Cannulated Pedicle Screws Research Articles

Effect of surgical factors on the augmentation of cement-injectable cannulated pedicle screw fixation by a novel calcium phosphate-based nanocomposite.

Bone cement-augmented pedicle screw system demonstrates great efficacy in spinal disease treatments. However, the intrinsic drawbacks associated with clinically used polymethylmethacrylate (PMMA) cement demands for new bone cement formulations. On the basis of our previous studies, a novel injectable and biodegradable calcium phosphate-based nanocomposite (CPN) for the augmentation of pedicle screw fixation was systematically evaluated for its surgical feasibility and biomechanical performance by simulated and animal osteoporotic bone models, and the results were compared with those of clinical PMMA cement. ASTM-standard solid foam and open-cell foam models and decalcified sheep vertebra models were employed to evaluate the augmentation effects of CPN on bone tissue and on the cement-injected cannulated pedicle screws (CICPs) placed in osteoporotic bone. Surgical factors in CICPs application, such as injection force, tapping technique, screw diameter, and pedicle screw loosening scenarios, were studied in comparison with those in PMMA. When directly injected to the solid foam model, CPN revealed an identical augmentation effect to that of PMMA, as shown by the similar compressive strengths (0.73 ± 0.04 MPa for CPN group vs. 0.79 ± 0.02 MPa for PMMA group). The average injection force of CPN at approximately 40-50 N was higher than that of PMMA at approximately 20 N. Although both values are acceptable to surgeons, CPN revealed a more consistent injection force pattern than did PMMA. The dispersing and anti-pullout ability of CPN were not affected by the surgical factors of tapping technique and screw diameter. The axial pullout strength of CPN evaluated by the decalcified sheep vertebra model revealed a similar augmentation level as that of PMMA (1351.6 ± 324.2 N for CPN vs. 1459.7 ± 304.4 N for PMMA). The promising results of CPN clearly suggest its potential for replacing PMMA in CICPs augmentation application and the benefits of further study and development for clinical uses.

A novel calcium phosphate–based nanocomposite for the augmentation of cement-injectable cannulated pedicle screws fixation: A cadaver and biomechanical study

Background/objectiveBoth polymethylmethacrylate (PMMA) and traditional calcium phosphate–based cements have some deficiencies as augmentation materials for pedicle screw fixation. Here, a novel calcium phosphate–based nanocomposite (CPN) for the augmentation of pedicle screw fixation was developed based on previous study, and the handling properties, biomechanical performance, and biodegradation behaviour of CPN were evaluated and compared with clinical PMMA by means of a cadaver study and animal tests. MethodsBone mineral density of the lumbar vertebrae was tested. Pedicle screws were placed into the lumbar vertebrae under the guidance of three dimensionally printed templates; each of which was designed based on computed tomography (CT) reconstruction of each vertebrae ​and augmented with either PMMA or CPN. X-ray and CT scan were used to evaluate the accuracy of screw placement and dispersion as well as interdigitation of bone cement. The axial pull-out strength and maximum torque were tested using a mechanical testing machine. Degradation behaviour of CPN was evaluated by in vitro immersion tests for 8 weeks and in vivo rabbit femur defect model for up to 6 months, respectively. ResultsStandard mechanical tests revealed that PMMA was much stronger than CPN after setting (compressive strength 95 vs. 49 ​MPa, respectively, p ​< ​0.001). Results of the projection area and volume distribution of cement along the distal end of the screws revealed that CPN exhibited unique dispersing and interdigitation abilities compared with PMMA. Specifically, CPN dispersed uniformly and symmetrically along the screw, while PMMA was limited to the proximal part of the screw. Axial pull-out test results showed that the axial pull-out strengths of CPN- and PMMA-augmented pedicle screws were similar (1199 ​± ​225 ​N vs 1337 ​± ​483 ​N, respectively) and not significantly different (p ​= ​0.47), although CPN was an intrinsically weaker material than PMMA. Similarly, CPN showed average torque values of 0.72 ​± ​0.31 ​N·m slightly lower than those of PMMA (0.96 ​± ​0.23 ​N·m), but statistically there was no significant difference between CPN and PMMA (p ​= ​0.21). In a rabbit model of femoral bone defect, the implanted CPN maintained its clear boundary and there is no disintegration in the cement clump after 20 days and 24 weeks, and there was moderate bioabsorption of CPN and clearly new bone ingrowth at the absorbed sites after 24 weeks. ConclusionA new nanocomposite cement CPN, designed for replacing the nondegradable PMMA cement and overcoming the mechanical inferiority of calcium phosphate cement, was evaluated for its biomechanical and biodegradation behaviours in cement-injectable cannulated pedicle screws (CICPS) application. Although CPN is a mechanically weaker material than PMMA, CPN demonstrates similar biomechanical properties to PMMA in the application of augmentation for CICPS fixation in cadaveric vertebrae. This improvement in biomechanical property is attributed to a better dispersion and interdigitation mode of CPN. In addition, the animal study results suggest the in vivo absorption of CPN is slow enough and matches the bone ingrowth. The translational potential of this articleThis work reports a cadaveric and biomechanical study of novel CPN for the application in the augmentation of CICPS. The results suggest that CPN has equivalent or better biomechanical and interdigitation performance compared with PMMA. Together with the biodegradability and ossointegration capability, CPN reveals high translational potential as a new bone cements for load-bearing bone fixation and repair.

