Do Intervertebral Discs Degenerate Before They Herniate, or After? 

P. Lama, et al.

University of Bristol, United Kingdom

Bone and Joint 2013; 95-B: 1127-33

 

The authors report their findings that tissue changes in disc herniations differ from those in discs that degenerate without herniation.  They studied tissues obtained at surgery from 21 herniated discs and 11 non-herniated discs of similar degeneration, and comparative studies were made of the nucleus, inner annulus and outer annulus. 

They found that herniated discs demonstrated significantly greater proteoglycan loss, neovascularization, innervation, and cellularity with inflammation in the outer annulus and expression of matrix-degrading enzymes in the inner annulus than degenerated discs. 

They did not find significant difference in the nuclear tissue from herniated and degenerated discs.  They found that degenerative changes start in the nucleus and therefore it would seem unlikely that advanced degeneration caused herniation.  They pointed out that specific changes in the annulus can be interpreted as the consequences of herniation when disruption allows local swelling, proteoglycan loss, and ingrowth of blood vessels, nerves, and inflammatory cells. 

The authors note that herniated discs often show inflammatory changes, which are attributable to neovascularization and healing following injury, which is supported by an increased expression of growth factors in herniated discs in comparison with microscopically normal discs in patients of similar age.  They found other reported changes in herniated discs, which include nerve terminals positive for substance P, invasion by macrophages and lymphocytes, increased expression of MMPs (matrix degrading enzymes), prostaglandins, and increased apoptosis, which is itself associated with soft tissue injury and swelling.   

They note that discs that degenerate without herniating show slowly progressive and widespread changes that could not easily be distinguished from normal changes, which are more advanced in the nucleus pulposus, including reduced hydration, loss of pressure within the nucleus, decreased viable cells, increased production of matrix degrading enzymes, and a decrease in the nutrient transport across the endplate, which does increase with age and degeneration and which impairs healing, especially in the center of the disc. 

They find that herniation is not a normal progression from degeneration, but involves additional biochemical processes that primarily affect the annulus and therefore changes occur from the outside in. 

They find that discs that degenerate in situ often cause no major symptoms.  They note that some herniated discs may possibly herniate because of constitutional degenerative changes and genetic factors, which would explain why degenerative discs are sometimes seen at levels adjacent to herniated discs.  They do note that herniation is a known risk factor for further disc degeneration.

They conclude that degenerative changes in herniated discs are the consequence rather than the cause of herniation and that it should not be assumed that degenerative changes always precede or cause a disc herniation. 

Editor’s Commentary:  This study is enlightening and can be helpful on many levels of diagnosis and treatment for the back pain patient.  This information also could be helpful in assessing workers’ compensation or personal injury issues, particularly with respect to causation.  Given that this information can be helpful in evaluating the patient, it does not preclude the need for a comprehensive and detailed medical history and physical examination and a thorough review of the past medical records in order to obtain relevant clinical information.    

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