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Background Context: Transforaminal endoscopic decompression is an emerging minimally invasive surgical technique in spine surgery. The biomechanical effects and limitations of resections associated with this technique are scarce. Purpose: The objective of this study was to analyze the effects of three different extents of reduction at the craniomedial pedicle (10%, 25%, and 50%) and to compare them with the intact native side. In addition, the influence of bone quality on the resistance of the pedicle after reduction was investigated. Study Design: Biomechanical cadaveric study. Methods: Thirty lumbar vertebrae originating from six fresh frozen cadavers were tested under uniaxial compression load in a ramp-to-failure test: (1) the reduced pedicle on one side, and (2) the native pedicle on the other side. Of the 30 lumbar vertebrae, ten were assigned to each reduction group (10%, 25%, and 50%). Results: On the intact side, the median axial compression force to failure was 593 N (442.4–785.8). A reduction of the pedicle by 10% of the cross-sectional area resulted in a decrease of the axial load resistance by 4% to 66% compared to the intact opposite side (p=.046). The median compression force to failure was 381.89 N (range: 336–662.1). A reduction by 25% resulted in a decrease of 7% to 71% (p=.001). The median compression force to failure was 333 N (265.1–397.3). A reduction by 50% resulted in a decrease of 39% to 90% (p, The Spine Journal, 23 (7), ISSN:1529-9430, ISSN:1878-1632

The ligamentum flavum (LF), the inter- and supraspinous ligament (ISLSSL) 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.The aim of this study was to assess the material properties of the ITL, ISLSSL and LF and to correlate parameters of biomechanical function with LF-thickness, intervertebral disc (IVD) degeneration and age.Biomechanical cadaveric study.MRI- 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, ISLSSL 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.With 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 ISLSSL 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. ISLSSL-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).Aging 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 ISLSSL, 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.Patient 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.

Background Context The contribution of anatomical structures to the stability of the spine is of great relevance for diagnostic, prognostic and therapeutic evaluation of spinal pathologies. Although a plethora of literature is available, the contribution of anatomical structures is still not well understood. Purpose We aimed to quantify the biomechanical relevance of each of the passive spinal structure trough deliberate biomechanical test series using a stepwise reduction approach on cadavers. Study design Biomechanical cadaveric study. Methods Fifty lumbar spinal segments originating from 22 human lumbar cadavers were biomechanically tested in a displacement-controlled stepwise reduction study: the intertransverse ligaments, the supraspinous and interspinous ligaments, the facet joint capsules (FJC), the facet joints (FJ), the ligamentum flavum (LF), the posterior longitudinal ligament (PLL), and the anterior longitudinal ligament were subsequently reduced. In the intact state and after each transection step, the segments were physiologically loaded in flexion, extension, axial rotation (AR), lateral bending (LB) and with anterior (AS), posterior (PS) and lateral shear (LS). Thirty-two specimens with only minor degeneration, representing a reasonably healthy subpopulation, were selected for the here presented evaluation. Quantitative values for load and spinal level dependent contribution patterns for the anatomical structures were derived. Results Small variability between of the contribution patterns are observed. The intervertebral disc (IVD) is exposed to about 67% of the applied load in LB and during shear loading, but less by load in flexion, extension and AR (less than 35%). The FJ&FJC are the main stabilizers in AR with 49%, but provide only 10% of the stability in extension. Beside the IVD, the LF and the PLL contribute mainly in flexion (22% and 16%, respectively), while the ALL plays a major role during extension (40%) and also contributes during LB (15%). The contribution of the intertransverse ligaments and the supraspinous and interspinous ligaments are very small in all loading directions ( Conclusion The IVD takes the main load in LB and absorbs shear loading, while the FJ&FJC stabilize AR. The ALL resists extension while LF and PLL stabilize flexion. With the small variability of contribution patterns, suggesting distinct adaptation of the structures to one another, the biomechanical characteristics of one structure have to be put in context of the whole spinal segment. CLINICAL SIGNIFICANCE The novel information on load distribution helps predict the biomechanical consequences of surgical procedures in more detail.