The Modified Iliac Screw: An Anatomic Comparison and Technical Guide

Comparison of Complications and Revisions After Sacral 2 Alar Iliac Screw and Iliac Screw Fixation for Sacropelvic Fixation in Pediatric and Adult Populations: Systematic Review and Meta-Analysis

Neurovascular Relations in Modified Iliac Screws and Traditional Iliac Screw: Anatomic Study

Retrospective, single-institution review of adult deformity patients who underwent iliac screw (IS) removal placed during fusion to the sacrum. To demonstrate whether IS removal offered benefit in terms of hip/buttock pain overlying the IS and whether IS could be removed without significant complications. ISs are effective at countering cantilever forces imparted on sacral pedicle screws. Despite the efficacy of IS fixation, pain or implant prominence can lead to elective IS removal. There has been no study about IS removal in adult spinal deformity patients. A total of 395 consecutive walking adult spinal deformity patients fused to the sacrum with IS fixation and minimum 2-year follow-up met study inclusion criteria. Clinical/radiographical data were analyzed. Because there is no validated pain outcomes instrument specific to this situation, an 8-question IS removal questionnaire was designed and used for the sole purpose of this inquiry, within which a universally accepted numeric rating scale for pain was included. RESULTS.: Twenty-four of 395 (6.1%) patients (2 men and 22 women) with mean age of 50.5 ± 10.8 years underwent elective IS removal at mean 2.6 ± 1.3 years from index surgery. Mean follow-up from initial surgery was 6.3 ± 4.0 years. Symptoms included hip/buttock pain in all 24 patients and IS prominence in 5 patients (20.8%). Screw removal was bilateral in 18 (75%) patients and unilateral in 6 (25%) patients. Using a numeric rating pain scale (0-10), hip/buttock pain improved after IS removal: preoperative 6.9 ± 1.8, postoperative 2.0 ± 2.7 (P < 0.05). Patients reported hip/buttock symptoms post-IS removal as "much improved" (78.3%), "somewhat improved" (8.7%), and "unchanged" (13.0%). Two of 24 (8.3%) patients sustained complications from IS removal (wound infection, n = 1; coronal/sagittal imbalance, n = 1). Presented with the same set of circumstances, 22 of 24 (91.7%) patients would have their IS removed again, including one of the patients who had a complication. Of 395 consecutive walking patients who had ISs placed during fusion to the sacrum for adult spinal deformity, 24 (6.1%) underwent elective removal. Patients had a statistically significant improvement in hip/buttock pain after IS removal, and a low prevalence of complications after the procedure was observed.

Comparative biomechanical testing in calf spines. To biomechanically evaluate 4 techniques of lumbosacral fixation. Pelvic fixation is a problematic area, and currently, the preferred method of pelvic fixation is controversial. Clinically, iliac screws have demonstrated decreased rod breakage rates, and better correction of pelvic obliquity than unthreaded rods (Galveston technique), but several modern methods of iliac fixation have not been compared. A total of 32 male calf spines were tested under axial rotation, flexion/extension, and lateral bending. Following intact testing, specimens were instrumented in the following groups: group 1-Modified Galveston technique with rods connected directly to iliac screws (no S1 fixation); group 2-S1 screws and iliac screws with offset connectors distal to S1; group 3-S1 screws and iliac screws with offset connectors coupled to the longitudinal rod between L6 and S1; and group 4-S1 and S2 screws without iliac fixation. Pedicle screws were placed from L3 to L6. Following nondestructive testing, specimens were fixed at the cephalad aspect of the construct and flexed to failure, with peak failure moment (Nm). Group 1 demonstrated significantly more flexion/extension than groups 2, 3, 4 (P<0.001). There were no significant differences between groups for lateral bending or axial rotation at L3-S1 or L6-S1. During destructive testing, group 4 showed a significant reduction in peak failure compared to group 1 (P<0.001), group 2 (P=0.001), and group 3 (P<0.001). There was no significant difference between groups 1, 2, and 3 and all specimens failed at the distal fixation. With extension of instrumentation across the lumbosacral junction, our results indicate significant improvement in stability with the use of S1 screws and iliac screw fixation. Furthermore, there does not appear to be any significant difference in the location of the connector for the iliac screw.

