No abstract available.
Pedicle Screws* ; Spondylolisthesis*

STUDY DESIGN: Biomechanical study. PURPOSE: To determine the effect of density, insertion angle and reinsertion on pull-out strength of pedicle screw in single and two screw-rod configurations. OVERVIEW OF LITERATURE: Pedicle screw pull-out studies have involved single screw construct, whereas two screws and rod constructs are always used in spine fusions. Extrapolation of results using the single screw construct may lead to using expensive implants or increasing the fusion levels specifically in osteoporotic bones. METHODS: Single screw and two screw pull-out strength tests were carried out according to American Society for Testing and Materials F 543-07 on foam models to test the effect of density, insertion angle and reinsertion using poly axial pedicle screws. RESULTS: Bone density was the most significant factor deciding the pull-out strength in both single and two screw constructs. The difference in pull-out strength between single screw and two screw configurations in extremely osteoporotic bone model (80 kg/m3) was 78%, whereas in the normal bone model it was 48%. Axial pull-out value was highest for the single screw configuration; in the two screw configuration the highest pull-out strength was at 10°-15°. There was an 18% reduction in pull-out strength due to reinsertion in single screw configuration. The reinsertion effect was insignificant in the two screw configuration. CONCLUSIONS: A significant difference in response of various factors on holding power of pedicle screw between single and two-screw configurations is evident. The percentage increase in pull-out strength between single and two screw constructs is higher for osteoporotic bone when compared to normal bone. Reinsertion has no significant effect on pull-out strength in the two screw rod configuration.
Bone Density ; Osteoporosis ; Pedicle Screws* ; Spine

STUDY DESIGN: Biomechanical study. PURPOSE: To determine the effect of density, insertion angle and reinsertion on pull-out strength of pedicle screw in single and two screw-rod configurations. OVERVIEW OF LITERATURE: Pedicle screw pull-out studies have involved single screw construct, whereas two screws and rod constructs are always used in spine fusions. Extrapolation of results using the single screw construct may lead to using expensive implants or increasing the fusion levels specifically in osteoporotic bones. METHODS: Single screw and two screw pull-out strength tests were carried out according to American Society for Testing and Materials F 543-07 on foam models to test the effect of density, insertion angle and reinsertion using poly axial pedicle screws. RESULTS: Bone density was the most significant factor deciding the pull-out strength in both single and two screw constructs. The difference in pull-out strength between single screw and two screw configurations in extremely osteoporotic bone model (80 kg/m3) was 78%, whereas in the normal bone model it was 48%. Axial pull-out value was highest for the single screw configuration; in the two screw configuration the highest pull-out strength was at 10°-15°. There was an 18% reduction in pull-out strength due to reinsertion in single screw configuration. The reinsertion effect was insignificant in the two screw configuration. CONCLUSIONS: A significant difference in response of various factors on holding power of pedicle screw between single and two-screw configurations is evident. The percentage increase in pull-out strength between single and two screw constructs is higher for osteoporotic bone when compared to normal bone. Reinsertion has no significant effect on pull-out strength in the two screw rod configuration.
Bone Density ; Osteoporosis ; Pedicle Screws* ; Spine

STUDY DESIGN: The strength effects of a pedicle screw-rod system supplemented with a novel cross-link configuration were biomechanically evaluated in porcine spines. PURPOSE: To assess the biomechanical differences between a conventional cross-link pedicle screw-rod system versus a novel cross-link instrumentation, and to determine the effect of the cross-links. OVERVIEW OF LITERATURE: Transverse cross-link systems affect torsional rigidity, but are thought to have little impact on the sagittal motion of spinal constructs. We tested the strength effects in pullout and flexion-compression tests of novel cross-link pedicle screw constructs using porcine thoracic and lumbar vertebrae. METHODS: Five matched thoracic and lumbar vertebral segments from 15 porcine spines were instrumented with 5.0-mm pedicle screws, which were then connected with 6.0-mm rods after partial corpectomy in the middle vertebral body. The forces required for construct failure in pullout and flexion-compression tests were examined in a randomized manner for three different cross-link configurations: un-cross-link control, conventional cross-link, and cross-link passing through the base of the spinous process. Statistical comparisons of strength data were analyzed using Student's t-tests. RESULTS: The spinous process group required a significantly greater pullout force for construct failure than the control group (p=0.036). No difference was found between the control and cross-link groups, or the cross-link and spinous process groups in pullout testing. In flexion-compression testing, the spinous processes group required significantly greater forces for construct failure than the control and cross-link groups (p<0.001 and p=0.003, respectively). However, there was no difference between the control and cross-link groups. CONCLUSIONS: A novel cross-link configuration that features cross-link devices passing through the base of the spinous processes increased the mechanical resistance in pullout and flexion-compression testing compared to un-cross-link constructs. This configuration provided more resistance to middle-column damage under flexion-compression testing than conventional cross-link configuration.
Lumbar Vertebrae ; Pedicle Screws ; Spinal Fusion ; Spine

