S2 Alar Iliac Research Articles

Acute failure of S2-alar-iliac screw pelvic fixation in adult spinal deformity: novel failure mechanism, case series, and review of the literature.

Pelvic fixation with S2-alar-iliac (S2AI) screws is an established technique in adult deformity surgery. The authors' objective was to report the incidence and risk factors for an underreported acute failure mechanism of S2AI screws. The authors retrospectively reviewed a consecutive series of ambulatory adults with fusions extending 3 or more levels, and which included S2AI screws. Acute failure of S2AI screws was defined as occurring within 6 months of the index surgery and requiring surgical revision. Failure occurred in 6 of 125 patients (5%) and consisted of either slippage of the rods or displacement of the set screws from the S2AI tulip head, with resultant kyphotic fracture. All failures occurred within 6 weeks postoperatively. Revision with a minimum of 4 rods connecting to 4 pelvic fixation points was successful. Two of 3 (66%) patients whose revision had less fixation sustained a second failure. Patients who experienced failure were younger (56.5 years vs 65 years, p = 0.03). The magnitude of surgical correction was higher in the failure cohort (number of levels fused, change in lumbar lordosis, change in T1-pelvic angle, and change in coronal C7 vertical axis, each p < 0.05). In the multivariate analysis, younger patient age and change in lumbar lordosis were independently associated with increased failure risk (p < 0.05 for each). There was a trend toward the presence of a transitional S1-2 disc being a risk factor (OR 8.8, 95% CI 0.93-82.6). Failure incidence was the same across implant manufacturers (p = 0.3). All failures involved large-magnitude correction and resulted from stresses that exceeded the failure loads of the set plugs in the S2AI tulip, with resultant rod displacement and kyphotic fractures. Patients with large corrections may benefit from 4 total S2AI screws at the time of the index surgery, particularly if a transitional segment is present. Salvage with a minimum of 4 rods and 4 pelvic fixation points can be successful.

Bilateral open sacroiliac joint fusion during adult spinal deformity surgery using triangular titanium implants: technique description and presentation of 21 cases.

Pelvic fixation enhances long constructs during deformity surgery. Subsequent loosening of iliac screws and pain at the pelvis occur in as many as 29% of patients. Concomitant sacroiliac (SI) fusion may prevent potential pain and failure. The objective of this study was to describe a novel surgical technique and a single institution's experience using bilateral SI fusion during adult deformity surgery with S2-alar-iliac (S2AI) screws and triangular titanium rods (TTRs) placed with navigation. The authors reviewed open SI joint fusions with TTR performed between August 2019 and March 2020. All patients underwent lumbosacral fusion through a midline approach and bilateral S2AI pelvic fixation in the caudal teardrop, followed by TTR placement just proximal and cephalad to the S2AI screws using intraoperative CT imaging guidance. Twenty-one patients were identified who received 42 TTRs, ranging in size from 7.0 × 65 mm to 7.0 × 90 mm. Three TTRs (7%) were malpositioned intraoperatively, and each was successfully repositioned during index surgery without negative sequelae. All breaches occurred in a medial and cephalad direction into the pelvis. Incremental operative time for adding TTR averaged 8 minutes and 33 seconds per implant. Image-guided open SI joint fusion with TTR during lumbosacral fusion is technically feasible. The bony corridor for implant placement is narrower cephalad, and implants tend to deviate medially into the pelvis. Detection of malpositioned implant is aided with intraoperative CT, but this can be salvaged. A prospective randomized clinical trial is underway that will better inform the impact of this technique on patient outcomes.

Three cases of fracture or set screw dislodgement of S2 alar iliac screw

Three cases of fracture or set screw dislodgement of S2 alar iliac screw

S2-Alar-Iliac Screw Fixation versus Iliac Screw Fixation in the Treatment of Sacral Fractures

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.