Retrospective chart review. To compare short-term clinical and radiographic complications between iliac screw (IS) and S2 alar-iliac (S2AI) screw fixation techniques in the adult and pediatric populations. Pelvic fixation with lumbosacral implants is in widespread practice with numerous indications. Several techniques for spinopelvic fixation have been described in the literature. Although the iliac screw technique is widely practiced, it presents several challenges, including the use of connectors, more lateral surgical dissection, and some complaints of pain over the posterior pelvis. The S2AI method has recently been proposed as an alternative technique that minimizes these complications. We retrospectively reviewed the charts of 65 adult patients (43 IS, 22 S2AI) and 55 pediatric patients (40 IS/unit rod, 15 S2AI) in a consecutive series who underwent spinopelvic fixation. Acute, spinopelvic implant-related, and delayed complications, including persistent pain over the gluteal region occurring longer than 3 months postoperatively, were recorded from both clinical and radiographic encounters. Statistical analyses were performed among the adult and pediatric group, respectively, as well as a pooled cohort. The adult cohort found an 18.6% absolute risk reduction (ARR) in implant loosening (P=0.029) and a 21.1% ARR (P=0.05) in late pain with the S2AI method. In the pediatric population, the S2AI method demonstrated a 22.2% ARR (P=0.049) in both occurrence of revision surgery secondary to spinopelvic implant failure and late pain. In the pooled cohort, the S2AI method had a 13% ARR (P=0.033) in acute infections, 18.1% ARR (P=0.003) in implant loosening, 14.5% ARR (P=0.009) in revision surgery, 18.7% ARR (P=0.015) in late pain, and a 10.8% ARR (P=0.031) in delayed wound issues. The S2AI technique is associated with significantly less clinical and radiographic complications in both the pediatric and adult populations when compared with the iliac screws technique. Level III.

PurposeSpinopelvic fixations involving the S2-alar-iliac (S2AI) and iliac screws are commonly used in various spinal fusion surgeries. This study aimed to compare the biomechanical characteristics, specifically the risk of screw and adjacent bone failures of S2AI screw fixation with those of iliac screw fixation using a finite element analysis (FEA).MethodsA three-dimensional finite element (FE) model of a healthy spinopelvis was generated. The pedicle screws were placed on the L3-S1 with three different lengths of the S2AI and iliac screws (60 mm, 75 mm, and 90 mm). In particular, two types of the S2AI screw, 15°- and 30°-angled polyaxial screw, were adopted. Physiological loads, such as a combination of compression, torsion, and flexion/extension loads, were applied to the spinopelvic FE model, and the stress distribution as well as the maximum von Mises equivalent stress values were calculated.ResultsFor the iliac screw, the highest stress on the screw was observed with the 75-mm screw, rather than the 60-mm screw. The bones around the iliac screw indicated that the maximum equivalent stress decreased as the screw length increased. For the S2AI screw, the lowest stress was observed in the 90-mm screw length with a 30° head angle. The bones around the S2AI screw indicated that the lowest stress was observed in the 90-mm screw length and a 15° head angle.ConclusionsIt was found that the S2AI screw, rather than the iliac screw, reduced the risk of implant failure for the spinopelvic fixation technique, and the 90-mm screw length with a 15° head angle for the S2AI screw could be biomechanically advantageous.

Purpose To compare the short-term therapeutic effects of S2-alar-iliac (S2AI) screw fixation and iliac screw fixation techniques in managing sacral fractures. Methods From September 2015 to May 2020, 42 patients with sacral fractures who underwent lumbopelvic fixation by a single surgeon were analyzed. The patients were divided into the S2AI screw group (19 patients) and the iliac screw group (23 patients). Operative data, reduction quality, postoperative complications, and functional outcomes were evaluated. Results The incidence of unplanned reoperation was significantly different between patients treated with S2AI screws than in those treated with iliac screws (0 versus 6, p = 0.02). The mean intraoperative estimated blood loss was 405.26 ± 229.67 mL in the S2AI screw group and 539.13 ± 246.32 mL in the iliac screw group (P = 0.08). No significant difference was observed in either group regarding the quality of reduction, functional outcome, or low back pain. The reduction quality based on the Matta criteria and excellent/good outcomes were 21/2 in the iliac screw group and 17/2 in the S2AI screw group. The functional outcomes based on the Majeed score and excellent/good/fair outcomes were 17/3/3 in the iliac screw group and 17/1/1 in the S2AI screw group. No complications, including implant breakage, loosening of the implant, or loss of reduction were found in either group during follow-up. Conclusion Both S2AI screws and iliac screws were effective in the treatment of sacral fractures. The use of S2AI screws, however, was independently associated with fewer unplanned reoperations for surgical site infection, wound dehiscence, and symptoms of screw protrusion than the use of iliac screws.