To the best of our knowledge, there has been no domestic report on posterior atlantoaxial fusion with segmental screw fixation using C2 laminar screws and C1 lateral mass screws for atlantoaxial subluxation. We report the result of this operation performed in a patient with old atlantoaxial rotary subluxation who required posterior fusion. We chose this technique in this patient because wire fixation was not suitable due to osteoporosis, and transarticular screw fixation and use of C2 pedicle screws were not feasible due to the peculiar bony anatomy of the axis.
Arthrodesis* ; Humans ; Osteoporosis ; Pedicle Screws ; Vertebral Artery*

Posterior pedicle screw fixation has become a popular method for treating thoracolumbar burst fractures. However, it remains unclear whether additional fixation of more segments could improve clinical and radiological outcomes. This meta-analysis was performed to evaluate the effectiveness of fixation levels with pedicle screw fixation for thoracolumbar burst fractures. MEDLINE, EMBASE, the Cochrane Central Register of Controlled Trials, Springer, and Google Scholar were searched for relevant randomized and quasirandomized controlled trials that compared the clinical and radiological efficacy of short versus long segment for thoracolumbar burst fractures managed by posterior pedicle screw fixation. Risk of bias in included studies was assessed using the Cochrane Risk of Bias tool. Based on predefined inclusion criteria, Nine eligible trials with a total of 365 patients were included in this meta-analysis. Results were expressed as risk difference for dichotomous outcomes and standard mean difference for continuous outcomes with 95% confidence interval. Baseline characteristics were similar between the short and long segment fixation groups. No significant difference was identified between the two groups regarding radiological outcome, functional outcome, neurologic improvement, and implant failure rate. The results of this meta-analysis suggested that extension of fixation was not necessary when thoracolumbar burst fracture was treated by posterior pedicle screw fixation. More randomized controlled trials with high quality are still needed in the future.
Bias (Epidemiology) ; Humans ; Methods ; Pedicle Screws* ; Spine

PURPOSE: This study compared the clinical and radiological results between two groups of patients with percutaneous fixation or conventional fixation after hardware removal.MATERIALS AND METHODS: The study analyzed 68 patients (43 open fixation and 43 percutaneous screw fixation [PSF] 25) who had undergone fixation for unstable thoracolumbar fractures. The radiologic results were obtained using the lateral radiographs taken before and after the fixation and at the time of hardware removal. The clinical results included the time of operation, blood loss, time to ambulation, duration of the hospital stay and the visual analogue scale.RESULTS: The percutaneous pedicle screw fixation (PPSF) group showed better results than did the conventional posterior fixation (CPF) group (p<0.05) in regard to the perioperative data such as operation time, blood loss, and duration of the hospital stay. There were no significant differences in wedge angle, local kyphotic angle, and the ΔKyphotic angle on the postoperative plane radiographs between the two groups (p>0.05). There were no significant differences in the wedge angle and local kyphotic angle after implant removal (p>0.05) between the two groups as well. However, there were significant differences in the segmental montion angle (p<0.001), and the PPSF group showed a larger segmental motion angle than did the CPF group (CPF 1.7°±1.2° vs PPSF 5.9°±3.2°, respectively).CONCLUSION: For the treatment of unstable thoracolumbar fractures, the PPSF technique could achieve better clinical results and an improved segmental motion angle after implant removal within a year than that of the conventional fixation method.
Humans ; Length of Stay ; Methods ; Pedicle Screws ; Walking

