Spinal Fixation System Research Articles

Carbon Fiber Reinforced Hybrid Polyaryl–Ether–Ether–Ketone (PEEK) Spinal Fixation System: Technical Features and Preliminary Clinical Trial

Carbon Fiber Reinforced Hybrid Polyaryl–Ether–Ether–Ketone (PEEK) Spinal Fixation System: Technical Features and Preliminary Clinical Trial

Tribological properties of titanium alloy with micro-nano multiscale texturing against bone under simulated implant contact conditions

The stability of a titanium alloy screw implant in a spinal internal fixation system is primarily influenced by its tribological properties. We integrated laser texturing and anodic oxidation technology to fabricate surface micro/nanostructures on titanium alloys. The tribological properties of titanium alloys against bone were investigated by mimicking the progress of screw implantation. The results demonstrated that surface structure reduced the dynamic friction of the titanium alloy under dry conditions and increased the static friction under wet conditions. The low sliding friction in the dry state facilitated the initial implantation of the titanium alloy screws. Conversely, the high static friction in the wet state prevents post-implantation loosening of the titanium alloy screw and enhances its stability within bone tissue.

Biomechanical Analysis of the Impact of Transverse Connectors of Pedicle-Screw-Based Fixation on Thoracolumbar Compression Fracture

Contemporary clinical practice is progressively shifting towards percutaneous minimally invasive surgery. Conversely, the incorporation of transverse connectors in the design of spinal fixation systems is associated with more invasive open surgical procedures. The primary objective of this investigation was to evaluate the influence of transverse connectors in posterior spinal fixation system designs in cases involving vertebral compression fractures, specifically on selected mechanical parameters of the thoracolumbar spine in situations of instability. This research objective was achieved through a combination of experimental tests and numerical simulations. From the experimental tests conducted, critical mechanical parameters were ascertained, including the bending stiffness coefficient and energy dissipation. Numerical simulations were employed to determine additional parameters, such as the angular range of motion for individual spinal segments, intradiscal pressure within individual intervertebral discs, and stress distribution on the articular facets. Analyzing the impact of transverse connectors on the obtained results revealed that their inclusion in a fixation system results in a minor increase in stiffness and a decrease in mobility in comparison to fixation systems devoid of connectors. These findings create the potential for utilizing minimally invasive surgery as a viable alternative to open surgical procedures.

Biomechanical evaluation and optimal design of a pedicle screw with double bent rods internal fixation system based on PE-PLIF fusion

Problems, such as broken screws, broken rods, and cage subsidence after clinical spinal fusion surgery affect the success rate of fusion surgery and the fixation effect of fusion segments, and these problems still affect the treatment and postoperative recovery of patients. In this study, we used the biomechanical finite element analysis method to analyze and study the fixation effect of three kinds of spinal internal fixation systems on L4–L5 lumbar spine segments in percutaneous endoscopic posterior lumbar interbody fusion (PE-PLIF). The three different fixation systems compared in this study include bilateral pedicle screw fixation (M1); bilateral pedicle screw with cross-link fixation (M2); bilateral pedicle screws with double bent rods fixation (M3). The internal fixation systems with different structures were analyzed with the help of Hypermesh, and Abaqus. It was found that the internal fixation system with double bent rods reduced screw stresses by 23.8 and 22.2% in right and left axial rotation than the traditional bilateral pedicle screw system, while titanium rod stresses were reduced by 9.6, 3.7, 9.6, and 2.9% in flexion, left and right lateral bending, and right axial rotation, respectively, and L5 upper endplate stresses were reduced by 35.5, 18.9, 38.4, 10.2, and 48.3% in flexion, left and right lateral bending, and left and right axial rotation, respectively. The spinal range of motion (ROM) of the M3 internal fixation system was less than that of the M1 and M2 internal fixation systems in left lateral bending, left lateral rotation, and right axial rotation, and the intact vertebral ROM was reduced by 93.7, 94.9, and 90.9%, respectively. The double bent rod structure of the spinal internal fixation system has better biomechanical properties, which can effectively reduce the risk of screw breakage, loosening, cage subsidence, and endplate collapse after fusion surgery.

