Transverse Connector Research Articles

Biomechanical Study of Horizontal Screw-screw Crosslink in C1-2 Pedicle Screw-rod Fixation.

This is a biomechanical study in vitro. To investigate the biomechanical differences between horizontal rod-rod crosslink (hR-R CL) and the horizontal screw-screw crosslink (hS-S CL) implementation in C1-2 pedicle screw-rod (C1-2 PSR) fixation. To improve internal fixation stability, transverse connector (TC) is used in C1-2 PSR to increase torsional stiffness. The connection mode of horizontal connection includes hR-R CL and hS-S CL. hS-S CL adopted in C1-2 PSR was rarely reported and its biomechanics are still unclear. Six fresh cadaveric cervical spine specimens were each tested as an Intact model, then modified and tested as an Instability model (unstable odontoid fractures), and then as 3 internal fixation models, including C1-2 PSR, C1-2 pedicle screw-rod+horizontal rod-rod crosslink (C1-2 PSR+ hR-R CL), C1-2 pedicle screw-rod+horizontal screw-screw crosslink (C1-2 PSR+ hS-S CL). The ROM of the C1-2 segments was measured by applying 1.5nm load in 6 loading conditions, including flexion-extension (FE), left and right lateral bending (LB), and left and right axial rotation (AR). The C1-2 PSR+hR-R CL and C1-2 PSR+hS-S CL models, respectively, showed 60% and 75% lower ROM than the C1-2 PSR model in LB and AR conditions ( P <0.05). ROM was comparable between the C1-2 PSR+hR-R CL and the C1-2 PSR+hS-S CL models in all loading conditions ( P >0.05). Both types of crosslinks showed superior C1-2 stability under LB and AR conditions than PSR without crosslinks. The C1-2 segment stability was comparable between the 2 types of crosslinks themselves.

Biomechanical effects of transverse connectors on total en bloc spondylectomy of the lumbar spine: a finite element analysis

BackgroundThe influence of total en bloc spondylectomy (TES) on spinal stability is substantial, necessitating strong fixation to restore spinal stability. The transverse connector (TC) serves as a posterior spinal instrumentation that connects the left and right sides of the pedicle screw-rod system. Several studies have highlighted the potential of a TC in enhancing the stability of the fixed segments. However, contradictory results have suggested that a TC not only fails to improve the stability of the fixed segments but also might promote stress associated with internal fixation. To date, there is a lack of previous research investigating the biomechanical effects of a TC on TES. This study aimed to investigate the biomechanical effects of a TC on internal fixation during TES of the lumbar (L) spine.MethodsA single-segment (L3 segment) TES was simulated using a comprehensive L spine finite element model. Five models were constructed based on the various positions of the TC, namely the intact model (L1-sacrum), the TES model without a TC, the TES model with a TC at L1–2, the TES model with a TC at L2–4, and the TES model with a TC at L4–5. Mechanical analysis of these distinct models was conducted using the Abaqus software to assess the variations in the biomechanics of the pedicle screw-rod system, titanium cage, and adjacent endplates.ResultsThe stability of the surgical segments was found to be satisfactory across all models. Compared with the complete model, the internal fixation device exhibited the greatest constraint on overextension (95.2–95.6%), while showing the least limitation on left/right rotation (53.62–55.64%). The application of the TC had minimal effect on the stability of the fixed segments, resulting in a maximum reduction in segment mobility of 0.11° and a variation range of 3.29%. Regardless of the use of a TC, no significant changes in stress were observed for the titanium cage. In the model without the TC, the maximum von Mises stress (VMS) for the pedicle screw-rod system reached 136.9 MPa during anterior flexion. Upon the addition of a TC, the maximum VMS of the pedicle screw-rod system increased to varying degrees. The highest recorded VMS was 459.3 MPa, indicating a stress increase of 335.5%. Following the TC implantation, the stress on the adjacent endplate exhibited a partial reduction, with the maximum stress reduced by 27.6%.ConclusionThe use of a TC in TES does not improve the stability of the fixed segments and instead might result in increased stress concentration within the internal fixation devices. Based on these findings, the routine utilisation of TC in TES is deemed unnecessary.

Finite element analysis of minimally invasive nail placement and traditional nail placement in the treatment of lumbar 1 vertebral compression fracture.

