Is the term degenerative “spinal canal stenosis” a misnomer?

The terms “lumbar canal stenosis” and “cervical canal stenosis” and rarely “dorsal canal stenosis” have been widely accepted and used terminologies. These terms are suggestive of the fact that degenerative alterations in the spine lead to physical encroachment of spinal canal that compresses or deforms the spinal neural structures and produce symptoms related to radiculopathy and/or myelopathy. The word “stenosis” is indicative of the pathological events and is suggestive of the treatment format that may be necessary. Bulging discs, osteophyte formation, ligamentum flavum bulging, facet arthropathy, and similar such known “pathological” entities encroach into the spinal or neural canal and result in spinal canal or neural canal stenosis and related symptoms.

Age-related disc degeneration or reduction in its “water content” has been widely accepted to be an initiating point of pathogenesis of spinal degeneration. Disc space reduction has been incriminated to result in osteophyte formation and other spinal alterations. Modern computer-based imaging shows the compression of the spinal neural structures vividly and directs a surgeon to formulate an appropriate surgical strategy that would relieve the neural structures of compression. Accordingly, decompressive laminectomy, laminoplasty and cervical discectomy, and osteophytic resection and corpectomy have gained ground and are popularly and widely used surgical procedures.

In 2010, we identified that it is not the disc degeneration, but weakness of muscles that maintain erect human posture is the nodal point of pathogenesis of spinal degeneration.[1,2] Muscle weakness can be related to disuse, abuse, or injury and results in vertical telescoping of the spinal segments.[3] The muscles work with their activity that is focused on the facets that are the fulcrum of the spinal movements. We related the intervertebral disc to odontoid process and identified that while the muscles form the “brawn,” the odontoid process and the intervertebral disc form the “brain” of spinal movements.[4] This can be appreciated by the fact that while majority of muscle bulk is located in the posterior spinal segments and their activity is focused on the facets, only thin and relatively insignificant muscle bundles are located in the anterior spinal segment in proximity to the vertebral bodies. Both intervertebral disc and odontoid process are like opera conductors that drive the entire show without directly playing any instrument. Listhesis of inferior facet of the rostral vertebra over the superior facet of the caudal vertebra forms the initial pathological event. As muscle weakness is not focal but is generalized, multisegmental spinal affection is a more common event. Ligamentous buckling and infolding that includes ligamentum flavum “hypertrophy” and osteophyte formation are the secondary results of facetal listhesis. Disc space reduction also appears to be a secondary event to primary facetal listhesis. In 2011, we proposed facet distraction-arthrodesis using Goel facet spacers as treatment for single/multiple-level cervical and lumbar spinal degeneration.[5,6] A single act of facet distraction results in reversal of all known “pathological” features incriminated to be associated with spinal degeneration. The process of spinal facet distraction eventually results in restoration of spinal and neural canal dimensions. Remarkable clinical improvement in the immediate postoperative phase is the testimony to the validity of the proposed hypothesis.

As we further matured in our understanding of spinal degeneration, we observed that more than spinal neural deformation or compression, it is subtle instability-related microtrauma that results in symptoms.[7] The neural structures are remarkably elastic and supple and can easily tolerate deformity. The lateral location of the facet joints away from the neural structures and subtleness of the dislocation makes preoperative identification of instability even on dynamic computer-based imaging difficult or impossible.[8] However, clinical and radiological evidence can point toward the site of spinal instability. In cervical spine, altered cord signals can be prominent even in the absence of adjoining osteophytes or ligamental buckling. It appears that these cord signals are a consequence of vertical spinal instability. The symptoms related to both cervical and lumbar spinal degeneration are initiated on activity. In context to lumbar spine, the symptom of “claudication” pain is a frequent or a constant clinical presentation.[9] The very fact that these symptoms are not prominent at rest and are only initiated on activity is suggestive of the fact that the spinal canal is not inherently stenosed, but activity that leads to muscle exhaustion and dynamic listhesis of the facets probably initiates the symptoms. Our understanding is that it is not “stenosis” of the spinal segment that is the issue, but it is subtle, chronic, and progressive instability related to developing muscle weakness that is the initiator and propeller of clinical and radiological signs and symptoms. Essentially, it is not stenosis that is the issue, but it is muscle weakness-related spinal instability that is the problem.

Manual manipulation and physical observation of the facetal articulation is probably the only way to identify the levels of instability. Presence of osteophytes in the vicinity of the facets, open articular cavity, and excessive movements on manipulation are the indicators of instability. We observed that there could be spinal instability even in the absence of radiological features of the presence of osteophytes or ligamental buckling. High degree of clinical suspicion and experience in facetal handling and manipulation is probably the only definitive way to identify and treat the unstable spinal segments. We have identified that spinal instability is the issue and spinal stabilization is the treatment for spinal degeneration.[10,11,12,13,14] The term “spinal stenosis” should be replaced by “spinal instability” as it conveys the pathogenesis and directs the surgical treatment.