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Annulus-endplate anchorage more vulnerable to failure in axial tension vs. torsion, in-plane torsion
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Researchers recently reported annulus-endplate anchorage was more vulnerable to failure in axial tension compared with both torsion and in-plane tension, most likely due to acute fiber bending at the soft-hard interface of the tidemark.
The researchers performed loading experiments on the anchorage systems of ovine lumbar motion segments until they failed in each of three modes: torsion using intact motion segments, in-plane tension of the anterior annulus-endplate along one of the oblique fiber angles and axial tension of the anterior annulus-endplate. The mechanical influence of the mineralized component was investigated using decalcification, and both the intact and failed samples underwent structural analysis using differential interference contrast optical microscopy and scanning electron microscopy.
Failure was observed at both the tidemark and the cement line. According to the researchers, the samples subjected to axial tension were observed to have more tidemark failures compared with the samples subjected to torsion and in-plane torsion.
Samples that decalcified before testing was performed were found to more frequently have extensive damage at the cement line compared with fresh samples. Additionally, through the analysis of intact samples at their anchorage sites, the researchers found annular sub-bundle fibrils penetrated beyond the cement line to a limited depth and appeared to merge with those in the vertebral and cartilaginous endplates.
The researchers concluded their findings supported the theory that flexion, which induces a similar pattern of axial tension, increases the risk of herniation involving endplate failure. – by Robert Linnehan
Disclosure: The researchers report no relevant financial disclosures.
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