Treatment of Unstable Posterior Pelvic Ring Injury with S2-Alar-Iliac Screw and S1 Pedicle Screw Fixation

The S2-alar-iliac (S2AI) screws have been described as an alternative method for lumbosacropelvic fixation in place of iliac screws. However, the clinical effect of the short-segment S2AI screw fixation technique in the treatment of unstable posterior pelvic ring injuries remains unclear. In this study, we report the preliminary clinical results of the internal fixation connecting a S2-alar-iliac screw and a S1 pedicle screw (i.e., S2AI-S1 fixation) in the treatment of unstable pelvic posterior ring injuries. Twenty-five patients with unstable posterior pelvic ring injury were treated with S2AI-S1 fixation from February 2019 to June 2020. The incision length, surgical time, blood loss, frequency of intraoperative fluoroscopy, quality of reduction, complications, and functional outcome were analyzed. A total of 29 groups of S2AI-S1 fixation were used in 25 patients. The mean incision length was 8.3 (6.2- 10.3) cm, mean operative time was 86.4 (60- 142) minutes, mean frequency of intraoperative fluoroscopy was 7.9 (4- 12) times, and mean blood loss was 148 (50- 500) mL. The mean postoperative follow-up time was 17.8 (10- 26) months. The satisfaction rate of pelvic reduction quality was 25/29, and the satisfactory rate of functional outcome was 23/25. There were no obvious signs of screw prominence, screw loosening, or implant failure. The case series presented in this study show the successful use of S2AI-S1 fixation to treat unstable posterior pelvic ring injuries. The S2AI-S1 fixation, not including the lumbar spine in the fixation range, is a simple, safe, and effective fixation method.

Robotic-guidance allows for accurate S2AI screw placement without complications.

The study design is retrospective, multi-surgeon, single-center review. The objective is to evaluate complication rates, revision rates, and accuracy grading for robotic-guided S2 alar-iliac (S2AI) screws. Sixty-five consecutive patients underwent S2AI fixation (118 screws) as part of a posterior spine fusion using robotic-guidance. Screws were placed percutaneously in 14 cases and 51 were placed in an open fashion by three board-certified spine surgeons using the Mazor core technology robotic systems (Mazor X, n = 42; Mazor XSE, n = 23). Medical charts were retrospectively reviewed for revisions and complications. All patients were followed for 90days or greater. Postoperative CT scans were obtained in 22 of the 51 patients, allowing for 46 screws to be reviewed by an independent neuroradiologist who graded the screws for accuracy. There were no intraoperative or postoperative complications associated with S2AI screw placement. There were no revisions found to be related to the S2AI screw placement. All 46 screws evaluated with postoperative CT scans were reported as being at the highest level of accuracy, grade A, with a breach distance of 0mm (no breach). The robotic-guided technique for S2AI screw placement is a reliable method to achieving pelvic fixation with low complication and revision rates. In addition, a high degree of accuracy can be achieved without relying on visible and tactile landmarks needed for the freehand technique or the additional radiation associated with fluoroscopic-guidance.

Preliminary experience using S1-alar iliac fixation with navigation: technical note.

Traditional iliac screws and S2-alar iliac (S2-AI) screws are common methods used for pelvic fixation, and many surgeons advocate pelvic fixation for long-segment fixation to the sacrum. However, in patients without severe deformities and only degenerative conditions, many surgeons may choose S1 screws only. Moreover, even with S2-AI screws, there is more muscular dissection than with using S1 screws, and the rod connection can be cumbersome in both S2-AI fixation and placing iliac screws. Using a surgical video, artist's illustration, and intraoperative photographs, the authors describe the S1-AI screw fixation technique that allows for single-screw sacral and iliac fixation, requires less distal dissection of the sacrum, allows for easier rod connection, and may be an option in degenerative conditions needing pelvic fixation. However, this is a preliminary feasibility study, and in long fusion constructs, this type of fixation has only been used in conjunction with L5-S1 anterior lumbar interbody fusion (ALIF), and there are no long-term data on the use of this screw fixation technique without ALIF. In short-segment revision fusions, this technique may be considered for salvage in cases of large halos in the sacrum from loosened S1 screw fixation.

Letter: Sacroplasty Augmentation of Instrumented Pelvic Reconstruction After High Sacrectomy: A Technical Case Report.

Letter: Sacroplasty Augmentation of Instrumented Pelvic Reconstruction After High Sacrectomy: A Technical Case Report.

