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Background The cortical bone trajectory (CBT) has attracted attention as a new minimally invasive technique for lumbar instrumentation by minimizing soft-tissue dissection. Biomechanical studies have demonstrated the superior fixation capacity of CBT; however, there is little consensus on the selection of screw size, and no biomechanical study has elucidated the most suitable screw size for CBT. The purpose of the present study was to evaluate the effect of screw size on fixation strength and to clarify the ideal size for optimal fixation using CBT. Method A total of 720 analyses on CBT screws with various diameters (4.5–6.5 mm) and lengths (25–40 mm) in simulations of 20 different lumbar vertebrae (mean age: 62.1 ± 20.0 years, 8 males and 12 females) were performed using a finite element method. First, the fixation strength of a single screw was evaluated by measuring the axial pullout strength. Next, the vertebral fixation strength of a paired-screw construct was examined by applying forces simulating flexion, extension, lateral bending, and axial rotation to the vertebra. Lastly, the equivalent stress value of the bone-screw interface was calculated. Results Larger-diameter screws increased the pullout strength and vertebral fixation strength and decreased the equivalent stress around the screws; however, there were no statistically significant differences between 5.5-mm and 6.5-mm screws. The screw diameter was a factor more strongly affecting the fixation strength of CBT than the screw fit within the pedicle (%fill). Longer screws significantly increased the pullout strength and vertebral fixation strength in axial rotation. The amount of screw length within the vertebral body (%length) was more important than the actual screw length, contributing to the vertebral fixation strength and distribution of stress loaded to the vertebra. Conclusions The fixation strength of CBT screws varied depending on screw size. The ideal screw size for CBT is a diameter larger than 5.5 mm and length longer than 35 mm, and the screw should be placed sufficiently deep into the vertebral body.

Background Surgical site infections can complicate posterior spine surgery. Multiple hospital admissions may be required to adequately treat a surgical site infection, which is associated with increased costs and lower patient satisfaction. The objective of this study was to evaluate the efficacy of prophylactic intra-wound vancomycin powder in reducing the incidence of repeat surgery for infections after posterior instrumented and noninstrumented spine surgery. Methods A series of consecutive patients who underwent instrumented or noninstrumented posterior spine surgery for any indication by two surgeons from July 2010 to July 2012 were reviewed. The preoperative antibiotic regimens of both surgeons were identical, except that one surgeon applied 1 g vancomycin powder directly to the surgical bed before wound closure, while the other did not. Patient demographics, operative details, and rates of reoperation for wound infection in the control and the treatment groups were compared. Results Both the control group and treatment group consisted of 150 patients; mean ages were 58.33 and 54.14 years, respectively. Both groups had low rates of deep infection requiring surgical intervention. The treatment group had a significantly lower rate of infection requiring reoperation or surgical debridement (0 %; 95 % CI: 0 %–2.4 %) compared with the control group (4 %; 95 % CI: 1.5 %–8.5 %) ( P  = 0.0297). The six infections identified in the control group resulted in 12 repeat operative debridement procedures. Gram-positive organisms were identified in 66.7 % of infections. No complications were related to the application of vancomycin powder. Conclusions The results of this study demonstrate that adjunctive vancomycin powder applied directly to the surgical bed before closure seems effective in preventing deep infections that require operative debridement following posterior spine surgery.

