The intervertebral disc is the cornerstone of the joint complex that comprises the spinal motion segment. The disc functions to permit limited motion and flexibility, while maintaining segmental stability and absorbing and distributing external loads.

Intervertebral Disc Structure

The structure of the normal intervertebral disc includes:

• A nucleus, composed primarily of proteoglycans and Type II collagen with a capacity to absorb and distribute load,
  
   
• An outer annulus with well-organized layer of Type I collagen that serve to stabilize the motion segment.

The structure and function of the disc may be altered by processes including normal physiological aging, mechanical factors including trauma and repetitive stress, segmental instability of the spine, and inflammatory and biochemical factors.

 

Degenerative Disc Disease

Structural instability and dysfunction of the disc are important and significant causes of low back pain, and may be broadly encompassed by the term Degenerative Disc Disease (DDD). The pathology of the disc has an important role in the cause of low back pain. Treatment of low back pain may be most effective if disc function can be restored.

 

Chronic Low Back Pain

Back pain is the most common ailment of the working-age adult, affecting over 4 million individuals each year in the United States, and weighing an economic burden on our health care system of up to $100 billion.

While most acute episodes of low back pain are self-limited and respond well to non-operative therapies, the management of chronic low back pain remains a difficult challenge for the non-operative and operative physician. Surgical management of chronic low back pain encompasses techniques including:

• Intervertebral disc excision (discectomy),
  
   
• Arthrodesis (fusion) of the spine using posterior, anterior, or combined approaches,
  
   
• Intradiscal procedures including injections (epidurals), electrothermal exposure, and implantable neural stimulators and medication dispensers (spinal pumps).

Treatment Diversity

The diversity of approaches and the variation observed in treatment strategies for low back pain indicates an absence of evidence-based support for any single method. While the rate of back surgeries including fusion of the spine has increased by over 600% between 1979 and 1990, there remains no operative treatment that has yielded reliable and reproducible good results in patients affected by chronic low back pain. The common denominator is that none of the techniques listed above are directed toward the restoration of normal structure and function of the affected spinal motion segment, and of the disc at the center of that motion segment.

Disc Restoration

Approaches to restoration of the function of a degenerated or dysfunctional disc include techniques of biological reconstruction and techniques of artificial disc replacement. The Spinal Disorders Division at UC San Francisco is currently investigating intervertebral disc regeneration using techniques of cellular and molecular biology, and investigating intervertebral disc arthroplasty (artificial joint creation) at a clinical trial center.

Indications for Disc Replacement

Intervertebral disc replacement may be indicated for patients with degenerative disc disease at one or two levels of the spine. Patients may be candidates for one or both of the Investigational Trials on Intervertebral Disc Replacement in the United States if they have the following conditions:

1) Degenerative disc disease in one or two adjacent vertebral levels between L3 and S1
2) Age between 18 and 60
3) Failed at least 6 months of conservative therapy