Multiscale structural characterization of the vertebral endplate in animal models.

Research in the field of spinal biomechanics, including analyses of the impact of implants on the stability of the spine, is conducted extensively in animal models. One of the basic problems in spinal implantation is the transfer and distribution of loads carried by the spine on the surfaces of the vertebral bodies. An important factor in proper cooperation of spinal implants with the vertebrae is the endplate (EP), which is why the EP in the animal model used for testing should be as similar as possible to the human EP. Therefore, this study involved multiscale structural and morphometric analyses of the animal models most commonly used in spinal biomechanics research, i.e. pig, ovine, and bovine tail. The tests were performed on 28 lumbar porcine, ovine, and bovine vertebrae. Both cranial and caudal EPs were analysed in three selected areas: anterior, middle, and posterior EPs. The conducted tests included a morphometric analysis of the trabecular bone (TB) layer of the EP as well as microscopic analysis at the mesoscale (total thickness) and microscale (thickness of the individual EP layers). The porcine EP had a characteristic increased circumferential thickness (~3 mm) with a significant narrowing in the central region (50%-60%). The convex cranial ovine EP had a constant thickness throughout the cross-section and the concave caudal EP showed ~35% narrowing in the central region. The thickest EPs were observed in the bovine tail model with negligibly small narrowing in the central region (~5%). The thickness of the cartilaginous layer in the porcine and bovine models reached up to 1 mm in the peripheral regions and decreased in the central part. The growth plate layer had a similar thickness in all the models. On the other hand, the narrowing of the total thickness of the EPs in the central region was mainly due to a decrease in the VEP thickness. In the ovine and bovine models, the central region of the EP was characterized by large isotropy and trabeculae of mixed or rod-like shape. By contrast, in the pig, this region had plate-like trabeculae of anisotropic nature. The porcine model was identified as best reflecting the shape and structure of the human EP and as the best surrogate model for the human EP model. This choice is particularly important in the context of biomechanical research.

PGS/HAp Microporous Composite Scaffold Obtained in the TIPS-TCL-SL Method: An Innovation for Bone Tissue Engineering.

In this research, we synthesize and characterize poly(glycerol sebacate) pre-polymer (pPGS) (1H NMR, FTiR, GPC, and TGA). Nano-hydroxyapatite (HAp) is synthesized using the wet precipitation method. Next, the materials are used to prepare a PGS-based composite with a 25 wt.% addition of HAp. Microporous composites are formed by means of thermally induced phase separation (TIPS) followed by thermal cross-linking (TCL) and salt leaching (SL). The manufactured microporous materials (PGS and PGS/HAp) are then subjected to imaging by means of SEM and µCT for the porous structure characterization. DSC, TGA, and water contact angle measurements are used for further evaluation of the materials. To assess the cytocompatibility and biological potential of PGS-based composites, preosteoblasts and differentiated hFOB 1.19 osteoblasts are employed as in vitro models. Apart from the cytocompatibility, the scaffolds supported cell adhesion and were readily populated by the hFOB1.19 preosteoblasts. HAp-facilitated scaffolds displayed osteoconductive properties, supporting the terminal differentiation of osteoblasts as indicated by the production of alkaline phosphatase, osteocalcin and osteopontin. Notably, the PGS/HAp scaffolds induced the production of significant amounts of osteoclastogenic cytokines: IL-1ß, IL-6 and TNF-α, which induced scaffold remodeling and promoted the reconstruction of bone tissue. Initial biocompatibility tests showed no signs of adverse effects of PGS-based scaffolds toward adult BALB/c mice.

Feasibility and accuracy of new insertion technique of S1 transpedicular screw. Computed tomography-based morphometric analysis.

OBJECTIVE: To assess feasibility and accuracy of a new insertion technique of S1 transpedicular screw. SUMMARY OF BACKGROUND DATA: Transpedicular stabilization in the first sacral vertebra (S1) is a technically demanding surgical procedure with inherent risk of loosening of the implant. A modification of the technique was recently proposed, along with the analytical verification which was performed based on the available literature. In the study, we performed radiological assessment of screws inserted into the S1 using the classical and modified techniques. METHODS: The analysis was performed in two parts. The first part was performed on eight cadaver specimens after implantation of the screws. In the second part, we used computed tomography images of patients with degenerative disk disease with a superimposed representation of screws. The thickness of the posterior cortex adherent to the screws, screw trajectory and their position with regard to the spinal canal was measured. The area of posterior cortex in contact with the screws was also calculated. RESULTS: The contact length and area was found to be two times greater for screws introduced with the modified technique. The convergence angle was comparable between the techniques, despite the shift of entry point. There was no canal breach, although with the modified technique the screws passed closer to the spinal canal. CONCLUSIONS: The modified technique is considered safe. In this technique, the screws pass through a thicker portion of the posterior cortex compared to the classical technique that aims at improving the stability of the fixation.

Mechanical and Structural Evaluation of the PA12 Desktop Selective Laser Sintering Printed Parts Regarding Printing Strategy.

Despite the dynamic development of additive manufacturing technologies, including selective laser sintering (SLS), there is still limited information on the impact of key factors in printing strategy, on the properties of three-dimensional (3D) printed parts. Such factors, such as the orientation of printed layers toward the powder bed or elements target dimensions, seem to be particularly important, from both a mechanical and a structural point of view. Besides, the scientific articles mainly focus on the analysis of one type of loading condition in the samples, that is, the uniaxial tensile test, which were printed on industrial SLS printers. This is a considerable limitation because very often not only tensile forces but also compressive forces act on the structural elements. Therefore, this study aimed at evaluating the influence of desktop SLS printed parts' orientation and diameter on their structural and mechanical parameters. The mechanical properties of samples printed from PA12 powder on the desktop SLS 3D printer were tested in uniaxial tensile and compression tests, as well as structural properties were investigated. For the purposes of this article, 5 angular orientations of the samples in relation to the powder bed and three diameters of cylindrical samples were analyzed. The research has shown that in the case of samples subjected to tensile load, the printing strategy is important, and the best mechanical parameters are obtained for parts printed at an angle of 0°, that is, in the powder bed's plane. The highest values of mechanical parameters were obtained for a part oriented at an angle of 0°. In the case of the uniaxial compression test and structural parameters, the parts orientation turned out to be an insignificant factor affecting the tested parameters. However, the diameter of printed elements was proven to have a significant influence; the best geometric and dimensional representation was observed for parts biggest in size.