Background Cortical bone trajectory (CBT), a relatively new technique for pedicle screw insertion in the lumbar spine, is believed to have equivalent pullout and toggle characteristics compared with the traditional trajectory (TT). It has been hypothesized that the new trajectory offers higher cortical bone contact with the pedicle screws and therefore has an improved anchoring property over the traditional trajectory where the screws are inserted into the vertebral body trabecular space. The aim of this study is to evaluate the pedicle screw-cortical bone contact between the two trajectories from a radiological standpoint. Methods Two hundred twenty-two patients with degenerative lumbar spine disease underwent computed tomography scanning. For each patient, axial slices of the L4 and L5 vertebra were cut in two planes, one horizontal to the pedicle representing the plane at which pedicle screws are inserted using the TT and another in a more caudo-cranial plane representing the plane at which pedicle screws are inserted using CBT. For each trajectory, a region of interest (ROI) was selected within the area in which the screws are inserted. A CT number (Hounsfield scale) was then calculated within each ROI to compare the bone density. Results The CT numbers within the ROI for CBT were constantly almost over four times higher than that for the TT, and there was a significant difference between the values ( p  < 0.0001). Conclusions This study has demonstrated that, with the cortical bone trajectory, the pedicle screws penetrate a region that is richer in cortical bone compared to when using the traditional trajectory. This is in keeping with previous hypotheses that the new trajectory offers higher cortical bone contact.

Background The surgical management of cervical brachialgia utilising anterior cervical discectomy and fusion (ACDF) or posterior cervical foraminotomy (PCF) is a controversial area in spinal surgery. Previous studies are limited by utilisation of non-validated outcome measures and, importantly, absence of pre-operative analysis to ensure both groups are matched. The authors aimed to compare the effectiveness of ACDF and PCF using validated outcome measures. To our knowledge, it is the first study in the literature to do this. Methods The authors conducted a 5-year retrospective review (2008–2013) of outcomes following both the above procedures and also compared the effectiveness of both techniques. Patients with myelopathy and large central discs were excluded. The main outcome variables measured were the neck disability index (NDI) and visual analogue scores (VAS) for neck and arm pain pre-operatively and again at 2-year follow-up. The Wilcoxon signed-rank test and Student t -tests were used to test differences. Results A total of 150 ACDFs and 51 PCFs were performed for brachialgia. There was no differences in the pre-operative NDI, VAS neck and arm scores between both groups ( p  > 0.05). As expected, both ACDF and PCF delivered statistically significant improvement in NDI, VAS-neck and VAS-arm scores. The degree of improvement of NDI, VAS-neck and VAS-arm were the same between both groups of patients ( p  > 0.05) with a trend favouring the PCF group. In the ACDF group, two (1.3 %) patients needed repeat ACDF due to adjacent segment disease. One patient (0.7 %) needed further decompression via a foraminotomy. In the PCF group one (2.0 %) patient needed ACDF due to persistent brachialgia. Conclusions We found both interventions delivered similar improvements in the VAS and NDI scores in patients. Both techniques may be appropriately utilised when treating a patient with cervical brachialgia.

Background The aim of this work is to evaluate the utility of multimodal intraoperative monitoring (IOM) during intramedullary spinal cord tumor (IMSCT) surgery in our institution, and to investigate which IOM events are likely to be encountered during critical surgical phases. Methods Twenty-five patients who underwent IMSCT surgery with IOM were included in this study. Our multimodal IOM assessment included SSEP, mMEP, and fEMG monitoring. Positive predictive value (PPV), negative predictive value (NPV), sensitivity, and specificity were assessed 24 h and 1 month after surgery. The IOM events during three main surgical phases were also investigated. For mMEP assessment, two warning criteria (>50 % decrease in mMEP amplitude and all-or-none mMEP amplitude presence) were employed. Results Long-term outcome prediction was better when the all-or-none criterion was applied than when the >50 % amplitude decrease criterion was applied. Based on the all-or-none criterion, the PPV, NPV, sensitivity, and specificity were 60, 100, 100, and 91 %. Frequent IOM events were observed during the three major main surgical phases. Seven (29 %) patients showed SSEP events during opening of the spinal cord. During tumor removal, 21 of 25 patients (84 %) had IOM events, and 13 of 18 (72 %) of the fEMG events occurred prior to the mMEP events. Conclusions Based on the association of fEMG events with upcoming mMEP events during tumor removal, we recommend inclusion of fEMG monitoring in IOM. Multimodal IOM provides useful electrophysiological information during IMSCT surgery, especially during the main surgical phases.

