BurtRepLogo02.gif (3938 bytes)

 

The Concept of "Flexible Stabilization"
(Dynamic Spine Stabilization)


The sacrum is normally solid and the lumbar spine is normally flexible.  Mother Nature seems to have wanted it this way and this appears to work well for those humans who have chosen to walk on two legs, rather than four, on our high gravity planet.  When normally flexible spine segments become fused together prior to birth (a congenital abnormality) increased stress is directed to the adjacent segments.  The same process, involving significant stress being directed to adjacent spinal segments occurs when techniques involving rigid spine fixation are employed.  This production of "Transitional Syndromes" is a serious complication of rigid fusion, particularly when employed in individuals with underlying genomic disorders.  This problem not infrequently is the cause for additional surgery this creating more problems for the patient than were present to start with.
 
The living proof proof of the "Transitional Syndrome" is demonstrated by the case shown on the left.  This patient was born with a congenital "block vertebrae" involving the L2 and L3 segments (green dot).  The stress-related adjacent disc degeneration is shown next to the red dots.  Fortunately for the public-at-large block vertebrae are uncommon, but unfortunately for unsuspecting patients problems resulting from multi-level rigid instrumented fusions, as opposed to flexible stabilizations, are not uncommon.  "Transitional Syndromes" can result in disability and often create the need for additional spine surgery.  

 It is a basic tenant of medicine that the physician's responsibility is to not only treat and relieve disease but also, in this process, to avoid creating recurrent, or additional, disease.  It is in this regard that the concept of "flexible (or dynamic) stabilization" has become an important consideration.

Rigid Spine Fusion is inherently a non-physiologic procedure.  The Editor's  interest in developing more patient-friendly procedures began in the 1970s.  This interest was initiated by the need to "salvage" many patients with rigid fusions who then developed incapacitating "transitional" degenerative changes at adjacent spinal segments and became "failed back surgery" patients.  

In 1988 and then in 1990, following extensive testing and development in physiologic spine stabilization the Editor first began to publish, for the spine care community, the science of "flexible stabilization" and "non-metallic flexible stabilization systems" as a means of extending the vistas of the spine surgery community (
Burton CV: The Liabilities of Fusion.  In Cauthen JC (editor) Lumbar Spine Surgery.  Baltimore: Williams and Wilkins, 1987).  Patents issued by the United States Patent Office (1988 and 1994) and other patents pending have reflected these endeavors.  
The conceptual basis in regard to flexible stabilization, was outlined in the 1990 International Society for the Study of the Lumbar Spine textbook "The Lumbar Spine" and subsequently supported in the British Medical Journal "Lancet."

It is a sad, but true, observation that organized medicine is only now beginning to express  concern.  The July, 2004 issue of the BackLetter  makes the statement: "The world of spinal medicine, unfortunately, is producing patients with failed back surgery syndrome at an alarming rate" (
Lippincott Williams & Wilkins, Vol. 19, Number 7, pp. 79).  Only a few enlightened spine care business organizations have recognized that rigid spinal fusion represents a less-than-optimal solution to the management of spine disorders for many patients, particularly those afflicted with multi-level degenerative and  genomic disorders.

  Present Clinical Applications of Flexible Stabilization  
In 1994 Henri Graff , of Lyon, France, pointed out that: "a fused" spine is not a physiologic state.  He subsequently introduced a spine stabilization system designed to provide less stressful load-sharing.  

Shown on the left is the Dynesys device (DYnamic NEutralization SYstem).  This flexible instrumented stabilization system was developed by Gilles Dubois in France and by Hans Müller in Germany.  Dynesys was first introduced in June, 1998 in Innsbruck, Austria.
Dynesys was initially introduced in Europe where it was being marketed as "a more gentle alternative to fusion" and has now been introduced into North America as an investigative device over 30 clinical centers.  As with all implanted spinal devices clinical success is more often dependent on good patient selection and good surgical judgment than the device itself.  This point is well illustrated by an important case presentation.  The problem was not with the device but in failure to adequately diagnose and treat lateral spinal stenosis.  
 
A more recent introduction into the family of dynamic stabilization devices is the NFix II from N Spine.  This device has a titanium and elastomeric rodto allow for energy absorption and the avoidance of stress on adjacent spine structures.

What is clear, at this point  in time is that a united professional viewpoint in regard to spine stabilization simply does not yet exist.  A particular problem continues to be the misuse of the term "fusion" to represent all forms of spinal stabilization.  In the American Medical Associations 2004 text on clinical procedural terminology (CPT) the word "Fusion" has been replaced by the more appropriate term "Arthrodesis"  (from L Arthros-joint, desis- to bind).

Equally important is the skyrocketing high cost of spine implants. 
Inherent in the discussions regarding the use of autogenous bone for the purpose of stabilization is the importance of stressing the deleterious role of cigarette smoking in causing failure of all of these surgical methods.  It is the primary physician's responsibility, as well as the spine surgeon's, to communicate this important information to the patient to improve clinical outcome as well as assure that appropriate informed consent exists prior to performing any major surgical procedure.