Applicable safety analysis and biomechanical study of iliosacral triangular osteosynthesis

BackgroundThe aim of this study was to investigate the applicable safety and biomechanical stability of iliosacral triangular osteosynthesis (ITO) through 3D modeling and finite element (FE) analysis.MethodsPelvic CT imaging data from 100 cases were imported into Mimics software for the construction of 3D pelvic models. The S2-alar-iliac (S2AI) screws and S2 sacroiliac screws were placed in the S2 segment with optimal distribution and their compatibility rate on the S2 safe channel was observed and analyzed. In the FE model, the posterior pelvic ring was fixed with two transsacral screws (TTS), triangular osteosynthesis (TO) and ITO, respectively. Four different loading methods were implemented in sequence to simulate the force in standing, flexion, right bending, and left twisting, respectively. The relative displacement and change in relative displacement of the three fixing methods were recorded and analyzed.ResultsThe theoretical compatibility rate of S2AI screw and S2 sacroiliac screw in S2 segment was 94%, of which 100% were in males and 88% in females. In the FE model, in terms of overall relative displacement, TTS group showed the smallest relative displacement, the ITO group showed the second smallest, and the TO group the largest relative displacement. The change in relative displacement of the TTS group displayed the smaller fluctuations in motion. The change in relative displacement of the TO group under right bending and left twisting displayed larger fluctuations, while the ITO group under flexion displayed larger fluctuations.ConclusionsThe simultaneous placement of S2AI screw and S2 sacroiliac screw in the S2 segment is theoretically safe. Although the biomechanical stability of ITO is slightly lower than TTS, it is better than TO, and can be used as a new method for the treatment of posterior pelvic ring injuries.

Robotic Sacroiliac Fixation Technique for Triangular Titanium Implant in Adult Degenerative Scoliosis Surgery: 2-Dimensional Operative Video.

Corrective surgery remains a definitive treatment for adult spinal deformity, improving pain and disability. With these cases, instrumentation to the pelvis with iliac fixation is recommended. Whether iliac or S2-Alar-Iliac (S2AI) trajectories are used, sacroiliac joint pain and long-term sacroilitis can be common after long-fusion constructs.1-3 Sacroiliac fusion with triangular titanium implants during fusion can reduce back pain associated with sacroiliac joint degeneration,3 provides reduction in sacroiliac joint motion and stress when added to S2AI screws, and potentially enhances mechanical stability of fusion constructs.4 Here, we present a technique for placing triangular titanium sacroiliac implants (iFuse BedrockTM; SI-BONE Inc, Santa Clara, California) alongside S2AI screws using a robotic platform (Mazor X; Medtronic Sofamor Danek, Medtronic Inc, Dublin, Ireland). Navigated robotics allows reduction in human error with implant placement, and potentially decreased operative time/fluoroscopy.5-7 Key surgical steps include placement of K wires for S2AI and bilateral SI-implants, tapping, replacing SI-implant K wires with guide pins, placing S2AI screws, and finally placing the SI-implant. Final placement is verified with intraoperative fluoroscopy. The patient described is a 61-yr-old woman with worsening adult degenerative scoliosis, lower back pain, left leg radicular pain, and mild right leg pain who failed conservative treatment. Examination revealed diminished strength in both legs. Imaging was significant for moderate sigmoid scoliosis, discogenic disease, and osteoarthritis at all levels. She consented to undergo corrective surgery. Postoperatively, the patient experienced resolution of her leg weakness and pain. Imaging demonstrated appropriate positioning of hardware. Prospective studies on the efficacy of the SI-implant are underway.

S2-alar-iliac screw and S1 pedicle screw fixation for the treatment of non-osteoporotic sacral fractures: a finite element study