P22. Lumbar intervertebral spacer with cement augmentation of endplates and integrated screws as a fixation device in an osteoporotic model: an in vitro kinematic and load-to-failure study

BACKGROUND CONTEXT Integrated LLIF stabilizes the spine and avoids complications related to posterior fixation. However, contraindications such as low bone mineral density (BMD) and older age can increase risk of subsidence. Traditional cement augmentation through cannulated pedicle screws enhances pedicle fixation and cage-endplate interface, yet may be disadvantageous due to associated paraspinal dissection, blood loss, and iatrogenic infection. Nevertheless, cement augmentation may be sufficient in preventing subsidence of stand-alone LLIF reconstructions in elderly patients. The lateral application of cement with integrated LLIF fixation has been introduced and requires kinematic and failure characterizations. PURPOSE To evaluate kinematic and load-to-failure properties of a novel cement augmentation technique with an integrated lateral lumbar interbody fusion (LLIF) device, both alone and with unilateral pedicle fixation, in comparison with bilateral pedicle screws and non-integrated LLIF (BPS+S). STUDY DESIGN/SETTING In vitrohuman cadaveric study. PATIENT SAMPLE 12 cadaveric specimens. OUTCOME MEASURES Range of motion (ROM) and ultimate load to failure. METHODS Twelve specimens (L3–S1) underwent discectomy (L4–L5). Specimens were separated into 3 groups: (1) BPS+S, (2) polymethylmethacrylate (PMMA), integrated LLIF, and unilateral pedicle screws. (PMMA+UPS+iS), and (3) PMMA with iSA (PMMA+iSA). Before LLIF insertion, a vertebroplasty needle inserted 3mm deep from the endplate at the vertical midline of the vertebral body (VB). The needle was repeatedly inserted through the cancellous bone, creating a cavity deep to the endplate. PMMA (3cc) was injected into the cavity, limited to approximately 25% of the operative endplates, followed by insertion of the LLIF device. After cement curing, flexion-extension, lateral bending and axial rotation were applied. Finally, a compressive load was applied to the segments until failure to assess spacer-endplate strength. RESULTS No significant differences in BMD T-scores between BPS+S (-1.9±0.7), PMMA+UPS+iS (-1.8±0.5), and PMMA+iS (-1.8±0.7) groups were observed (P = 0.992). Operative constructs significantly reduced motion relative to intact specimens in all motion planes (P 0.05). PMMA+UPS+iS provided the greatest resistance to failure (2290 N), followed by PMMA+iSA (1970 N), and lastly, BPS+S (1390 N); no significant differences were observed (P > 0.05). CONCLUSIONS A novel technique of vertebral endplate cement augmentation via the lateral approach with an integrated interbody device for osteoporotic patients who would otherwise require posterior fixation to reduce likelihood of subsidence is proposed. The integrated lateral interbody spacer with vertebral endplate cement augmentation, both prior to and following unilateral pedicle fixation, was biomechanically equivalent to traditional anteroposterior fixation with non-integrated LLIF. The integrated device with cement augmentation moderately improved spacer-endplate interface compared to BPS+S in an osteoporotic model, increasing failure loads compared by 41.7%; the addition of unilateral fixation further increased resistance to failure (64.7%). Overall, results suggest integrated LLIF with cement may be a viable alternative in the presence of osteoporosis. FDA DEVICE/DRUG STATUS Unavailable from authors at time of publication.

