S2 Alar Iliac Research Articles

Life-threatening postoperative hemorrhage caused by lumbar artery injury in asymmetrical pedicle subtraction osteotomy for severe spinal deformity: two case reports.

To present two cases of life-threatening hemorrhage related to lumbar artery injury in adult spinal deformity (ASD) patients following S2‑alar‑iliac (S2AI) fixation and asymmetrical pedicle subtraction osteotomy (PSO), and discuss the possible reasons for postoperative hemorrhage in these patients. Patient A was a 52-year-old female with degenerative lumbar scoliosis who underwent posterior spinal fusion from T8-S2 and one-level PSO at L2. Patient B was a 24-year-old male with severe kyphoscoliosis due to non-ambulatory cerebral palsy, who underwent posterior spinal fusion from T3-S2 and one-level PSO at L1. Both patients underwent asymmetric PSO, where a larger wedge was resected from the convex side of the vertebral body rather than the concave side. Both patients occurred a sudden increase in drainage within 3h postoperatively, who were under anesthesia in AICU. Digital subtraction angiography (DSA) was emergently performed and revealed that the bleeding sites were from the lumbar artery, which was adherent to the convex side of the osteotomized vertebra in both cases. Then successful bleeding control was achieved through vascular embolization. Postoperative CT revealed spike formation at the anterior edges of the open wedge at the PSO level due to sagittal translation (ST), with noticeable derotation of the osteotomized vertebra. For patients with severe kyphoscoliosis, asymmetrical PSO increases the risk of lumbar artery injury on the convex side, and postoperative ST may further contribute to this risk. In cases where a sudden increase in drainage is observed postoperatively, it is crucial to consider the possibility of lumbar artery injury, particularly on the convex side of the osteotomized vertebra.

Augmented Reality Versus Freehand Spinopelvic Fixation in Spinal Deformity: A Case-Control Study.

This study sought to compare screw placement accuracy and outcomes between freehand (FH) and AR-guided pelvic fixation. While pelvic fixation is a critical technique in spinal deformity surgery, S2-alar iliac (S2AI) screw placement poses challenges. We conducted a case-control study of 50 consecutive patients who underwent spinopelvic fixation at a single institution. AR guidance was performed using a head-mounted display (Xvision, Augmedics). Patient demographics, surgical characteristics, spinopelvic parameters, and screw breach grade were compared using univariate and multivariate statistics. Pelvic fixation was performed FH in 21 patients (median age, 64; female, 38.1%; median BMI 32.3kg/m2) and AR-guided in 29 patients (median age, 66; female, 51.7%; median BMI 28.4kg/m2). Mean follow-up was longer in the FH group (28 mos vs 11 mos, P < 0.001). Pelvic fixation in the FH group was performed using either S2AI (90.5%) or dual S2AI (9.5%) screws. There were no significant differences in length of surgery (FH, 439 minutes; AR, 490 minutes; P = 0.1) or estimated blood loss (FH, 2.1L; AR, 1.9L; P = 0.7). Accuracy of FH pelvic fixation was 95.6% (43/45 screws) and accuracy of AR pelvic fixation was 96.5% (55/57 screws). Multivariable logistic regression for screw breach revealed no significant association with AR guidance when controlling for age, BMI, osteoporosis, and smoking. We present the first case-control study of AR-guided spinopelvic fixation, with findings suggesting parity between FH and AR-guidance, serving as foundation for prospective controlled studies with longitudinal follow-up to interrogate the benefits of AR-guidance in spinal deformity surgery.

Analysis of the accuracy between orthopedic robot-assisted and traditional manual pedicle screw placement techniques in adult degenerative scoliosis posterior surgery

