Biomechanics Posterior Lumbar Articulating Elements: Jan 2007 Neurosurg Focus

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TFAS (Total Facet Arthoplasty System)<UL TYPE=SQUARE> "The TFAS replaces the diseased facets (and laminae, if necessary to attain adequate decompression) after surgical removal. The TFAS implant offers an alternative to rigid spinal fusion fixation, enabling intervertebral motion and restoration of stability and sagittal balance to the spine.

Flexibility tests were performed on each specimen in the intact and injured states and following implantation of the TFAS."[/list]FIG. 3 Three-dimensional reconstruction of the Archus TFAS implanted in a model spine. (Archus Orthopedics, Inc, Redmond, WA.)


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PMID: 17608330
Neurosurg Focus 22 (1):E1, 2007 (PDF - Full Text 1.83 MB)

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

1 Research and Technology, DePuy Spine, Inc., Raynham, Massachusetts;
2 Big Sky Neuroscience and Spine Institute, Butte, Montana; and
3 Department of Orthopaedic Surgery and Rehabilitation, Loyola University Medical Center, Maywood, Illinois

Abstract
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.

KEY WORDS • facet replacement • facet arthroplasty • posterior column biomechanics • biomechanical study



Conclusions
At the present time in North America there is a great deal of enthusiasm about the introduction of total disc arthroplasty for the treatment of degenerative disc disease. To maximize the clinical benefit, understanding of the origins of back pain must also evolve as a necessary companion to the rapid advancements in motion preservation technologies. Our current focus continues to be on interventions and devices that relieve discogenic pain and reestablish the structure and normal function of the spine. We are now entering the era of partial and complete FSU replacement. The shift in usage of motion-sparing technology to replace a portion of arthrodesis procedures will most likely occur in the near future. Nevertheless, indications for facet replacements and posterior stabilization systems are still broad and unproven, and should be carefully considered. Furthermore, no prospective randomized controlled trial has been completed on these devices yet, which is an essential need for the practice of evidence based medicine.

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