Clinical evaluation of a bone cement-injectable cannulated pedicle screw augmented with polymethylmethacrylate: 128 osteoporotic patients with 42 months of follow-up

OBJECTIVES:To evaluate the safety and efficacy of a novel bone cement-injectable cannulated pedicle screw augmented with polymethylmethacrylate in osteoporotic spinal surgery.METHODS:This study included 128 patients with osteoporosis (BMD T-score –3.2±1.9; range, –5.4 to –2.5) who underwent spinal decompression and instrumentation with a polymethylmethacrylate-augmented bone cement-injectable cannulated pedicle screw. Postoperative Visual Analogue Scale scores and the Oswestry Disability Index were compared with preoperative values. Postoperative plain radiographs and computed tomography (CT) scans were performed immediately after surgery; at 1, 3, 6, and 12 months; and annually thereafter.RESULTS:The mean follow-up time was 42.4±13.4 months (range, 23 to 71 months). A total of 418 polymethylmethacrylate-augmented bone cement-injectable cannulated pedicle screws were used. Cement extravasations were detected in 27 bone cement-injectable cannulated pedicle screws (6.46%), mainly in cases of vertebral fracture, without any clinical sequela. The postoperative low back and lower limb Visual Analogue Scale scores were significantly reduced compared with the preoperative scores (<0.01), and similar results were noted for the Oswestry Disability Index score (p<0.01). No significant screw migration was noted at the final follow-up relative to immediately after surgery (p<0.01). All cases achieved successful bone fusion, and no case required revision. No infection or blood clots occurred after surgery.CONCLUSIONS:The polymethylmethacrylate-augmented bone cement-injectable cannulated pedicle screw is safe and effective for use in osteoporotic patients who require spinal instrumentation.

Effect of pedicle screw augmentation with a self-curing elastomeric material under cranio-caudal cyclic loading\u2014a cadaveric biomechanical study

BackgroundPedicle screws can be augmented with polymethylmethacrylate (PMMA) cement through cannulated and fenestrated pedicle screws to improve screw anchorage. To overcome the drawbacks of PMMA, a modified augmentation technique applying a self-curing elastomeric material into a balloon-created cavity prior to screw insertion was developed and evaluated. The aim of the study was to compare the effect of the established and novel augmentation technique on pedicle screw anchorage in a biomechanical in vitro experiment.MethodsIn ten lumbar vertebral bodies, the right pedicles were instrumented with monoaxial cannulated and fenestrated pedicle screws and augmented in situ with 2 ml PMMA. The left pedicles were instrumented with monoaxial cannulated pedicle screws. Prior to left screw insertion, a balloon cavity was created and filled with 3 ml of self-curing elastomer (silicone). Each screw was subjected to a cranio-caudal cyclic load starting from − 50 to 50 N while the upper load was increased by 5 N every 100 load cycles until loosening or 11,000 cycles (600 N). After cyclic loading, a pullout test of the screws was conducted.ResultsThe mean cycles to screw loosening were 9824 ± 1982 and 7401 ± 1644 for the elastomer and PMMA group, respectively (P = 0.012). The post-cycling pullout test of the loosened screws showed differences in the failure mode and failure load, with predominantly pedicle/vertebrae fractures in the PMMA group (1188.6 N ± 288.1) and screw pullout through the pedicle (671.3 N ± 332.1) in the elastomer group.ConclusionThe modified pedicle screw augmentation technique involving a balloon cavity creation and a self-curing elastomeric silicone resulted in a significantly improved pedicle screw anchorage under cyclic cranio-caudal loading when compared to conventional in situ PMMA augmentation.

Application of Cement-Injectable Cannulated Pedicle Screw in Treatment of Osteoporotic Thoracolumbar Vertebral Compression Fracture (AO Type A): A Retrospective Study of 28 Cases

To evaluate safety and effectiveness of the novel polymethyl methacrylate-augmented bone cement-injectable cannulated pedicle screw (CICPS) in patients with thoracolumbar vertebral compression fractures (AO type A) associated with osteoporosis. We conducted a retrospective cohort study of 28 patients treated for osteoporosis-related thoracolumbar vertebral body compression fracture at our facility between 2011 and 2015. Treatment involved posterior thoracolumbar fusion or lumbar fusion using CICPS. Treatment effectiveness was evaluated using visual analog scale and Oswestry Disability Index scores, degree of fracture reduction, and correction of kyphosis. The safety of CICPS was mainly assessed in terms of intraoperative and postoperative complications. Radiography, computed tomography, and magnetic resonance imaging outcomes were also assessed. All 28 patients had severe osteoporosis. The visual analog scale score at final follow-up (0.50 ± 0.69) was significantly (P < 0.001) lower compared with before surgery (4.93 ± 1.30). The Oswestry Disability Index score had also decreased from 57.39% ± 14.46% to 6.83% ± 15.38% at final follow-up (P < 0.001). Radiologic evaluation of vertebral height and Cobb angle showed good fracture reduction and satisfactory correction of kyphosis (preoperative vs. final follow-up, P < 0.001). There were no instances of screw loosening or symptomatic complications except for a few cases of cement leakage from CICPS (10.3%; cement leakage most common in AO type A3.3). The use of CICPS and polymethyl methacrylate is an effective and safe surgical technique for management of osteoporosis-related vertebral fractures (AO type A), with good clinical outcomes and low complications rates.