Objective: To comparing the accuracy of pedicle screw placement in posterior surgery for adult degenerative scoliosis (ADS) between robotic-assisted and traditional freehand techniques. Methods: This retrospective study included 92 patients with ADS who underwent posterior spinal surgery at the First Affiliated Hospital of Nanjing Medical University (Jiangsu Province Hospital) between March 2019 and December 2023. There were 19 males and 73 females with a mean age of (63.6±9.8) years. The patients were divided into two groups based on the technique used for pedicle screw placement: robot-assisted group (34 cases) and manual group (58 cases). Operative duration, intraoperative blood loss, facet joint violation, postoperative complications, magnitude of curve correction, visual analogue scale (VAS) and Oswestry Disability Index (ODI) scores preoperatively, 1 week postoperatively, and 1 month postoperatively were compared and analyzed between the two groups. The Gertzbein-Robbins classification criteria was used to assess the accuracy of screw placement. Results: Differences in baseline data, operative duration, intraoperative blood loss, magnitude of curve correction, and VAS and ODI scores preoperatively, 1 week postoperatively, and 1 month postoperatively between the two groups exhibited no statistically significant differences (all P>0.05). The accuracy of pedicle screw placement in the robot-assisted group was significantly higher than that in the manual group [90.9% (416/458) vs 80.1% (697/870), P<0.001]. In terms of surgical segments, in T1-T12 and L1-S1 segments, the accuracy of pedicle screw placement in the robot group were both significantly higher than those in the control group [91.5% (130/142) vs 77.8% (186/239), P=0.001; 90.3% (271/300) vs 80.8% (502/621), P<0.001]. However, no significant differences was observed in the accuracy of S2-alar-iliac (S2AI) screw placement between the two groups [90.0%(9/10) vs 93.8%(15/16), P=0.727]. Moreover, no significant differences was found in the deviation direction of the cortical screw penetration between both groups (P=0.133). Significant differences were observed in the accuracy of screw placement between the Nash Moe 2 and 3 vertebral bodies in the robot group compared with those in the control group [88.9% (88/99) vs 71.0% (115/162), P=0.001; 89.2% (83/93) vs 60.2% (68/113), P<0.001]. Additionally, the incidence and grade of facet joint violation in the manual group were both significantly higher than those in the robot-assisted group (both P<0.001). No statistically significant differences was identified in postoperative complications between the two groups (P=0.841). Conclusion: It suggests that robot-assisted pedicle screw placement in posterior surgery for patients with ADS can significantly improve the accuracy of screw placement and reduce the incidence of facet joint violation.

"Ultralow-dose" CT Without Sedation in Pediatric Patients With Neuromuscular Scoliosis.

Children with neuromuscular scoliosis undergoing scoliosis surgery face substantial rates of complications. To mitigate surgical risks such as blood loss in pediatric patients with neuromuscular scoliosis, this study focuses on enabling instrumentation planning for their abnormal vertebral and pelvic anatomy and osteopenia. This study assessed the feasibility of an "ultralow-dose" CT (ULD CT) protocol without sedation in pediatric patients with neuromuscular scoliosis who often have comorbid movement disorders. Our prospective quality improvement study aims: (1) to determine if ULD CT without sedation is feasible in this patient group; (2) to quantify the radiation dose from ULD CT and compare it with preoperative spine radiographs (XR); and (3) to assess if ULD CT allows accurate anatomical assessment and intraoperative navigation given the prevalence of movement disorders. Children with neuromuscular scoliosis underwent spine XR and ULD CT scans. Chart reviews assessed disease etiology and comorbidities. Radiation dose was quantified through Monte-Carlo simulations giving dose indices and effective dose, with statistical analysis done using a paired student's t-test (α=0.05). CT image quality was assessed for its use in preoperative planning and intraoperative navigation. Fourteen patients (5 males, 9 females, average age 14±3y) participated. One patient needed sedation due to autism spectrum disorder and global developmental delay. The radiation dose for spine XR was 0.5±0.2mSv, and ULD CT was 0.6±0.1mSv. There was no statistically significant difference in radiation doses between methods. All ULD CT scans had adequate quality for preoperative assessment of pedicle diameter and orientation, obstacles impeding pedicle entry, S2 Alar-Iliac screw orientation, and intraoperative navigation. ULD CT without sedation is feasible for children with neuromuscular scoliosis. Radiation doses were comparable to standard radiographs. ULD CT provided accurate anatomical assessments and supported intraoperative navigation, proving beneficial despite movement disorders in these patients. Level 2-Development of diagnostic criteria on basis of consecutive patients (with universally applied reference widely accepted standard).

3D CT modeling demonstrates the anatomic feasibility of S1AI screw trajectory for spinopelvic fixation in neuromuscular scoliosis.

In patients with neuromuscular scoliosis undergoing posterior spinal fusion, the S2 alar iliac (S2AI) screw trajectory is a safe and effective method of lumbopelvic fixation but can lead to implant prominence. Here we use 3D CT modeling to demonstrate the anatomic feasibility of the S1 alar iliac screw (S1AI) compared to the S2AI trajectory in patients with neuromuscular scoliosis. This retrospective study used CT scans of 14 patients withspinal deformity to create 3D spinal reconstructions and model the insertional anatomy, max length, screw diameter, and potential for implant prominence between 28 S2AI and 28 S1AI screw trajectories. Patients had a mean age of 14.42 (range 8-21), coronal cobb angle of 85° (range 54-141), and pelvic obliquity of 28° (range 4-51). The maximum length and diameter of both screw trajectories were similar. S1AI screws were, on average, 6.3 ± 5mm less prominent than S2AI screws relative to the iliac crests. S2AI screws were feasible in all patients, while in two patients, posterior elements of the lumbar spine would interfere with S1AI screw insertion. In this cohort of patients with neuromuscular scoliosis, we demonstrate that the S1AI trajectory offers comparable screw length and diameter to an S2AI screw with less implant prominence. An S1AI screw, however, may not be feasible in some patients due to interference from the posterior elements of the lumbar spine.

