Establishing finite element model credibility of a pedicle screw system under compression-bending: An end-to-end example of the ASME V&V 40 standard.

Computational modeling and simulation (CM&S) is a key tool in medical device design, development, and regulatory approval. For example, finite element analysis (FEA) is widely used to understand the mechanical integrity and durability of orthopaedic implants. The ASME V&V 40 standard and supporting FDA guidance provide a framework for establishing model credibility, enabling deeper reliance on CM&S throughout the total product lifecycle. Examples of how to apply the principles outlined in the ASME V&V 40 standard are important to facilitating greater adoption by the medical device community, but few published examples are available that demonstrate best practices. Therefore, this paper outlines an end-to-end (E2E) example of the ASME V&V 40 standard applied to an orthopaedic implant. The objective of this study was to illustrate how to establish the credibility of a computational model intended for use as part of regulatory evaluation. In particular, this study focused on whether a design change to a spinal pedicle screw construct (specifically, the addition of a cannulation to an existing non-cannulated pedicle screw) would compromise the rod-screw construct mechanical performance. This question of interest (?OI) was addressed by establishing model credibility requirements according to the ASME V&V 40 standard. Experimental testing to support model validation was performed using spinal rods and non-cannulated pedicle screw constructs made with medical grade titanium (Ti-6Al-4V ELI). FEA replicating the experimental tests was performed by three independent modelers and validated through comparisons of common mechanical properties such as stiffness and yield force. The validated model was then used to simulate F1717 compression-bending testing on the new cannulated pedicle screw design to answer the ?OI, without performing any additional experimental testing. This E2E example provides a realistic scenario for the application of the ASME V&V 40 standard to orthopedic medical device applications.

Determination of Availability of Safety Margin for Placement of C3-C6 Pedicle Screw on CT Angiography.

BACKGROUND: Cervical pedicle screws (CPS) in the subaxial cervical spine (C3-C6) are faced with high incidence of perforating the lateral pedicular cortex endangering the vertebral artery (VA). The present study analyzes the pedicle width (PW) from C3 to C6 and defines the relation of VA with regard to pedicle and transverse foramen (TF) to determine the safety margin in cases of lateral pedicular breach. METHODS: Computed tomography angiograms of 500 patients were retrospectively studied to identify the pedicle width (PW), VA area, TF area, and the lateral pedicle to vertebral artery distance (LPVA). Occupancy ratio (OR; the percentage area of transverse foramen occupied by VA) and safety margin (SM; permissible displacement of VA in TF), along with LPVA were considered to be protective parameters against VA injury if lateral pedicle breach happens. RESULTS: PW was 4.7 mm at C3, 4.83 mm at C4, 5.26 mm at C5 and 5.41 mm at C6. Mean LPVA at different levels was between 0.97 mm and 1.15 mm, OR was around 20% at all levels, and mean SM was between 2.34 mm and 2.92 at various levels. Sex differences were statistically significant for PW but not for LPVA, SM, or OR. CONCLUSIONS: This study gives us an idea about the various parameters in placement of cervical pedicle screw in subaxial cervical spine and the probable reasons there are few vertebral artery injuries despite high incidence of cervical pedicle breach. LPVA, safety margin, and OR may explain why even very significant CPS misplacement does not lead to vascular injury or neurologic deficit.

The Influence of Different Injection Hole Designs of Augmented Pedicle Screws on Bone Cement Leakage and Distribution Patterns in Osteoporotic Patients.

OBJECTIVE: To compare cement distribution and leakage for 2 bone cement-augmented screws with different designs of injection holes in patients and the impact of screw locations and bone mineral density (BMD) on the results. METHODS: This study recruited 40 patients who underwent instrumentation with cement-augmented screws. Screw holes of group A were 4 holes located in the distal one third of screws, while screw holes of group B were 6 holes located in distal, middle, and proximal sites. Postoperative computed tomography images were obtained to evaluate the rate and type of cement leakage and the distribution pattern of cement. The lateral or center position of screw tip, BMD, and T-score were also analyzed for their influence on the results. RESULTS: Of 192 screws, 80 (41.7%) exhibited cement leakage on postoperative computed tomography. The incidence of cement distribution in the posterior half and type B leakage in group B was significantly higher compared with group A. In group A, the probability of cement distribution in the posterior half was significantly increased when the screw was laterally inserted. For both groups, the higher incidence of cement distribution in the posterior half was correlated with lower BMD and T-score. CONCLUSIONS: Our results showed that screws with injection holes closer to the screw tip had higher incidences of distribution in the anterior half of the body and lower incidences of type B leakage. Patients with lower BMD and T-scores should be closely monitored, and a more centered position is recommended for screw insertion.