Using the finite element analysis method to help us better understand the biomechanical changes of the spine after surgery and the changes in the stress distribution around the screw implantation area. The finite element model of L1 vertebral compression fracture was constructed by using a large number of finite element programs. On the fracture model, 2 kinds of internal fixation devices are set up, namely: the first type of 4 screws across the injured vertebra through the adjacent upper and lower vertebrae + transverse connector; the second type of 4 screws crosses the injured vertebra through the adjacent upper and lower vertebrae + non-transverse connector. To study the distribution of the maximum displacement and von Mises stress of the intramedullary pedicle screws and rods of the 2 types of internal fixation devices after implantation in the spine under certain loading conditions. In traditional open pedicle screw fixation, the maximum stress in the pedicle screw fixation system in the direction of 3D movement is higher than in percutaneous pedicle screw fixation. There is no significant difference in the Von Mises stress of the pedicle screw between the 2 procedures when the spine performs flexion-extension and lateral flexion activities. When the spine is rotating axially, the Von Mises stress of the pedicle screw in conventional open surgery is significantly less than that of the screw in percutaneous pedicle screw fixation. Traditional open internal fixation produces stress peaks of 891.7 MPa and 886.34 MPa at the transverse joint during axial rotation. Only when the spine is rotating in the axial direction, the maximum displacement of traditional open pedicle screw fixation is smaller than that of percutaneous pedicle screw fixation. There is no significant difference in the maximum displacement between the 2 procedures when the spine is moving in other directions. Traditional open pedicle screw fixation can strengthen the stability of the spine in the direction of axial rotation, and can also be greater to reduce the maximum stress of the pedicle screw axial rotation, so the clinical treatment of unstable fractures of the thoracolumbar spine instability is of great significance.

Biomechanical analysis of variants of spinopelvic fixation of longitudinal sacral fractures by the finite element method

Objective. To analyze the strength of three types of spinopelvic fixation system configurations in longitudinal fracture of the sacrum by the finite element method.Material and Methods. Biomechanical analysis was carried out by the finite element method. A three-dimensional model of a segment of the spinopelvic complex (SPC), including the pelvic bones, sacrum and L4 and L5 vertebrae, was created on the basis of the CT scan results of a healthy patient. Then, a longitudinal fracture of the sacrum was simulated on the developed model of the sacrum on the left side in zone 1 according to the Denis classification. Further, a comparative assessment of three variants of spinopelvic fixation systems with the help of biomechanical computer modeling was carried out: bilateral spinopelvic system L4–S2Alar, bilateral spinopelvic system L4–S2Alar with transverse connector installation, and bilateral spinopelvic system L4–S2Alar with L-shaped rod installation. The stability of fixation, as well as the amount of loads acting on the fixation elements and bone tissues were determined.Results. As the rigidity of the structure increases by means of a transverse connector or an L-shaped rod, the load is redistributed between the screws located to the left and right of the fracture. The rigidity of the L4–S2Alar system with parallel, unconnected rods is much lower, which leads to a critical increase in loads on instrumentation and vertebrae.Conclusion. Analysis of three variants of spinopelvic fixation of longitudinal fractures of the sacrum by finite element method revealed that bilateral spinopelvic system with pedicle screws installed in the L4 and L5 vertebrae and pelvic screws installed in the iliac bones through the lateral masses of S2, two on each side (L4–S2 Alar) and connected by two parallel rods (variant 1) is the least strong in comparison with the other variants. The strength of the fixation increases when the structure is supplemented with a transverse connector between the rods (variant 2). The L4–S2 Alar design with an L-shaped rod on the side of the longitudinal fracture of the sacrum (variant 3) proved to be the most strong.

Hybridized energy harvesting device based on high-performance triboelectric nanogenerator for smart agriculture applications

