Finite element analysis.
To investigate the biomechanical effect of four posterior fixation tcehniques on stability and adjacent segment degeneration in treating thoracolumbar burst fractures with ...osteoporosis.
In terms of stability and adjacent segment degeneration, there remains no consensus or guidelines on the optimal technique for the treatment of thoracolumbar burst fractures in patients with osteoporosis.
Images of CT scans were imported into MIMICS and further processed by Geomagic to build 3-dimensional models of the T10-L5 region. A v-shaped osteotomy was performed on the L1 vertebral body to simulate a burst fracture in the setting of osteoporosis. Subsequently, four fixation techniques were designed using SolidWorks software. Range of motion (ROM) of the global spine, ROM distribution, ROM of adjacent segment, Von Mises stress on adjacent intervertebral discs and facet joints were analyzed.
Among the four groups, the cortical bone screw fixation (CBT) showed the highest global ROM at 1.86°, while long-segmented pedicle screw fixation (LSPS) had the lowest global ROM at 1.25°. The LSPS had the smallest percentage of ROM of fractured vertebral body to fixed segment at 75.04%, suggesting the highest stability after fixation. The maximum ROM of the adjacent segment was observed in the CBT at 1.32°, while the LSPS exhibited the smallest at 0.89°. However, the LSPS group experienced larger maximum stress on the adjacent intervertebral discs (9.60MPa) and facet joints (3.36MPa), indicating an increasing risk of adjacent segment disease.
LSPS provided the greatest stability, while CBT provided the smallest amount of stability. However, the elevated stress on adjacent intervertebral discs and facet joints after LSPS fixation increased the possibility of adjacent segment degeneration. Cement-augmented pedicle screw fixation (CAS) and combined cortical bone screw and pedicle screw fixation (CBT-PS) demonstrated significant biomechanical advantages in providing moderate fixation strength while reducing stress on the intervertebral discs and facet joints.
Study Design. Biomechanical cadaveric study. Objective. The goal of this study was to analyze the effects of an endoscopic transpedicular approach with different drill diameters (6 and 8 mm) and ...compare them with the intact native side. In addition, the influence of bone quality on the resistance of the pedicle was investigated. Summary of Background Data. Clinical studies have repeatedly highlighted the benefits of endoscopic transpedicular decompression for downmigrated lumbar disc herniations. However, the biomechanical effects on pedicle stability have not been studied up to now. Materials and Methods. Twenty-four vertebras originating from four fresh-frozen cadavers were tested under uniaxial compression load in a ramp-to-failure test: (1) the tunneled pedicle on one side, and (2) the native pedicle on the other side. Twelve lumbar vertebrae were assigned to drill diameter of 6 mm and the other 12 to diameter of 8 mm. Results. The median ratio of sustained force for the operated side compared with the intact contralateral side is equal to 74% (63–88) for both drill diameters combined. An 8 mm transpedicular approach recorded an axial resistance of 77% (60–88) compared with the intact contralateral side ( P =0.002). A 6 mm approach resulted in an axial resistance of 72% (66–84) compared with the intact opposite side ( P =0.01). No significant difference between the two different drill diameters was recorded ( P =1). For all three subgroups (intact, 8 mm, 6 mm) the Hounsfield units-values and the absolute resistance force showed significant correlations (intact: ρ=0.859; P <0.001; 8 mm: ρ=0.902; P <0.001; 6 mm: ρ=0.835; P <0.001). Conclusion. The transpedicular approach significantly reduces the axial resistance force of the pedicle, which may lead to pedicle fracture. Bone quality correlated positively with the absolute resistance force of the pedicle, whereas the influence of the drill hole diameter plays only a limited role.
BackgroundAn increasing number of commercially available wearables provide real‐time feedback on running biomechanics with the aim to reduce injury risk or improve performance.ObjectiveInvestigate ...whether real‐time feedback by wearable insoles (ARION) alters running biomechanics and improves running economy more as compared to unsupervised running training. We also explored the correlation between changes in running biomechanics and running economy.MethodsForty recreational runners were randomized to an intervention and control group and performed ~6 months of in‐field training with or without wearable‐based real‐time feedback on running technique and speed. Running economy and running biomechanics were measured in lab conditions without feedback pre and post intervention at four speeds.ResultsTwenty‐two individuals (13 control, 9 intervention) completed both tests. Both groups significantly reduced their energetic cost by an average of −6.1% and −7.7% for the control and intervention groups, respectively. The reduction in energy cost did not significantly differ between groups overall (−0.07 ± 0.14 J∙kg∙m−1, −1.5%, p = 0.63). There were significant changes in spatiotemporal metrics, but their magnitude was minor and did not differ between the groups. There were no significant changes in running kinematics within or between groups. However, alterations in running biomechanics beyond typical session‐to‐session variation were observed during some in‐field sessions for individuals that received real‐time feedback.ConclusionAlterations in running biomechanics as observed during some in‐field sessions for individuals receiving wearable‐based real‐time feedback did not result in significant differences in running economy or running biomechanics when measured in controlled lab conditions without feedback.