Comparison of Morphometric Measurements of Traditional Posterior Cervical Screw and Paravertebral Foramen Screw in Chinese Population.

STUDY DESIGN: A morphometric measurement study. OBJECTIVE: To measure the length and angle parameters of the screw paths of pedicle screws (PS), lateral mass screws (LMS), and paravertebral foramen screws (PVFS) of subaxial cervical spine in Chinese population. SUMMARY OF BACKGROUND DATA: Aramomi proposed a novel internal fixation technology, named PVFS, as an alternative to LMS and PS for subaxial cervical vertebrae (C3-C7). METHODS: This study measured the length and medial angles of screw paths on the three-dimensional reconstruction model of cervical computerized tomography data of 50 patients (25 men and 25 women) in our hospital from January 2018 to June 2018. RESULTS: In general, the optimum length and medial angle of the PVFS in Chinese population were 10.65 mm and 21.12° at C3; 10.12 mm, 22.62° at C4; 9.82 mm, 23.66° at C5; 9.19 mm, 24.13° at C6; and 9.10 mm, 27.54° at C7. The optimum axial length and medial angle of PS in Chinese population were 30.94 mm, 33.92° at C3; 30.50 mm, 34.95° at C4; 31.92 mm, 33.42° at C5; 30.50 mm, 31.94° at C6; and 29.87 mm, 31.01° at C7. The optimum lengths of LMS paths in Chinese population were C3, 14.84 mm; C4, 15.33 mm; C5, 15.44 mm; C6, 14.74 mm; and C7, 14.06 mm. CONCLUSION: Although the length of PVFS is limited, it still can be used as an effective substitute for LMS and PS. The PVFS does not have the risk of directly injuring the vertebral artery, its safety angle of insertion is larger than that in PS, and it has higher surgical safety.Level of Evidence: 3.

Biomechanical Evaluation of a Dynamic Stabilization System for the Prevention of Proximal Junctional Failure in Adult Deformity Surgery.

STUDY DESIGN: Biomechanical spine model. Comparison of stress in the implant and the adjacent cranial segment was done with conventional rigid versus dynamic stabilization system (DS) fixation. OBJECTIVE: The aim of this study was to study stress at the proximal end of spinal fixation with a novel DS. SUMMARY OF BACKGROUND DATA: High stress at the implant bone junction may cause proximal junctional failure (PJF) in adult deformity surgery. METHODS: Five life-size spine models were instrumented with pedicle screws and a 5.5-mm Titanium rod from T8-S1. The same models were subsequently instrumented with a similar rod and DS between T8-9 pedicle screws. The spine model was loaded with 25 Nm static load cranial to the proximal fixation in six directions. Strains were measured from the proximal screws. Disc pressure was measured from the proximal instrumented segment (T8-9) and cranial adjacent segment (T7-8). RESULTS: Rigid fixation produced highest strain at T8, followed by T10 then T9. In contrast, DS fixation produced highest strain at T10, followed by T9 then T8. Strain at T8 was significantly less with DS fixation than rigid fixation (P = 0.019). The T10 screw strain was not significantly higher with DS stabilization compared to rigid fixation (P = 0.091). Rigid fixation allowed no load-sharing or pressure rise at T8-9 but an abrupt rise at T7-8. DS system permitted load-sharing and pressure rise in T8-9; the difference compared to rigid fixation was significant in flexion loading (P = 0.04) and similar trend but not significant in extension (P = 0.09). DS system produced a rise in the adjacent segment disc pressure (T7-8), which was smaller than rigid fixation but not significant. CONCLUSION: Long spinal fixation using rigid rods produces maximum stress at the proximal end screw and increases adjacent disc pressure, possibly leading to PJF. Dynamic stabilization at the cranial end segment may prevent PJF by reducing these factors.Level of Evidence: N/A.

Comparison of Cranial Facet Joint Violation Rate and Four Other Clinical Indexes Between Robot-assisted and Freehand Pedicle Screw Placement in Spine Surgery: A Meta-analysis.