UTILIZAÇÃO DO SISTEMA uCentrum NO TRATAMENTO CIRÚRGICO DAS DOENÇAS DA COLUNA VERTEBRAL

ABSTRACT Objectives: Evaluate the treatment outcome and the performance of the uCentum spinal fixation system in treating traumatic, degenerative, and tumoral diseases of the spine. Methods: This is a therapeutic study to investigate treatment outcomes and level of evidence III, including twenty-three adult patients of both sexes undergoing surgical treatment of degenerative (13 patients), traumatic (04 patients), or tumor diseases (06 patients). Patients were prospectively evaluated using clinical parameters: pain (visual analog scale), clinical and functional assessment questionnaires (SF-36, Oswestry and Roland-Morris), and radiological criteria (arthrodesis consolidation, loosening, breakage or deformation of the implants). Results: Twenty patients were followed for a period of 01 month to 12 month (mean 6,5±7,77). Three patients died due to complications unrelated to the primary disease (traumatic brain injury, septicemia, and lung tumor). Improvements were observed in clinical parameters and scores of the evaluation questionnaires used. No implant-related complications (breakage, loosening, deformation) were observed. Conclusion: the uCentum fixation system showed great versatility for performing the surgical treatment, allowing the performance of open, percutaneous procedures, the introduction of acrylic cement inside the implants, and conversion of polyaxial screws into monoaxial screws intraoperatively. Level of Evidence III; Therapeutic Studies - Investigating the Results of Treatment.

Biomechanical comparison of different rod-to-rod connectors to a conventional titanium- and cobalt chromium posterior spinal fixation system

IntroductionSeveral types of rod-to-rod connectors are available for the extension of spinal fixation systems. However, scientific literature regarding the mechanical performance of different rod-to-rod connector systems is lacking. Research questionThe goal of this study was to evaluate the mechanical characteristics of axial and lateral rod connectors in comparison to a conventional pedicle screw rod (titanium and cobalt chromium) construct. Material and methodSix types of instrumentations were investigated in a standardized test model to quantify the mechanical differences: 1: titanium rod; 2: titanium rod with axial connector; 3: titanium rod with lateral connector; 4: cobalt chromium rod; 5: cobalt chromium rod with axial connector; 6: cobalt chromium rod with lateral connector. All groups were tested in static compression, static torsion and dynamic compression and statistically compared regarding failure load and stiffness. ResultsIn static compression loading, the use of connectors increased the construct stiffness, but unaffected the yield load. The use of a cobalt chromium rod significantly increased by approximately 40% the yield load and stiffness in comparison to the titanium rod configurations. Under dynamic compression, a similar or higher fatigue strength for all tested groups in comparison to the titanium rod configuration was evaluated, with the exception of titanium rod with axial connector. ConclusionBiomechanically, using rod connectors is a secure way for the extension of a construct and is mechanically equal to a conventional screw rod construct. However, in clinical use, attention should be paid regarding placement of the connectors at high loaded areas.

Finite Element Analysis-Based Evaluation of the Patient-Specific Spinal Rods for a Reduced Risk of Adjacent Segment Disease

Adjacent Segment Disease (ASD) is a postoperative drawback of spinal fusion surgery which yields an increase in the range of motion in the adjacent spinal level. Therefore, the main aim of this study is to investigate the optimum mechanical properties of the spinal rod allowing a reduced rigidity in the spinal fixation level for decreasing the displacement of the adjacent segment. In this study, the spinal fixation system was modelled and attached to L3-L4 level. The elasticity modulus of the rods and the follower load were parametrically defined in order to investigate their optimum values under physiological loading conditions of extension. The maximum displacement value determined for the upper adjacent intervertebral disc was defined as the output parameter. Thereafter, the biomechanical response of the spinal bone-implant complex was simulated using Finite Element Analysis (FEA). Using the parametric FEA results, a polynomial mathematical model was constructed and Response Surface Method (RSM) was used to plot the relationship between input and output parameters. According to the results of the study, the optimum elasticity modulus of the rods and the suggested follower load have been determined as 80.8 GPa and 303.84 N, respectively. The maximum principal strain values obtained in the pedicle screws were 746 µℇ, 1563 µℇ, 3037 µℇ and 2937 µℇ, respectively. However, since the results are strongly associated with anatomical and biomechanical differences, the proposed patient-specific approach may enhance the accuracy for a more successful spinal fusion surgery operation in terms of minimizing the risk of ASD.