The Influence of Radiographic Parameter on the S2 Alar-Iliac Screw Virtual Trajectory in Degenerative Lumbar Scoliosis Patients: A Computed Tomography Study.

S2 alar-iliac (S2AI) screw had been widely used in the pelvic fusion for degenerative lumbar scoliosis (DLS) patients. However, whether S2AI screw trajectory was influenced by sagittal profile in DLS patients had not been comprehensively investigated. The objective of this study was to evaluate the associations between the optimal S2 alar-iliac (S2AI) screw trajectory and sagittal spinopelvic parameters in DLS patients. Computed tomography (CT) scans of pelvis were performed in 47 DLS patients for three-dimensional reconstruction of S2AI screw trajectory from September 2019 to November 2021. Five S2AI screw trajectory parameters were measured in CT reconstruction images, including: 1) angle in the transverse plane (Tsv angle); 2) angle in the sagittal plane (Sag angle); 3) maximal screw length; 4) screw width; and 5) skin distance. The lumbar Cobb angle, lumbar apical vertebral translation (AVT); global kyphosis (GK); thoracic kyphosis (TK); lumbar lordosis (LL); sagittal vertical axis (SVA); sacral slope (SS); pelvic tilt (PT); and pelvic incidence (PI) were measured in standing X-ray films of the whole spine and pelvis. Both Tsv angle and Sag angle had significant positive associations with SS (p < 0.05) but negative associations with both PT (p < 0.05) and LL (p < 0.05) in all cases. Patients with SS less than 15° had both smaller Tsv angle and Sag angle than those with SS equal to or more than 15° (p < 0.05). The decreased LL would lead to the backward rotation of the pelvis, resulting in a more cephalic and less divergent trajectory of S2AI screw in DLS patients. For DLS patients with lumbar kyphosis, spine surgeons should avoid both excessive Tsv and Sag angles for S2AI screw insertion, especially when using free-hand technique.

Do Iliac Screws Placed Close to the Sciatic Notch Have Greater Pullout Strength?

Optimal iliac screw position in relation to the sciatic notch remains unknown. In 12 cadavers undergoing S2 alar-iliac (S2AI) screw placement, we tested the pullout strength of screws placed in proximity to the sciatic notch (≤5 mm) vs farther away from the sciatic notch (>5 mm). A biomechanical, cadaver-based study was performed on 12 cadavers undergoing bilateral S2AI screw insertion. The position of the S2AI screw regarding the sciatic notch was dichotomized as ≤5 mm from the sciatic notch on the right side and >5 mm on the left side, confirmed using c-arm fluoroscopy. The primary outcome was the pullout strength of the screw (N). Secondary outcomes were stiffness (N/mm), yield force (N), and work to failure (N mm). Ischial tuberosity was embedded into polymethyl methacrylate and secured to a custom 3-axis vise grip mounted to a 14.5-kN load cell. Pullout testing was performed at 5 mm/min. Force and displacement data were collected at 100 Hz and evaluated using MATLAB. The Mann-Whitney test was performed. Of 24 S2AI screws, 3 screws could not be tested because of cement-bone interface failure. A positive though nonsignificant trend of screw pullout strength was found for screws close to the notch compared with those farther from the notch (861.8 ± 340.7 vs 778.7 ± 350.8 N, P = .859). Similarly, screws close to the notch demonstrated a higher trend of stiffness (149.4 ± 145.4 vs 111.34 ± 128.2 N/mm, P = .320) and force to yield (806.9 ± 352.0 vs 618.6 ± 342.9 N, P = .455). Conversely, screws farther from the notch had a higher but similarly nonsignificant area under the force-displacement curve (10 867.0 ± 9565.0 vs 14 196.6 ± 9578.3 N mm, P = .455), which might be due to excess sheer/translation force that could not be reliably quantified. Although placing S2AI screws ≤5 mm of the sciatic notch provided stronger fixation in 3 of 4 biomechanical testing categories, these results were not statistically significant. Therefore, placing S2AI screws ≤5 mm of the sciatic notch did not provide stronger fixation.