STUDY DESIGN: A meta-analysis. OBJECTIVE: Through meta-analysis, whether RA techniques are superior to conventional freehand (FH) techniques was determined in terms of cranial facet joint protection and four other clinical indexes, namely, the accuracy of pedicle screw placement, the number of surgical revision due to malposition, intraoperative radiation dose, and operative time. SUMMARY OF BACKGROUND DATA: Cranial facet joint violation (FJV) is an important risk factor for adjacent segment degeneration. Some studies recommended the use of robot-assisted (RA) pedicle screw placement in reducing the rate of cranial FJV instead of conventional FH pedicle screw placement. However, the superiority of RA techniques to FH techniques remains controversial. METHODS: A comprehensive search on PubMed, EMBASE, Cochrane, Web of Science, CNKI, and WanFang was conducted for the selection of potential eligible literature. The outcomes were evaluated in terms of odds ratio (OR) or standardized mean difference and corresponding 95% confidence interval (CI). The meta-analysis was conducted using RevMan 5.3. The subgroup analyses of the violation of the cranial facet joint and the accuracy of pedicle screw placement were performed on the basis of robot type. RESULT: Three randomized controlled trials, two prospective cohort study, and one retrospective cohort study consisting of 783 patients and 2694 cranial pedicle screws were included in the meta-analysis. RA pedicle screw placement was associated with significantly fewer cranial FJVs than FH screw placement. Subgroup analyses showed that the Renaissance (OR = 0.19, 95% CI = 0.07-0.56) and TINAVI (OR = 0.19, 95% CI = 0.09-0.38) robots under RA techniques were associated with significantly fewer cranial FJVs than FH techniques. Furthermore, the RA techniques showed more accurate pedicle screw placement and lower intraoperative radiation dose, equivalent number of surgical revision due to malposition, but longer operative time than the FH techniques. CONCLUSION: The RA (Renaissance and TINAVI) techniques are superior to conventional FH techniques in terms of protecting the cranial facet joint. RA techniques are accurate and safe in clinical application. LEVEL OF EVIDENCE: 2.

Robot-Assisted Percutaneous Pedicle Screw Placement: Evaluation of Accuracy of the First 100 Screws and Comparison with Cohort of Fluoroscopy-guided Screws.

OBJECTIVE: Percutaneous pedicle screws (PPS) are used to stabilize the spine after interbody fusion in minimally invasive approaches. Recently, robotic assistance has been developed to improve the accuracy of PPS. We report our initial experience with ExcelsiusGPS and compare its accuracy with our historical cohort of fluoroscopy-guided PPS. METHODS: We reviewed prospectively collected data from our first 100 robot-assisted PPS. We graded accuracy of screws on computed tomography imaging and compared it with a previous cohort of 90 PPS placed using fluoroscopy. We also analyzed the effect of various demographic and perioperative metrics on accuracy. RESULTS: We placed 103 PPS in the first 20 consecutive patients with postoperative computed tomography imaging using ExcelsiusGPS. All screws were placed at L2 to S1. Our robot-assisted cohort had 6 breaches, with only 2 breaches >2 mm, yielding an overall breach rate of 5.8% and a significant breach rate of 1.9%. In comparison, our fluoroscopy-guided cohort had a breach rate of 3.3% and a significant breach rate of 1.1%, which was not significantly different. More breaches occurred in the first half of cases, suggesting a learning curve with robotic assistance. No demographic or perioperative metrics had a significant effect on accuracy. CONCLUSIONS: Our breach rates with ExcelsiusGPS were low and consistent with others reported in the literature, as well as with other robotic systems. Our series shows equivalent accuracy of placement of PPS with this robotic platform compared with fluoroscopic guidance and suggests a relatively short learning curve.

The implant density does not change the correction rate of the main and the accompanying curves: A comparison between consecutive and intermittent pedicle screw constructs.

OBJECTIVE: The aim of this study was to evaluate the clinical outcomes and the coronal correction rate of the main and accompanying curves of adolescent idiopathic scoliosis (AIS) corrected with pedicle screws inserted consecutively or intermittently. METHODS: The prospectively collected data of 60 patients (8 men and 52 women; mean age: 14.6±2.5 years) who underwent corrective surgery for AIS between January 2010 and December 2015 were reviewed retrospectively. Two groups were constituted according to the pedicle screw construct type: consecutive pedicle screw construct (CPSC) and intermittent pedicle screw construct (IPSC) groups. The preoperative, early postoperative, and 24-month follow-up radiographs and the Scoliosis Research Society-22 (SRS-22) scores were reevaluated. The Cobb angle of the main and accompanying curves, the correction rate, and the flexibility of the curves were calculated. RESULTS: The mean preoperative Cobb angles were 57.03° and 57.46°, the mean postoperative Cobb angles were 14.93° and 14.4°, and the mean correction rates were 76.22% and 75.31% in IPSC and CPSC groups, respectively (p>0.05). The preoperative and postoperative accompanying curve magnitudes and correction rates were similar (p>0.05). These radiographic outcomes were also consistent with the SRS-22 scores. CONCLUSION: Both the pedicle screw constructs had satisfactory outcomes following the surgery, which were confirmed by both the SRS-22 scores and radiographs taken perioperatively and at follow-ups. The IPSC and CPSC groups did not demonstrate a significant change in the correction rate of the main and minor or major accompanying structural and nonstructural curves, and also in the SRS-22 scores. LEVEL OF EVIDENCE: Level III, Retrospective comparative study.