Global stiffness and residual stresses in spinal fixator systems: A validated finite element study on the interconnection mechanism

Posterior spinal fixation systems are the gold standard to treat different column disorders using rods and screws. The proper connection between them is guaranteed by the Interconnection Mechanism (IM), consisting of different metallic subcomponents held together through the application of tightening torque. The response of the fixation system is defined by its overall stiffness, which in turn is governed by the local residual stress field arising during tightening. Although literature computational models for studying spinal fixation are becoming increasingly anatomically complex, most studies disregard completely the realistic modeling of the IM, namely choosing elastic-plastic material models and proper contact interactions. In this frame, the present study aims at increasing awareness in the field of spinal fixation modeling by investigating the mechanical response of the IM in terms of overall stiffness and local residual stresses. Once validated through dedicated experiments, the results of the proposed model have been compared with the current literature, highlighting the key role of the IM in the reliable modeling of spinal fixation.

Cortical Bone Trajectory Pedicle Screw Fixation in Surgical Treatment of Monosegmental Pyogenic Lumbar Spondylodiskitis.

Pedicle screw fixation has been widely used in surgical treatment for infective lumbar spondylodiskitis to prevent instability and deformity. The cortical bone trajectory pedicle screw (CBTPS) fixation is a minimally invasive posterior spinal fixation system that runs from the pedicle's entry point of the caudiomedial region toward the cephalad-divergent direction. Successful results with CBTPS fixation have been reported to treat degenerative and osteoporotic spinal diseases. This study aims to investigate the clinical feasibility of CBTPS in the surgical treatment of pyogenic lumbar spondylodiskitis. We retrospectively retrieved 20 consecutive patients from two academic centers who were surgically treated for monosegmental lumbar pyogenic spondylodiskitis. The primary surgical treatment was the anterior lumbar interbody fusion with decompression, debridement, and reconstruction using an autogenous iliac strut bone graft. One to 2 weeks after the primary surgery, patients underwent a second surgery for posterior instrumentation using conventional pedicle screws (CPS; group I) and CBTPS (group II). Radiographic parameters of the deformity angle at the fusion segment and clinical parameter of visual analog scale (VAS) scores were assessed preoperatively, postoperatively, and at the last follow-up. There were 10 patients in each group. The mean follow-up periods of groups I and II were 51.10 ± 6.95 and 28.60 ± 9.31 months, respectively. Intergroup analysis indicated the two groups area age-matched (p = 0.38), but initial C-reactive protein (CRP; mg/dL, p = 0.04), CRP normalization (months, p = 0.00), and follow-up duration (months, p = 0.00) were heterogeneous. Meanwhile, deformity angles (segmental lordosis) between the two groups were not significantly different preoperatively (p = 0.25), postoperatively (p = 0.13), and at last follow-up (p = 0.38). The intragroup analysis indicated a significant postoperative increase of lordosis in both group I and II (p = 0.00 and 0.04, respectively) with subsequent subsidence. Lordosis remained increased at the last follow-up with or without significance (group I, p = 0.02; group II, p = 0.62). Both groups showed significant improvement in VAS scores (group I, p = 0.00; group II, p = 0.00). In monosegmental lumbar spondylodiskitis, posterior stabilization of the anterior strut bone graft by CBTPS and CPS was comparable via the radiographic parameter of segmental lordosis or deformity angle. Our observation suggests the clinical feasibility of CBTPS in the treatment of relatively mild monosegmental pyogenic lumbar spondylodiskitis.

A Finite Element Study on the Treatment of Thoracolumbar Fracture with a New Spinal Fixation System.

Objective In this study, the mechanical properties of the new spinal fixation system (NSFS) in the treatment of thoracolumbar fractures were evaluated by the finite element analysis method, so as to provide a mechanical theoretical basis for the later biomechanical experiments and clinical experiments. Methods T12-L2 bone model was constructed to simulate L1 vertebral fracture, and three models of internal fixation systems were established on the basis of universal spinal system (USS): Model A: posterior short-segment fixation including the fractured vertebra (PSFFV); Model B: short-segment pedicle screw fixation (SSPF); Model C: new spinal fixation system (NSFS). After assembling the internal fixation system and fracture model, the finite element analysis was carried out in the ANSYS Workbench 18.0 software, and the stress of nail rod system, fracture vertebral body stress, vertebral body mobility, and vertebral body displacement were recorded in the three models. Results The peak values of internal fixation stress, vertebral body stress, vertebral body maximum displacement, and vertebral body maximum activity in Model C were slightly smaller than those in Model B. Conclusions Compared with the traditional internal fixation system, the new spinal internal fixation system may have the mechanical advantage and can provide sufficient mechanical stability for thoracolumbar fractures.