Smart agriculture can be deemed as the deep cross-boundary integration of modern information technologies such as Internet of things (IoTs), intelligent equipment, and big data with agriculture, among which the numerous distributed sensors play a vital role in providing precise planting management. However, the lack of efficiency and low-cost energy harvesting approaches to power distributed sensor nodes has become a severe challenge. This challenge will seriously inhibit the development of smart agriculture. Herein, a hybridized energy harvesting device (HEHD) for capturing wind and solar energy was designed by combining two electromagnetic generators (EMGs), two triboelectric nanogenerators (TENGs), and two solar cells (SCs) to enable environmental energy collection. The rotation motion can be transformed into translational motion by introducing a transverse connector to link TENG and EMG, which favors the durability of the TENG. The output performance of TENGs and EMGs increases with increasing wind speed, and the open-circuit voltage (VOC) and short-circuit current (ISC) of the individual TENG and EMG can reach up to nearly 570 V, 40 μA, and 0.8 V, 1.85 mA at the 7 ms−1 wind speed, respectively. The self-powered temperature and humidity (Temp&Humid) monitoring system was established by combining the HEHD, a self-developed mobile phone application and a commercial Temp&Humid sensor, which can realize remote monitoring and multi-points connection of farmland environmental Temp&Humid data through the Internet. Moreover, a farm peripheral security alarm system based on the HEHD was constructed to achieve passive remote infrared monitoring. This work makes a beneficial attempt to realize self-powered sensor nodes, indicating broad potential for the use of TENGs in smart agriculture applications.

Radiological comparison of the biomechanical characteristics of short segment posterior instrumentation (Moss- Miami system), with and without transverse connector, in unstable thoraco-lumbar fracture

Introduction: Wedge compression fracture was most common type of fracture (66.6 %) and first Lumbar vertebra (L1) was the most common fracture site (38 %). The choice of surgical approach and instrumentation depends on fracture type, injury level and degree of neural injury. This paper evaluated efficacy of transpedicular screw fixation by Moss Miami instrumentation with transverse connector for surgical treatment in traumatic unstable thoraco-lumbar fractures.&#x0D; Materials and Method: Fifty-five cases were prospectively studied over three years. Comparison was done between two groups- Group 1 without transverse connector and Group 2 with transverse connector. Radiologically evaluation was done in both groups pre-operatively, tenth day, six weeks and six months interval. All X-rays were assessed by lateral and dynamic antero- posterior views for measuring kyphotic (cobb’s) angle and inter-rod angle.&#x0D; Results: In both groups post-operative Mean Cobb’s angle level were increased and remained same until 6months. Variation in Group 2 with transverse connector was slightly higher in initial period (i.e.) after 10 days and then it remains minimal from 6 weeks to 6 months. But in Group 1 without transverse connector the change in angle variation was minimal which worsen over 6 weeks and it continues to remain worse at 6 months, suggestive of parallelogram effect.&#x0D; Conclusion: Transverse connector does play role in preventing parallelogram effect of implants and provides additional stability to the construct. This is first study done in vivo which is done to study the role of transverse connector and evaluate any parallelogram effect in spinal instrumentation.&#x0D; Key words&#x0D; Transverse connector, Thoraco-lumbar fracture, parallelogram effect

Direct Internal Fixation for Unstable Atlas Fractures.

PurposeTo investigate the radiologic and clinical outcomes of direct internal fixation for unstable atlas fractures.Materials and MethodsThis retrospective study included 12 patients with unstable atlas fractures surgically treated using C1 lateral mass screws, rods, and transverse connector constructs. Nine lateral mass fractures with transverse atlantal ligament (TAL) avulsion injury and three 4-part fractures with TAL injury (two avulsion injuries, one TAL substance tear) were treated. Radiologic outcomes included the anterior atlantodental interval (AADI) in flexion and extension cervical spine lateral radiographs at 6 months and 1 year after treatment. CT was also performed to visualize bony healing of the atlas at 6 months and 1 year. Visual Analog Scale (VAS) scores for neck pain, Neck Disability Index (NDI) values, and cervical range of motion (flexion, extension, and rotation) were recorded at 6 months after surgery.ResultsThe mean postoperative extension and flexion AADIs were 3.79±1.56 (mean±SD) and 3.13±1.01 mm, respectively. Then mean AADI was 3.42±1.34 and 3.33±1.24 mm at 6 months and 1 year after surgery, respectively. At 1 year after surgery, 11 patients showed bony healing of the atlas on CT images. Only one patient underwent revision surgery 8 months after primary surgery due to nonunion and instability findings. The mean VAS score for neck pain was 0.92±0.99, and the mean NDI value was 8.08±5.70.ConclusionC1 motion-preserving direct internal fixation technique results in good reduction and stabilization of unstable atlas fractures. This technique allows for the preservation of craniocervical and atlantoaxial motion.