Pedicle screw placement in spinal neurosurgery using a 3D-printed drill guide template: a systematic review and meta-analysis.

BACKGROUND: Many surgeons believe that the use of a 3D-printed drill guide template shortens operative time and reduces intraoperative blood loss compared with those of the free-hand technique. In this study, we investigated the effects of a drill guide template on the accuracy of pedicle screw placement (the screw placed completely in the pedicle), operative time, and intraoperative blood loss. MATERIALS/METHODS: We systematically searched the major databases, such as Medline via PubMed, EMBASE, Ovid, Cochrane Library, and Google Scholar, regarding the accuracy of pedicle screw placement, operative time, and intraoperative blood loss. The χ2 test and I2 statistic were used to examine heterogeneity. Odds ratios (ORs) with 95% confidence intervals (CIs) were used to calculate the accuracy rate of pedicle screw placement, and weighted mean differences (WMDs) with 95% CIs were utilized to express operative time and intraoperative blood loss. RESULTS: This meta-analysis included 13 studies (seven randomized controlled trials and six prospective cohort studies) involving 446 patients and 3375 screws. The risk of research bias was considered moderate. Operative time (WMD = - 20.75, 95% CI - 33.20 ~ - 8.29, P = 0.001) and intraoperative blood loss (WMD = - 106.16, 95% CI - 185.35 ~ - 26.97, P = 0.009) in the thoracolumbar vertebrae, evaluated by a subgroup analysis, were significantly different between groups. The 3D-printed drill guide template has advantages over the free-hand technique and improves the accuracy of pedicle screw placement (OR = 2.88; 95% CI, 2.39~3.47; P = 0.000). CONCLUSION: The 3D-printed drill guide template can improve the accuracy rate of pedicle screw placement, shorten operative time, and reduce intraoperative blood loss.

Computed Tomography-Based Morphometric Analysis of Thoracic Pedicles: An Analysis of 1512 Pedicles and Their Correlation with Sex, Age, Weight and Height.

AIM: To examine the morphological features of thoracic pedicles in a Turkish population. MATERIAL AND METHODS: This retrospective study was performed with the patients who were underwent thoracic CT for any reason such as trauma or pulmonary disorder. Patient's age, height, weight, and sex were recorded and pedicle length (PL), transverse pedicle diameter (TPD), sagittal pedicle diameter (SPD) and, transverse pedicle angle (TPA) were measured. The right and left pedicles were separately measured. The data obtained was analyzed and compared with other studies in the literature. RESULTS: The highest mean TPA value was 33° at T1, whereas the lowest mean TPA value was 3° at T12. The highest mean PL value was 39.6 mm at T11, whereas the lowest mean PL value was 33.7 mm at T1. The lowest mean SPD value was 7.2 mm, which was measured on T1, and the maximum mean SPD was 11.7 mm on T12. The minimum mean TPD value was 3.8 mm at T5 and the maximum value was 6.2 mm at T1. There was a statistically significant positive correlation between pedicle length and height in all vertebrae. Age had no effect on the morphological features of the thoracic pedicle. In males, PL, TPD, and SPD were higher than females. CONCLUSION: Compared with other populations, the Turkish population has a smaller pedicle width on sagittal and transverse planes, and their PL and medial angling is similar to those of other populations. Male patients who are taller and overweight have higher pedicle width and length.

Pullout strength of reinserted pedicle screws using the previous entry point and trajectory.

PURPOSE: This study compared the biomechanics of reinserted pedicle screws using the previous entry point and trajectory with those of correctly inserted pedicle screws. METHODS: The study used 18 lumbar vertebrae (L1-6) from three fresh calf spines to insert 6.5 × 40-mm pedicle screws. A control screw was inserted correctly along the axis of one pedicle, while an experimental screw was reinserted completely using the previous entry point and trajectory in the other pedicle. The experimental screw was removed after being completely inserted in group A and after 80% of the total trajectory inserted in group B. And the experimental screw was removed after 60% of the total trajectory was reached in group C. The biomechanical values of the pedicle screws were measured. RESULTS: There were no significant differences in pedicle screw axial pullout strength between reinserted screws and correct screws in the 3 groups (PA = 0.463, PB = 0.753, PC = 0.753). Stiffness measurement increased for the reinserted screw compared with that of the control screw. Fracturing was observed between the vertebral body and pedicle. CONCLUSION: Theoretically, a surgeon can remove the pedicle screw when necessary, inspect the trajectory, and reinsert the screw using the previous entry point and trajectory.

