The Present Role of Titanium Cage Fusions In Spine Care

Lumbar spinal fusion instrumentationThe first spinal fusion in the U.S. was performed by Albee and Hibbs only 86 years ago. Since then at least 6 million additional fusions have been performed. The least controversial use of fusion has been to stabilize the spine following traumatic injury. All other applications remain the subject for continuing discussion. The long-term success rate of fusion has ranged from a dismal 40% to 80%. Smokers have typically had a 3-4 times higher failure rate than non-smokers. Before the advent of modern CT and MRI imaging to improve diagnostic accuracy many past such procedures were simply performed for the wrong reasons.

While there is always controversy regarding actual numbers there is no difference of opinion that fusion has always been major surgery as to risk, high cost, high failure rate and the likelihood of continuing problems producing low levels of patient satisfaction. Despite these observations fusion is a necessary surgical procedure for many patients.

The real issue, therefore is how to make fusion better. In the 1980s Orthopedic Surgeon George Bagby introduced the use of anterior interbody cervical fusion in horses as a means of treating "wobbler's syndrome", a degenerative condition making the neck unstable and necessitating destruction of the horse. Dr. Bagby designed a cylindrical metal cage (with drill holes) in which the horses' own bone was packed allowing for successful fusion and salvage of a sometimes very valuable animal. Dr. Bagby's presentations at medical meetings started "the wheels turning" of his spine surgeon peers. By 1988 Drs. Michelson, Ray and Kuslich ("MRK") had each introduced new cylindrical and perforated cages designed for human use. Since that time at least half a dozen additional designs have emerged throughout the world.

It is not surprising that because the "MRK" cage designs came "out of the starting gate" at about the same time they each showed some design similarity. All were cylindrical and composed of biologically unreactive titanium.

Charles D. Ray, spine neurosurgeon at the Institute for Low Back and Neck Care (ILBNC), initiated clinical testing of his version of the Bagby cage in 1989. This device incorporated a number of important, and different, design characteristics including:

Deep, self-tapping threads with high pull-out resistance
Unique window design allowing optimal bone-to-bone contact
70% of cage wall perforated with high strength internal arches
Side barrier to disc or fibrous tissue ingrowth

On the basis of the accumulated data from the clinical investigational studies in the U.S. the FDA approved the Ray and Kuslich ("BAK") cases for general clinical use at the end of 1996. At ILBNC our staff of orthopedic and neurosurgical spine specialists have had the opportunity of investigationally testing and comparing a number of different cage devices since 1989. At this point in time our group has performed over 300 such procedures. The ILBNC experience is now among the largest for a single clinic in the U.S.

World Experience Titanium Cage Fusions
At this time the world experience regarding titanium cages has been quite variable. The results in some small series have been downright "awful" due to excessive blood loss and frequent post-operative complications. This has not been our experience. Although cages are inherently simple and typically require much less operative time compared to pedicle screw and rod fixation systems it is clear that that the better results occur in the hands of orthopedic and neurosurgeon spine specialists. Those who have developed prior skill, and expertise, in performing anterior and posterior interbody fusions (with bone and other materials) have an additional advantage. Cage implantation requires a significant "learning curve" in order for a surgeon to gain the skills necessary to avoid the many potential pitfalls of this type of surgery. Despite this admonition it appears fair to observe that the success of fusion with cages is presently higher than that with other methods with no statistical difference in success-rate existing between smokers and non-smokers.

Anterior versus Posterior Approach
There is no risk-free state in any form of spine surgery. Any patient can die, be paralyzed, have a nerve injury, wound infection, medical problem or drug reaction. The anterior approach risks focus on injury to the large blood vessels (i.e. abdominal aorta, inferior vena cava) as well as the potential risk of impotence and sterility in males. The posterior approach risks focus on potential injury to dura as well as spinal cord and nerves of the cauda equina. When decompression and fusion are required the posterior approach can be more expedient (less operative time). The posterior approach also tends to provide greater segmental stabilization at the time of surgery because of the preservation of the anterior disc annulus.

Why a Titanium Cage?
When performed by well-trained spine surgeons (orthopedic and neurosurgical) titanium cages offer the following potential advantages:

Less invasive to surrounding tissue with less time under general anesthesia
Better surgical access to pathology (i.e. the presence of lateral spinal stenosis)
Less blood loss
Shorter hospitalization
Faster recovery
Less post-operative problems
Less "donor-graft site problems"
Routine second operative procedure to remove hardware not required
Earlier return to function
Less cost

Which Cage Is Best?
Despite the fact that the Ray cage was developed and initially tested at our Institute it is clear, at this point in time, that its unique design has allowed for better clinical results than other such devices tested to-date. In this author's personal series of 160 cases a 98% over-all fusion rate was achieved. Because of the high fusion rate there has been the unique opportunity to further study the small group of patients who, despite solid fusion, indicate that they have not done well. The primary reasons found to-date to account for this are:

Continuation of a previously present deconditioned state despite adequate therapy
Persistence of previous or new nerve-related pain syndrome
Persistence of a "disabled state" mentality on part of patient
Malingering for perceived personal gain

What Constitutes A Successful Outcome?
This is actually a pretty simple determination based on three factors:

High post-operative patient satisfaction
Significant reduction of cost
Making the patient independent of the health care system

How Can A Patient Stay Independent Of The Health Care System?
To begin with the surgeon must choose a patient who is willing to take responsibility for their own care in the future. Without this the chances for long-term success are very poor. The challenge begins with a healthy life style. This includes good nutrition, exercise and avoiding body insults such as smoking. Typically this author's patients are required to participate in a 5 day rehabilitation program providing training in these basic areas:

High-quality multi-faceted spine educational program
Exercise and stretching instruction
Daily anti-gravitational spine unloading therapy

What Is The Next Step Beyond Titanium Cages?
If we in the U.S. started spinal screening at an early age and provided high risk youngsters with appropriate daily spine health maintenance programs it is likely that the need for spine surgery and fusion would significantly decrease in the future. The prevention of spine degeneration is an important goal. This would, however, require a major paradigm shift in our present health care thinking. We would have to change from being solely a "disease"system (where we wait for disease to occur and then treat it) to a true "health system" where we also support preventing disease. Less invasive surgical techniques will certainly evolve. Worldwide research on "artificial discs" is proceeding but given the regulatory hurdles that will have to be crossed these are probably 5-10 years away from clinical trial at this time. Two members of our group have produced designs for artificial discs, which are now in the developmental stage.

Material Provided by The Institute for Low Back and Neck Care
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Updated on: 08/21/19
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