Preoperative supine pelvic incidence predicts standing pelvic incidence following S2AI fixation in patients with adult spinal deformity: a prospective study.

A prospective study. The aim of this study was to investigate the PI change in different postures and before and after S2‑alar‑iliac (S2AI) screw fixation, and to investigate whether pre-op supine PI could predict post-op standing PI. Previous studies have reported PI may change with various positions. Some authors postulated that the unexpected PI change in ASD patients could be due to sacroiliac joint laxity, S2-alar-iliac (S2AI) screw placement, or aggressive sagittal cantilever technique. However, there was a lack of investigation on how to predict post-op standing PI when making surgical strategy. A prospective case series of ASD patients undergoing surgical correction with S2AI screw placement was conducted. Full-spine X-ray films were obtained at pre-op standing, pre-op supine, pre-op prone, as well as post-op standing postures. Pelvic parameters were measured. Spearman correlation analysis was used to determine relationships between each parameter. A total of 83 patients (22 males, 61females) with a mean age of 58.4 ± 9.5years were included in this study. Pre-op standing PI was significantly lower than post-op standing PI (p = 0.004). Pre-op prone PI was significantly lower than post-op standing PI (p = 0.001). By contrast, no significant difference was observed between pre-op supine and post-op standing PI (p = 0.359) with a mean absolute difference of 2.2° ± 1.9°. Correlation analysis showed supine PI was significantly correlated with post-op standing PI (r = 0.951, p < 0.001). This study revealed the PI changed after S2AI screw fixation. The pre-op supine PI can predict post-op standing PI precisely, which facilitates to provide correction surgery strategy with a good reference for ideal sagittal alignment postoperatively.

S2 alar-iliac screws are superior to traditional iliac screws for spinopelvic fixation in adult spinal deformity: a systematic review and meta-analysis.

Spinopelvic fixation (SPF) using traditional iliac screws has provided biomechanical advantages compared to previous constructs, but common complications include screw prominence and wound complications. The newer S2 alar-iliac (S2AI) screw may provide a lower profile option with lower rates of complications and revisions for adult spinal deformity (ASD). The purpose of this study was to compare rates of complications and revision following SPF between S2AI and traditional iliac screws in patients with ASD. A PRISMA-compliant systematic literature review was conducted using Cochrane, Embase, and PubMed. Included studies reported primary data on adult patients undergoing S2AI screw fixation or traditional IS fixation for ASD. Primary outcomes of interest were rates of revision and complications, which included screw failure (fracture and loosening), symptomatic screw prominence, wound complications (dehiscence and infection), and L5-S1 pseudarthrosis. Fifteen retrospective studies with a total of 1502 patients (iliac screws: 889 [59.2%]; S2AI screws: 613 [40.8%]) were included. Pooled analysis indicated that iliac screws had significantly higher odds of revision (17.1% vs 9.1%, OR = 2.45 [1.25-4.77]), symptomatic screw prominence (9.9% vs 2.2%, OR = 6.26 [2.75-14.27]), and wound complications (20.1% vs 4.4%, OR = 5.94 [1.55-22.79]). S2AI screws also led to a larger preoperative to postoperative decrease in pain (SMD = -0.26, 95% CI = -0.50, -0.011). The findings from this review demonstrate higher rates of revision, symptomatic screw prominence, and wound complications with traditional iliac screws. Current data supports the use of S2AI screws specifically for ASD. CRD42022336515. III.

Pedicle screw accuracy placed with assistance of machine vision technology in patients with neuromuscular scoliosis.

