Acute Hemoptysis Caused by Eroding Spinal Fusion Hardware Into the Left Lower Lobe of the Lung.

Hemoptysis can occur in rare cases as a late complication of anterior approach spinal rod surgery in the spine. Our patient presented with hemoptysis. At age 14, he underwent an anterior approach spine surgery for scoliosis. He underwent bronchoscopy, and a round serrated metal object was visible in the left lower lobe. Multiple attempts were unsuccessful in retrieving the metal object. A review of the imaging did not show obvious penetration of the spinal instrumentation into the lung; however, the metallic object was believed to be a round serrated metal object from the fusion spinal hardware. Due to low lung function and the risk of injuring the surrounding tissue, the patient was not deemed a candidate for lobectomy or removal of the hardware. Instead, the patient underwent a left bronchial arterial embolization (BAE) procedure, which successfully stopped the hemoptysis.

How do additional rods reduce loads on the primary rods in adult spinal instrumentation with pedicle subtraction osteotomy?

BACKGROUND: Additional auxiliary rods have been used in spinal instrumentation across pedicle subtraction osteotomy to reduce stresses in the primary rods. The auxiliary rods can be connected through dual-rod-screws, fixed-angle multi-rod connectors or variable-angle multi-rod connectors. The objective was to assess rod bending in conventional bilateral-rod construct vs. constructs with auxiliary rods. METHODS: Computer models of two adult patients were developed to evaluate bending loads across a pedicle subtraction site in a control construct with bilateral rods vs. constructs with auxiliary rods bilaterally or unilaterally connected to the primary rods through either dual-rod-screws, fixed-angle multi-rod connectors, or variable-angle multi-rod connectors. Postoperative rod bending loads were computed and compared. FINDINGS: Normalizing loads on the primary rods in the multi-rod constructs to the control construct, primary rod loads in multi-rod constructs were 17% to 48% lower than the control construct. Constructs with bilateral auxiliary rods through dual-rod-screws, fixed-angle multi-rod connectors, or variable-angle multi-rod connectors could result in similar primary rod bending loads. Bending loads on the auxiliary rods were higher or lower than those on the primary rods depending on how their curvatures matched the primary rods, and how they were locked onto the primary rods. INTERPRETATION: Auxiliary rods noticeably reduced the bending loads on the primary rods compared with a standard bilateral-rod construct. Loads in the auxiliary rods were higher or lower than those in the primary rods depending on how their curvatures matched the primary rods, and how they were locked onto the primary rods.

Impact of an intraoperative coronal spinal alignment measurement technique using a navigational tool for a 3D spinal rod bending system in adult spinal deformity cases.

OBJECTIVE: In corrective spinal surgery for adult spinal deformity (ASD), the focus has been on achieving optimal spinopelvic alignment. However, the correction of coronal spinal alignment is equally important. The conventional intraoperative measurement methods currently used for coronal alignment are not ideal. Here, the authors have developed a new intraoperative coronal alignment measurement technique using a navigational tool for a 3D spinal rod bending system (CAMNBS). The purpose of this study was to test the feasibility of using the CAMNBS for coronal spinal alignment and to evaluate its usefulness in corrective spinal surgery for ASD. METHODS: In this retrospective cohort study, patients with degenerative lumbar kyphoscoliosis, a Cobb angle ≥ 20°, and lumbar lordosis ≤ 20° who had undergone corrective surgery (n = 67) were included. The pelvic teardrops on both sides, the S1 spinous process, the central point of the apex, a point on the 30-mm cranial (or caudal) side of the apex, and the central point of the upper instrumented vertebra (UIV) and C7 vertebra were registered using the CAMNBS. The positional information of all registered points was displayed as 2D figures on a monitor. Deviation of the UIV plumb line from the central sacral vertical line (UIV-CSVL) and deviation of the C7 plumb line from the CSVL (C7-CSVL) were measured using the 2D figures. Nineteen patients evaluated using the CAMNBS (BS group) were compared with 48 patients evaluated using conventional intraoperative radiography (XR group). The UIV-CSVL measured intraoperatively using the CAMNBS was compared with that measured using postoperative radiography. The prevalence of postoperative coronal malalignment (CM) and the absolute value of postoperative C7-CSVL were compared between the groups on radiographs obtained in the standing position within 4 weeks after surgery. Postoperative CM was defined as the absolute value of C7-CSVL ≥ 30 mm. Further, the measurement time and amount of radiation exposure were measured. RESULTS: No significant differences in demographic, sagittal, and coronal parameters were observed between the two groups. UIV-CSVL was 2.3 ± 9.5 mm with the CAMNBS and 1.8 ± 16.6 mm with the radiographs, showing no significant difference between the two methods (p = 0.92). The prevalence of CM was 2/19 (10.5%) in the BS group and 18/48 (37.5%) in the XR group, and absolute values of C7-CSVL were 15.2 ± 13.1 mm in the BS group and 25.0 ± 18.0 mm in the XR group, showing statistically significant differences in both comparisons (p = 0.04 and 0.03, respectively). The CAMNBS method required 3.5 ± 0.9 minutes, while the conventional radiograph method required 13.3 ± 1.5 minutes; radiation exposure was 2.1 ± 1.1 mGy in the BS group and 2.9 ± 0.6 mGy in the XR group. Statistically significant differences were demonstrated in both comparisons (p = 0.0002 and 0.03, respectively). CONCLUSIONS: From this study, it was evident that the CAMNBS did not increase postoperative CM compared with that seen using the conventional radiographic method, and hence can be used in clinical practice.