Spinal fixation using pedicle screws has recently been the focus of increased attention, but the adequate size of pedicle screw and maximum percentage fill as related to the pedicle diameter and are not well known. The objects of this study were to determine the ideal ratio among pedicle, drill and screw diameter, and to determine the maximum percentage fill of the screw without significant decrease of pull-out strength. The materials used for the experiments were 376 thoracic pedicles obtained from the 38 young pigs, and the diameters of pedicles ranged from 3.0 to 8.5mm. After 40% to 100% drilling as compared to pedicle diameter, screws were inserted carefully, and measurements were taken of the outer pedicle changes and pull-out strengths, and adequate drill and screw sizes as related to the diameters of given pedicles were determined. It was found that pull-out strength was the strongest after 60% drill, and the larger the drill diameter, the smaller the holding power, and the larger the screw diameter, the greater the holding power. Maximum pull-out strength was seen at 80-90% fill with 60% drill. After sequentially drilling each pedicle with increasingly larger drill bits, larger screws could be inserted with pedicle changes such as expansion, cutout, split fracture, and comminuted fracture. after larger drilling up to 100%, pedicle screws with diameters smaller than 115% of measured pedicle diameters could be safly inserted without fracture and significant decrease of pull-out strength. It is concluded that effective percentages of drill and screw diameters to the pedicle diameter are 60% and 80-90% respectively, and pedicle screw up to 115% of measured pedicle diameter can be safely inserted into pedicle without significant decrease of pull-out strength. It is thought that fresh pedicle has elasticity and larger screw can be inserted to the pedicle with strong holding after larger drilling.
Elasticity ; Fractures, Comminuted ; Pedicle Screws ; Swine

OBJECTIVETo explore the impact of pedicle cortex perforation on the stability of internal fixation of the vertebral body fracture, and to compare the stability of the vertebrae with pedicle cortex perforation after the injured vertebra transpedicular screw fixation by different ways.

METHODSA total of 36 fresh thoracic and lumbarvertebrae samples of adult sheep (T₁₃-L₁) were equally divided into four groups (A, B, C and D) by using the random number table method. The vertebral compression fracture was performed in the L1 vertebral body of the four groups using the Chiba's method. Four pedicle screws were fixed on the upper and lower injured vertebrae of four groups. In addition, the group C was fixed into a pedicle screw through the injured vertebrae; D group was set two pedicle screws through the injured vertebrae. Then the samples of group B, C, and D were removed a quarter of either side of lateral T₁₄ thoracic pedicle, which was considered as the pedicle cortex perforation model. Four groups were performed fatigue test of 10 000 times by (300 ± 105)N load. The drawing force of the screw and the stability of injured thoracolumbar vertebrae were measured and the differences in every group were compared.

RESULTSThe axial compressive stiffness and maximum drawing force of screws in the other three groups were significantly higher than those in group B (all P=0.000). The maximum range of motion in four directions of group B were significantly larger than those of the other three groups (all P=0.000). The stiffness and the drawing force in groups C and D were significantly larger than those in the group A (all P=0.000), and the maximum range of motion in four directions of the two groups were lower than that of group A (P=0.002, P=0.005). Every testing indicator in group C had no significant difference when compared with group D (P>0.05).

CONCLUSIONSThe pedicle cortex perforation seriously affects the stability of the fractured vertebral body. The injured vertebra transpedicular screw can increase the stability of internal fixation.

OBJECTIVE: Cervical pedicle screw (CPS) placement is very challenging due to high risk of neurovascular complications. We devised a new technique (medial funnel technique) to improve the accuracy and feasibility of CPS placement. METHODS: We reviewed 28 consecutive patients undergoing CPS instrumentation using the medial funnel technique. Their mean age was 51.4 years (range, 30–81 years). Preoperative diagnosis included degenerative disease (n=5), trauma (n=22), and infection (n=1). Screw perforations were graded with the following criteria: grade 0 having no perforation, grade 1 having < 25%, grade 2 having 25%–50% and grade 3 having >50% of screw diameter. Grades 0 and 1 were considered as correct position. The degree of perforation was determined by 2 junior neurosurgeons and 1 senior neurosurgeon. RESULTS: A total of 88 CPSs were inserted. The rate of correct placement was 94.3%; grade 0, 54 screws; grade 1, 29 screws; grade 2, 4 screws; and grade 3, 1 screw. No neurovascular complications or failure of instrumentation occurred. In perforated screws (34 screws), lateral perforations were 4 and medial perforations were 30. CONCLUSION: We performed CPS insertion using medial funnel technique and achieved 94.3% (83 of 88) of correct placement. And it can decrease lateral perforation.
Bone Screws ; Cervical Vertebrae ; Diagnosis ; Female ; Humans ; Neurosurgeons ; Pedicle Screws*