Pedicle screws are the primary method of vertebral fixation in scoliosis surgery, but there are lingering concerns over potential malposition. The rates of pedicle screw malposition in pediatric spine surgery vary from 10% to 21%. Malpositioned screws can lead to potentially catastrophic neurological, vascular, and visceral complications. Pedicle screw positioning in patients with neuromuscular scoliosis is challenging due to a combination of large curves, complex pelvic anatomy, and osteopenia. This study aimed to determine the rate of pedicle screw malposition, associated complications, and subsequent revision from screws placed with the assistance of machine vision navigation technology in patients with neuromuscular scoliosis undergoing posterior instrumentation and fusion. A retrospective analysis of the records of patients with neuromuscular scoliosis who underwent thoracolumbar pedicle screw insertion with the assistance of machine-vision image guidance navigation was performed. Screws were inserted by either a staff surgeon, orthopaedic fellow, or orthopaedic resident. Post-operative ultra-low dose CT scans were used to assess pedicle screw accuracy. The Gertzbein classification was used to grade any pedicle breaches (grade 0, no breach; grade 1, <2 mm; grade 2, 2-4 mm; grade 3, >4 mm). A screw was deemed accurate if no breach was identified (grade 0). 25 patients were included in the analysis, with a mean age of 13.6 years (range 11 to 18 years; 13/25 (52.0%) were female. The average pre-operative supine Cobb angle was 90.0 degrees (48-120 degrees). A total of 687 screws from 25 patients were analyzed (402 thoracic, 241 lumbosacral, 44 S2 alar-iliac (S2AI) screws). Surgical trainees (fellows and orthopaedic residents) inserted 46.6% (320/687) of screws with 98.8% (4/320) accuracy. The overall accuracy of pedicle screw insertion was 98.0% (Grade 0, no breach). All 13 breaches that occurred in the thoracic and lumbar screws were Grade 1. Of the 44 S2AI screws placed, one screw had a Grade 3 breach (2.3%) noted on intra-operative radiographs following rod placement and correction. This screw was subsequently revised. None of the breaches resulted in neuromonitoring changes, vessel, or visceral injuries. Machine vision navigation technology combined with careful free-hand pedicle screw insertion techniques demonstrated high levels of pedicle screw insertion accuracy, even in patients with challenging anatomy.

Incidence and Risk Factors of the Caudal Screw Loosening after Pelvic Fixation for Adult Spinal Deformity: A Systematic Review and Meta-analysis.

The purpose of this study was to assess the factors affecting caudal screw loosening after spinopelvic fixation for adult patients with spinal deformity. This meta-analysis calculated the weighted mean difference (WMD) and odds ratio (OR) using Review Manager ver. 5.3 (RevMan; Cochrane, London, UK). The loosening group was older than the control group (WMD, 2.17; 95% confidence interval [CI], 0.48-3.87; p=0.01). The S2 alar-iliac (S2AI) could prevent the caudal screw from loosening (OR, 0.43; 95% CI, 0.20-0.94; p=0.03). However, gender distribution (p=0.36), the number of fusion segments (p=0.24), rod breakage (p=0.97), T-score (p=0.10), and proximal junctional kyphosis (p=0.75) demonstrated no difference. Preoperatively, only pelvic incidence (PI) in the loosening group was higher (WMD, 5.08; 95% CI, 2.71-7.45; p<0.01), while thoracic kyphosis (p=0.09), lumbar lordosis (LL) (p=0.69), pelvic tilt (PT) (p=0.31), pelvic incidence minus lumbar lordosis (PI-LL) (p=0.35), sagittal vertical axis (SVA) (p=0.27), and T1 pelvic angle (TPA) demonstrated no difference (p=0.10). PI-LL (WMD, 6.05; 95% CI, 0.96-11.14; p=0.02), PT (WMD, 4.12; 95% CI, 0.99-7.26; p=0.01), TPA (WMD, 4.72; 95% CI, 2.35-7.09; p<0.01), and SVA (WMD, 13.35; 95% CI, 2.83-3.87; p=0.001) were higher in the screw loosening group immediately postoperatively. However, TK (p=0.24) and LL (p=0.44) demonstrated no difference. TPA (WMD, 8.38; 95% CI, 3.30-13.47; p<0.01), PT (WMD, 6.01; 95% CI, 1.47-10.55; p=0.01), and SVA (WMD, 23.13; 95% CI, 12.06-34.21; p<0.01) were higher in the screw loosening group at the final follow-up. However, PI-LL (p=0.17) demonstrated no significant difference. Elderly individuals were more susceptible to the caudal screw loosening, and the S2AI screw might better reduce the caudal screw loosening rate than the iliac screws. The lumbar lordosis and sagittal alignment should be reconstructed properly to prevent the caudal screw from loosening. Measures to block sagittal alignment deterioration could also prevent the caudal screw from loosening.