Wednesday, September 26, 2018 1:00 PM – 2:00 PM Navigation and Intraoperative Monitoring: 49. Novel technology for C-arm based pedicle navigation

Wednesday, September 26, 2018 1:00 PM – 2:00 PM Navigation and Intraoperative Monitoring: 49. Novel technology for C-arm based pedicle navigation

Feasibility and Accuracy of Thoracolumbar Minimally Invasive Pedicle Screw Placement With Augmented Reality Navigation Technology.

Study Design.Cadaveric laboratory study.Objective.To assess the feasibility and accuracy of minimally invasive thoracolumbar pedicle screw placement using augmented reality (AR) surgical navigation.Summary of Background Data.Minimally invasive spine (MIS) surgery has increasingly become the method of choice for a wide variety of spine pathologies. Navigation technology based on AR has been shown to be feasible, accurate, and safe in open procedures. AR technology may also be used for MIS surgery.Methods.The AR surgical navigation was installed in a hybrid operating room (OR). The hybrid OR includes a surgical table, a motorized flat detector C-arm with intraoperative 2D/3D imaging capabilities, integrated optical cameras for AR navigation, and patient motion tracking using optical markers on the skin. Navigation and screw placement was without any x-ray guidance. Two neurosurgeons placed 66 Jamshidi needles (two cadavers) and 18 cannulated pedicle screws (one cadaver) in the thoracolumbar spine. Technical accuracy was evaluated by measuring the distance between the tip of the actual needle position and the corresponding planned path as well as the angles between the needle and the desired path. Time needed for navigation along the virtual planned path was measured. An independent reviewer assessed the postoperative scans for the pedicle screws’ clinical accuracy.Results.Navigation time per insertion was 90 ± 53 seconds with an accuracy of 2.2 ± 1.3 mm. Accuracy was not dependent on operator. There was no correlation between navigation time and accuracy. The mean error angle between the Jamshidi needles and planned paths was 0.9° ± 0.8°. No screw was misplaced outside the pedicle. Two screws breached 2 to 4 mm yielding an overall accuracy of 89% (16/18).Conclusion.MIS screw placement directed by AR with intraoperative 3D imaging in a hybrid OR is accurate and efficient, without any fluoroscopy or x-ray imaging during the procedure.Level of Evidence: N/A

In vitro validation of a novel mechanical model for testing the anchorage capacity of pedicle screws using physiological load application.

Biomechanical in vitro tests analysing screw loosening often include high standard deviations caused by high variabilities in bone mineral density and pedicle geometry, whereas standardized mechanical models made of PU foam often do not integrate anatomical or physiological boundary conditions. The purpose of this study was to develop a most realistic mechanical model for the standardized and reproducible testing of pedicle screws regarding the resistance against screw loosening and the holding force as well as to validate this model by in vitro experiments. The novel mechanical testing model represents all anatomical structures of a human vertebra and is consisting of PU foam to simulate cancellous bone, as well as a novel pedicle model made of short carbon fibre filled epoxy. Six monoaxial cannulated pedicle screws (Ø6.5 × 45mm) were tested using the mechanical testing model as well as human vertebra specimens by applying complex physiological cyclic loading (shear, tension, and bending; 5Hz testing frequency; sinusoidal pulsating forces) in a dynamic materials testing machine with stepwise increasing load after each 50.000 cycles (100.0N shear force + 20.0N per step, 51.0N tension force + 10.2N per step, 4.2Nm bending moment + 0.8Nm per step) until screw loosening was detected. The pedicle screw head was fixed on a firmly clamped rod while the load was applied in the vertebral body. For the in vitro experiments, six human lumbar vertebrae (L1-3, BMD 75.4 ± 4.0mg/cc HA, pedicle width 9.8 ± 0.6mm) were tested after implanting pedicle screws under X-ray control. Relative motions of pedicle screw, specimen fixture, and rod fixture were detected using an optical motion tracking system. Translational motions of the mechanical testing model experiments in the point of load introduction (0.9-2.2mm at 240N shear force) were reproducible within the variation range of the in vitro experiments (0.6-3.5mm at 240N shear force). Screw loosening occurred continuously in each case between 140N and 280N, while abrupt failures of the specimen were observed only in vitro. In the mechanical testing model, no translational motion was detected in the screw entry point, while in vitro, translational motions of up to 2.5mm in inferior direction were found, leading to a slight shift of the centre of rotation towards the screw tip. Translational motions of the screw tip of about 5mm in superior direction were observed both in vitro and in the mechanical testing model, while they were continuous in the mechanical testing model and rapidly increasing after screw loosening initiation in vitro. The overall pedicle screw loosening characteristics were qualitatively and quantitatively similar between the mechanical testing model and the human vertebral specimens as long as there was no translation of the screw at the screw entrance point. Therefore, the novel mechanical testing model represents a promising method for the standardized testing of pedicle screws regarding screw loosening for cases where the screw rotates around a point close to the screw entry point.

