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J Orthop Res. 2015 Aug;33(8):1255-64. doi: 10.1002/jor.22900. Epub 2015 Apr 27.

Biological responses to flexion/extension in spinal segments ex-vivo.

Author information

1
Department of Physical Medicine and Rehabilitation, University of Pittsburgh, 3471 5th Avenue, Pittsburgh, Pennsylvania, 15213.
2
Department of Bioengineering, University of Pittsburgh, 300 Technology Drive, 360B Center for Bioengineering, Pittsburgh, Pennsylvania, 15219.
3
Department of Orthopaedic Surgery, University of Pittsburgh, 200 Lothrop Street, E1641 Biomedical Science Tower, Pittsburgh, Pennsylvania, 15261.
4
McGowan Institute for Regenerative Medicine, 450 Technology Drive, Suite 300, Pittsburgh, Pennsylvania, 15219.

Abstract

Mechanical loading is a salient factor in the progression of spinal disorders that contribute to back pain. Biological responses to loading modes like flexion/extension (F/E) in relevant spinal tissues remain unstudied. A novel, multi-axial experimental system was developed to subject viable functional spinal units (FSUs) to complex, in-situ loading. The objective was to determine biological effects of F/E in multiple spinal tissues-annulus fibrosus, nucleus pulposus, facet cartilage, and ligamentum flavum. Rabbit lumbar FSUs were mounted in a bioreactor within a robotic testing system. FSUs underwent small (0.17/0.05 Nm) and large (0.5/0.15 Nm) range-of-motion F/E for 1 or 2 h of cycling. Outcomes in each tissue, compared to unloaded FSUs, included (i) relative mRNA expression of catabolic (MMP-1, 3 and ADAMTS-5), pro-inflammatory (COX-2), and anabolic (ACAN) genes and (ii) immunoblotting of aggrecan degradation. Total energy applied to FSUs increased in groups subject to large range-of-motion and 2-h cycling, and moment relaxation was higher with large range-of-motion. F/E significantly modulated MMP1,-3 and COX-2 in facet cartilage and MMP-3 and ACAN in annulus fibrosus. Large range-of-motion loading increased MMP-mediated aggrecan fragmentation in annulus fibrosus. Biological responses to complex loading ex vivo showed variation among spinal tissues that reflect tissue structure and mechanical loading in F/E.

KEYWORDS:

facet cartilage; flexion/extension; intervertebral disc; ligamentum flavum; mechanobiology

PMID:
25865090
DOI:
10.1002/jor.22900
[Indexed for MEDLINE]
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