. New technologies for the treatment of spinal disk disease were evaluated.

A cerebral aneurysm is an abnormally dilated segment of a blood vessel surrounding the brain. In some cases, the entire blood vessel widens and expands to resemble a balloon-like structure. Several factors can induce the weakening of the blood vessel wall that allows the aneurysm. These include infection, trauma, tumor and abnormal blood vessel development. Cerebral aneurysms occur in 3% to 5% of the general population. They are more common in patients older than 30 and are almost twice as common in women than men. Nearly 25% of all cerebrovascular deaths are due to ruptured aneurysms. The annual incidence of cerebral aneurysm rupture in the U.S. is approximately seven for every 100,000 persons.

Surgeons and neuroradiologists at the AANS meeting described recent work treating cerebral aneurysms. Robert Rosenwasser, MD, presented the work of physicians working at UCLA Medical Center (Los Angeles, California). The authors reported on 11 years of experience embolyzing cerebral aneurysms using the Guglielmi Detachable Coil (GDC) from Target Therapeutics (Fremont, California), acquired by Boston Scientific (Natick, Massachusetts) in 1997 and now known as Boston Scientific/ Target. The device provides the interventionalist the ability to insert a coil into an aneurysm, assess its position and withdraw it if the result is less than satisfactory. Since December 1990, 741 patients harboring 835 aneurysms were treated with GDC embolization. For comparative purposes, the patients were divided into two groups. Group A included patients who underwent treatment in the first five years. Group B included those who underwent treatment in the most recent six years.

Rosenwasser and his associates determined that complete angiographic occlusion was achieved in 56.6% of patients. Overall morbidity/mortality was 8.9%. Recanalization rate (recurrence of the aneurysm) was associated with the size of the dome and neck of the aneurysm. Overall incidence of delayed rupture was 1.4%. The interventionalists noted a desire to better understand the flow and sheer stresses affecting the inflow zone of aneurysms. Additionally, Rosenwasser noted the introduction of a new generation of bioactive coils. These new devices may have an impact on the problem of recanalization, he said.

MicroVention (Aliso Viejo, California) received FDA approval for its HydroCoil Embolic System for the treatment of cerebral aneurysms in August 2002. The HydroCoil Embolic System uses a microporous polymer combined with a detachable platinum coil to fill cerebral aneurysms. The expansile hydrogel forms a matrix for aneurysmal healing by providing a continuous surface for endothelial tissue growth across the neck of the aneurysm. The product's denser packing and resistance to compaction are key factors in preventing aneurysm regrowth and recurrence. Hydrogels are 3-D networks of hydrophilic polymers produced by the simple reaction of one or more monomers. The most characteristic property of a hydrogel is that it swells in the presence of water and shrinks in the absence of water. Other applications of hydrogels in biomedical fields include contact lenses, intraocular lenses, wound dressing materials and catheter coatings.

Placing coils in tiny cerebral aneurysms or doing any kind of brain surgery is difficult. The surgeon or interventionalist cannot rely on direct vision to guide his hands. For the neuroradiologist and neurosurgeons, GE Medical Systems (Waukesha, Wisconsin) is introducing the next generation in surgical navigation electromagnetic navigation technology. Electromagnetic technology eliminates line-of-sight restriction inherent in alternative tracing technologies. Navigation of surgical instruments and catheters is not interrupted by position of personnel or other equipment.

Older optical navigational systems and the new electromagnetic system are designed to correlate the precise movement of surgical instruments to a corresponding point on the patient's anatomy. Older technology optical systems require a direct line-of-sight between a camera and the marking balls attached to the surgical instruments. Any obstruction to this line-of-sight stops the surgical navigation frustrating the surgeon. GE's next-generation electromagnetic technology (the OEC FluroTrak 9800 Plus) consists of a low-profile transmitter attached to the patient and a small receiver on the surgical instrument. Line-of-sight concerns are nonexistent and ease of use and versatility are enhanced.

Back pain is ubiquitous and a part of the human condition. Fully 80% to 90% of the population in the U.S. will suffer at least one debilitating episode of back pain sometime in their life. Each year, 10% to 20% of the U.S. population will experience an episode of low back pain. About 90% will recover within six weeks. Surgical intervention is offered only to the small number who fail to respond to conservative treatment. In the U.S., 100,000 laminectomies and more than 200,000 spinal fusions are performed each year.

Spine fusion surgery is becoming more frequent, both in the U.S. and abroad. The spine implant market was a half-billion-dollar industry in 1997, a $1 billion industry in 2000 and is projected to be a $2.2 billion business in 2005. Internationally, the growth is parallel but 2.5 times as large.

Spinal fusion is not a perfect cure. The average successful fusion rate is reported to be only 85%, and the average clinical success rate is 75%. It takes an average of 15 months for healing and recuperation and causes adverse effects on adjacent levels of the spine. Conservative estimates are that 30% of present spinal fusion patients will choose arthroplasty (artificial replacement). More aggressive prognosticators feel that as much as two-thirds of the current lumbar fusion market will be supplanted by disc replacement or other arthroplasty technologies, including nuclear replacement, facet arthroplasty, ligamentous augmentation and even biologic treatments.

Link Spine Group's (Branford, Connecticut) SB Charit 's Intervertebral Dynamic Disc Spacer is limited by the FDA to investigational use. Differing from spinal fusion techniques, total disc replacement is intended to maintain motion at the operative level once the damaged disc has been removed. Total disc replacement theoretically protects the discs at adjacent levels by sharing or distributing the stress though the lower back during normal activities. Similar in function to total hip or knee replacement, the Disc Spacer is biomechanically complex. The product has, however, been used in Europe for 14 years, treating nearly 4,000 patients. The SB Charit is a prosthesis system consisting of two endplates made of cobalt chromium alloy with an ultra high molecular weight polyethylene sliding core placed between them. The endplates are attached to the vertebral bodies of the spine by means of anchoring teeth along their edge. The polyethylene sliding core is placed between these articulating endplates and is designed to allow near normal physiological movement.

In early May, DePuy AcroMed (Raynham, Massachusetts), a Johnson & Johnson (New Brunswick, New Jersey) company, reported a definitive agreement to acquire Link Spine Group.