Biomechanical study of a newly-designed Y type pedicle screw in osteoporotic synthetic bone

To evaluate the biomechanical stability of a newly-designed Y type pedicle screw (YPS) in osteoporotic synthetic bone. The osteoporotic synthetic bone were randomly divided into 3 groups ( n=20). A pilot hole, 3.0 mm in diameter and 30.0 mm in deep, was prepared in these bones with the same method. The YPS, expansive pedicle screw (EPS), and bone cement-injectable cannulated pedicle screw (CICPS) were inserted into these synthetic bone through the pilot hole prepared. X-ray film examination was performed after 12 hours; the biomechanical stability of YPS, EPS, and CICPS groups was tested by the universal testing machine (E10000). The test items included the maximum axial pullout force, the maximum running torque, and the maximum periodical anti-bending. X-ray examination showed that in YPS group, the main screw and the core pin were wrapped around the polyurethane material, the core pin was formed from the lower 1/3 of the main screw and formed an angle of 15° with the main screw, and the lowest point of the inserted middle core pin was positioned at the same level with the main screw; in EPS group, the tip of EPS expanded markedly and formed a claw-like structure; in CICPS group, the bone cement was mainly distributed in the front of the screw and was dispersed in the trabecular bone to form a stable screw-bone cement-trabecular complex. The maximum axial pullout force of YPS, EPS, and CICPS groups was (98.43±8.26), (77.41±11.41), and (186.43±23.23) N, respectively; the maximum running torque was (1.42±0.33), (0.96±0.37), and (2.27±0.39) N/m, respectively; and the maximum periodical anti-bending was (67.49±3.02), (66.03±2.88), and (143.48±4.73) N, respectively. The above indexes in CICPS group were significantly higher than those in YPS group and EPS group ( P<0.05); the maximum axial pullout force and the maximum running torque in YPS group were significantly higher than those in EPS group ( P<0.05), but there was no significant difference in the maximum periodical anti-bending between YPS group and EPS group ( P>0.05). Compared with EPS, YPS can effectively enhance the maximum axial pullout force and maximum rotation force in the module, which provides a new idea for the design of screws and the choice of different fixation methods under the condition of osteoporosis.

Accuracy of cannulated pedicle screw versus conventional pedicle screw for extra-pedicular screw placement in dysplastic pedicles without cancellous channel in adolescent idiopathic scoliosis: a computerized tomography (CT) analysis.

This study aimed at studying the accuracy and safety of extra-pedicular screw insertion for dysplastic pedicles in AIS comparing cannulated screw system versus conventional screw system. 104 AIS patients with 1524 pedicle screws were evaluated using CT scan. 302 screws were inserted in dysplastic pedicles using fluoroscopic guidance technique. 155 screws were inserted using a cannulated system (Group 1), whereas 147 screws were inserted using standard screws (Group 2).The pedicle perforations were assessed using a classification by Rao et al.; G0: no violation; G1: <2mm perforation; G2: 2-4mm perforation; and G3: >4mm perforation). For anterior perforations, the pedicle perforations were assessed using a modified grading system (Grade 0: no violation, Grade 1: less than 4mm perforation; Grade 2: 4mm to 6mm perforation; and Grade 3: more than 6mm perforation). The perforation rate in Group 1 was4.5%and in Group 2 was15.6%(p=0.001). Most of the perforations were anterior perforations (53.3%). The anterior perforation rate in Group 1 was 1.9% compared to 8.8% in Group 2 (p=0.009). Group 1 has a medial perforation rate of 1.3% compared to Group 2, 6.1% (p=0.031). The rate of critical pedicle perforation in Group 1 was2.6%and in Group 2 was6.8%(p=0.102). InGroup 1, there wereno critical medial perforationbut there wasone G2 lateral perforation, one G2 superior perforation and two G3 anterior perforations. In Group 2, there werethree G2 medial perforations, one G2 lateral perforation, one G2 anterior perforation and five G3 anterior perforations. Usage of cannulated screw system significantly increases the accuracy of pedicle screw insertion in dysplastic pedicles in AIS.

