Optimizing Lumbar Pedicle Screw Trajectory Utilizing a 3D-Printed Drill Guide to Ensure Placement of Pedicle Screws Into Higher Density Bone May Improve Pedicle Screw Pullout Resistance.

BACKGROUND: Lower preoperative Hounsfield Unit (HU) values of vertebral body are associated with pedicle screw (PS) loosening after implantation with traditional trans-pedicular trajectory. However, the relationship between trajectory HU value and PS fixation quality remains unknown. This study aimed to investigate if 3-dimensionally (3D)-printed guider directed accurate implantation of pedicle screw could increase the anti-pulling properties of screws. METHODS: 3D models of cadaveric spines were reconstructed by using computed tomography image and PS trajectories were designed for both sides of vertebra. The designed trajectories were divided into high HU group and low HU group. PS implantation with 3D-printed screw guide can be in complementary shape with target vertebra. Throughout 3D finite element analysis and biomechanical tests, the pull-out strength of screws in high or low trajectory HU groups were compared. RESULTS: The HU value was 132 ± 13 (mean ± standard deviation) in low HU group and 189 ± 17 in high HU group. The distance between planned trajectories and actual trajectories was 1.69 ± 0.4 mm. Biomechanical tests showed that in the high trajectory HU group the pull-out strength of screws was 750.41 ± 80.65 N; compared with 655.83 ± 74.31 N in the low trajectory HU group, the difference was statistically significant. When simulated with the finite element method, the pull-out strength of low HU trajectory pedicle screws was lower than that of high HU trajectory pedicle screws. CONCLUSIONS: Preoperative computer-assisted trajectory design using a 3D-printed screw guide may direct more accurate implantation with optimal implantation trajectory, and may provide a new way to improve pedicle screw fixation.

Effect of a New Annular Incision on Biomechanical Properties of the Intervertebral Disc.

OBJECTIVE: To compare the biomechanical properties of a novel annular incision technique, an oblique incision made approximately 60° to the spinal column, with the traditional transverse and longitudinal annular slit incision in an ex vivo sheep lumbar spine model. METHODS: Sixteen sheep lumbar spines were used for the current ex vivo biomechanical comparative study. Functional spine unit (FSU) specimens composed of two vertebrae and one disc in the middle was cut from the whole lumbar spine. Annular slit incisions of 5 mm were made in different directions with a 15-blade knife at the intervertebral disc, following which partial discectomy was performed to produce the following groups: control with no incision, transverse slit, longitudinal slit and oblique slit groups. The specimens were then subjected to flexion-extension, lateral bending, axial rotation and compression tests. RESULTS: As expected, the control group showed the least range of motion (ROM) in the flexion-extension test. The oblique slit group showed a trend toward a smaller ROM than the transverse and longitudinal groups in 1, 2, 3 and 5 Nm flexion-extension tests; these differences were not statistically significant (P > 0.05). In addition, the transverse (5.80° ± 0.20°), longitudinal (5.77° ± 0.67°) and oblique (5.47° ± 0.43°) slit groups showed a significantly larger ROM than the control group (3.22° ± 0.28°) in 2 Nm lateral bending tests (P < 0.05). Compared with the transverse and longitudinal groups, the oblique group also showed a trend toward a smaller ROM in lateral bending tests (P > 0.05). Following increments in the axial torsion force, the ROM was greater in all four experimental groups than the ROM with 1 Nm axial torsion. Furthermore, a significantly smaller axial rotational ROM was found in the oblique than the transverse group for 1 and 5 Nm force (P < 0.05). With increase in the axial force to 5 Nm, the ROM in the oblique slit group (4.71° ± 0.52°) was significantly smaller than that in the transverse group (7.25° ± 0.46°, P < 0.05), but not significantly different from that of the longitudinal slit group (5.84° ± 0.23°, P > 0.05). Comparable ultimate loads to failure were found in the oblique, transverse and longitudinal groups; the highest ultimate load to failure being in the control group (P > 0.05). CONCLUSION: The novel oblique slit annular incision to the intervertebral disc showed a trend toward better biomechanical properties than the traditional transverse and longitudinal slit incisions.

Beta1 integrin inhibits apoptosis induced by cyclic stretch in annulus fibrosus cells via ERK1/2 MAPK pathway.