Iliac screws (is) vs. S2 alar iliac screws (S2AI) for pelvic fixation in adult spinal deformity patients. A propensity score-matched study

Iliac screws (is) vs. S2 alar iliac screws (S2AI) for pelvic fixation in adult spinal deformity patients. A propensity score-matched study

Obturator inlet and iliac oblique technique for safe, convenient, and reliable iliac screw placement

BackgroundThere are many described techniques for the placement of posterior iliac screws for extension of lumbar posterior spinal instrumentation to the pelvis. However, each one has its limitations. We describe our technique for fluoroscopic guidance of iliac screw placement utilizing the obturator inlet (OI) and iliac oblique (IO) views as well as a detailed review of how to obtain and interpret these views for safe iliac screw placement. MethodsRetrospective chart review of patients undergoing iliac screw placement utilizing the obturator inlet (OI) and iliac oblique (IO) views as part of spine instrumentation between January 2019 and March 2022. Screw length and bony breaches are reported utilizing this technique Results12 patients underwent posterior lumbopelvic fixation with a total of 23 screws placed via either open or percutaneous technique. The mean screw length was 96.5 mm (Range 80 - 110, standard dev 7.75). There were no recorded breaches or recannulation attempts. ConclusionsWe show how this technique is a much more convenient alternative to placement of iliac screws under the obturator outlet oblique (“teardrop” view) which necessitates that the C-arm be in line with instruments being placed. These described views can be used to place screws with either open or percutaneous techniques and with either the posterior superior iliac spine (PSIS) or S2 alar iliac (S2AI) starting points.

Feasibility analysis and nail planning ofS2 iliac crest screw placement in children

To evaluate the feasibility of S2 alar iliac screw insertion in Chinese children using computerized three-dimension reconstruction and simulated screw placement technique, and to optimize the measurement of screw parameters. A total of 83 pelvic CT data of children who underwent pelvic CT scan December 2018 to December 2020 were retrospectively analyzed, excluding fractures, deformities, and tumors. There were 44 boys and 39 girls, with an average age of (10.66±3.52) years, and were divided into 4 groups based on age (group A:5 to 7 years old;group B:8 to 10 years old;group C:11-13 years old;group D:14 to 16 years old). The original CT data obtained were imported into Mimics software, and the bony structure of the pelvis was reconstructed, and the maximum and minimum cranial angles of the screws were simulated in the three-dimensional view with the placement of 6.5 mm diameter S2 alar iliac screws. Subsequently, the coronal angle, sagittal angle, transverse angle, total length of the screw, length of the screw in the sacrum, width of the iliac, and distance of the entry point from the skin were measured in 3-Matic software at the maximum and minimum head tilt angles, respectively. The differences among the screw parameters of S2 alar iliac screws in children of different ages and the differences between gender and side were compared and analyzed. In all 83 children, 6.5 mm diameter S2 iliac screws could be placed. There was no significant difference between the side of each screw placement parameter. The 5 to 7 years old children had a significantly smaller screw coronal angle than other age groups, but in the screw sagittal angle, the difference was more mixed. The 5 to 7 years old children could obtain a larger angle at the maximum head tilt angle of the screw, but at the minimum cranial angle, the larger angle was obtained in the age group of 11 to 13 years old. There were no significant differences among the age groups. The coronal angle and sagittal angle under maximum cephalic angle and minimum cranial angle of 5 to 7 years old male were (40.91±2.91)° and (51.85±3.75)° respectively, which were significantly greater than in female. The coronal angle under minimum cranial angle was significantly greater in girls aged 8-10 years old than in boys. For the remaining screw placement angle parameters, there were no significant differences between gender. The differences in the minimum iliac width, the screw length, and the length of the sacral screws showed an increasing trend with age in all age groups. The distance from the screw entry point to the skin in boys were significantly smaller than that of girls. The minimum width of the iliac in boys at 14 to 16 years of age were significantly wider than that in girls at the same stage. In contrast, in girls aged 5 to 7 years and 11 to 13 years, the screw length was significantly longer than that of boys at the same stage. The pelvis of children aged 5 to 16 years can safely accommodate the placement of 6.5 mm diameter S2 alar iliac screws, but the bony structures of the pelvis are developing and growing in children, precise assessment is needed to plan a reasonable screw trajectory and select the appropriate screw length.

A radiological analysis of pelvic fixation trajectories: patient series.

Three well-defined methods for pelvic fixation are used for biomechanical support in spine fusion constructs: iliac, recessed iliac, and S2-alar-iliac (S2AI) screws. The authors compared the maximum screw sizes that could be placed with these techniques by using image-guidance software and high-resolution computed tomography scans from 20 randomly selected patients. Six trajectories were plotted per side, beginning at recognized starting points (standard or recessed posterior superior iliac spine [PSIS] or S2AI screw) and ending at the anterior inferior iliac spine (AIIS) or supra-acetabular notch (SAN). The mean maximum screw length and width ranged from 80.0 ± 32.2 mm to 140.8 ± 22.6 mm and from 8.25 ± 1.2 mm to 13.0 ± 2.7 mm, respectively, depending on the trajectory. Statistically significant differences in length were found between the standard and recessed PSIS trajectories to the AIIS (p < 0.001) and between the standard PSIS-to-AIIS trajectory and the S2AI-to-AIIS (p = 0.007) or S2AI-to-SAN (p < 0.001) trajectories. The most successful trajectory was the PSIS to SAN (95%, 38/40). The traditional iliac screw trajectory enabled the longest and widest screw trajectories and highest rate of successful screw placement with the fewest theoretical breaches more reliably than recessed and S2AI trajectories. These findings may help surgeons plan for maximum screw purchase for pelvic fixation.