Advances in Spinal Fusion Strategies in Adult Deformity Surgery.

BACKGROUND: As the frequency of adult deformity surgery (ADS) continues to increase, our understanding of techniques that enhance fusion must continue to evolve because pseudarthrosis can be a serious and costly event. PURPOSES/QUESTIONS: We sought to conduct a review of the literature investigating techniques that can enhance outcomes of ADS. METHODS: Two databases were searched for keywords such as "advances in spinal fusion," "new technology in adult spinal deformity," "interbody devices for adult spinal deformity," "adult spinal deformity rods," and "screw design in adult spinal deformity" to examine recent literature and trends in ADS. RESULTS: We identified 45 articles for our review. Topics studied include the use of multiple rods, interbody fusion, distal fixation techniques, and bone morphogenetic protein or iliac crest bone graft. CONCLUSIONS: Many recent innovations in treatments to enhance fusion in ADS have been studied, some more controversial than others. Further research into the efficacy of these techniques may increase fusion rates in ADS.

Are precontoured cobalt-chromium spinal rods mechanically superior to manually contoured rods?

STUDY DESIGN: Laboratory based study. OBJECTIVE: To compare reduction force and plastic deformation of cobalt-chromium (Co-Cr) spinal rods using a rigid, thoracolumbar spinal deformity model. Pre-contoured spinal rods are growing in their utilization for spinal deformity. Although there are theoretical advantages to pre-contouring rods, no previous studies have compared pre-contoured and manually contoured rods for their ability to maintain sagittal contour and resist mechanical load. METHODS: A spinal deformity model was utilized, simulating a rigid, thoracolumbar spinal deformity fixated with pedicle screws. Roll-formed pre-contoured and manually contoured 5.5 mm and 6.0 mm Co-Cr rods were reduced to the model with a load cell attached to the apical screw to measure corrective force. Rods remained reduced in the model for 20 min and change in contour was assessed to characterize plastic deformation. RESULTS: Twenty-four rods were tested with six rods per group (Table 1). The load to reduction was significantly lower in the 5.5 mm rods compared to the 6.0 mm rods (95% CI -254.0 to -61.42; p = 0.008). Although there was no difference in the corrective forces for manual and pre-contoured 5.5 mm rods (p = 0.722), the 6.0 mm rod produced significantly less corrective force compared to the manually contoured 6.0 mm rods (95% CI -134.42 to -5.317; p = 0.039). Additionally, rod contour for the manual group showed significantly less plastic deformation than the pre-contoured group in both 5.5 mm and 6.0 mm rods (5.5 mm: 57.1% vs. 61.6%, p = 0.006; 6.0 mm: 54.3% vs. 62.28%, p = 0.003). CONCLUSIONS: Roll formed, pre-contoured Co-Cr rods demonstrated significantly greater plastic deformation when compared with manually contoured rods of the same diameter. Furthermore, 6.0 mm pre-contoured rods required significantly lower load for rod reduction, the equivalent of 15 lb-force. Post-manufacturing, roll-formed pre-contouring of larger diameter Co-Cr may impair the rods mechanical properties.