Effects of transverse connector on reduction and fixation of atlantoaxial dislocation and basilar invagination using posterior C1–C2 screw-rod technique

BACKGROUND CONTEXTThe mechanical strength provided by internal fixation is crucial for maintaining reduction and facilitating bony fusion. Though satisfactory results with the C1–C2 technique have been acquired in most clinical reports, the related problems of fusion delay and pseudarthrosis still exist. To increase the chance of bony fusion, a transverse connector (TC) is frequently used to augment torsional stiffness of thoracolumbar screw/rod constructs. Nevertheless, the clinical implication of TC in the management of atlantoaxial dislocation (AAD) and basilar invagination (BI) remains largely unknown. PURPOSETo evaluate the effects of TC application on C1–C2 screw-rod constructs based on consecutive adult patients with AAD and BI in a single institution over a 10-year period. STUDY DESIGNA retrospective study. PATIENT SAMPLEPatients with AAD and BI, who were treated with posterior C1–C2 screw-rod technique with or without TC usage from June 2007 to June 2017 at a single institution. OUTCOME MEASURESThe radiological measurements included the anterior atlantodental interval (AADI), posterior atlantodental interval (PADI), height of odontoid process above Chamberlain line, and cervicomedullary angle (CMA). Patients’ neurologic status was evaluated with the Japanese Orthopaedic Association (JOA) score. Fusion status was evaluated at different follow-up periods. METHODSWe compared the difference of clinical, radiological, and surgical outcomes between the TC and NTC groups postoperatively. RESULTSIn total, there were 149 consecutive patients in the TC group and 168 patients in the NTC group. On average, 1.2 TCs per patient were used in the TC group. No significant differences were identified for operative time and blood loss between groups. There was also no statistical difference in the radiological measurements of AADI, PADI, Chamberlain line, and CMA between the TC and NTC groups preoperatively and postoperatively. A significantly higher JOA score was obtained in the TC group than that in the NTC group postoperatively. The fusion rates were higher in the TC group than those in the NCT group at the early stage postoperatively (3 and 6 months; p<.01). CONCLUSIONSUse of TCs seems to improve bony fusion and neurologic outcomes in the treatment of AAD and BI with C1–C2 screw-rod technique.

TREATMENT OF THORACOLUMBAR BURST FRACTURES FIXED WITH INTERMEDIATE PINS BY THE POSTERIOR APPROACH

Objective:Radiographic evaluation of patients with thoracolumbar burst fractures treated with unconvencional transpedicular fixation, which includes additional fixation of the fractured vertebra associated with transverse connector - Crosslink clamp.Methods:Retrospective study evaluating a total of 68 patients operated at the Hospital do Trabalhador de Curitiba, Orthopedics Service, of which 15 were eligible for the study. All patients were treated with posterior pedicle fixation and intermediate screw. The assessment by the Cobb angle method was performed on preoperative, immediate postoperative and one year after surgery radiographs.Results:It was observed an average reduction of kyphosis of 8.3o (77%), with a loss of 1.34o in late postoperative compared to the immediate postoperative period.Conclusion:The method of fixation of burst-type fractures of the thoracolumbar spine by the posterior approach with intermediate screw was effective in maintaining the reduction achieved in the immediate postoperative period and after one year of evolution.

Comparison of Dynamic Stability of Lumbosacral Fixation using L5/S1 Pedicle Screws between with and without a Transverse Connector: A Finite Element Analysis Study

Introduction Fixation failure and pseudoarthrosis at the lumbosacral junction continue to be a big problem for spine surgeons. The poor bone quality of the sacrum, relative displacement between a screw and a screw head of a polyaxial screw and between a screw head and a rod and the substantial biomechanical forces at the lumbosacral junction are major risk factors for the high rates of instrumentation failure. It has already been believed that a transverse connector is necessary to achieve lumbosacral fusion. The purpose of our study is to investigate the dynamic stability of lumbosacral fixation using L5/S1 pedicle screws and a transverse connector with CT/finite element analysis quantitatively. Material and Methods CT Dicom data including L4, L5, and pelvis was obtained from the patient who had kyphoscoliotic spine and prepared for the correction surgery. The data were changed to the biomechanical model for analysis. On the computer, four pedicle screws (6 × 40 mm) were applied to L5 and S1 (PS) of the model. In addition to PS, a transverse connector was applied to bilateral rods (PS–TR). The flexion, extension, bending, and rotation force was loaded on L4 and the displacement of L5 was calculated with finite element analysis. The larger displacement was defined as the lower stability. The software of finite element analysis was MechincalFinder7.0EE. Results As to flexion, the displacement of L5 was reduced to 82% (PS–TR) compared with PS. As to extension, the displacement of L5 was reduced to 85% (PS–TR) compared with PS. As to right bending, the displacement of L5 was reduced to 77% (PS–TR) compared with PS. As to right rotation, the displacement of L5 was reduced to 13% (PS–TR) compared with PS. Conclusion As to flexion, extension, bending, and rotation, PS–TR tended to have higher stability than PS. As to rotation, the displacement of L5 (PS) is remarkably larger than that of PS–TR and it indicates that as to L5/S1 pedicle screw fixation, a transverse connector plays a significant role for lumbosacral stability and L5/S1 pedicle screw fixation without a transverse connector may be one reason for the higher rate of pseudoarthrosis.