Low back pain is associated with intervertebral disc degeneration (IVDD) due to cellular loss through apoptosis. Mechanical factors play an important role in maintaining the survival of the annulus fibrosus (AF) cells and the deposition of extracellular matrix. However, the mechanisms that excessive mechanical forces lead to AF cell apoptosis are not clear. The present study was to look for how AF cells sense mechanical changes. In vivo experiments, the involvement of mechanoreceptors in apoptosis was examined by RT-PCR and/or immunoblotting in the lumbar spine of rats subjected to unbalanced dynamic and static forces. In vitro experiments, we investigated apoptotic signaling pathways in untransfected and transfected AF cells with the lentivirus vector for rat ß1 integrin overexpression after cyclic stretch. Apoptosis in AF cells was assessed using flow cytometry, Hoechst 33258 nuclear staining. Western blotting was used to analyze expression of ß1 integrin and caspase-3 and ERK1/2 MAPK signaling molecules. In the rat IVDD model, unbalanced dynamic and static forces induced apoptosis of disc cells, which corresponded to decreased expression of ß1 integrin. Cyclic stretch-induced apoptosis in rat AF cells correlated with the activation of caspase-3 and with decreased levels of ß1 integrin and the phosphorylation levels of ERK1/2 activation level. However, the overexpression of ß1 integrin in AF cells ameliorated cyclic stretch-induced apoptosis and decreased caspase-3 activation. Furthermore, ERK1/2-specific inhibitor promotes apoptosis in vector ß1-infected AF cells. These results suggest that the disruption of ß1 integrin signaling may underlie disc cell apoptosis induced by mechanical stress. Further work is necessary to fully elucidate the pathophysiological mechanisms that underlie IVDD caused by unbalanced dynamic and static forces.

[Determination of trace element silver in animal serum, tissues and organs by microwave digestion-ICP-MS].

Nowadays, the silver is widely used in the biological field and its biological safety catches great attention. It is important to know the distribution of silver ions within the biological organism and the toxic threshold concentration in the tissue. Therefore, a highly sensitive method for measurement of trace amount of silver ion in the medical biological samples is needed. With its high sensitivity for detection of metal ions, inductively coupled plasma mass spectrometry (ICP-MS) method is well suited for quantification of trace amount of silver ion in such samples, but method development is still in its infancy. Consequently, a simple and convenient method for determination of trace amount of silver in the animal serum, tissues or organs was developed, in which the samples were subjected to the microwave digestion, followed by the ICP-MS analysis. To begin with, the samples of serum, muscle, bone marrow, bone, heart, liver, spleen, and kidney were sequently processed in 5 mL of HNO3 and 2 mL of H2O2 solution. Then the samples were completely digested by microwave with the power of 2 000 watts. The temperature was raised gradually by 3-step program. Moreover, the data achieved were reproducible and the method was time saving and especially for large amounts of sample processing. Then the digested solutions were diluted to constant volume. Finally, the concentration of 107Ag in the samples was analyzed by the method of ICP-MS under the optimized conditions. Element yttrium (Y) was used as the internal standard to compensate for matrix suppression effect and improve the accuracy of measurement. For one thing, the analytical results showed that the detection limit of the trace element 107Ag was 0.98 µg · kg(-1), and furthermore, the correlation coefficient of standard curve was 0.999 9. For another thing, the recovery rate of the silver element ranged from 98% to 107%, which was calculated according to measured quantity before adding standard, adding standard and measured quantity after adding standard. At the same time, the relative standard deviation (RSD) of the method was in the range of 2.0%-4.3%. The concentrations of element silver in animal serum, tissues and organs were determined by the aboved method. The obtained results showed that silver ions were mainly accumulated in the liver after they were intaken into the body. The results suggested that the microwave digestion-ICP-MS method could accurately determine the trace element Ag in the body. The method developed has good feasibility and is suitable for the determination of trace element Ag in various types of medical and biological samples, especially for large quantities of biological samples. The process has the advantages of easysample processing and it is simple and convenient. In addition, the accurate results could be obtained in a short time with high sensitivity. Last but not least, the method provides the guidance for the determination of trace elements in other biological samples.

Unilateral versus bilateral instrumented transforaminal lumbar interbody fusion in two-level degenerative lumbar disorders: a prospective randomised study.