Stability and Instrumentation Stresses Among Sacropelvic Fixation Techniques With Novel Porous Fusion/Fixation Implants: A Finite Element Study.

Sacropelvic fixation is frequently combined with thoracolumbar instrumentation for correcting spinal deformities. This study aimed to characterize sacropelvic fixation techniques using novel porous fusion/fixation implants (PFFI). Three T10-pelvis finite element models were created: (1) pedicle screws and rods in T10-S1, PFFI bilaterally in S2 alar-iliac (S2AI) trajectory; (2) fixation in T10-S1, PFFI bilaterally in S2AI trajectory, triangular implants bilaterally above the PFFI in a sacro-alar-iliac trajectory (PFFI-IFSAI); and (3) fixation in T10-S1, PFFI bilaterally in S2AI trajectory, PFFI in sacro-alar-iliac trajectory stacked cephalad to those in S2AI position (2-PFFI). Models were loaded with pure moments of 7.5 Nm in flexion-extension, lateral bending, and axial rotation. Outputs were compared against 2 baseline models: (1) pedicle screws and rods in T10-S1 (PED), and (2) pedicle screws and rods in T10-S1, and S2AI screws. PFFI and S2AI resulted in similar L5-S1 motion; adding another PFFI per side (2-PFFI) further reduced this motion. Sacroiliac joint (SIJ) motion was also similar between PFFI and S2AI; PFFI-IFSAI and 2-PFFI demonstrated a further reduction in SIJ motion. Additionally, PFFI reduced max stresses on S1 pedicle screws and on implants in the S2AI position. The study shows that supplementing a long construct with PFFI increases the stability of the L5-S1 and SIJ and reduces stresses on the S1 pedicle screws and implants in the S2AI position. The findings suggest a reduced risk of pseudarthrosis at L5-S1 and screw breakage. Clinical studies may be performed to demonstrate applicability to patient outcomes. Not applicable (basic science study).

Anatomic trajectory for iliac screw placement adapts better to the morphological features of the pelvis of each individual than the S2 alar iliac screw: a radiological study

PurposeThe iliac fixation (IF) through the S2 ala permits the minimization of implant prominence and tissue dissection. An alternative to this technique is the anatomic iliac screw fixation (AI), which considers the perpendicular axis to the narrowest width of the ileum and the width of the screw. The morphological accuracy of the iliac screw insertion of two low profile iliac fixation (IF) techniques is investigated in this study.MethodsTwenty-nine patients operated on via low profile IF technique were divided into two groups, those treated using 28 screws with the starting point at S2, and those treated with 30 AI entry point. Radiological parameters (Tsv-angle, Sag-Angle, Max-length, sacral-distance, iliac-width, S2-midline, skin-distance, iliac-wing, and PSIS distance) and clinical outcomes (early and clinic complications) were evaluated by two blinded expert radiologists, and the results were compared in both groups with the real trajectory of the screws placed.ResultsDifferences between ideal and real trajectories were observed in 6 of the 9 evaluated parameters in the S2AI group. In the AI group, these trajectories were similar, except for TSV-Angle, Max-length, Iliac-width, and distance to iliac-wing parameters. Moreover, compared with S2AI, AI provided better adaptation to the pelvic morphology in all parameters, except for sagittal plane angulation, skin distance, and iliac width.ConclusionsAI ensures the advantages of low profile pelvic fixation like S2AI, with a starting point in line with S1 pedicle anchors and low implant prominence, and moreover adapts better to the morphological features of the pelvis of each individual.

Bilateral sacroiliac joint fusion in long constructs using self-harvesting porous S2-alar iliac screws with an integrated tulip: technical considerations and early clinical and radiographic experience.