A novel scoliosis instrumentation using special superelastic nickel-titanium shape memory rods: a biomechanical analysis using a calibrated computer model and data from a clinical trial.

STUDY DESIGN: Biomechanical analysis of scoliosis instrumentation using superelastic Nickel-titanium shape memory (SNT) rods. OBJECTIVE: To compare SNT with conventional Titanium (Ti) and Cobalt-chrome (Co-Cr) rods. A clinical trial has documented comparable efficacy between two adolescent idiopathic scoliosis (AIS) cohorts instrumented using SNT versus conventional Ti rods. The shape memory and superelasticity of the SNT rod are thought to allow easy rod insertion, progressive curve correction, and correction from spinal tissue relaxation, but study is yet to be done to assess the effects of the shape memory and superelasticity. METHODS: Instrumentations of AIS patients from the clinical trial were computationally simulated using SNT, Ti and Co-Cr rods (5.5 or 6 mm; 30°, 50° or 60° sagittal contouring angles; 0°, 25° or 50° coronal over-contouring angles). Curve correction, its improvement from stress relaxation in the spine, and loads in the instrumentation constructs were computed and compared. RESULTS: The simulated main thoracic Cobb angles (MT) and thoracic kyphosis with the SNT rods were 4°-7° higher and 1°-2° lower than the Ti and Co-Cr rods, respectively. Bone-implant forces with Ti and Co-Cr rods were higher than the SNT rods by 84% and 130% at 18 °C and 35% and 65% at 37 °C, respectively (p < 0.001). Further corrections of the MT from the simulated stress relaxation in the spine were 4°-8° with the SNT rods versus 2°-5° with the Ti and Co-Cr rods (p < 0.001). CONCLUSION: This study concurs with clinical observation that the SNT rods are easier to insert and can result in similar correction to the conventional rods. The SNT rods allow significantly lower bone-implant forces and have the ability to take advantage of post-instrumentation correction as the tissues relax.

Biomechanical analysis of spinal implants with different rod diameters under static and fatigue loads: an experimental study.

Spinal implants are commonly used in the treatment of spinal disorders or injuries. However, the biomechanical analyses of them are rarely investigated in terms of both biomechanical and clinical perspectives. Therefore, the main purpose of this study is to investigate the effects of rod diameter on the biomechanical behavior of spinal implants and to make a comparison among them. For this purpose, three spinal implants composed of pedicle screws, setscrews and rods, which were manufactured from Ti6Al4V, with diameters of 5.5 mm, 6 mm and 6.35 mm were used and a bilateral vertebrectomy model was applied to spinal systems. Then, the obtained spinal systems were tested under static tension-compression and fatigue (dynamic compression) conditions. Also, failure analyses were performed to investigate the fatigue behavior of spinal implants. After static tension-compression and fatigue tests, it was found that the yield loads, stiffness values, load carrying capacities and fatigue performances of spinal implants enhanced with increasing spinal rod diameter. In comparison to spinal implants with 5.5 mm rods, the fatigue limits of implants showed 13% and 33% improvements in spinal implants having 6 mm and 6.35 mm rods, respectively. The highest static and fatigue test results were obtained from spinal implants having 6.35 mm rods among the tested implants. Also, it was observed that the increasing yield load and stiffness values caused an increase in the fatigue limits of spinal implants.

Preventing Instrumentation Failure in Three-Column Spinal Osteotomy: Biomechanical Analysis of Rod Configuration.