Background There are limited scientific data on the impact of smoking on patient-reported outcomes following minimally invasive spine surgery. The aim of this multicenter observational study was to examine the relationship between daily smoking and patient-reported outcome at 1 year using the Oswestry Disability Index (ODI) after microdecompression for single- and two-level central lumbar spinal stenosis (LSS). Secondary outcomes were the length of hospital stays, perioperative and postoperative complications. Method Data were collected through the Norwegian Registry for Spine Surgery (NORspine). Results A total of 825 patients were included (619 nonsmokers and 206 smokers). For the whole patient population there was a significant difference between preoperative ODI and ODI at 1 year (17.3 points, 95 % CI 15.93–18.67, p  < 0.001). There was a significant difference in ODI change at 1 year between nonsmokers and smokers (4.2 points, 95 % CI 0.98–7.34, p  = 0.010). At 1 year 69.6 % of nonsmokers had achieved a minimal clinically important difference (≥10 points ODI improvement) compared to 60.8 % of smokers ( p  = 0.008). There was no difference between nonsmokers and smokers in the overall complication rate (11.6 % vs. 9.2 %, p  = 0.34). There was no difference between nonsmokers and smokers in length of hospital stays for either single-level (2.3 vs. 2.2 days, p  = 0.99) or two-level (3.1 vs. 2.3 days, p  = 0.175) microdecompression. Smoking was identified as a negative predictor for ODI change in a multiple regression analysis ( p  = 0.001) Conclusions Nonsmokers experienced a significantly larger improvement at 1 year following microdecompression for LSS compared to smokers. Smokers were less likely to achieve a minimal clinically important difference. However, it should be emphasized that considerable improvement also was found among smokers.

Background Few have studied the correlation between patients’ and spine surgeons’ perception on outcomes, or compared these with patient-reported outcome scores. Outcomes studies are increasingly important in evaluating costs and benefits to patients and surgeons, and in developing metrics for payer evaluation and health care policy-making. Objective To compare patients’ and surgeons’ assessment of spine treatment outcome in a prospective blinded patient-driven spine surgery outcomes registry, and to correlate perceived outcomes ratings to validated outcomes scores. Methods Patients filled out surveys at baseline, 3 months and 6 months postoperatively, including Visual Analog Scale (VAS), and Neck Disability Index (NDI) or Oswestry Disability Index (ODI). Outcome was rated independently by patients and surgeons on a 7-point Likert-type scale. Results Two-hundred and sixty-five consecutive adult patients were surgical candidates. Of these, 154 (58.1 %) opted for surgery, with 69 (44.8 %) cervical and 85 (55.2 %) lumbar patients. One hundred and thirty-five (87.7 %) had both patient and surgeon postoperative ratings. Surgeons’ and patients’ ratings correlated strongly (Spearman rho = 0.53, p  < 0.0001, 45.9 % identical, 88.2 % +/− 1 grade). The surgeon rated outcomes were better than patients in 29.8 % and worse in 21.15 %. Patient rating correlated better with the most recent NDI/ODI and pain scores than with incremental change from baseline. In multivariate analysis, age, location (cervical vs lumbar), pain ratings, and functional scores (NDI, ODI) did not have significant impact on the discrepancy between patient and surgeon ratings. Conclusions Patients’ and surgeons’ global outcome ratings for spinal disease correlate highly. Patients’ ratings correlate better with most recent functional scores, rather than incremental change from baseline.