The incidence of sacroiliac joint (SIJ) dysfunction after lumbosacral fusion is high. Upfront bilateral SIJ fusion using novel fenestrated self-harvesting porous S2-alar iliac (S2AI) screws could reduce the incidence of SIJ dysfunction and need for subsequent SIJ fusion. In this study, the authors report their early clinical and radiographic results of SIJ fusion using this novel screw. The authors began using self-harvesting porous screws in July 2022. This is a retrospective review of consecutive patients at a single institution who underwent long thoracolumbar surgery with extension to the pelvis using this porous screw. Radiographic parameters of regional and global alignment were collected preoperatively and at the time of last follow-up. The incidence of intraoperative complications and need for revision were collected. The incidences of mechanical complications, including screw breakage, implant loosening/pullout, and screw cap dislocation at the time of last follow-up were also collected. Ten patients with a mean age of 67 years were included, 6 of whom were male. Seven patients had a thoracolumbar construct with extension to the pelvis. Three patients had upper instrumented vertebrae at the proximal lumbar spine. Intraoperative breach was not encountered in any of the patients (0%). Postoperatively, 1 patient (10%) had screw breakage at the neck of the tulip of the modified iliac screw discovered at routine follow-up without clinical sequalae. Use of self-harvesting porous S2AI screws incorporated into long thoracolumbar constructs was safe and feasible, demanding unique technical considerations. Long-term clinical and radiographic follow-up with a large patient cohort is necessary to determine their durability and efficacy to achieve SIJ arthrodesis and prevent SIJ dysfunction.

Single position robot-assisted pedicle screw placement with S2-alar-iliac fixation in lateral decubitus: cadaveric feasibility study and early clinical experience.

Single position lateral fusion with robotic assistance eliminates the need for surgical staging while harnessing the precision of robotic adjuncts. We expand on this technique by demonstrating the technical feasibility of placing bilateral pedicle screws with S2-alar-iliac (S2AI) fixation while in the lateral position. A cadaveric study was performed using 12 human specimens. A retrospective clinical series was also performed for patients who had undergone robot-assisted placement of S2AI screws in lateral decubitus between June 2020 and June 2022. Case demographics, implant placement time, implant size, screw accuracy, and complications were recorded. Early postoperative radiographic outcomes were reported. In the cadaveric series, a total of 126 screws were placed with robotic assistance in 12 cadavers of which 24 screws were S2AI. There were four breaches from pedicle screws and none with S2AI screws for an overall accuracy rate of 96.8%. In the clinical series, four patients (all male, mean age 65.8years) underwent single position lateral surgery with S2AI distal fixation. Mean BMI was 33.6 and mean follow-up was 20.5months. Mean radiographic improvements were lumbar lordosis 12.3 ± 4.7°, sagittal vertical axis 1.5 ± 2.1cm, pelvic tilt 8.5 ± 10.0°, and pelvic incidence-lumbar lordosis mismatch 12.3 ± 4.7°. A total of 42 screws were placed of which eight screws were S2AI. There were two breaches from pedicle screws and none from S2AI screws for an overall accuracy rate of 95.2%. No repositioning or salvage techniques were required for the S2AI screws. We demonstrate here the technical feasibility of single position robot-assisted placement of S2-alar-iliac screws in the lateral decubitus position for single position surgery.

Safety of robotic-assisted screw placement for spine surgery: Experience from the initial 125 cases

BackgroundThe present study aimed to evaluate the safety of robot-assisted screw placement in 125 cases after introducing a spinal robotics system and to identify the situations where deviation was likely to occur. MethodsThe subjects were 125 consecutive patients who underwent robotic-assisted screw placement using a spinal robotics system (Mazor X Stealth Edition, Medtronic) from April 2021 to January 2023. The 1048 screws placed with robotic assistance were evaluated. We investigated intraoperative adverse events of the robotics system and complications occurring within 30 days after surgery. We evaluated screw accuracy and deviation and compared them for vertebral levels, screw insertion methods (open traditional pedicle screw [Open-PS], cortical bone trajectory screw [CBT], percutaneous pedicle screw [PPS], and S2 alar iliac screw [S2AIS]), diagnosis, and phases of surgical cases. ResultsThe deviation rate of robotic-assisted screw placement for spine surgery was 2.2%. Complications were reoperation due to implant-related neurological deficit in 0.8% and surgical site infection in 0.8%. There was significant difference in the deviation rate between vertebral levels. The deviation rate of the T1–T4 level was high at 10.0%. There was significant difference in the deviation rate between Open-PS, CBT, PPS, and S2AIS. The PPSs had a high deviation rate of 10.3%. The deviation rates were not significantly different between patients with and without deformity. The deviation rate did not change depending on the experience of surgical cases, and the deviation rate was favorable from the onset. ConclusionAlthough the robotic-assisted screw placement was safe, we should be extra vigilant when placing screws in the upper thoracic region (deviation rate 10.0%) and when using PPSs (deviation rate 10.3%).