Augmented pedicle trajectory applied on the osteoporotic spine with lumbar degenerative disease: mid-term outcome.

PURPOSE: To compare the safety and efficiency of cement-augmented pedicle screw with traditional pedicle screw technique applied on the patients in the osteoporotic spine with lumbar degenerative diseases. METHODS: Fifty-six patients followed up at least 2 years were enrolled in our institute with retrospectively reviewed from January 2009 to June 2014, diagnosed as lumbar spondylolisthesis, or lumbar stenosis, with T score ≤- 2.5 SD of BMD, and received less than three-segment PLIF or TLIF. All patients were divided into 2 groups: 28 (2 males, 26 females) in polymethylmethacrylate-augmented pedicle screw group (PSA) group, the other 28 (3 males, 25 females) in traditional pedicle screw group (TPS). Surgical data including the operation time, intra-operative blood loss, hospitalization day and surgical complications were recorded, as well as the radiological parameters measured from the postoperative X-rays and CT scans containing the rates of fusion, screw loosening, and cage subsidence incidence. In addition, the visual analog scores (VAS) and Oswestry Disability Index (ODI) were evaluated preoperatively and postoperatively. RESULTS: The average follow-up period was 34.32 months (ranging from 24 months to 51 months). Compared with PSA group, operation time and average hospital stay in the TPS group decreased significantly (P < 0.05). While no statistical difference for blood loss between 2 groups (P > 0.05). At 2 years postoperation, from CT-scans, 2/172 screws loosening and 1/56 segment non-union occurred in PSA group, with significantly lower incidence than those in TPS group (8/152 screws loosening and 6/50 segments non-union occurred, P < 0.05). Regarding the cage subsidence, 24 segments found height loss (5.30 ± 1.92 mm) in PSA group without difference compared with that of 19 segments (4.78 ± 1.37 mm) in TPS group (P > 0.05). Besides, the number and the location of cages and the leakage of the cement were found out little related with the subsidence in the PSA group (P > 0.05). After surgeries, VAS and ODI at 1 month, 6 months, 12 months, and last follow-up improved significantly in two groups (P < 0.05). There were no significant differences in VAS and ODI preoperatively and postoperatively between 2 groups (P > 0.05). In addition, eight patients with asymptomatic trajectory PMMA leakages were detected. CONCLUSION: Cement-augmented pedicle screw technique is effective and safe in the osteoporotic spine with lumbar degenerative diseases, with better fusion rates and less screw loosening incidence. There is no difference in the fusion rate and loosening rate between the two groups in the single segment patients; however, there are better fusion rate and lower pedicle screw loosening rate of the PSA group in the double or multiple group patients.

Patient-specific drill template for C2 transoral pedicle insertion in complete reduction of atlantoaxial dislocation: cadaveric efficacy and accuracy assessments.

BACKGROUND: The transoral atlantoaxial reduction plate (TARP) is an effective advance in the treatment of atlantoaxial dislocation (AAD) and can enable the performance of anterior atlantoaxial release, reduction, decompression, and internal fixation in a one-stage operation. However, accurate transoral C2 pedicle insertion (C2TOPI) remains a challenge. The aim of this study is to develop a grouped patient-specific drill template (PDT) specifically for AAD with complete reduction and, furthermore, to compare its efficacy and accuracy in facilitating C2TOPI. METHODS: After CT scanning, ten cadaveric C2 specimens were randomly assigned to two groups (the PDT and freehand group). A grouped PDT specifically for AAD with complete reduction was designed and manufactured. C2TOPI was performed using the PDT or the fluoroscopy-guided freehand technique. Postoperative CT scans were subsequently performed to analyze the deviations at the centroid of the cross section at the midpoint of the pedicle. Screw position grades were also assessed in both groups. RESULTS: Compared to the freehand group, the PDT group had a significantly shorter surgery time (p < 0.001). Significant differences between the two groups were observed in the absolute value of the deviations at the centroid of the pedicle on either the axial or sagittal planes (p < 0.05). No significant difference was found in the screw positions between the two groups (p > 0.05); however, two unacceptable breaches (20%) occurred in the freehand group. CONCLUSION: A specifically designed PDT could provide an accurate and easy-to-apply method for C2TOPI in AAD with complete reduction.

Guideline for Thoracolumbar Pedicle Screw Placement Assisted by Orthopaedic Surgical Robot.