Background: Posterior lumbar interbody fusion (PLIF) is performed using various interbody spacers. Wang and colleagues (2014) created an interbody cage by compressing morselized corticocancellous ...bone chips. They concluded that the newly morselized bone interbody fusion (MBIF) cage can provide appropriate stiffness at the physiologic loads. The purposes of this study were to replicate Wang and colleagues study by creating the MBIF cage and in case of failure, to redesign the MBIF cage and assess its biomechanical properties in comparison with the PEEK cage. Methods: Lamina and spinous processes of fresh frozen spine segments were morselized and placed in a bullet-shaped mold and compressed with 8 kN force. When we redesigned the MBIF cage, the mold was lined with a thin layer of stainless-steel mesh acting as a scaffold. The redesigned MBIF (n = 6) and PEEK (n = 6) cages were place between 2 blocks of solid polyurethane foam, simulating healthy bone, and underwent axial compression while we recorded compressive force and displacement curve. The experiment was repeated with polyurethane foam simulating osteoporotic bone. Results: The MBIF cage collapsed under axial compression. In the healthy bone group, peak force at 3-mm displacement was significantly lower in the redesigned MBIF cage compared with the PEEK cage. At 5-mm displacement, peak force did not differ significantly between the 2 cages. At lower levels of displacement, the redesigned MBIF construct failed by loss of height of the cage, while the PEEK cage construct failed by destruction of polyurethane foam contact surface. In osteoporotic bone, peak forces at 3 and 5 mm were significantly higher in the redesigned MBIF cage than in the PEEK cage constructs. Conclusion: The results of Wang and colleagues (2014) were not reproducible in our study. The redesigned MBIF cage showed comparable biomechanical properties to those of the PEEK cage in healthy bone construct and outperformed the PEEK cage in osteoporotic bone construct. The redesigned MBIF can be a viable option instead of a synthetic cage in patients with poor bone quality.
The brain is one of the softest organs in the human body and is protected from mechanical perturbation by the skull. In contrast, the enteric nervous system of our intestines is embedded in a ...compliant contractile tissue and is constantly subject to high mechanical strain. Here we investigate the mechanical properties of enteric ganglia in the adult mouse gut by combining atomic force microscopy, immunohistochemistry and collagen I mapping by second harmonic generation microscopy. We find that collagen is most enriched in the submucosa and could image the thin collagen shell surrounding each enteric ganglion. Smooth muscle was the stiffest tissue in the gut. The relative stiffness of ganglia, submucosa and epithelium is respectively 70%, 25% and 70% that of the muscle, indicating that myenteric ganglia are softer than the surrounding musculature, and that the softest part of the gut is the collagen rich submucosa. We could not detect a contrast of stiffness between neural and glial cells. We conclude by discussing the mechanically supportive role attributed to glial cells in the light of previous studies in the central nervous system.
Objectives:
To evaluate the biomechanical characteristics of an all-inside meniscal root repair procedure versus transtibial repair
Methods:
Nine paired cadaveric knees were prepared with pressure ...mapping sensors and underwent pressure testing to obtain peak pressures, average pressures, and femorotibial contact area in both the medial and lateral compartments. Testing was performed in three states: meniscus intact, meniscal root cut, and following meniscal root repair with all-inside repair technique. Additionally, testing was completed on eight pairs of cadaveric knees to compare stiffness and maximal load to failure between all-inside and transtibial meniscal root repair techniques.