Introduction Osteotomy of the posterior superior iliac spine for preparation of traditional iliac screw entry point exposes the cancellous bone of the inner ilium and causes loss of circumferential cortical starting point which may compromise biomechanical stability. For this reason, traditional iliac screws may not provide the desired primary stability especially in osteopenic and osteoporotic patients. We describe a new free-hand technique with a starting point located at the posterior inferior iliac spine (PIIS), which does not require any decortication for entry and courses very close to the rigid subcortical bone over sciatic notch while providing a low profile fixation and easier connection with S1 screw. The aim of this study is to evaluate the result of this new iliac bolt fixation technique. Patients and Methods A total of 26 patients (21 F and 5 M) having lumbopelvic fixation with the new technique were reviewed. The new entry point is located at the midpoint of PIIS. Lateral cortex of distal iliac wing is exposed subperiosteally and sciatic notch was palpated for safe trajectory. Screw trajectory is intended to be parallel to the outer cortex of ilium, passing 1 to 1.5 cm above the sciatic notch. PIIS provides a rigid circumferential cortical starting point for entrance and trajectory through thick cortical iliac bone over sciatic notch which provides very strong screw purchase even in osteopenic and osteoporotic spine. New entry point also enables easier connection to S1 screw. Free-hand technique eliminates radiation exposure. Pre-op, post-op, and follow-up X-rays were reviewed for the radiological data. Results Mean age was 63.6 years (range, 19–84 years) and mean follow-up was 14 months (range, 12–18 months). Mean screw length was 93.46 mm (range, 80–110 mm). Screw diameters were 8.5 mm in 22 patients and 7.5 mm in 4 patients. Lumbosacral fusion was achieved in all the cases. There were no neurovascular injuries related to the sciatic nerve and gluteal artery during screw placement. There were no implant failures or screw breakage at end of final follow-up. Conclusion This new technique seems to be a viable option in patients undergoing fusion to the sacrum for iliac bolt fixation. PIIS provides a circumferential cortical starting point and low profile fixation with stronger screw purchase especially in osteoporotic patients.

Introduction Prior biomechanical studies have examined the role of the iliac screw in lumbosacral fixation [Lebwohl, 2002; Cunningham, 2010] and while found to be significant, the ideal screw device and fixation technique have yet to be identified. An initial effort to define this biomechanical fixation includes measurements of current screw insertion torque across screw length was developed. The objective of this study was to measure the intraoperative torque required to place an S2-Alar iliac screw for spino-pelvic fixation. This fixation method often results in variable screw fixation strength and an improved understanding of the local torques required along the length of the screw will aid in improving this surgical fixation. Materials and Methods This IRB approved study involves obtaining informed consent of patients receiving long spinal fusions either for adult deformity. The surgical trajectory for the S2-Iliac screw will be identified as is currently practiced using O-arm Stealth Navigation. Next, the insertion torque of the iliac screw will be measured using the standard driver handle fitted with a torque cell sensor by the surgeon under 3D navigation (Stealth). Results There were 6 patients who underwent spino-pelvic fixation. 12 S2-Iliac screws were placed however Insertional torque was recorded in only 6 screws. Screw maps show that peak torques range from 0.71 to 9.73 Nm. Highest torques recorded were when the head of the screw approached the bone during insertion. These peak torques recorded are 1.91 times higher than Iliac screw insertional torques reported in a previous study. Conclusion Peak insertional torques range from 0.71 to 9.73 Nm and occurred as head of the screw approached the bone during insertion. However higher insertional torques were not recorded because it went beyond the capacity of the driver.