The pedicle screw placement procedure is the most commonly used technique for spinal fixation and can provide reliable three-column stabilization. Accurate screw placement is necessary in clinical practice. To avoid screw malposition, which may decrease the stiffness of the screw-rod construct or increase the likelihood of neural and vascular injuries, the surgeons must fully understand the regional anatomy. Deformities, such as scoliosis, kyphosis or congenital anomalies, may complicate the application of the pedicle screw placement technique and increase the chance of screw encroachments. Incidences of pedicle screw malposition vary in different districts and hospitals and with surgeons and techniques. Today, the minimally invasive spinal surgery is well developed. However, the narrow corridors and limited views for surgeons increase the difficulty of pedicle screw placement and the possibility of screw encroachment. Evidenced by previous studies, robotic surgery can provide accurate screw placement, especially in settings of spinal deformities, anatomical anomalies, and minimally invasive procedures. Based on the consensus of consultant specialists, the literature review and our local experiences, this guideline introduces the robotic system and describes the workflow of robot-assisted procedures and the precautions to take during procedures. This guideline aims to outline a standardized method for robotic surgery for thoracolumbar pedicle screw placement.

Comparison of Circular and Sagittal Reinforced Rod Options on Sagittal Balance Restoration in Adolescents Undergoing Pedicle Screw Instrumentation for Idiopathic Scoliosis.

OBJECTIVE: Pedicle screw instrumentation is widely used for spinal deformity correction and fusion in adolescents for idiopathic scoliosis. The goal is to achieve and sustain good alignment in all 3 planes. We compared 2 different cobalt-chromium (CoCr) rod designs with different stiffnesses with regard to the restoration of coronal and sagittal balance in adolescents operated on for idiopathic scoliosis. MATERIAL AND METHODS: A prospective comparative study was made of 90 consecutive adolescents, mean age (standard deviation) 15.6 years (2.1 years), with idiopathic scoliosis who underwent posterior spinal fusion by the use of bilateral segmental pedicle screw instrumentation (PSI) with 6.0 Co-Cr rods. Fifty-four adolescents (43 girls) were operated on by the use of circular rods and 36 (27 girls) by the use of sagittal reinforced rods, with a 2-year follow-up. RESULTS: Preoperative major coronal curves were similar and at 2 years: 11° (5.0) and 17° (7.2) with correction percentages of 78% (10) and 69% (12) in the circular and reinforced rod groups (P < 0.01). Thoracic kyphosis at 2 years measured 16° (7) and 21° (6) in the circular and reinforced rod groups (P < 0.01). The number of patients with hypokyphosis was lower in the reinforced rod group at 2 years (P = 0.02). In the reinforced rod group, there was a negative correlation between coronal correction and thoracic kyphosis (r = -0.52, P < 0.01). CONCLUSIONS: Both circular and sagittal reinforced 6.0-mm CoCr rods provide adequate coronal correction for adolescents with idiopathic scoliosis. The use of sagittal reinforced rods provided better thoracic kyphosis restoration and a lower risk for postoperative hypokyphosis.

Pedicle screw loosening: the value of radiological imagings and the identification of risk factors assessed by extraction torque during screw removal surgery.

BACKGROUND CONTEXT: Pedicle screw loosening is a common complication after spine surgeries. Traditionally, it was assessed by radiological approaches, both X-ray and CT (computed tomography) scan, while reports using mechanical method to study screw loosening after spine surgery are rare. The primary objective was to study the prevalent of pedicle screw loosening according to extraction torque during screw removal surgery and access the sensitivity and specificity of both X-ray and CT scan for diagnosing screw loosening. The second objective was to identify the risk factors for low extraction torque of pedicle screw that might lead to loosening. METHODS: Thirty-three patients who underwent pedicle screw removal surgery after at least 2 years from primary surgery were evaluated preoperatively for fixation stability by X-ray and CT scan. In total, 236 screws were taken out, and the extraction torque data was recorded and analyzed to identify the sensitivity and specificity of both imaging studies for screw loosening. Furthermore, risk factors that might contribute to low extraction torque were also studied. RESULTS: The mean extraction torque of removed screws was 1.55 ± 1.00 Nm; a torque force of less than 1.02 Nm was used to define a screw as loosened. According to such criterion, the loosening rate was found to be 33%. X-ray had a sensitivity of 24% and a specificity of 98%, while CT scan had a sensitivity of 22% and a specificity of 96%. Extraction torque of pedicle screws inserted in fractured vertebrae was significantly lower than those in non-fractured vertebrae (p = 0.009); meanwhile, screws of non-fusion surgery had lower extraction torque when compared to those in fusion surgery (p = 0.001). BMD (bone mineral density) and age had low but significant linear relationship with screw extraction torque (p = 0.01, R2 = 0.304; p = 0.045, R2 = 0.123). CONCLUSIONS: Our findings showed that both X-ray and CT scan had high specificity for screw loosening detection, but their sensitivities were relatively low. Surgeons needed to be more cautious when assessing screw loosening merely according to radiological examination, and aware of that screws in fractured vertebrae or non-fusion surgery were vulnerable to loosening.

