Intervertebral Disc Replacement
A Role in the Management of Chronic Low Back Pain Caused by Degenerative Disc Disease
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).
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.
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.
This article is intended to provide the background that led to support of a clinical trial, and the methodology of the investigation.
Motion within the musculoskeletal system is dependent upon functional joints. Joint dysfunction can be an important source of pain (arthralgia), and functional limitation. Arthrodesis, or “binding of a joint” was introduced in the 19th Century by the Austrian surgeon E. Albert (1841-1900).
The goal of arthrodesis (fusion) is to eliminate motion of a segment or joint, and thereby relieve pain. The results of fusion include both failure to gain effective immobilization (pseudoarthrosis), and the induction of pathology in adjacent segments. For example, fusion of the hip for the treatment of degenerative joint disease is associated with a high rate of secondary low back and knee pathology. Total joint arthroplasty of the hip and knee has been recognized as one of the most effective surgical interventions of the 20th Century because of the efficacy of the procedure in relieving pain from an affected segment, while sparing adjacent segments or structures from pathologic stress or loads.
Fusion of the spine was introduced in 1911, by F. Albee for the management of infection and by R. Hibbs for the management of deformity. Fusion of the lumbar spine has increased at the highest rate of any spinal procedure in the last 10 years. However, the indications, techniques, and results remain controversial and unclear. Intervertebral disc replacement is an attractive alternative to fusion of the spine with theoretical advantages that include restoration of segmental mobility, elimination of pain, and sparing of abnormal biomechanical forces on adjacent segments.
Prosthetic devices of replacement of the intervertebral disc may be broadly divided into devices that replace the nucleus only, leaving the annulus and cartilaginous portions of the endplate intact, and devices that replace the entire intervertebral disc. Currently there are several devices that are under clinical investigation in the United States such as the PRODISC® (Spine Solutions, New York, NY, USA).
PRODISC® (Spine Solutions, New York, NY, USA)
CHARITÉ? Artificial Disc (DePuy Spine, Inc.)
Photograph Courtesy of DePuy Spine, Inc.
The Food and Drug Administration (FDA) has approved the CHARITÉ? Artificial Disc (DePuy Spine, Inc. of Raynham, MA) for use in treating pain associated with degenerative disc disease. The device was approved for use at one level in the lumbar spine (from L4-S1) for patients who have had no relief from low back pain after at least six months of non-surgical treatment.
Both devices are composite in design with a cobalt chromium alloy endplate and an ultra high molecular weight polyethylene core. Both devices have been used in Europe for over 10 years, with similar results in retrospective evaluations. In a review of patients a minimum of five years after implantation of the SB Charité disc replacement, Dr, Bradford reported good or better results in 68% of patients. Similarly, a review of the work of Drs. Marnay and Villette using the PRODISC® in 64 patients with a minimum of seven years of follow-up demonstrated a significant improvement of back pain and leg pain (p
Current Clinical Trials
The efficacy of intervertebral disc replacement has not been demonstrated in prospective, randomized study. In the United States, several spinal surgery centers are participating in Investigational Device Evaluations (IDEs) with either the PRODISC® or SB Charité III Dynamic Disc Spacer. In the PRODISC® study, investigational patients will be compared to patients undergoing a combined interbody and posterolateral fusion. In the SB Charité III Dynamic Disc Spacer study, investigational patients will be compared with patients undergoing interbody fusions with a BAK device. Both studies are designed with standardized outcome assessment tools for a reliable evaluation of change in pain, function, and well-being after surgery.
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
Intervertebral disc replacement is a surgical technique for the treatment of low back pain related to degenerative disc disease. Theoretical advantages of intervertebral disc replacement over fusion of the spine include preservation or restoration of segmental motion in the spine, restoration of intervertebral architecture and foraminal height, sparing of adjacent segments from abnormal stresses, and restoration of normal biomechanics across the lumbar spine.
Initial experience with composite devices in Europe suggests safety and efficacy of these devices. Prospective randomized study compared with fusion will offer an evidence-basis for the role of disc replacement in the current and future management of degenerative disc disease.