"Segmental" spinal instability as related to the degenerative disc

Though the precise definition of "segmental spinal instability" is not agreed upon, its existence, as a potential cause of low back pain, is acknowledged. The pathophysiological changes that occur to the aging spine are known. The problem stems from a lack of understanding of the normal anatomic structural integrity of the functional spinal unit beyond which symptoms occur. The diagnosis, at present, hinges upon the detection of sometimes subtle radiographic findings (Table 1). Gross abnormalities in motion of the order of several millimeters, such as in anterior or retrolisthesis may be seen, representing the extreme, and perhaps obvious alterations, in the instability spectrum. The physical examination and the history remain too vague to be useful, or reliable, in the diagnosis. Better diagnostic acumen will depend on the evolution of more sensitive, hopefully noninvasive, imaging techniques. This is particularly important since a large percentage of low back pain is often attributed to "segmental spinal instability." Fusion with or without instrumentation is the surgical solution to most instabilities, assuming the diagnosis can be accurately made. The indications for fusion, as well as the success rates in treating the symptoms attributed to instability, require further studies and documentation.