Results:
In the medial compartment, there were significant increases in both median peak pressures (p=0.017) and median average pressures (p=0.047) in the root cut state compared to the intact state (+636 kilopascal (kPA) 246-1026 95% confidence interval (95%CI) and +190 kPA 49-330 95%CI respectively). All-inside meniscal root repair restored median peak pressures and median average pressures to approach that of the intact meniscus (p=0.293; +311 kPA -79-701 95%CI and p=0.171; +137 kPA -3-277 95%CI respectively). In the lateral compartment, there were also significant increases in both median peak pressures (p=0.025) and median average pressures (p=0.05) in the root cut state compared to the intact state (+718 kPA 246-1191 95%CI and +203 kPA 51-355 95%CI) respectively). All-inside meniscal root repair restored median peak pressures and median average pressures to be not significantly different from the intact state (p=0.399; +322 kPA -150-795 95%CI and p=0.97; +18 kPA - 134-171 95%CI respectively). There was no difference between repair techniques regarding load to failure (p=0.896).
Conclusions:
All-inside meniscal root repair restores median peak and average pressures that approach that of the native, intact meniscus. Compared to a transtibial meniscal root repair technique, all-inside repair demonstrated equivalent load to failure.
Objectives:
To limit risk of recurrent dislocation, subsequent injury, and more complex surgeries, it is critical to understand the best techniques to repair a soft-tissue Bankart lesion in the ...setting of minimal bone loss. To the authors’ knowledge, there is no current biomechanical data comparing tensionable knotless all-suture anchors to knotted all-suture anchors and hardbody knotless anchors in labral repair constructs. Therefore, the purpose of this study was to perform a quantitative biomechanical comparison of three labral fixation devices for soft-tissue Bankart lesions: soft body tensionable knotless anchor (SB knotless), knotted soft body anchor (SB knotted), knotless interference polyetheretherketone (PEEK) hardbody anchor (HB knotless). The authors hypothesized that the three anchor types would exhibit similar biomechanical properties including elongation, failure load, and stiffness but that the SB knotless would display different failure mechanisms from the SB knotted and HB knotless anchors.
Methods:
Twenty-one glenoid cadavers were randomized to 3 groups: SB knotless (Arthrex 1.8mm FiberTak Knotless All-suture Anchor), SB knotted (Arthrex 1.8mm FiberTak Knotted single loaded All- Suture Anchor), and HB knotless (Arthrex 2.9mm PushLock Knotless PEEK anchor). The humeral head was disarticulated and artificial Bankart lesions were created at the anteroinferior (AI) labrum. Anchors were placed at the 3:30, 4:30, and 5:30 positions, and sutures were passed through 1cm of tissue (Figure 1). Knotted anchors were tied with five square knots. Anchors were tested simultaneously as one construct by pulling the capsular tissue connected to the AI quadrant. Cyclic loading (5-25 N, 100 cycles) was followed by load-to-failure testing (15mm/min). Mechanical testing variables were collected, and failure mechanisms were recorded per individual anchor. Statistical comparisons were made among groups including ANOVA for normally-distributed continuous variables, Kruskal-Wallis for non- parametric continuous variables, and Fisher’s Exact test for categorical variables.
Results:
There were no significant differences among groups in cadaveric age (p = 0.43), body mass index (p = 0.42), bone mineral density (p = 0.84), laterality (p = 0.26), or sex (p = 0.098). There was no significant difference between groups in cyclic elongation measured from the first to last cycle during cyclic loading (p = 0.40). Ultimate load to failure between SB knotless (309.7 ± 125.6 N), SB knotted (226.40 ± 34.8 N), and HB knotless (256.5 ± 90.5 N) did not significantly differ (p = 0.25) (Table 1). Failure mechanisms significantly differed among groups; mechanisms included anchor pull-out (SB knotless 33.3%; SB knotted 23.8%; HB knotless 28.6%), suture pull-through (SB knotless 66.7%; SB knotted 38.1%; HB knotless 33.3%), and anchor fixation failure, defined as knot failure for knotted anchors or locking mechanism failure for knotless anchors (SB knotless 0%; SB knotted 38.1%; HB knotless 38.1%, p = 0.008) (Figure 2).
Conclusions:
The SB knotless, SB knotted, and HB knotless labral fixation anchors studied exhibit comparable elongation during cyclic loading, stiffness, and ultimate loads to failure. However, the SB knotless anchor avoids the risk of knot failure and interference failure inherent to SB knotted and HB knotless interference anchors, respectively. This data supports the benefit of SB knotless anchors for anteroinferior labral repair in limiting knot failure seen with knotted anchors and perhaps demonstrating that all- suture anchors may have better locking mechanism quality than their PEEK counterpart. How and if these mechanical properties of the anchors correlate with clinical results for soft-tissue Bankart repair requires further investigation, and likely one with high power from multi- center studies to detect if subtle differences exist.