Effect of different inner core diameters on structural strength of cannulated pedicle screws under various lumbar spine movements

BackgroundCurrently, cannulated pedicle screws have been widely used in minimal invasive or navigation techniques. However, the stress distribution and the strength of different core diameters of cannulated screw are not clear. This study aimed to investigate the mechanical strength of cannulated screws with different inner core diameter under various lumbar spine movements using finite element analysis.ResultsThe results showed that the von-Mises stress of a cannulated screw was larger than that of a solid screw in all loading conditions, especially above 2 mm in cannulated core diameter. In lateral bending, extension, and flexion, the maximum von-Mises stress was found approximate to the proximal thread for all types of screws. In rotation condition, the maximum von-Mises stress was located at the middle of the screw. Additionally, the difference in stiffness of instrumented levels was not significant among four screws under the same loading condition.ConclusionCannulated screws could provide enough stability for the vertebral body fusion comparing to solid screws. The diameter of cannulated core is suggested not to exceed 2.0 mm.

Radiofrequency-activated PMMA-augmentation through cannulated pedicle screws: A cadaver study to determine the biomechanical benefits in the osteoporotic spine.

PMMA-augmentation of pedicle screws strengthens the bone-screw-interface reducing cut-out risk. Injection of fluid cement bears a higher risk of extravasation, with difficulty of application because of inconsistent viscosity and limited injection time. To test a new method of cement augmentation of pedicle screws using radiofrequency-activated PMMA, which is suspected to be easier to apply and have less extravasations. Twenty-seven fresh-frozen human cadaver lumbar spines were divided into 18 osteoporotic (BMD ≤ 0.8 g/cm2) and 9 non-osteoporotic (BMD > 0.8 g/cm2) vertebral bodies. Bipedicular cannulated pedicle screws were implanted into the vertebral bodies; right screws were augmented with ultra-high viscosity PMMA, whereas un-cemented left pedicle screws served as negative controls. Cement distribution was controlled with fluoroscopy and CT scans. Axial pullout forces of the screws were measured with a material testing machine, and results were analyzed statistically. Fluoroscopy and CT scans showed that in all cases an adequately big cement depot with homogenous form and no signs of extravasation was injected. Pullout forces showed significant differences (p < 0.001) between the augmented and non-augmented pedicle screws for bone densities below 0.8 g/cm2 (661.9 N ± 439) and over 0.8 g/cm2 (744.9 N ± 415). Pullout-forces were significantly increased in osteoporotic as well as in non-osteoporotic vertebral bodies without a significant difference between these groups using this standardized, simple procedure with increased control and less complications like extravasation.

The Effect of Position and Different Size of Radial Hole on Performance of Cannulated Pedicle Screw

Cannulated Pedicle Screw (CPS) is the instrumentation that has been introduced in Biomedical field in order to stabilize the spine structure and also to enhance the pullout strength in osteoporotic patient. The cement is injected through the CPS which is flow from the screw head to the radial hole and then distributed around the CPS to give higher performance of pullout strength. However, the fracture still reported to happened around the radial hole. This paper is aim to focus on the effect of the position and different diameter of radial hole on the CPS. Three designs were constructed using SolidWork software where two of it are the current models whereas the third was the proposed design which the radial holes were position differently (skewed to each other) and its size is smaller than the current model, 1.0 mm and 1.5mm respectively. The software used for Finite Element Analysis (FEA) is Ansys workbench 16.0. The Finite Element Models were verified with FEA result of the previous research. The FEA results of torsional stress for current and proposed design were then compared to obtain the maximum torque that both designs are able to resist before fracture. It can be concluded that the performance of CPS can be improved by the proposed design which is 2 radial hole skewed to each other and smaller radial hole diameter (1.0mm) than the current cannulated pedicle screw (1.5mm).

Segmental polymethylmethacrylate-augmented fenestrated pedicle screw fixation for lumbar spondylolisthesis in patients with osteoporosis - A case series and review of literature.

