Lumbar ligamentum flavum hypertrophy is due to accumulation of inflammation-related scar tissue.
METHODS
A histologic, biologic, and immunohistochemical assessment using human samples of the lumbar ligamentum flavum.


OBJECTIVE
To prove our hypothesis that hypertrophy of the ligamentum flavum is caused by accumulation of inflammation-related scar tissue.


BACKGROUND
Lumbar spinal canal stenosis is 1 of the most common spinal disorders in elderly patients. Canal narrowing, in part, results from hypertrophy of the ligamentum flavum. The hypertrophy mechanism remains unclear. Based on our preliminary analyses, we have previously proposed that the hypertrophy may be due to accumulation of scar tissue in the ligament. Scar tissue is reported to develop after inflammation; however, there is no report, including our previous study, on inflammation in the ligamentum flavum. There is a need for an in-depth investigation of any relationship between inflammation and scar formation in the ligamentum flavum. If inflammation is related to hypertrophy, we may control/delay the hypertrophy by inhibiting the inflammation.


METHODS
Twenty-one ligamentum flavum samples were obtained for the histologic study. Trichrome and Verhoeff-van Gieson stains were used to assess the degree of fibrosis (scarring) and content of elastic fibers, respectively. Two ligamentum flavum samples, hypertrophied and thin control ligaments, were used for a global genetic assessment by oligonucleotide gene array technology with gene chips. Messenger ribonucleic acid expression of cyclooxygenase (COX)-2 was quantitatively measured from 16 ligamentum flavum samples using real-time reverse transcriptase polymerase chain reaction. Immunohistochemistry evaluated the cellular location of COX-2 in ligamentum flavum.


RESULTS
In the hypertrophied ligament, severe fibrosis (scarring) was observed in the entire area of the ligamentum flavum, and the severity of scarring showed a significant (r = 0.79; P < 0.0001) and positive linear correlation with ligamentum flavum thickness. Gene array results showed in both thin/control and hypertrophied ligaments expression of inflammation-related genes such as COX-2, tumor necrosis factor-alpha, and interleukin-1, 6, 8, and 15. Real-time polymerase chain reaction showed COX-2 messenger ribonucleic acid expression in all ligamentum flavum samples. Its expression showed weak positive linear correlation with the thickness of ligament. COX-2 was released from vascular endothelial cells in ligamentum flavum as per the immunohistochemical analysis.


CONCLUSIONS
Accumulation of fibrosis (scarring) causes hypertrophy of the ligamentum flavum. Inflammation-related gene expression is found in the ligamentum flavum. It might be possible to prevent the hypertrophy of ligamentum flavum with antiinflammatory drugs.
Sairyo
Koichi
K
Spine Research Center, Department of Bioengineering and Orthopedics, University of Toledo, Toledo, OH 43606, USA.
Biyani
Ashok
A
Goel
Vijay K
VK
Leaman
Douglas W
DW
Booth
Robert
R
Thomas
Jean
J
Ebraheim
Nabil A
NA
Cowgill
Ian A
IA
Mohan
Suneeth E
SE
D000328:Adult; D000368:Aged; D002921:Cicatrix / Q000150:complications* / Q000209:etiology / Q000378:metabolism / Q000473:pathology; D051546:Cyclooxygenase 2 / Q000032:analysis / Q000235:genetics; D005355:Fibrosis; D015870:Gene Expression; D020869:Gene Expression Profiling; D006801:Humans; D006984:Hypertrophy; D007150:Immunohistochemistry; D007249:Inflammation / Q000150:complications* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D007378:Interleukins / Q000032:analysis / Q000235:genetics; D017843:Ligamentum Flavum / Q000737:chemistry / Q000473:pathology*; D016014:Linear Models; D008159:Lumbar Vertebrae; D008565:Membrane Proteins / Q000032:analysis / Q000235:genetics; D008875:Middle Aged; D020411:Oligonucleotide Array Sequence Analysis; D012333:RNA, Messenger / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012720:Severity of Illness Index; D013130:Spinal Stenosis / Q000209:etiology* / Q000378:metabolism / Q000473:pathology; D014409:Tumor Necrosis Factor-alpha / Q000032:analysis / Q000235:genetics
D007378:Interleukins; D008565:Membrane Proteins; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human