Iliac screw fixation and anterior column support are highly recommended to prevent lumbosacral pseudarthrosis after long-level adult spinal deformity (ASD) surgery. Despite modern instrumentation techniques, a considerable number of patients still experience nonunion at the lumbosacral junction. However, most previous studies evaluating nonunion relied only on plain radiographs and only assessed when the implant failures occurred. Therefore, using CT, it is important to know the prevalence after iliac fixation and to evaluate risk factors for nonunion at L5-S1. Seventy-seven patients who underwent ≥ 4-level fusion to the sacrum using iliac screws for ASD and completed a 2-year postoperative CT scan were included in the present study. All L5-S1 segments were treated by interbody fusion. Lumbosacral fusion status was evaluated on 2-year postoperative CT scans using Brantigan, Steffee, and Fraser criteria. Risk factors for nonunion were analyzed using patient, surgical, and radiographic factors. The metal failure and its association with fusion status at L5-S1 were evaluated. Of the 77 patients, 12 (15.6%) showed nonunion at the lumbosacral junction on the 2-year CT scans. Multivariate analysis using logistic regression revealed that only higher American Society of Anesthesiologists (ASA) grade was a risk factor for nonunion (OR 25.6, 95% CI 3.196-205.048, p = 0.002). There were no radiographic parameters associated with fusion status at L5-S1. Lumbosacral junction rod fracture occurred more frequently in patients with nonunion than in patients with fusion (33.3% vs 6.2%, p = 0.038). Although iliac screw fixation and anterior column support have been performed to prevent lumbosacral nonunion during ASD surgery, 15.6% of patients still showed nonunion on 2-year postoperative CT scans. High ASA grade was a significant risk factor for nonunion. Rod fracture between L5 and S1 occurred more frequently in the nonunion group.

A 3-dimensional multi detector computed tomography study. To analyze the optimal trajectory of the transsacral iliac screw (TSIS) to overcome the disadvantages of the conventional iliac screw. Iliac screw fixation increased lumbosacral fusion rate. However, its disadvantages have been reported including extensive muscle dissection, loss of the posterior superior iliac spine (PSIS), need of additional connecting device, screw breakage, and pain from prominence. Three-dimensionally reconstructed multi detector computed tomography images on the pelvis of 60 patients (M:F=30:30, age 20 to 50) were analyzed. The virtual trajectory started from the point where the center of S2 ala met the lateral sacral crest and targeted the superior rim of acetabulum, across the sacroiliac joint. On the basis of the virtual trajectory, the oblique sagittal, oblique axial, oblique coronal plane, and 3-dimensional surface rendering images were obtained. The optimal insertion angle in the 3 planes, the maximal length and diameter of screw were measured. Relationships between the trajectory and structures under risk were analyzed. The safe insertion angle was 38±3.5 degrees in the axial plane and 86±6.5 degrees in the sagittal plane based on the posterior surface of the sacrum. The mean length and maximal diameter of optimal trajectory was 91 and 18 mm, respectively. When the screw was inserted within 25 degrees in the axial plane, and exceeding 95 degrees in the sagittal plane, the external iliac vessels and the superior gluteal arteries were at risk. The TSIS could be safely inserted without increasing the general risk of conventional iliac screw. On the basis of the result of this study, we consider the TSIS technique a useful option for lumbopelvic fixation to overcome disadvantages of iliac screw.

What do we know about the biomechanics of the sacroiliac joint and of sacropelvic fixation? A literature review

BackgroundPosterior fusion of the spine to the pelvis in paediatric and adult spinal deformity is still challenging. Especially assembling of the posterior rod construct to the iliac screw is considered technically difficult. A variety of spinopelvic fixation techniques have been developed. However, extreme bending of the longitudinal rods or the use of 90-degree lateral offset connectors proved to be difficult, because the angle between the rod and the iliac screw varies from patient to patient.MethodsWe adopted a new spinopelvic fixation system, in which iliac screws are side-to-side connected to the posterior thoracolumbar rod construct, independent of the angle between the rod and the iliac screw. Open angled parallel connectors are used to connect short iliac rods from the posterior rod construct to the iliac screws at both sides. The construct resembles in form and function an architectural Flying Buttress, or lateral support arches, used in Gothic cathedrals.Results and discussionThree different cases that illustrate the Flying Buttress construct for spinopelvic fixation are reported here with the clinical details, radiographic findings and surgical technique used.ConclusionThe Flying Buttress construct may offer an alternative surgical option for spinopelvic fixation in circumstances wherein coronal or sagittal balance cannot be achieved, for example in cases with significant residual pelvic obliquity, or in revision spinal surgery for failed lumbosacral fusion.