Применение транспедикулярной спинальной системы и блок-решетки при оперативном лечении посттравматической деформации таза: случай из практики и краткий анализ литературы

Introduction The problem of treating chronic unstable pelvic injuries is characterized by the complexity of delayed one-step or staged reduction, difficulties in choosing the technology and treatment options, complexity of selecting criteria for evaluating planning along with the effectiveness of treatment. The use of spinal systems to perform reduction manipulations and fixation of the pelvis is described in few clinical observations. Therefore, the assessment of the effectiveness of the sequential use of various fixation systems in one patient was regarded by the authors as a rare opportunity and determined the purpose of the study. Purpose Demonstration of the possibilities of various osteosynthesis methods and their combination in reconstructive surgery of the pelvis in a case of its severe chronic injury. Materials and methods We present a clinical case and a brief analysis of the literature. This is a case of a patient with posttraumatic pelvic deformity and imbalance syndrome as a leading component of pelvic ring deformity. The effectiveness of reconstruction options, including those with the use of spinal systems, was analyzed. The treatment was assessed with radiological study methods (X-ray and CT) with balance evaluation on a digital platform and functional scores for the quality of life. Results Correction of frontal deformity of the pelvis was achieved with compensation for a relative shortening of the left lower extremity, restoration of the center of rotation of the hip joints, and relief of pain in the lumbar region. The functional state according to the Majeed score system and clear radiological signs of stabilization of the pelvic ring while maintaining the position of the acetabulum in the frontal plane prove the effectiveness of hybrid osteosynthesis with the use of spinal fixation systems. Conclusion The leading syndromic complexes are instability with clinical manifestations of non-union and pain along with an imbalance syndrome, manifested by a gross deformation of the pelvic ring. Syndromic evaluation determines the tactics of surgical treatment while a detailed planning of the sequence of intervention, choice of the level of osteotomy, combination of osteosynthesis options using spinal fixation systems provide the solution of reconstructive pelvic surgery tasks in one session.

Biomechanical characterization of vertebral body replacement in situ: Effects of different fixation strategies

Background and ObjectiveArtificial vertebral implant with a lateral or posterior screw-rod fixation system are usually employed in lumbar reconstruction surgery to rebuild the lumbar spine after partial resection due to a tumor or trauma. However, few studies have investigated the effect of the various fixation systems on the biomechanics of the reconstructed lumbar system. This study aims to evaluate the influence of different surgical fixation strategies on the biomechanical performance of a reconstructed lumbar spine system in terms of the strength and long-term stability. MethodsTwo typical lumbar spine reconstruction case models that correspond to lateral or posterior fixation systems were built based on the clinical data. Finite element analyses were performed, and comparisons were made between the two models based on the predicted stress distribution of the reconstructed lumbar spine model, bone-growth area of the endplate, and the range of motion under various normal daily activities. ResultsThe load from the upper vertebral body was found to be effectively transmitted onto the lower vertebral body by a vertebral implant with the lateral fixation system; this was favorable for bone growth after surgery. However, significantly high stresses were concentrated around the interaction region between the screws and bone, owing to the uneven lateral fixation structure; this may increase the risk of bone fractures and screw loosening in the long term. For the posterior fixation case, stably posterior fixation structure was favorable to maintain stability for the reconstructed lumbar spine. However, the load was mainly transmitted via the fixation rod rather than the vertebral implant, owing to the stress shielding effect. Therefore, the predicted strain on the endplate were insufficient for bone ingrowth under most of the spinal activates, which could cause bone loss and prosthesis loosening. ConclusionsIn this study, the comparisons of the reconstructed lumbar spine system with lateral and posterior fixation strategies were conducted. The Pros and Cons of these two fixation strategies was deeply discussed and the associated clinical issues were provided. The results of this study will have a clear impact in understanding the biomechanics of the lumbar spine with different fixation strategies and providing necessary instructions to the design and application of the lumbar spinal fixation system.