Biomechanical Stability of Transverse Connectors in the Setting of a Thoracic Pedicle Subtraction Osteotomy

Introduction The biomechanical effect of augmentation of a longitudinal constructs with one or two transverse connectors (TC) after a thoracic pedicle subtraction osteotomy (PSO) has not been evaluated previously. Previous investigations have suggested the role of transverse connectors for long segment thoracic constructs in enhancing torsional rigidity. We set out to evaluate the biomechanical contribution of TC to the stability of a long-segment pedicle screw–rod construct after a thoracic PSO. Methods Seven human cadaveric thoracic spines were prepared and instrumented from T4 to T10 with bilateral pedicle screws/rods and a PSO was performed at T7. Intact range of motion (ROM) testing was performed with nondestructive loading and analyzed by loading modality (axial rotation, flexion/extension, and lateral bending). ROM analysis was performed in the unaugmented construct, the construct augmented with one TC, and the construct augmented with two TC. No outside funding sources were utilized for this study. The authors have no potential conflicts of interest to report. Results Following PSO and an unaugmented longitudinal pedicle screw–rod construct, T4–T10 (overall construct) and T6–T8 (PSO site). ROM was significantly reduced in all planes of motion compared with intact condition ( p &lt; 0.05). Augmentation of longitudinal construct with either one or two TC did not significantly increase construct stability in flexion-extension or lateral bending compared with the unaugmented construct ( p &gt; 0.05). In contrast, during axial rotation, global ROM was significantly reduced by 43% and by 48% at T6–T8 following addition of two TC ( p &lt; 0.05). One TC did not significantly reduce torsional ROM. Conclusions Two transverse connectors significantly improved torsional rigidity of the entire construct and at the PSO site, with no differences in stability for flexion-extension and lateral bending, or with the addition of only one transverse connector. In the setting of a PSO and long segment pedicle screw–rod construct, augmentation with at least two transverse connectors should be considered to improve torsional rigidity.

New Instrumentation Technique for Growing Rod

Introduction The spine is a key factor in the growth of thorax, abdomen, and pelvis. By the age of 5 years, the spine reaches 50% of its adult length. Therefore, spinal fusion in a 5-year-old child can result in about 12.5 cm loss of spinal growth. Disruption of the growth of the spine due to fusion performed in the treatment of early-onset scoliosis leads to thoracic insufficiency syndrome. The ideal technique should maintain the correction of the deformity, allow continued spinal growth, should not require postoperative immobilization, and also should have low complication rates. There are several growing rod techniques which have been defined but none of them fulfill all of these conditions. The aim of this article is to define a new modification on the growing rod technique. Patients and Methods Ten children have been operated in authors' institution, at an average age of 8 (range, 4–9) years. The surgical technique involved short segment instrumentation applied on the convex side of the apex of the deformity. Pedicle screws or hooks were used at stable anchor levels of the concave side of the deformity. Two rods, one proximal and one distal, were fixed to anchor sites and connected by a domino connector. After distracting the concave side, a transverse connector was used between the short segment and the long one, and this connector was compressed to maintain a translational force on the apex of the deformity. The frequency of lengthening procedure is 6 to 9 months. Results The average follow-up was 11 months. The average preoperative coronal plane curve was 46 degree and corrected to 13 degree showing 74% scoliosis correction after index surgery. Conclusion The main goal of the treatment of early-onset spinal deformities in children is to correct the deformity while maintaining the growth of the spine. All the described techniques up to now have been based on distraction of the concave side and the compression of the convex side of the deformity at stable vertebrae. The technique defined in this study, distracts the concave side while applying a translational force at the apex of the deformity by a transverse connector. The authors believe that this new technique will maintain more effective correction. Other advantages include less surgical dissection so less likely to cause a spontaneous fusion of the spine, shorter operation time, and low risk of surgery-associated complications. Long-term outcomes of the treatment by this new technique should be investigated by the mean spinal growth, and the correction of the spinal deformity.