Background Few studies have compared methods of stem cell transplantation. The aim of the present study was to determine the optimal method of delivery of therapeutic stem cells in spinal cord injury (SCI). We compared functional and histologic outcomes after administration of human bone marrow stromal cells (BMSCs) by intralesional (ILT), intracisternal (ICT), and intravenous transplantation (IVT). Method A rat model of spinal cord injury was produced by dropping a 10-g weight, 2 mm in diameter, onto the exposed spinal cords of animals from a height of 25 mm. In each treatment group, 24 animals were randomly assigned for functional assessment and 24 for histologic examination. BMSCs (3 × 10 5 , ILT; 1 × 10 6 , ICT; 2 × 10 6 , IVT) were transplanted 1 week after SCI in numbers determined in previous studies. Basso-Beattie-Bresnahan scoring was performed in all animals weekly for 6 weeks. Spinal cord specimens were obtained from eight animals in each group 2, 4, and 6 weeks after SCI. Viable BMSCs were counted in six sagittal sections from each spinal cord. Results All three treatment groups showed improved functional recovery compared to controls beginning 2 weeks after stem cell injection ( P  < 0.01). The ICT group showed the best functional recovery, followed by the ILT and IVT groups, respectively ( P  < 0.01). Histological analysis showed the largest number of viable BMSCs in the ILT group, followed by the ICT and IVT groups, respectively ( P  < 0.01). Conclusions ICT may be the safest and most effective method for delivering stem cells and improving functional outcome in SCI when no limits are placed on the number of cells transplanted. As research on enhancing engraftment rates advances, further improvement of functional outcome can be expected.

Background Wnt proteins are bifunctional axon guidance molecules, several of which appear to mediate guidance of corticospinal tract axons along the spinal cord. Here, we studied increasing effect on regeneration by Wnt-containing alginate scaffolds on spinal cord injury (SCI). Methods A total of 32 rats were injured at the T7–8 level with an NYU impactor. According to transplantation materials, rats were classified into four groups: a Wnt3a-secreting fibroblast transplantation group (Wnt group, n  = 8), a Wnt3a-secreting fibroblast with alginate transplantation group (Wnt + alginate group, n  = 8), an alginate transplantation group (alginate group, n  = 8), and a contusion-only group (sham group, n  = 8). Behavioral tests were performed on the first, second, and third days after injury, and then weekly for 8 weeks. Five of the eight rats from each group were selected for manganese-enhanced magnetic resonance imaging (ME-MRI). Two rats from each group were examined for GAP43 and MAP2 expression using monoclonal and polyclonal primary antibodies, respectively. Results Seven weeks after transplantation (8 weeks after SCI), Wnt + alginate group rats achieved an average Basso–Beattie–Bresnahan locomotor score of 19.0, which was significantly higher than that of other groups. ME-MRI at 8 weeks after SCI revealed significantly higher relative signal intensities in the Wnt + alginate group. Gap43 and Map2 immunostaining, showed strong positive in the Wnt + alginate group. Conclusion The Wnt + alginate complex exerted significantly enhanced recovery in a rat SCI model compared to alginate or Wnt3a alone. These results suggest that alginate scaffolds facilitate the regeneration of axon working with Wnt3a protein that promotes regeneration of the injured spinal cord.

Background Spinal cord injury (SCI) is a devastating and irreversible event, and much research using fibroblast growth factor-2 (FGF-2) has been performed to test its capacity to blunt the effects of SCI as well as to provide an environment conducive for SCI repair. Methods We tested how the in vitro release of FGF-2 from heparin-conjugated poly(L-lactide-co-glycolide) (PLGA)-conjugated nanospheres (HCPNs) affected the growth of human bone marrow-derived mesenchymal stem cells (hBMSCs), as well as the effects of their co-transplantation in an animal model of SCI. Results Our results showed that sustained, long-term release of FGF-2 from HCPNs significantly increased hBMSCs proliferation in vitro, and that their co-transplantation following rat SCI lead to increased functional improvement, a greater amount of hBMSCs surviving transplantation, and a greater density of neurofilament-positive cells in the injury epicenter. Conclusion These results suggest a proliferative, protective, and neural inductive potential of FGF-2 for transplanted hBMSCs, as well as a possible role for sustained FGF-2 delivery along with hBMSCs transplantation in the injured spinal cord. Future studies will be required to ascertain the safety FGF-2-containing HCPNs before clinical application.