Finite element study of sagittal fracture location on thoracolumbar fracture treatment.

Background: Posterior internal fixation is the main method used for the treatment of thoracolumbar fractures. Fractures often occur in the upper 1/3 of the vertebral body. However, they can also occur in the middle or lower 1/3 of the vertebral body. At present, there is no report discussing the potential effects of sagittal location on instrument biomechanics or surgical strategy. The object of this study was to investigate the effect of the sagittal location of the fracture region of the vertebral body on the biomechanics of the internal fixation system and surgical strategy. Methods: A finite element model of the T11-L3 thoracolumbar segment was established based on a healthy person's CT scan. Different sagittal fracture location finite element models were created by resection of the upper 1/3, middle 1/3, and lower 1/3 of the L1 vertebral body. Three surgical strategies were utilized in this study, namely, proximal 1 level and distal 1 level (P1-D1), proximal 2 level and distal 1 level (P2-D1), and proximal 1 level and distal 2 levels (P1-D2). Nine fixation finite element models were created by combining fracture location and fixation strategies. Range of motion, von Mises stress, and stress distribution were analyzed to evaluate the effects on the instrument biomechanics and the selection of surgical strategy. Results: In all three different fixation strategies, the maximum von Mises stress location on the screw did not change with the sagittal location of the fracture site; nevertheless, the maximum von Mises stress differed. The maximum rod stress was located at the fracture site, with its value and location changed slightly. In the same fixation strategy, a limited effect of sagittal location on the range of motion was observed. P2D1 resulted in a shorter range of motion and lower screw stress for all sagittal locations of the fracture compared with the other strategies; however, rod stress was similar between strategies. Conclusion: The sagittal location of a fracture may affect the intensity and distribution of stress on the fixation system but does not influence the selection of surgical strategy.

[Preoperative standing to prone spinal-pelvic sagittal parameter changes in old traumatic spinal fractures with kyphosis].

Objective: To investigate the changes in spinal-pelvic sagittal parameters from preoperative standing to prone position in old traumatic spinal fractures with kyphosis. Methods: The clinical data of 36 patients admitted between December 2016 and June 2021 for surgical treatment of old traumatic spinal fractures with kyphosis, including 7 males and 29 females, aged from 50 to 79 years (mean, 63.9 years), were retrospectively analyzed. Lesion segments included 2 cases of T 11, 12 cases of T 12, 2 cases of T 11, 12, 4 cases of T 12 and L 1, 12 cases of L 1, 2 cases of L 2, 1 case of L 2, 3, and 1 case of L 3. The disease duration ranged from 4 to 120 months, with an average of 19.6 months. Surgical procedures included Smith-Petersen osteotomy in 4 cases, Ponte osteotomy in 6 cases, pedicle subtraction osteotomy in 2 cases, and improved fourth level osteotomy in 18 cases; the remaining 6 cases were not osteotomized. The bone mineral density ranged from -3.0 to 0.5 T, with a mean of -1.62 T. The spinal-pelvic sagittal parameters from preoperative standing to prone positions were measured, including local kyphosis Cobb angle (LKCA), thoracic kyphosis (TK), lumbar lordosis (LL), sacral slope (SS), pelvic tilt (PT), and PI and LL mismatch (PI-LL). The kyphotic flexibility=(preoperative standing LKCA-preoperative prone LKCA)/preoperative standing LKCA×100%. Spinal-pelvic sagittal parameters were compared between standing position and prone position before operation, and Pearson correlation was used to judge the correlation between the parameters of standing position and prone position before operation. Results: When the position changed from standing to prone, LKCA and TK decreased significantly ( P<0.05), while SS, LL, PT, and PI-LL had no significant difference ( P>0.05). Pearson correlation analysis showed that LL was significantly correlated with SS and PI-LL in both standing and prone positions ( P<0.05), and the correlation strength between LL and SS in prone position was higher than that in standing position. In the standing position, LKCA was significantly correlated with SS and PT ( P<0.05). However, when the position changed from standing to prone, the correlation between LKCA and SS and PT disappeared, while PT and PI-LL was positive correlation ( P<0.05). The kyphotic flexibility was 25.13%-78.79%, with an average of 33.85%. Conclusion: For the patients of old traumatic spinal fractures with kyphosis, the preoperative LKCA and TK decrease significantly from standing position to prone position, and the correlation between spinal and pelvic parameters also changed, which should be taken into account in the formulation of preoperative surgical plan.

Bidirectionally Regulating Gamma Oscillations in Wilson-Cowan Model by Self-Feedback Loops: A Computational Study.

The Wilson-Cowan model can emulate gamma oscillations, and thus is extensively used to research the generation of gamma oscillations closely related to cognitive functions. Previous studies have revealed that excitatory and inhibitory inputs to the model can modulate its gamma oscillations. Inhibitory and excitatory self-feedback loops are important structural features of the model, however, its functional role in the regulation of gamma oscillations in the model is still unclear. In the present study, bifurcation analysis and spectrum analysis are employed to elucidate the regulating mechanism of gamma oscillations underlined by the inhibitory and excitatory self-feedback loops, especially how the two self-feedback loops cooperate to generate the gamma oscillations and regulate the oscillation frequency. The present results reveal that, on one hand, the inhibitory self-feedback loop is not conducive to the generation of gamma oscillations, and increased inhibitory self-feedback strength facilitates the enhancement of the oscillation frequency. On the other hand, the excitatory self-feedback loop promotes the generation of gamma oscillations, and increased excitatory self-feedback strength leads to the decrease of oscillation frequency. Finally, theoretical analysis is conducted to provide explain on how the two self-feedback loops play a crucial role in the generation and regulation of neural oscillations in the model. To sum up, Inhibitory and excitatory self-feedback loops play a complementary role in generating and regulating the gamma oscillation in Wilson-Cowan model, and cooperate to bidirectionally regulate the gamma-oscillation frequency in a more flexible manner. These results might provide testable hypotheses for future experimental research.