BackgroundFive different sacral fracture fixation methods were compared using finite element (FE) analysis to study their biomechanical characteristics.MethodsDenis type I sacral fractures were created by FE modeling. Five different fixation methods for the posterior pelvic ring were simulated: sacroiliac screw (SIS), lumbopelvic fixation (LPF), transiliac internal fixator (TIFI), S2-alar-iliac (S2AI) screw and S1 pedicle screw fixation (S2AI-S1) and S2AI screw and contralateral S1 pedicle screw fixation (S2AI-CS1). Four different loading methods were implemented in sequence to simulate the force in standing, flexion, right bending and left twisting, respectively. Vertical stiffness, relative displacement and change in relative displacement were recorded and analyzed.ResultsAs predicted by the FE model, the vertical stiffness of the five groups in descending order was S2AI-S1, SIS, S2AI-CS1, LPF and TIFI. In terms of relative displacement, groups S2AI-S1 and S2AI-CS1 displayed a lower mean relative displacement, although group S2AI-CS1 exhibited greater displacement in the upper sacrum than group S2AI-S1. Group SIS displayed a moderate mean relative displacement, although the displacement of the upper sacrum was smaller than the corresponding displacement in group S2AI-CS1, while groups LPF and TIFI displayed larger mean relative displacements. Finally, in terms of change in relative displacement, groups TIFI and LPF displayed the greatest fluctuations in their motion, while groups SIS, S2AI-S1 and S2AI-CS1 displayed smaller fluctuations.ConclusionCompared with SIS, unilateral LPF and TIFI, group S2AI-S1 displayed the greatest biomechanical stability of the Denis type I sacral fracture FE models. When the S1 pedicle screw insertion point on the affected side is damaged, S2AI-CS1 can be used as an appropriate alternative to S2AI-S1.

Biomechanical effects of a novel posteriorly placed sacroiliac joint fusion device integrated with traditional lumbopelvic long-construct instrumentation.

S2-alar-iliac (S2AI) screw fixation effectively ensures stability and enhances fusion in long-segment constructs. Nevertheless, pelvic fixation is associated with a high rate of mechanical failure. Because of the transarticular nature of the S2AI screw, adding a second point of fixation may provide additional stability and attenuate strains. The objective of the study was to evaluate changes in stability and strain with the integration of a sacroiliac (SI) joint fusion device, implanted through a novel posterior SI approach, supplemental to posterior long-segment fusion. L1-pelvis human cadaveric specimens underwent pure moment (7.5 Nm) and compression (400 N) tests in the following conditions: 1) intact, 2) L2-S1 pedicle screw and rod fixation with L5-S1 interbody fusion, 3) added S2AI screws, and 4) added bilateral SI joint fixation (SIJF). The range of motion (ROM), rod strain, and screw bending moments (S1 and S2AI) were analyzed. S2AI fixation decreased L2-S1 ROM in flexion-extension (p ≤ 0.04), L5-S1 ROM in flexion-extension and compression (p ≤ 0.004), and SI joint ROM during flexion-extension and lateral bending (p ≤ 0.03) compared with S1 fixation. SI joint ROM was significantly less with SIJF in place than with the intact joint, S1, and S2AI fixation in flexion-extension and lateral bending (p ≤ 0.01). The S1 screw bending moment decreased following S2AI fixation by as much as 78% in extension, but with statistical significance only in right axial rotation (p = 0.03). Extending fixation to S2AI significantly increased the rod strain at L5-S1 during flexion, axial rotation, and compression (p ≤ 0.048). SIJF was associated with a slight increase in rod strain versus S2AI fixation alone at L5-S1 during left lateral bending (p = 0.048). Compared with the S1 condition, fixation to S2AI increased the mean rod strain at L5-S1 during compression (p = 0.048). The rod strain at L5-S1 was not statistically different with SIJF compared with S2AI fixation (p ≥ 0.12). Constructs ending with an S2AI screw versus an S1 screw tended to be more stable, with reduced SI joint motion. S2AI fixation decreased the S1 screw bending moments compared with fixation ending at S1. These benefits were paired with increased rod strain at L5-S1. Supplementation of S2AI fixation with SIJF implants provided further reductions (approximately 30%) in the sagittal plane and lateral bending SI joint motion compared with fixation ending at the S2AI position. This stability was not paired with significant changes in rod or screw strains.

The accuracy of robot-assisted S2 alar-iliac screw placement at two different healthcare centers.

