Abstract
BACKGROUND CONTEXTThe ligamentum flavum (LF), the inter- and supraspinous ligament (ISL&SSL) and the intertransverse ligament (ITL) are relevant spinal structures for segmental stability. The biomechanical effect of degeneration and aging on their biomechanical properties remains largely unknown. PURPOSEThe aim of this study was to assess the material properties of the ITL, ISL&SSL and LF and to correlate parameters of biomechanical function with LF-thickness, intervertebral disc (IVD) degeneration and age. STUDY DESIGNBiomechanical cadaveric study. METHODSMRI- and CT-scans of 50 human lumbar segments (Th12-L5) were used to assess the ISL (acc. to Keorochana), the grade of IVD degeneration (acc. to Pfirrmann) and to quantify LF-thickness. The ITL, ISL&SSL and LF were resected in the neutral position of the spinal segment with a specifically developed method to conserve initial strain. Ramp to failure testing was performed (0.5 mm/s) to record initial tension, slack length, stiffness and ultimate strength. The relationship between the biomechanical characteristics and age and radiological parameters were analyzed. There are no study-specific conflicts of interest and no external funding was received for this study. RESULTSWith aging, a significant reduction in initial tension (r=-0.5, p<.01) and ultimate strength (r=-0.41, p<.01) of the LF was observed, while the effect on LF-stiffness and the characteristics of the other ligaments was non-significant. IVD-degeneration was correlated with a significant reduction in stiffness (r=-0.47, p=.001; r=-0.36, p=.01) and ultimate strength (r=-0.3, p=.04; r=-0.36, p=.01) of the LF and ISL&SSL respectively and a significant reduction in initial tension (r=-0.4, p<.01) of the LF. For the ITL, no significant correlation was observed. Comparing Pfirrman 2 to 5, this reduction was 40% to 80% for stiffness 60% to 70% for ultimate strength and 88% for initial tension of the LF. ISL&SSL-stiffness between Kerorochana grade A and D differed significantly (p=.03), while all other comparisons were non-significant (p>.05). LF-thickness did not correlate with the biomechanical properties of the LF (p>.05). CONCLUSIONSAging is primarily related to biomechanical changes to the LF. IVD-degeneration is related to a relevant reduction in stiffness and ultimate strength of the LF and ISL&SSL, with a similar trend for the ITL. The ISL-specific Keorochana grading system provides only minimal biomechanical information and LF-thickness does not provide biomechanical information. CLINICAL SIGNIFICANCEPatient age and the degenerative state of the IVD can be used to evaluate the biomechanical characteristics of the dorsal spinal ligaments, which can be helpful in selecting the optimal surgical procedure (e.g. in decompression surgery) for a specific situation.
Highlights
The spinal ligaments provide stability, while permitting motion
In the neutral position of the spine, the ligamentum flavum (LF) and the anterior and posterior longitudinal ligaments have been shown to be under initial tension [4,5,8,19], while the intertransverse ligaments (ISL) and the supraspinous ligaments (SSL) were measured to be relaxed and engage only after a certain slack length [2,4,9]
The aim of this study was to relate the mechanical properties of spinal ligaments (LF, ISL&SSL and intertransverse ligament (ITL)) with age and clinically applicable radiological parameters: The Pfirrmann classification system [22], which is commonly used to evaluate the degenerative state of the intervertebral disc (IVD), the Keorochana grading system [23] for evaluation of the degenerative state of the ISL and LF-thickness, which has been proposed as a measure for the degenerative state of the LF [24−26]
Summary
The spinal ligaments provide stability, while permitting motion. Mechanical properties [1−10], composition [2,5,6], fiber orientation [5,7,11−13] as well as the biomechanical role in supporting the spine under load [13−16] have been investigated. PURPOSE: The aim of this study was to assess the material properties of the ITL, ISL&SSL and LF and to correlate parameters of biomechanical function with LF-thickness, intervertebral disc (IVD) degeneration and age. RESULTS: With aging, a significant reduction in initial tension (r=-0.5, p
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