PURPOSE: The aim of this study was to analyse the clinical and radiological outcomes of unilateral versus bilateral instrumented TLIF in two-level degenerative lumbar disorders. METHODS: A prospective randomised clinical study was performed from January 2008 to May 2011. Sixty-eight consecutive patients with severe low back pain and radicular pain were divided randomly into the unilateral (n = 33) or bilateral (n = 35) pedicle screw fixation group based on a random number list. Operative time, blood loss, duration of hospital stay, fusion rate, complication rate and implant costs were recorded and analysed statistically. Visual analog scale (VAS) scores, Oswestry Disability Index (ODI), and SF-36 were used to assess the preoperative and postoperative clinical results in the two groups. RESULTS: No differences were observed between the two groups with respect to demographic data. The patients of the two groups had significant improvement in functional outcome compared to preoperatively. There was no significant difference comparing fusion rate, complication rate and duration of hospital stay between the two groups at postoperative follow-up (P > 0.05). However, compared with the bilateral pedicle screw group, a significant decrease occurred in operative time, blood loss and implant costs in the unilateral group. CONCLUSION: Two-level unilateral instrumented TLIF is an effective and safe method with reduced operative time and blood loss for multiple-level lumbar diseases. But it is imperative that the larger cage should be appropriately positioned to support the contralateral part of the anterior column by crossing the midline of the vertebral body.

Quantitative T2 mapping to characterize the process of intervertebral disc degeneration in a rabbit model.

BACKGROUND: To investigate the potential of T2 mapping for characterizing the process of intervertebral disc degeneration (IDD) in a rabbit model. METHODS: Thirty-five rabbits underwent an annular stab to the L4/5 discs (L5/6 discs served as internal normal controls). Degenerative changes were graded according to the modified Thompson classification and quantified in T2 respectively at pre-operation, 1, 3, 6, 12 and 24 weeks postoperatively. After MRI analysis, expression analysis of aggrecan and type II collagen gene in nucleus pulposus (NP) was performed using real time polymerase chain reaction (real-time PCR). The longitudinal changes in NP T2 and gene expressions were studied by repeated measures and ANOVA, linear regression was performed for their correlations through the process of IDD. The reliability analysis of method of measurement of NP T2 was also performed. RESULTS: There was a strong inverse correlation between NP T2 and Thompson grades (r = -0.85). The decline of L4/5 NP T2 through 24 weeks was nonlinear, the most significant decrease was observed in 3 weeks postoperatively (P<0.05). The tendency was confirmed at gene expression levels. NP T2 correlated strongly with aggrecan (R² = 0.85, P<0.01) and type II collagen (R² = 0.78, P<0.01) gene expressions. The intraclass correlation coefficients for interobserver and intraobserver reliability were 0.963 and 0.977 respectively. CONCLUSIONS: NP T2 correlates well with aggrecan and type II collagen gene expressions. T2 mapping could act as a sensitive, noninvasive tool for quantitatively characterizing the process of IDD in longitudinal study, help better understanding of the pathophysiology of IDD, assist us to detect the degenerative cascade, and develop a T2-based quantification scale for evaluation of IDD and efficacy of therapeutic interventions.

[Using perfusion bioreactor for mesenchymal stem cell proliferation in large tricalcium phosphate scaffold].

OBJECTIVE: To investigate the feasibility of using perfusion culture bioreactor for bone mesenchymal stem cell proliferation in large scale beta-tricalcium phosphate (beta-TCP) scaffold. METHODS: In the dynamic perfusion culture group, the porous beta-TCP cylindrical scaffolds combined with the sheep mesenchymal stem cells were continuously perfused with the complete alpha-MEM medium by a peristaltic pump for 1, 2 and 4 weeks. While in the static culture group, the hybrid constructs were immersed in the medium without perfusion for 2 and 4 weeks. The cell proliferation and distribution were examined by the daily glucose consumption, the cell viability and undecalcified histological study. RESULTS: The daily glucose consumption increased with time. The increase was much more evident in the first 2 weeks than in the last 2 weeks. The daily glucose consumption was higher in the dynamic culture group than in the static culture group. The cell viability also increased with time. It was higher in the dynamic culture group. In comparison to 2-week culture, the cell viability was significantly higher after 4-week culture in the dynamic culture group (P < 0.05), while it was not significantly different after 4-week culture in the static culture group (P > 0.05). Under dynamic perfusion culture, the mesenchymal stem cells survived and proliferated through the scaffolds. However, the mesenchymal stem cells survived and proliferated only in the peripheral pores of the scaffolds under static culture. Histomorphometrical study indicated that there were much more cells in dynamic culture group than in the static group. The cell/pore rate was not significantly different between 2-week static culture and 4-week static culture (P > 0.05). However, the cell/pore rate was significantly higher after 4-week dynamic culture than after 2-week dynamic culture (P < 0.05). CONCLUSION: Perfusion culture permitted the persistent nutrition supply and gas exchange into the centre of large scaffold. This perfusion bioreactor makes the mesenchymal stem cells survive and proliferate through a large three-dimensional scaffold.