Decreasing Radiation Emission in Minimally Invasive Spine Surgery Using Ultra-Low-Radiation Imaging with Image Enhancement: A Prospective Cohort Study.

BACKGROUND: Visualization of the anatomy in minimally invasive surgery (MIS) of the spine is limited and dependent on radiographic imaging, leading to increased radiation exposure to patients and surgical staff. Ultra-low-radiation imaging (ULRI) with image enhancement is a novel technology that may reduce radiation in the operating room. The aim of this study was to compare radiation emission between standard-dose and ULRI fluoroscopy with image enhancement in patients undergoing MIS of the spine. METHODS: This study prospectively enrolled 60 consecutive patients who underwent lateral lumbar interbody fusion, lateral lumbar interbody fusion with percutaneous pedicle screws, or MIS transforaminal lumbar interbody fusion. Standard-dose fluoroscopy was used in 31 cases, and ULRI with image enhancement was used in 29 cases. All imaging emission and radiation doses were recorded. RESULTS: Radiation emission per level was significantly less with ULRI than with standard-dose fluoroscopy for lateral lumbar interbody fusion (36.4 mGy vs. 119.8 mGy, P < 0.001), per screw placed in lateral lumbar interbody fusion (15.4 mGy per screw vs. 47.1 mGy per screw, P < 0.001), and MIS transforaminal lumbar interbody fusion (24.4 mGy vs. 121.6 mGy, P = 0.003). These differences represented reductions in radiation emission of 69.6%, 67.3%, and 79.9%. Total radiation doses per case were also significantly decreased for the transpsoas approach by 68.8%, lateral lumbar interbody fusion with percutaneous pedicle screws by 65.8%, and MIS transforaminal lumbar interbody fusion by 81.0% (P ≤ 0.004). CONCLUSIONS: ULRI with image enhancement has the capacity to significantly decrease radiation emission in minimally invasive procedures without compromising visualization of anatomy or procedure safety.

Optimal satellite rod constructs to mitigate rod failure following pedicle subtraction osteotomy (PSO): a finite element study.

BACKGROUND CONTEXT: Pedicle subtraction osteotomy (PSO) is a challenging restoration technique for sagittal imbalance and is associated with significant complications. One of the major complications is rod fracture and there exists a need for a biomechanical assessment of this complication for various instrumentation configurations. PURPOSE: To evaluate and compare the global range of motion (ROM), rod stress distribution, and the forces on the pedicle subtraction site in various instrumentation configurations using finite element analysis. STUDY DESIGN/SETTING: A computational biomechanical analysis. METHODS: A previously validated osseoligamentous three-dimensional spinopelvic finite element model (T10-pelvis) was used to develop a 30° PSO at the L3 level. In addition to the standard bilateral cobalt chromium primary rod instrumentation of the PSO model, various multirod configurations including constructs with medially, laterally, and posteriorly affixed satellite rods and the short-rod technique were assessed in spinal physiological motions. T10-S1 global ROM, maximum von Mises stress on the rods and at the PSO level, factor of safety (yield stress of the rod material/maximum actual stress in the rod) and the load acting across the PSO site were compared between various instrumentation configurations. The higher the factor of safety the lesser the chances of rod failure. RESULTS: Among all multirod constructs, posteriorly affixed satellite rod construct showed the greatest motion reduction compared to the standard bilateral rod configuration followed by medially and laterally affixed satellite rod constructs. Compared to the standard bilateral rod configuration, recessed short-rod technique resulted in 4% to 49% reduction in T10-S1 ROM recorded in extension and lateral bending motions, respectively, while the axial rotation motion increased by approximately 31%. Considering the maximum stress values on the rods, the recessed short-rod technique showed the greatest factor of safety (FOS = 4.1) followed by posteriorly (FOS = 3.9), medially (FOS = 3), laterally affixed satellite rod constructs (FOS = 2.8), and finally the standard bilateral rod construct (FOS = 2.7). By adding satellite rods, the maximum von Mises stress at the PSO level of the rods also reduced significantly and at this level resulted in the greatest FOS in the posteriorly affixed satellite rod construct. Compared to the standard bilateral rod construct, the load magnitude acting on the osteotomy site decreased by 11%, 16%, and 37% in the laterally, medially, and posteriorly affixed satellite rod constructs, respectively, and did not change with the short-rod technique. CONCLUSIONS: Adding satellite rods increases the rigidity of the construct, which results in an increase in the stability and the reduction of the global ROM. Additionally, having satellite rods reduces the stress on the primary rods at the PSO level and shifts the stresses from this PSO region to areas adjacent to the side-by-side connectors. The data suggest a significant benefit in supplementing medial over lateral satellite rods at the PSO by reducing stress on the primary rods. Except the recessed short-rod technique, all other multirod constructs decrease the magnitude of the load acting across the osteotomy region, which could cause a delayed or non-union at the PSO site. CLINICAL SIGNIFICANCE: The study evaluates the mechanical performance of various satellite rod instrumentation configurations following PSO to predict the risk factors for rod fracture and thereby mitigate the rate of clinically relevant failures.