Instrumentation in patients with osteoporosis is challenging. Bone cement-augmented fenestrated pedicle screw fixation is a new procedure for fixation in osteoporotic bone. Very few studies related to this procedure are published in literature. To evaluate the clinical and radiological outcome of polymethylmethacrylate (PMMA)-augmented fenestrated pedicle screw fixation in patients with spondylolisthesis having significant osteoporosis. This was a prospective, observational, single centre study. All the patients with lumbar spondylolisthesis and osteoporosis with symptomatic neural compression, managed surgically with PMMA-augmented fenestrated pedicle screws, were included in the study. Patients were evaluated preoperatively and postoperatively by means of Oswestry disability index (ODI), visual analog score (VAS); and, radiologically by plain radiography and computed tomography. Wilcoxon nonparametric test for paired samples with a level of significance of 0.05 was performed. A total of 25 patients of spondylolisthesis with osteoporosis (average T score of -3.0) were included in the study. The average age at presentation was 56.5 years. Females predominated with a female:male ratio of 3.16:1.Most of the patients had spondylolisthesis at the L4/L5 level followed by the L5/SI level. All the patients underwent spinal fusion with instrumentation and bone cement (PMMA)-augmentation through fenestrated cannulated pedicle screws. Preoperative and postoperative functional assessment done with VAS and ODI showed statistically significant improvement. All the patients had an evidence of bone fusion at follow-up. Fenestrated pedicle screw fixation with bone cement-augmentation in patients with lumbar spondylolisthesis and osteoporosis provided effective and lasting screw purchase.

Pullout performance comparison of pedicle screws based on cement application and design parameters.

Pedicle screws are the main fixation devices for certain surgeries. Pedicle screw loosening is a common problem especially for osteoporotic incidents. Cannulated screws with cement augmentation are widely used for that kind of cases. Dual lead dual cored pedicle screw has already given promising pullout values without augmentation. This study concentrates on the usage of dual lead dual core with cement augmentation as an alternative to cannulated and standard pedicle screws with cement augmentation. Five groups (dual lead dual core, normal pedicle screw and cannulated pedicle screw with augmentation, normal pedicle screw, dual lead dual cored pedicle screw) were designed for this study. Healthy bovine vertebrae and synthetic polyurethane foams (grade 20) were used as embedding test medium. Test samples were prepared in accordance with surgical guidelines and ASTM F543 standard testing protocols. Pullout tests were conducted with Instron 3300 testing frame. Load versus displacement values were recorded and maximum pullout loads were stated. The dual lead dual cored pedicle screw with poly-methyl methacrylate augmentation exhibited the highest pullout values, while dual lead dual cored pedicle screw demonstrated similar pullout strength as cannulated pedicle screw and normal pedicle screw with poly-methyl methacrylate augmentation. The dual lead dual cored pedicle screw with poly-methyl methacrylate augmentation can be used for osteoporotic and/or severe osteoporotic patients according to its promising results on animal cadaver and synthetic foams.

Effect of different radial hole designs on pullout and structural strength of cannulated pedicle screws

Cannulated pedicle screws are designed for bone cement injection to enhance fixation strength in severely osteoporotic spines. However, the screws commonly fracture during insertion. This study aims to evaluate how different positions/designs of radial holes may affect the pullout and structural strength of cannulated pedicle screws using finite element analysis. Three different screw hole designs were evaluated under torsion and bending conditions. The pullout strength for each screw was determined by axial pullout failure testing. The results showed that when the Von Mises stress reached the yield stress of titanium alloy the screw with four radial holes required a greater torque or bending moment than the nine and twelve hole screws. In the pullout test, the strength and stiffness of each screw with cement augmentation showed no significant differences, but the screw with four radial holes had a greater average pullout strength, which probably resulted from the significantly greater mean maximum lengths of cement augmentation. Superior biomechanical responses, with lower stress around the radial holes and greater pullout strength, represented by cannulated pedicle screw with four radial holes may worth recommending for clinical application.

Biomechanical and finite element analyses of bone cement-Injectable cannulated pedicle screw fixation in osteoporotic bone.

The objectives of this study were to investigate the safety and biomechanical stability of a polymethylmethacrylate (PMMA)-augmented bone cement-injectable cannulated pedicle screw (CICPS) in cancellous bone model, and to analyze the stress distribution at the screw-cement-bone interface. The OMEGA cannulated pedicle screw (OPS) and conventional pedicle screw (CPS) were used as control groups. Safety of the CICPS was evaluated by the static bending and bending fatigue tests. Biomechanical stability was analyzed by the maximum axial pullout strength and maximum torque tests. Stress distribution at the screw-cement-bone interface was analyzed by the finite element (FE) method. The CICPS and CPS produced statistically similar values for bending stiffness, bending structural stiffness, and bending yield moment. The maximum pullout force was 53.47 ± 8.65 N in CPS group, compared to 130.82 ± 7.32 N and 175.45 ± 43.01 N in the PMMA-augmented OPS and CICPS groups, respectively (p < 0.05). The CICPS had a significantly greater torque than the OPS and CPS. The FE model did not reveal excessive stress at the screw-cement-bone interface in the CICPS group. In conclusion, PMMA-augmentation with CICPS may be a potentially useful method to increase the stability of pedicle screws in patients with osteoporosis. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 960-967, 2016.