Comparison of fusion rates between rod-based laminar claw hook and posterior cervical screw constructs in Type II odontoid fractures

BackgroundThis study was aimed (i) to compare the fusion rates of rod-based laminar claw hook constructs to that of posterior C1/C2 screw constructs in odontoid fractures, and (ii) to evaluate any complications associated with claw hook/rod constructs. To our knowledge, no study in contemporary literature has presented the effects of using modern rod-based laminar claw hooks for treating odontoid fractures. Unlike laminar clamps from the 1980s, contemporary laminar hook–rod instrumentation systems provide better immobilisation of the cervical spine and allows for building reliable frame-like constructs similar to cervical screw–rod systems. MethodsA retrospective review of a series of 167 consecutive odontoid fractures from a single-institution was conducted. 30 cases from the series were treated using posterior atlantoaxial fusion, 12 using C1/C2 posterior screws (control group), and 18 with rod-based laminar claw hooks (study group). Hooks were mounted bilaterally in a claw manner on each individual lamina and were rigidly fixed to perpendicular rods with a transverse connector whenever feasible. The minimum follow-up period was one year. Bony union was determined using computed tomography (CT) scan, while stability at the fusion site was assessed using dynamic radiograms. ResultsThe study group had an overall fusion rate of 89% (non-geriatric 93% while geriatric subgroup 75%) with a 100% stability rate at the fusion site in all cases. In the control group fusion rate was 100%. There were no major complications in both control and study groups. Four minor complications, three in the control and one in the study group, were noted in 3 patients. ConclusionPreliminary results of this study suggest that laminar claw hook–rod systems are useful alternatives to posterior screw techniques. Moreover, the fusion rate in non-geriatric patients is comparable to that of posterior screws. Importantly, they are devoid of the disadvantages and complications posed by screw constructs. Further studies are necessary to confirm these promising results.

Comparative analysis of posterior fusion constructs as treatments for middle and posterior column injuries: An in vitro biomechanical investigation

BackgroundTitanium pedicle screw–rod instrumentation is considered a standard treatment for spinal instability; however, the advantages of cobalt-chromium over titanium is generating interest in orthopedic practice. The aim of this study was to compare titanium versus cobalt–chromium rods in posterior fusion through in vitro biomechanical testing. MethodsPosterior and middle column injuries were simulated at L3–L5 in six cadaveric L1-S1 human spines and different pedicle screw constructs were implanted. Specimens were subjected to flexibility tests and range of motion, intradiscal pressure and axial rotation energy loss were statistically compared among five conditions: intact, titanium rods (with and without transverse connectors) and cobalt–chromium rods (with and without transverse connectors). FindingsAll fusion constructs significantly (P<0.01) decreased range of motion in flexion–extension and lateral bending with respect to intact, but no significant differences (P>0.05) were observed in axial rotation among all conditions. Intradiscal pressure significantly increased (P≤0.01) after fusion, except for the cobalt–chrome conditions in extension (P≥0.06), and no significant differences (P>0.99) were found among fixation constructs. In terms of energy loss, differences became significant P≤0.05 between the cobalt−chrome with transverse connector condition with respect to the cobalt–chrome and titanium conditions. InterpretationThere is not enough evidence to support that the cobalt–chrome rods performed biomechanically different than the titanium rods. The inclusion of the transverse connector only increased stability for the cobalt–chromium construct in axial rotation.

