Biomechanics of the Posterior Lumbar Articulating Elements

Hassan A. Serhan, Ph.D.1; Gus Varnavas, M.D.2; Andrew P. Dooris, Ph.D.1; Avinash Patwardhan, Ph.D.3; Michael Tzermiadianos, M.D.3

Disclosures

Neurosurg Focus. 2007;22(1) 

In This Article

Summary and Introduction

The clinical success of lumbar spinal fusion varies considerably, depending on techniques and indications. Although spinal fusion generally helps to eliminate certain types of pain, it may also decrease function by limiting patient mobility. Furthermore, spinal fusion may increase stresses on adjacent nonfused motion segments, accelerating the natural degeneration process at adjacent discs. Additionally, pseudarthrosis, that is, incomplete or ineffective fusion, may result in an absence of pain relief. Finally, the recuperation time after a fusion procedure can be lengthy.

The era of disc replacement is in its third decade, and this procedure has demonstrated promise in relieving back pain through preservation of motion. Total joint replacement with facet arthroplasty of the lumbar spine is a new concept in the field of spinal surgery. The devices used are intended to replace either the entire functional spinal unit (FSU) or just the facets. These devices provide dynamic stabilization for the functional spinal segment as an adjunct to disc replacement or laminectomy and facetectomy performed for neural decompression. The major role of facet replacement is to augment the instabilities created by the surgical decompression or to address chronic instability. Additionally, facet joint replacement devices can be used to replace the painful facet joints, restore stability, and/or to salvage a failed disc or nucleus prosthesis without losing motion.

In this paper the authors review and discuss the role of the lumbar facet joints as part of the three-joint complex and discuss their role in intersegmental motion load transfer and multidirectional flexibility in a lumbar FSU.

Fusion has been applied to many types of human joints for various pathological conditions, the primary rationale being relief from pain, although correction of deformity and restoration of normal force transmission may also be motivating factors.[20] In contrast with other joints, a spinal segment may be surgically treated for many reasons, including some that directly involve the posterior osseous elements, such as degenerative spondylolisthesis, osteoarthritis, ankylosing spondylolysis, or traumatic injury. Damaged posterior elements may result in misalignment, failure to articulate, or a general inability to support axial, torsional, or shear forces. Loads on the facet joints of the lumbar spine may play a major role in low-back pain, which may limit mobility and function.[3,15,28] Damaged posterior elements may also cause hypermobility or disfigurement.

Currently there is no optimum intervention procedure for facet joint disorders. Facetectomy may provide relief, but the resultant instability generally requires spinal fusion. This type of operation, however, may cause in creased stress and hypermobility at the adjacent motion segments over a 5- to 10-year period after surgery.[16,19,20] As an alternative to fusion, initial attempts have focused on restoring the functional properties of the spinal segment through the use of artificial discs, but these devices alone do not fully address the mechanics of motion in the spinal column.[2,8,17,22,27]

Basic understanding of prosthetic spinal joint replacement is primarily derived from experiences with joint arthroplasty dating back to the early 1960s, when Sir J. Charnley developed the first low-friction total hip replacement.[7] Total joint replacement has revolutionized the treatment of limb arthritis, and it has been proposed that spine surgeons use the same principles in the treatment of facet disorders by replicating, to some degree, the function of the posterior elements with implantable devices.

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