STUDY DESIGN: Biomechanical analysis. OBJECTIVES: To show the role of additional rods and long-term fatigue strength to prevent the instrumentation failure on three-column osteotomies. SUMMARY OF BACKGROUND DATA: Three-column osteotomy such as pedicle subtraction osteotomy (PSO) and vertebral column resections are surgical correction options for fixed spinal deformity. Posterior fixation for the PSO involves pedicle screw-and rod-based instrumentation, with the rods being contoured to accommodate the accentuated lordosis. Pseudarthrosis and instrumentation failure are known complications of PSO. METHODS: Unilateral pedicle screw and rod constructs were mounted in ultra-high-molecular-weight polyethylene blocks using a vertebrectomy model with the rods contoured to simulate posterior fixation of a PSO. Each construct was cycled under a 200 N load at 5 Hz in simulated flexion and extension to rod failure. Three configurations (n = 5) of titanium alloy rods were tested: single rod (control), double rod, and bridging rod. Outcomes were total cycles to failure and location of rod failure. RESULTS: Double-rod and bridging-rod constructs had a significantly higher number of cycles to failure compared with the single-rod construct (p < .05). Single-rod constructs failed at or near the rod bend apex, whereas the majority of double-rod and bridging-rod constructs failed at the screw-rod or rod-connector junction. CONCLUSIONS: Double-rod and bridging-rod constructs are more resistant to fatigue failure compared with single-rod constructs in PSO instrumentation and could be considered to mitigate the risk of instrumentation failure.

Biomechanical assessment of the stabilization capacity of monolithic spinal rods with different flexural stiffness and anchoring arrangement.

BACKGROUND: Spinal disorders can be treated by several means including fusion surgery. Rigid posterior instrumentations are used to obtain the stability needed for fusion. However, the abrupt stiffness variation between the stabilized and intact segments leads to proximal junctional kyphosis. The concept of spinal rods with variable flexural stiffness is proposed to create a more gradual transition at the end of the instrumentation. METHOD: Biomechanical tests were conducted on porcine spine segments (L1-L6) to assess the stabilization capacity of spinal rods with different flexural stiffness. Dual-rod fusion constructs containing three kinds of rods (Ti, Ti-Ni superelastic, and Ti-Ni half stiff-half superelastic) were implanted using two anchor arrangements: pedicle screws at all levels or pedicle screws at all levels except for upper instrumented vertebra in which case pedicle screws were replaced with transverse process hooks. Specimens were loaded in forward flexion, extension, and lateral bending before and after implantation of the fusion constructs. The effects of different rods on specimen stiffness, vertebra mobility, intradiscal pressures, and anchor forces were evaluated. FINDING: The differences in rod properties had a moderate impact on the biomechanics of the instrumented spine when only pedicle screws were used. However, this effect was amplified when transverse process hooks were used as proximal anchors. INTERPRETATION: Combining transverse hooks and softer (Ti-Ni superelastic and Ti-Ni half stiff-half superelastic) rods provided more motion at the upper instrumented level and applied less force on the anchors, potentially improving the load sharing capacity of the instrumentation.

The Effect of Contouring on Fatigue Strength of Spinal Rods: Is it Okay to Re-bend and Which Materials Are Best?

STUDY DESIGN: Small-diameter spinal rods were tested in fatigue loading before and after contouring in pedicle screw constructs using dynamic testing machines. OBJECTIVE: To characterize the change in fatigue performance of spinal rods resulting from contouring. BACKGROUND SUMMARY: Spine surgeons have a variety of rod materials to choose from, and selecting the best rod depends on patient characteristics and rod material properties, including fatigue performance. METHODS: Four rod materials were tested, all 4.5 mm in diameter: titanium alloy (Ti), cobalt-chromium alloy (CoCr), and 2 different grades of stainless steel (SS and ultra SS). Three conditions were tested: straight (virgin rods), bent (rods bent to a radius of curvature of 100 mm), and re-bent (rods over-bent to a radius of 50 mm, then partially straightened to a 100-mm radius). Fatigue testing was conducted on unilateral vertebrectomy constructs with polyaxial screws. RESULTS: In all conditions, the endurance limit of the CoCr rods was at least 25% higher than the other materials but could not be determined because screw failure precluded rod failure. In the bent condition, the endurance limits of Ti, standard SS and ultra SS were reduced between 20% and 40%. In the re-bent condition, the endurance limit of Ti, standard SS, and ultra SS increased compared with the bent condition. Changes in fatigue performance are best explained by residual rod stresses induced during contouring. CONCLUSIONS: It appears safe to over-bend and then re-bend, for 1 cycle, small-diameter spinal rods made of the materials tested in this study using tube benders, and CoCr rods were clearly superior for all conditions. However, larger rods, multiple cycles of bending and re-bending, and rods bent using other instruments such as French benders were not studied and may result in different performance under the same conditions.