The Biomechanical Effect of Transverse Connectors Use in a Pre- and Postlaminectomy Model of the Posterior Cervical Spine

An in vitro biomechanical study investigating the effect of transverse connectors on posterior cervical stabilization system in a laminectomy model. To evaluate the optimal design, number, and location of the transverse connectors in stabilizing long segment posterior instrumentation in the cervical spine. In the cervical spine, lateral mass screw (LMS) fixation is used for providing stability after decompression. Transverse connectors have been used to augment segmental posterior instrumentation. However, in the cervical region the optimal design, number, and the location of transverse connectors is not known. Seven fresh human cervicothoracic cadaveric spines (C2-T1) were tested by applying ±1.5 Nm moments in flexion (F), extension (E), lateral bending (LB), and axial rotation (AR). After testing the intact condition, LMS/rods were placed and then were tested with two different transverse connectors (top-loading connector [TL] and the head-to-head [HH] connector) in multiple levels, pre- and postlaminectomy (PL). LMS significantly reduced segmental motion by 77.2% in F, 75.6% in E, 86.6% in LB, and 86.1% in AR prelaminectomy and by 75.4% in F, 76% in E, 80.6% in LB, and 76.4% in AR postlaminectomy compared to intact (P < 0.05). Only in AR, PL constructs with HH connectors at C3 & C7, TL connectors at C4-C5 & C5-C6, and at C3-C4 & C6-C7 significantly reduced the range of motion by 12.9%, 11.9%, and 11.9%, respectively, compared to PL LMS (P < 0.05). No statistical significance was observed between TL connector and HH connector in all loading directions. The biomechanical advantage of transverse connectors is significant in AR, when using two connectors at the proximal and distal ends, compared to one connector. In a clinical setting, this data may guide surgeons on transverse connector configurations to consider during posterior cervical instrumentation.

EXPERIMENTAL VALIDATION OF TRANSPEDICULAR FIXATION SYSTEM MODIFICATION

Objective. To compare the strength resistance of seriesproduced and modified spinal systems to continuous cyclic loading. Material and Methods. Assembled transpedicular four-screw systems with monoaxial screws of equal configuration were tested. The study group included modified fixation system, and the control group – series-produced domestic fixation systems. All devices were fixed in textolite vertebra models with the account for average pedicle angle and interpedicular distance, with equal interval between vertebrae, and using one transverse connector. The models were exposed to axial cyclic loading. Results. In dynamic loading conditions with 150 kg load (1,500 Newton) and the frequency of 6 cycles per second, the maximum strength of transpedicular fixation system from the study group was at average statistically reliably 22.1 % higher than that from the control group (p ≤ 0,05). Conclusion. The performed study appeared to be a scientific rationale for transpedicular screw modification. Suggested modification statistically reliably increases the maximum strength of fixation system, which reduces complication rate after transpedicular fixation and allows extending indications for transpedicular spinal fusion alone.

An S-2 alar iliac pelvic fixation

Multiple techniques of pelvic fixation exist. Distal fixation to the pelvis is crucial for spinal deformity surgery. Fixation techniques such as transiliac bars, iliac bolts, and iliosacral screws are commonly used, but these techniques may require separate incisions for placement, leading to potential wound complications and increased dissection. Additionally, the use of transverse connector bars is almost always necessary with these techniques, as their placement is not in line with the S-1 pedicle screw and cephalad instrumentation. The S-2 alar iliac pelvic fixation is a newer technique that has been developed to address some of these issues. It is an in-line technique that can be placed during an open procedure or percutaneously.

Analysis of instrumentation/fusion survivorship without reoperation after primary posterior multiple anchor instrumentation and arthrodesis for idiopathic scoliosis

Background During the past 25 years, spinal instrumentation systems and surgical techniques used to treat idiopathic scoliosis have evolved, achieving fewer patient restrictions during arthrodesis healing, shorter constructs, and better correction. The purposes of this retrospective comparative study were to determine the survivorship of the implant/fusion without reoperation and the risk factors influencing such survival. Methods From 1989 through 2002, 208 consecutive patients (index patient included, age 10–20 years) underwent primary posterior instrumentation and arthrodesis with the same multiple anchor implant system by one surgeon, a co-designer of the system. Two hundred seven were followed for more than 2 years; reoperation status was available for them at an average follow-up of 8.3 years. Twenty-one independent demographic, deformity, instrumentation, and process variables possibly influencing the need for reoperation were studied by comparing the reoperated group with the unreoperated group. Results Nineteen patients (9.2%) had reoperation; 16 (7.7%) were for indications related to posterior spine instrumentation. Survival of the implant/fusion without reoperation for spine instrumentation–related indications was 96% (95% confidence interval [CI], 93.2–98.7%) at 5 years, 91.6% (95% CI, 86.9–96.3%) at 10 years, 87.1% (95% CI, 79.5–94.6%) at 15 years, and 73.7% (95% CI, 48.6–98.6%) at 16 years, when the number at risk was nine. Reoperation need was significantly influenced by two implant variables: transverse connector design (p=.0012) and the lower instrumented vertebra anchors used (p=.0004). At 9 years, the longest interval allowing comparison, survival of the implant/fusion without reoperation for these two variables was 100% (six subjects at risk) compared to 82% (95% CI, 74.2–90.3%) with 59 patients still at risk for reoperation for those who did not have them, p=.0014. Conclusions The most stable lower instrumented vertebra anchor configuration, bilateral pedicle screws, and the stronger transverse connector design, closed drop entry, provided the best survival of the implant/fusion without reoperation with this system and the techniques used at 9-year follow-up. We hope that this post-market study using survivorship techniques will be a guide for studies of other spinal implants.