Safety and Efficacy of Spinecall Spinal Fixation System for Adolescent Idiopathic Scoliosis

Study design: Retrospective case series including patient outcome assessment. Objective: To study the safety and the efficacy of the Spine call spinal fixation system in comparison with similar series. Background: The purpose was to determine the safety and the efficacy of a system which has been widely used in Brazil for over 15 years. Methods: A total of 76 consecutive patients were treated by posterior instrumentation and arthrodesis from 2011 through 2017. Safety was evaluated by complications, reoperation type and occurrence. Efficacy was studied by the incidence of deformity corrections. Results: There were no deaths, spinal cord or nerve root problems, or acute posterior wound infections. Proven pseudo-arthrosis occurred in one patient (1.3%) and in two cases was necessary debridement to remove infected tissue (2.6%). The implant-related reoperation rate was 1.3%, where an increased curvature was observed. The break of one screw (0.07% per screw) was reported, which did not lead to the need for reoperation. The largest Cobb angle averaged 57° pre-operative and 20.7° at latest follow-up, which means a 63.3% correction (p<0.001). Conclusions: Spinecall spinal fixation system seems to be at least as safe and effective as other instrumentations as used for the surgical treatment of adolescent idiopathic scoliosis.

Thoracolumbar Dorsal Ramus Nerve Block Using Continuous Multiorifice Infusion Catheters: A Novel Technique for Postoperative Analgesia After Scoliosis Surgery.

This is a brief technical report about a novel regional anesthesia technique in which local anesthetic was deposited around the thoracolumbar dorsal rami nerves via 4 multiorifice pain catheters to obtain analgesia for posterior spinal fusion surgery on scoliosis patients. Scoliosis is the most common deformity of the spine. Currently, most surgeons prefer a dual rod, segmental spinal fixation system that allows multiple anchor points for attachment to the deformed spine. Scoliosis surgery is an extremely painful surgical procedure due to the large incision, surgical trauma to superficial and deep muscles of the back, and the insertion of pedicle screws and metal rods directly into the vertebral column. Postoperative pain management remains very challenging. Three patients presented with scoliosis. Intraoperatively, 4 multiorifice catheters were placed lateral to the implanted pedicle screws. Two catheters were placed on each side, and a continuous infusion of 0.2 % ropivacaine was initiated postoperatively to improve the patient's pain control. The catheters remained in place for 48 hours postoperatively and were removed by the surgical team. Gentle traction was applied similar to the way epidural catheters are removed. All 3 patients reported very low pain scores, low doses of opioid consumption, and satisfaction with their pain control throughout their hospitalization. Our study results suggest that a thoracolumbar dorsal ramus nerve block using continuous multiorifice infusion catheters significantly improved postoperative comfort and pain and that its implementation into a multimodal analgesic regimen is relatively easy to achieve.

Retracted: Minimally Invasive Unilateral vs. Bilateral Pedicle Screw Fixation and Lumbar Interbody Fusion in Treatment of Multi-Segment Lumbar Degenerative Disorders.

We have retracted this publication because we were informed that an image used by the authors was copied from the following article: J Korean Neurosurg Soc. 2011 Nov; 50(5): 441-445. Minimally Invasive Multi-Level Posterior Lumbar Interbody Fusion Using a Percutaneously Inserted Spinal Fixation System: Technical Tips, Surgical Outcomes (https: //www.ncbi.nlm.nih.gov/pmc/articles/PMC3259464/pdf/jkns-50-441.pdf) (https: //www.ncbi.nlm.nih.gov/pmc/articles/PMC3259464/). Reference: 1. Xiaoyang Liu, Guangrun Li, Jiefeng Wang, Heqing Zhang: Minimally Invasive Unilateral vs. Bilateral Pedicle Screw Fixation and Lumbar Interbody Fusion in Treatment of Multi-Segment Lumbar Degenerative Disorders. Med Sci Monit, 2015; 21: 3652-3657. DOI: 10.12659/MSM.894890.

