ObjectiveTo compare the fixation strength of optimum placed pedicle screw (OS) with re-directionally correctly placed pedicle screw (RS) following a violation of lateral pedicle. MethodsThirty fresh lumbar vertebrae (L1-5) were obtained from 6 pigs weighing 95-105 kg, male or female. Each vertebra was instrumented with a monoaxial pedicle screw into each pedicle using two different techniques. On one side, a perfect screw path was created using direct visualization and fluoroscopy. A pedicle screw of 5 mm in diameter and 35 mm in length was placed with a digital torque driver (OS). On the other side, a lateral pedicle wall violation was created at the pedicle-vertebral body junction with a guide wire, a cannulated tap, and a pedicle probe. This path was then redirected into a correct position, developed, and instrumented with a 5-mm-diameter by 35-mm-long pedicle screw (RS). For each pedicle screw, the maximal torque, seating torque, screw loosening force, and post-loosening axial pullout were measured. Screw loosening and axial pullout were assessed using an MTS machine. ResultsMaximal insertion torque was (111.4±8.2) N·cm and (78.9±6.4) N·cm for OS and RS respectively, showing significant difference (Z=3.038, P=0.002). The seating torque was (86.3±7.7) N·cm and (59.7±5.3) N·cm for OS and RS respectively, showing significant difference (Z=2.802, P=0.005). The screw loosening force was (76.3±6.2) N and (53.0±5.8) N for OS and RS respectively, showing significant difference (Z=2.861, P=0.004). The post-loosening axial pullout force was (343.0±12.6) N and (287.0±10.5) N for OS and RS respectively, showing significant difference (Z=2.964, P=0.003). ConclusionCompared with OS, RS placement after a lateral wall violation shows significantly decreased maximal insertion torque, seating torque, screw loosening force, and post-loosening axial pullout. On this occasion, RS augmentation is a probable option for remediation.
ObjectiveTo illustrate the role of epidermal growth factor (EGF) secreted by astrocytes in the process of tacrolimus (FK506) in promoting neurite outgrowth. MethodsThe spinal cord astrocytes and neuronal cells were isolated respectively from 2-day-old Sprague Dawley (SD) rats and 15-day SD pregnant rats, and cultured in vitro and identified by immunofluorescence staining. The spinal cord astrocytes were cultured with 20 μmol/L FK506 medium in the experimental group, and with FK506 free medium in the control group. The supernatant was collected after 24 hours for preparing conditioned medium, and astrocytes were collected. EGF proteins in the conditioned medium were detected with ELISA, and EGF gene expressions of astrocytes were detected with real-time quantitative PCR (RT-qPCR). The spinal cord neurons were cultured respectively with conditioned medium from the experimental group (FK506-CM) and the control group (C-CM) in group A and group B, also with neutralized C-CM and neutralized FK506-CM with anti-EGF neutralizing antibodies in group C and group D. Both the total neurite length and the longest neurite length were measured and compared among groups. ResultsBoth astrocytes and neurons were confirmed by immunofluorescence staining. The EGF content of experimental group (0.241±0.044) was significantly higher than that of the control group (0.166±0.014) (t=3.93, P=0.01); EGF gene expression of the experimental group (1.12±0.25) was significantly higher than that of the control group (0.46±0.11) (t=5.78, P=0.00). The neurite length measurement displayed that the total neurite length and the longest neurite length of groups C and D were significantly shorter than those of groups A and B (P<0.05). Both the total and longest neurite length of group A were significantly longer than those of group B (P<0.05), but no significant difference was shown between groups C and D (P>0.05). ConclusionThe EGF secreted by spinal cord astrocytes can promote the neurite outgrowth. So spinal cord astrocytes can be used as an important intermediary target of FK506 to promote the recovery of neurological function.