Biomechanical Contribution of Transverse Connectors to Segmental Stability Following Long Segment Instrumentation With Thoracic Pedicle Screws

An in vitro biomechanical cadaver study of long segment thoracic pedicle screw constructs with transverse connectors (TC). To determine the resultant degree of motion of the instrumented thoracic spine after segmental pedicle screw instrumentation with and without TC. SUMMARY OF BACKGROUND DATA.: TC are generally not thought to be necessary with thoracic pedicle screw constructs, yet to date no study has reported the effect of TCs after all pedicle screw long thoracic fusions. Eight human cadaveric spines were potted and then instrumented from T4-T10 with bilateral 5.5 mm multiaxial titanium (Ti) pedicle screws and 5.5 mm contoured Ti rods. Specimens were tested with a six-degree-of-freedom spine stimulator in the intact condition, after instrumentation, after placement of 1 TC (3 different locations) and after placement of both TCs. Data were analyzed by loading modality (axial rotation, flexion-extension, and lateral bending) using one-way analysis of variance with an alpha of 0.05. Paired t tests were used for post hoc analysis with correction for multiple comparisons. There was no difference with the addition of 1 or 2 TCs in terms of flexion-extension or lateral bending when compared to the instrumented condition (P > 0.05). Biomechanical testing of the long-segment thoracic constructs in axial rotation (torsion) loading modes generated the most significant findings of this study. After instrumentation with thoracic pedicle screws, T4-T10 full ROM was significantly reduced from the intact condition (P < 0.05). On average, TPS alone resulted in a 65% decrease in ROM. However, the addition of a transverse connector at 1 of the 3 positions tested yielded another 20% improvement in axial segmental stability as represented by further ROM reduction. These differences were significant from the TPS only group (no TCs), regardless of the TC position (P < 0.05). Furthermore, 2 TCs placed at the proximal and distal ends of the construct provided the greatest biomechanical axial stability to the instrumented specimens (P < 0.05). This was highlighted by an average of 35% ROM reduction from the stability level achieved with the TPS only constructs (P < 0.05), or an additional 15% improvement in axial stability over a single TC. For long thoracic pedicle screw constructs, the addition of 1 or 2 TCs significantly decreases construct axial rotation, which is the primary plane of motion for the thoracic spinal region. A single TC contributed to a significant reduction of T4-T10 ROM (an additional 20%) relative to TPS fixation alone (P < 0.05), while the location of the TC within the construct was irrelevant. A second TC had an additive effect (an additional 15% reduction) on axial stability. (P < 0.05) Flexion-extension and lateral bending are not affected. Single TC significantly improves axial rotation stability in long thoracic pedicle screw constructs. Two crosslinks, however, are better than one.

Intraspinal metalloma resulting in late paraparesis

The metal-related complications caused by orthopedic implants have long been a concern, but these problems have been considered mostly in the field of arthroplasty or internal fixation of fractures. The recent prevalence of spinal instrumentation has evoked a similar concern among spine surgeons. Here, we present a case of intraspinal metallosis adjacent to the pedicular hook occurring after treatment of vertebral fracture by posterior spinal instrumentation and fusion, and causing paraparesis at the 3rd postoperative year. Metallic granulomas can appear around the pedicular hooks as in the reported case. Crevice and fretting corrosion are results at the junctions of rod-screw, rod-hook, transverse connector rod and other connector rods in modular spinal implants. Adequate usage of transpedicular screws may inhibit the occurrence of such a complication. For this reason, further studies are necessary to increase metallic corrosive resistance to inhibit crevice and fretting corrosion.