A biomechanical investigation of the retentive force of pedicle screw structures for different screw tulip designs

BackgroundPedicle screw based spinal fixation systems have been widely used for treating a variety of spinal diseases. The retentive force is an important factor that determines structural stability. The screw tulip design and the magnitude of nut tightening torque influence the retentive force. This study investigated the influences of varied tilt angles between the shaft-rod interface and varied nut tightening torques on the retentive force of the monoaxial, polyaxial, and uniplanar screws. MethodsThree types of tulip constructs were biomechanically tested. Two parameters that affect the retentive force include the tilt angle and the nut tightening torque. The retentive force was investigated by an axial gripping capacity test and axial torque gripping capacity test. FindingAmong all combinations of screw designs and tilt angles, the 12 Nm nut tightening torque offered a greater retentive force than the 8 Nm, except for monoaxial screws with a 0 degree tilt angle. For monoaxial screws, the retentive force was negatively correlated with increasing tilt angles. For polyaxial and uniplanar screws, the retentive forces remained constant with increasing tilt angles. InterpretationIn monoaxial screws, when the axis of the shaft isn't perpendicular to the axis of the rod, a gap is formed between the tulip-rod interface. This results in a decreased retentive force. In polyaxial and uniplanar screws, the contact surfaces were the same in different tilt angles, therefore, the retentive force remained constant, which was attributed to the adjustable tulips always being perpendicular to the axis of the rods.

Treatment of thoracolumbar fractures with three-dimensional reduction method and external fixation devices under analgesia

To compare the clinical effects between open reduction internal fixation and three-dimensional reduction with external fixation under analgesia in treating fresh thoracolumbar fractures, and explore the simple and effective method for thoracolumbar fractures. The clinical data of 40 patients with thoracolumbar fractures who met the inclusion and exclusion criteria in the department of orthopaedics affiliated to Suzhou Hospital of Nanjing University of Chinese Medicine from February 2013 to August 2017 were retrospectively analyzed. According to therapeutic methods, the patients were devided into treatment group and control group, 20 cases in each group. Treatment group was treated by three-dimensional reduction method and external fixation devices under analgesia, and control group was treated by open reduction and common spinal fixation system. In treatment group, there were 9 males and 11 females, aged from 26 to 68 years old with an average of (52.8±11.3) years; and in control group, there were 10 males and 10 females, aged from 26 to 64 years old with an average of(50.6±8.8) years. Anterior vertebral body compression(AVBC), Cobb angle and visual analogue scale(VAS) were measured and compared in two group. All 40 patients finished follow-up. The follow-up time in treatment group was 5 to 37 months with average of (16.1±8.8) months, in control group was 5 to 29 months with an average of(17.3±6.0) months. There was no significant difference between two groups(P>0.05). AVBC, Cobb angle, VAS score were obviously improved in all patients after treatment(P<0.05), but there were no significant difference between two groups(P>0.05). Clinical effect of two methods was similar in treating thoracolumbar fractures, but three-dimensional reduction and external fixation devices under analgesia has advantage of easy operation, smaller trauma and no need secondary surgery for removed internal fixation.

Utilization of second sacral alar-iliac technique for lumbosacral fixation in patients with tuberculosis of lumbar and sacrum spine

Objective To evaluate the feasibility and clinical outcomes of second sacral alar-iliac (S2AI) technique utilized in patients with tuberculosis of Lumbosacral spine. Methods 24 cases (15 male, 9 female, aged 36-73 years old, average 47.1 years) of tuberculosis of Lumbosacral spine were collected for surgery using spinal and pelvic fixation system (S2AI or IS) between January 2014 and May 2016. Lumbosacral pain and restricted movement were noticed in all cases, of which 9 cases with radiating pain of lower limb and 7 cases with intermittent claudication, 2 cases with saddle anesthesia. Formal anti-tuberculosis medicine treatment was given for at least 2-3 weeks before operation. All patients with lumbosacropelvic fixation were compared by recording with ESR/CRP, preoperatively, postoperatively and the last following-up. The clinical effect oswestry disability index (ODI) score, visual analogue scale (VAS), ambulatory status, SF-36 scale and related complications of 2 groups were also compared. Results The average follow-up period was average 23.4 months in the two groups. The results show that operative time, blood loss, drainage time, hospitalization days and fusion time were not statistically significant; the recording of ESR, CRP, ODI, VAS scores and ambulatory status scores between S2AI and IS groups showed no significantly different, preoperatively, postoperatively and the last following-up. Comparisons within each group were improved at postoperatively and the last following-up related to preoperatively; The difference of the SF-36 scales in each group was statistically significant between preoperatively and the last following-up; There was no statistically difference in recurrence, sinus, pseudarthrosis between two groups, but The S2AI technique was associated with lower rates of symptomatic screw prominence compared to the IS technique. Conclusion Application of S2AI screw technique in the treatment of lumbosacral tuberculosis can achieve solid fixation and satisfactory clinical effect, and reduce the complications of traditional IS screws, which is an alternative method of posterior structure reconstruction of lumbosacral tuberculosis. Key words: Tuberculosis; Spinal diseases; Sacroiliac joint; Treatment outcome

The Effect of Transpedicular Screw Design on Its Performance in Vertebral Bone Under Tensile Loads: A Parametric Study.

