In 2005 the most definitive modern textbook on spinal instrumentation and surgical techniques was published by Thieme. The 135th Chapter by Ray and Jenny documented the clinical role of the Ray cage in regard to spinal instrumentation.
The key word regarding this presentation is the term “standalone.” When first given full market approval by the FDA on September 23, 1996 the product labeling stated that titanium cages were approved for use as posterior interbody “standalone” devices. Initially the recommendation was to use 2 cages but use of one cage was also included in the FDA approval at that time. The pioneers of standalone cages predicted that because of associated segmental energy absorption there would be a lesser incidence of the “transitional syndrome” as a cause of surgical failure. Shown above is a two level fusion utilizing bilateral “standalone” BAK cages. Ten years after surgery they are well healed with “sentinal” bone surrounding them. The CT image documents bone growth through the windows of the cage.
Shown to the left is a discogram being performed on a patient who had twin standalone L5-S1 BAK cages (seen at the bottom) implanted 10 years previously who had developed some back pain. The discogram at L4-5 showed only slight degeneration while at L3-4 the pattern was normal. This patient’s pain was satisfactorily treated by physical therapy alone.
In 1995 Tencer and associates published their studies on different cage implant configurations (shown below). Their observations, confirmed by other published studies and multi-surgeon clinical experience, including that of the Editor clearly demonstrated the scientifically demonstrated efficacy of “standalone” posterior interbody cages. Their major attraction being less invasive surgery, lower morbidity, less surgical time, and less surgical cost.
It is an unfortunate observation that the majority of spine stabilizations performed in the U.S. today are for the treatment of “low back pain” secondary to the presence of multilevel degenerative disc disease rather than for the treatment of individuals with progressive neurologic deficits who require adequate surgical decompression first and sensible spine stabilization second. It is a rare circumstance when spine surgeons agree on the type of surgery for the patient. It is even rarer when a spine surgeon presents a patient with a review of the many potential treatment options available to them.
A standalone posterior interbody cages are important options for patients to know about. Much like skyscrapers which are built with some degree of flexibility single Ray titanium cages have been shown to have as much as 5 degrees of energy absorbing movement.
The modern discipline of artificial disc surgery (“spine arthroplasty”) has been predicated on the concept of maintaining spine flexibility in order to avoid post-operative stress being directed to other body structures such as the adjacent spinal levels and sacral-iliac joints to avoid creating a “failed back surgery syndrome.”