A new concept for implant fixation: bone-to-bone biologic fixation.

Many attempts have been made to reduce complications of bone implant, such as pedicle screw loosening. To address this problem, the authors suggest a new concept of bone-to-bone biologic fixation using recombinant human bone morphogenetic protein-2 (rhBMP-2)-loaded cannulated pedicle screws. Recombinant human bone morphogenetic protein-2 is an osteoinductive cytokine. Four types of titanium pedicle screws were tested (uncannulated, cannulated with no loading, beta-tricalcium phosphate (TCP)-loaded, and TCP/BMP2 loaded) using 16 miniature pigs. Radiological evaluation was conducted to assess the fusion and loosening of pedicle screws. Twelve weeks after implantation, peak torsional extraction torque was measured, and the pedicle screw and bone interface was evaluated by micro-computed tomography (µCT) and histologic examination. The mean value of the radiological score was significantly greater in the TCP/BMP2 loaded group at 12 weeks post-operation compared to those in the other groups. CT images showed distinct bone formation surrounding TCP/BMP2 loaded cannulated pedicle screws compared to the other groups. Mean extraction torsional peak torque at 12 weeks postoperative was more than 10-fold higher in the TCP/BMP2 loaded pedicle screw group than in the other groups. Bone surface and bone volume, as quantitated through µCT, were higher in the TCP/BMP2 loaded group. Histologic examination revealed bone-to-bone fixation at the interface of pedicle screws and pre-existing bone. Bone-to-bone biologic fixation through the holes of TCP/BMP2 loaded pedicle screws significantly increased fixation strength and represents a novel method that can be applied to osteoporotic or tumour spine surgeries.

Reduction in Fluoroscopy Time, Radiation Dosage, and Complications Using an Innovative Guide Wire for Percutaneous Pedicle Screws

Introduction Despite the benefits of minimally invasive spine surgery (MIS), inherent risks to the patient and surgeon exist. Numerous studies demonstrate increased radiation exposure with MIS secondary to the need for increased fluoroscopy, thereby increasing the risk of cataracts and malignancy. Additionally, inadvertent advancement of standard guide wires through the vertebral body can occur, placing vital ventral structures at risk. This study evaluates the benefit of utilizing a novel split-tip guide wire for percutaneous pedicle screw placement. Methods A total of 30 consecutive cases of MIS transforaminal lumbar interbody fusion (TLIF) at L5–S1 were retrospectively evaluated. Group 1: Standard straight guide wire, 15 patients; group 2: split-tip guide wire, 15 patients. Except for the type of guide wire utilized, the same operative technique was used in each case, including bicortical S1 screw fixation. Total fluoroscopy time, radiation dosage, operative time, and complications were evaluated. Technique: (1) S1 pedicles are cannulated with standard Jamshidi needles. (2) Y-wires are placed through Jamshidi needles. (3) A cannulated Steffee probe cannulates the distal sacral promontory over the Y-wire. (4) The Steffee probe is retracted 50% and Y-wire is repositioned (Y-wire design prevents inadvertent advancement through sacral promontory). (5) The proximal S1 pedicle can be tapped over the Y-wire (not required). (6) Cannulated pedicle screws are placed over the Y-wire, engaging the distal sacral promontory for bicortical S1 purchase. Results Mean total fluoroscopy time per case for group 1 was 231.1 seconds versus 154.2 seconds for group 2 ( p = 0.017). Mean radiation dosage for group 1 was 16.22 versus 8.69 rads in group 2 ( p &lt; 0.001). There was no significant difference in operative time ( p = 0.18). Inadvertent advancement of two S1 guide wires occurred in two different patients in group 1. Postoperative abdominal CT scans with contrast were negative. Conclusion Utilizing a split-tip guide wire for percutaneous pedicle screw placement significantly decreased fluoroscopy time by 33% and radiation dosage by 46%. Cannulating the sacral promontory allows for bicortical S1 screw purchase, but removes the mechanical stop preventing inadvertent guidewire advancement. The split-tip guidewire may prevent wire advancement and decreases the need for fluoroscopic surveillance. This, in turn, reduces the risk of injury to structures ventral to the spine, while reducing the exposure to harmful radiation.