The Importance of the Pedicle Diameters at the Proximal Thoracic Vertebrae for the Correction of Proximal Thoracic Curve in Asian Patients With Idiopathic Scoliosis.

STUDY DESIGN: A retrospective comparative radiographic study. OBJECTIVE: The purpose of this study was to evaluate differences in the pedicle diameters of proximal thoracic vertebrae in relation to the severity of the proximal thoracic curve in Asian patients with idiopathic scoliosis. SUMMARY OF BACKGROUND DATA: A small pedicle diameter at the proximal thoracic vertebra has been reported in normal population, but the changes of pedicle diameter in patients with a proximal thoracic curve have not been properly evaluated. METHODS: One hundred eighty-two patients with adolescent idiopathic scoliosis involving a greater than 10-degree proximal thoracic curve were analyzed. Sixty-nine and 113 patients had a structural and nonstructural proximal thoracic curve, respectively. The pedicle width was evaluated from T1 to T4 using a reconstructed computed tomography (CT) scan. The pedicle widths were compared between the convex and concave side, and between the structural and nonstructural proximal thoracic curve groups. RESULTS: The pedicle widths at T3 (0.76 ±â€Š0.92 mm) and T4 (0.50 ±â€Š0.69 mm) on the concave side for the structural proximal thoracic curves were extremely narrow compared with those for the nonstructural proximal thoracic curves (T3,1.17 ±â€Š0.84 mm; T4,0.82 ±â€Š0.72 mm) (P = 0.002, 0.003, respectively). However, the T2 pedicle width was comparable on the concave side in both groups (2.44 ±â€Š0.94 mm for the nonstructural and 2.32 ±â€Š0.97 mm for the structural proximal thoracic curve, P = 0.430). CONCLUSION: A pedicle screw insertion at the T3 or T4 vertebra on the concave side is not always possible in cases of a structural proximal thoracic curve; however, the pedicle width of the T2 vertebra is very wide and safe for the standard pedicle screw insertion. These results should be considered when the surgeon decides the upper instrumented vertebra or the correction method for the structural proximal thoracic curve. LEVEL OF EVIDENCE: 3.

Is unilateral pedicle screw fixation superior than bilateral pedicle screw fixation for lumbar degenerative diseases: a meta-analysis.

BACKGROUND: To investigate whether unilateral pedicle screw fixation is superior than bilateral pedicle screw fixation for lumbar degenerative diseases. METHODS: Electronic databases including PubMed, Embase, and the Cochrane Library up to August 2018 were searched. All the high-quality randomized controlled trials (RCTs) and prospective clinical controlled studies comparing the unilateral pedicle screw fixation and bilateral pedicle screw fixation for lumbar degenerative diseases were enrolled in this study. Fusion rate was the main outcome. Stata 12.0 was used for the meta-analysis. RESULTS: Twelve RCTs including 808 patients (unilateral pedicle screw fixation = 393, bilateral pedicle screw fixation = 415) were included in our meta-analysis. There was a significant difference between unilateral pedicle screw fixation and bilateral pedicle screw fixation in terms of the fusion rate (risk ratio (RR) = 0.96, 95%CI [0.92, 1.00], P = 0.073), visual analog scale (VAS) at final follow-up, Oswestry Disability Index (ODI), Japanese Orthopedic Association scores (JOA), short-form health survey (SF-36), and length of hospital stay. Compared with bilateral pedicle screw fixation, unilateral pedicle screw fixation was associated with a reduction of the total blood loss and operation time (P < 0.05). Unilateral pedicle screw fixation was associated with an increase of the cage migration than bilateral pedicle screw fixation (17.1% vs 7.1%, RR = 2.40, 95% CI = 1.17 to 4.93; P = 0.017). CONCLUSIONS: Unilateral pedicle screw fixation and bilateral pedicle screw fixation has similar fusion rate when treating for lumbar degenerative diseases. Our meta-analysis suggested that compared with bilateral pedicle screw fixation, unilateral pedicle screw fixation significantly reduced total blood loss and operation time for lumbar degenerative diseases. The use of unilateral pedicle screw for lumbar degenerative diseases increases the cage migration.