The Latarjet procedure is a common procedure for treating critical glenoid bone loss in anterior shoulder instability. Implants such as the screw and cortical button are widely used. The aim of this study was to compare studies on screw versus button fixation techniques in the Bristow-Latarjet procedure for anterior shoulder instability in terms of clinical outcomes, union rates, and complications. The PubMed, Scopus, and Embase databases were searched to find comparative studies that reported outcomes of using screw versus button fixation in the Bristow-Latarjet procedure following the 2020 Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) guidelines. Studies that directly compared the screw and button fixation techniques and provided postoperative patient-reported outcomes, union rates, or complications were included. The Methodology Index for Non-Randomized Research (MINORS) criteria were used to assess the quality of the included studies. Odds ratios (ORs) were calculated for dichotomous outcomes whereas mean differences were calculated for continuous outcomes. Five articles included a total of 877 shoulders. All five studies had level 3 evidence. There was no statistically significant difference between the two techniques using the Walch-Duplay score, visual analog scale for pain, American Shoulder and Elbow Surgeons score, Simple Shoulder Test, range of motion, and graft union rates. However, the button fixation technique had statistically significantly higher recurrence rates than the screw fixation technique (OR, 0.24; 95% confidence interval, 0.10-0.58; p = 0.001). The screw fixation technique had statistically significantly lower recurrence rates than the button fixation technique. However, there was no significant difference between screw and button fixation techniques regarding postoperative patient-reported outcomes, range of motion, graft union rates, nerve injury rates, infection rates, and reoperation rates.

To provide radiographic parameters for optimal placement of posterior second sacral alar iliac (S2AI) screw for instrumentation and fusion of scoliosis to the second sacral level in a Chinese population. S2AI screw trajectories were mapped on three-dimensional computed tomography (3DCT) reconstructions of 60 normal adult pelvises. 1 mm inferior and 1 mm lateral to the S1 dorsal foramen were chosen as the entry point, and ideal S2AI screw trajectories were explored by rotating and cutting the 3D pelvis, ensuring that the trajectories were of maximum length and width. The directions and depth of these determined trajectories were then measured. The ideal S2AI screw trajectories could be found in each pelvis. The left and right screw trajectory parameters for males were shown as follows: angulation was L 29.15 ± 8.60° vs. R 29.96 ± 8.28° (p = 0.286) caudally in the sagittal plane and L 36.49 ± 3.14° vs. R 37.16 ± 3.14° (p = 0.165) laterally in the transverse plane. The maximal and intrasacral lengths of trajectory were L 121.25 ± 8.33 vs. R 120.63 ± 7.54 mm (p = 0.460) and L 26.20 ± 3.31 vs. R 26.92 ± 4.76 mm (p = 0.268). The entry point was L 28.87 ± 3.33 vs. R 29.79 ± 3.55 mm (p = 0.186) lateral to the second sacral midline, and L 44.14 ± 11.87 vs. R 43.89 ± 12.53 mm (p = 0.687) underneath the skin. The trajectories for females were more caudal (L: 34.50 ± 6.56° vs. 29.15 ± 8.60°, p = 0.009; R: 35.72 ± 7.53° vs. 29.96 ± 8.28°, p = 0.007) in the sagittal plane, but the lateral angulation in the transverse plane showed no difference between genders (p > 0.05). The female iliac medullar cavities were obviously narrower than those of males (L: 14.76 ± 2.46 vs. 16.98 ± 3.52, p = 0.006; R: 14.94 ± 2.60 vs. 17.00 ± 2.81, p = 0.005). Although the average maximal length of trajectories for females were about 5 mm shorter than those of males, intrasacral length were equal to those of males. Furthermore, both the distance from entry point to the S2 midline and skin in the transverse plane showed no difference between genders. The feasibility to insert S2AI screws to the sacrum and ilium in an Asian population along with the ideal entry angle and length of trajectory were identified for clinical practice.