Trabecular bone remodelling in the femur of C57BL/6J mice treated with diclofenac in combination with treadmill exercise.

PURPOSE: Analgesic treatment with diclofenac deteriorates bone structure and decreases biomechanical properties. This bone loss has been though to be reversed by training. The impact of exercise on bone treated with diclofenac (DF) has reminded elusive. In the present study, we assayed the combined impact of exercises and DF on mouse femur. METHODS: The femur samples we obtained from 30 days treated C57BL/6J female mice. The training group ran on a horizontal treadmill at 12 m/min by 30 min a day (5% grade/slope). The group of ten mice treated with DF received the drug subcutaneously every day (5 mg/kg of body weight/day). The combined group ran on the treadmill and obtained DF. After 30 days, we sacrificed mice and studied their femurs using microcomputed tomography (µCT), dynamic mechanical analysis (DMA) and nanoindentation. RESULTS: We observed that treadmill running and DF decreased trabecular bone volume and mineral density. Combined effect of training and DF was not additive. A significant interaction of both parameters suggested protective effect of training on bone loss provoked by DF. The femur cortical bone shell remained untouched by the training and treatment. The training and the DF treatment did not alter the storage modulus E' significantly. The unchanged storage modulus would be suggesting on the unaltered bone strength. CONCLUSIONS: We concluded that even relatively short time of training with concomitant DF treatment could be protective on trabecular bone. Although viscoelastic properties of the entire femur were not modulated, femur trabecular tissue was thinned by treatment with DF and protected by training.

Influence of body posture on foot load distribution in young school-age children.

Young school-age children are particularly prone to postural defects because they are in a period of development of the spine that is exposed to a number of factors impairing its normal growth. A change in the shape of the spinal column causes a shift in the centre of gravity. Therefore, this study attempted to assess the influence of body posture on distribution of the load transferred by the lower limbs. METHODS: For each of the examined children, this study determined the parameters describing the body posture with the use of the photogrammetric method and the parameters describing plantar force distribution. The statistical analyses were performed using the U Mann- Whitney test and the student's t-test. The correlations between the parameters of the body posture and the parameters describing the foot load distribution were analysed using the Pearson correlation coefficient. These analyses were performed at a statistically significant level of p < 0.05. RESULTS: The tests conducted showed an occurrence of postural defects in about 42% of the subjects and excessively uneven loading of the lower limbs in about 65% of the children. CONCLUSIONS: The authors obtained a medium intensity correlation between the analysed parameters for the groups of boys and girls.

Biomechanical analysis of the durability of a modified S1 vertebrae transpedicular screws insertion technique.

BACKGROUND: One of the most important elements of the transpedicular screw implantation technique, which enables a strong screw-bone interface, is the precise choice of the site of screw insertion and the screw's trajectory. Due to the complex biomechanics of the lumbosacral interface and different shape of the sacrum, fixation of this segment remains a challenge for surgeons. Because of this, Kubaszewski et al. proposed a modified technique in which the entry point for screw insertion in the S1 vertebra is changed. METHODS: Six human cadaver specimens of the S1 vertebrae were examined. Two transpedicular screws were inserted into the body of each examined vertebra using two implantation methods with different screw entry points and trajectories. The screws were subjected to cyclic preloading, followed by the pull-out test. The ultimate pull-out force, displacement, stiffness, and failure energy were measured. FINDINGS: The average pull-out force obtained for the standard method of implantation was 498 N (SD 201), whereas for the modified technique, it was 1308 N (SD 581). Displacement of the inserted screws in the new method was 36% higher than in the case of the standard method. This method is also characterized by the greater stiffness of the obtained interface and greater failure energy than the normally used technique. INTERPRETATION: The obtained results demonstrate that the use of the new technique of implantation significantly increases the strength of the obtained screw-bone interface. It should also increase the success rate of the performed fixations and increase the safety of such fixations in clinical practice.

Biomechanics of diving: the influence of the swimming speed on the kinematics of lower limbs of professional divers.

PURPOSE: The aim of this study is to evaluate the influence of the swimming speed during diving on the biomechanical parameters describing the movement of selected measurement points of the lower limb in professional divers. METHODS: The study involved a group of 4 professional divers whose movement was recorded during underwater swimming at slow (approx. 0.4 m·s-1), medium (approx. 0.5 m·s-1), and fast (approx. 0.8 m·s-1) pace. RESULTS: During swimming at medium speed, the divers made a smaller displacement (along the axes Y) of the midpoint of fin than during swimming at fast speed. The range of motion in the ankle joint increased in fast speed in comparison with low and medium swimming speed. The same relationship was noted for the obtained velocity and angular acceleration in the hip, knee and ankle joints. The authors observed that during swimming at slow pace the divers choose movement ensuring high swimming comfort while the efficiency of motion is a secondary factor. On the other hand, during swimming at higher pace, the applied movement pattern ensures far greater efficiency rather than swimming comfort. CONCLUSION: The conducted analysis showed that divers adjust the movement of their lower limbs to the swimming pace.