A biomechanical study using bovine thoracolumbar spines. To study investigated whether thread design parameters aimed at altering the state of stress at the screw-bone interface increase the screw's holding power. Internal spinal fixators utilizing transpedicular screw fixation are used to achieve early stabilization of the injured spine in a range of clinical conditions. Despite advances in the design of internal spinal fixation systems, implant loosening, and catastrophic failures at the screw-bone interface remains a serious complication in adult spine surgery. Although the performance of the screws in the vertebral bone critically depends on ability of screw thread design to provide and maintain adequate bone purchase, the effect of individual thread design parameters on screw performance and the failure process of the screw-bone interface, remains unclear. On the basis of the AO Schanz thread, this parametric study used 96 lumbar bovine vertebrae instrumented with 19 screw designs to investigate the effects of pitch, ratio of major to minor diameter, screw insertion depth, and major diameter, on screw performance under pure tensile loading. The effect of vertebral morphometry on screw performance and the extent of damage within the failed screw-bone interface were evaluated. The increase in screw insertion depth, screw pitch, and the ratio of major to minor diameter, significantly affected screw performance under tensile loads. Complex interactions existed between the major diameter and each of the design variables. Vertebral morphometry had little effect on screw performance while the damage within the failed bone-screw interface confined to the immediate region of the screw threads. Design variables, able to reduce shear stresses or modify the complex stress profile at the bone-screw interface, are more effective in preventing early failure of the interface.

Static Test of Flexo Compression in Posterior Thoracolumbar Spinal Fixation with Conical Cylindrical Screws

Introduction The aim of this paper is to describe the results obtained of a static test of flexo compression in polyaxial transpedicular conical cylindrical screws; which we have used for more than 20 years; in posteriors thoracolumbar spine fixings based on the ASTM F 1717–04 standard. This trial was made at the National Institute of Industrial Technology at its Center for Research and Development in Mechanical in Buenos Aires, Argentina. Material and Methods Two spinal fixation systems were evaluated, both composed by transpedicular conical soul and cylindrical thread screws, bars and tulips. In Table 1 the information provided by the manufacturer of the screws and identification adopted in the test for each sample is presented. [Table: see text] A universal testing machine Tinius Olsen H50-KT was used for the study. The proposed paragraph 8.1.1 of ASTM F1717–04 procedure was followed. The assembly of the samples was performed using the steps proposed by us, the tulips were set at the distance established by the Standard and the terminal screw of them was set by applying a torque of 10 Nm. The assays were performed at a speed of 10 mm / min and were interrupted when the load drop was observed in the instant graphic verifying in this way the loss of poliaxiality. The test setup used and the location of the devices during the test are shown in Fig. 1 . [Figure: see text] The active length of longitudinal component (L) was revealed (see Fig. 1 ). From this value the corresponding displacement of 2% of the permanent deformation was calculated, Point B =Lx 0, 02 (see Fig. 2 ). From the assay were obtained (see Fig. 2 ): The Load-displacement curve; The fluence load flexo-compression (N) (point D); The fluence displacement 2% (mm) (point A) # the elastic displacement (mm): difference between the value of point A and point B. Elastic displacement = Point A-Point B # the flexo-compression rigidity (N / mm): ratio between the loading of flexo-compression fluence and the elastic displacement. Rigidity = Point D Point A – Point B # the final displacement (mm), and # the final load (N) [Figure: see text] Results Fig. 3 shows the curve Load versus Displacement obtained for samples 018565- (1–2) [Figure: see text] In Table 2 the results are described. [Table: see text] Conclusion Screws and prisoners remained adjusted and there were not apparent permanent deformation in any of the system components. Its cylindrical thread and conical soul provides a high strength profile improving primary fixation and the resistance to the pull out. The major diameter of the soul in the pedicle region increases the bending and the resistance in fixations without arthrodesis preventing the breaking of the screw. All tests were performed within the framework of Management System for Quality Assurance of INTI-Mechanics.