Current literature on robot-assisted S2 alar-iliac (S2AI) screw placement shows favorable outcomes and screw accuracy; however, the data is limited by a few retrospective, single-surgeon studies. To the author's knowledge, this is the first multicenter study which evaluates the accuracy of robot-assisted S2AI screws. Adult (≥18 years old) patients who underwent robot-assisted S2AI screw placement from 2017-2019 were reviewed. All surgeries used the same proprietary robotic guidance system, Mazor X (Mazor Robotics Ltd). A total of 65 screws were assessed in 31 patients. The mean follow-up ± standard deviation was 362±190 days (minimum was 90 days). The mean age was 61.1±11 years old, and 54.8% (n=17) of patients were female. Nearly half of the patients had a primary diagnosis of degenerative scoliosis (48.4%, n=15). Other diagnosis included pseudarthrosis (22.6%, n=7), degenerative disc disease (16.1%, n=5), and high-grade spondylolisthesis (12.9%, n=4). The mean length and diameter of screws were 84.6±6.1 mm and 8.4±0.7, respectively. The mean axial and sagittal angles were 50.0±6.3 and 24.0±10.5, respectively. The overall screw accuracy was 93.8% (n=61). There were four iliac cortex breaches (anterior =3, inferior 1) with a mean breach distance of 3.5±3.2. No statistically significant differences in screw length, diameter, axial angle, and sagittal angle were observed between screws with and without a breach. No intraoperative neurologic, vascular, or visceral complications from the S2AI screw were observed. No post-discharge wound complications, screw prominence issues, or revision of S2AI screws were observed during the study's follow-up period. Robot-assisted S2AI screw placement was found to be safe and accurate in this multicenter study. This is largely attributed to the versatility of the robotic guidance software that allows for detailed and precise preoperative and intraoperative planning.

Fixation Strength of Modified Iliac Screw Trajectory Compared to Traditional Iliac and S2 Alar-Iliac Trajectories: A Cadaveric Study

Traditional iliac (TI) screws require extensive dissection, involve offset-connectors, and have prominent screw heads that may cause patient discomfort. S2 alar-iliac (S2AI) screws require less dissection, do not need offset connectors, and are less prominent. However, the biomechanical consequences of S2AI screws crossing the alar-iliac joint is unknown. The present study investigates the fixation strength of a modified iliac (MI) screw, which has a more medial entry point and reduced screw prominence, but does not cross the alar-iliac joint. Eighteen sacropelvic spines were divided into 3 groups (n= 6): TI, S2AI, and MI. Each specimen was fixed unilaterally with S1 pedicle screws and pelvic fixation according to its group. Screws were loaded at ±10 Nm at 3Hz for 1000 cycles. Motion of each screw and rod strain above and below the S1 screw was measured. Toggle of the S1 screw was lowest for the TI group, followed by the MI and S2AI groups, but there were no significant differences (P= 0.421). Toggle of the iliac screw relative to the pelvis was also lowest for the TI group, followed by the MI group, and was greatest for the S2AI group, without significant differences (P= 0.179). Rod strain was similar across all groups. No statistically significant differences were found between the TI, S2AI, and MI techniques with regard to screw toggle or rod strain. Advantages of the MI screw include its lower profile and a medialized starting point eliminating the need for offset-connectors.

Simultaneous Robotic Single Position Oblique Lumbar Interbody Fusion With Bilateral Sacropelvic Fixation in Lateral Decubitus.

Single position lateral fusion reduces the need for a secondary surgery and robotic guidance allows for potentially higher accuracy of screw placement. We expand the role of robotics with a simultaneous workflow where 2 surgeons can work in single position surgery and discuss the technical feasibility of placement of S2-alar-iliac (S2AI) screws in the lateral position. A 70-year-old male presented with chronic back pain and bilateral leg pain with the left side worse than the right. He subsequently underwent an L3–S1 oblique lumbar interbody fusion (OLIF) with a minimally invasive L3-ilium robotic posterior spinal fixation simultaneously in single lateral position with S2AI screws. The software planning requisite of robotics allowed for a preoperative plan where lumbar cortical screws were used to line up with bilateral S2AI screws. Intraoperatively, the OLIF was performed anterior to the patient which allowed for a second surgeon to perform the posterior stage of screw placement simultaneously in overlapping fashion during OLIF exposure. Once all screws were placed, the OLIF discectomy and cage placement were completed. As the OLIF incision is closed, rodding proceeds posteriorly with subsequent closure simultaneously as well. Operative time from skin incision to skin closure was 3 hours and 47 minutes. We present here a novel technical report on the recommended workflow of simultaneous robotic single position surgery OLIF and demonstrate the feasibility of placement of sacroiliac fixation in the lateral decubitus position. We believe this technique to be minimally invasive, effective, with the benefit of shortening valuable operating room case time.

An early experience of lumbopelvic fixation techniques at Alexandria University

BackgroundThe aim of lumbopelvic fixation is to obtain a solid fusion across the lumbosacral junction. There are many indications for lumbopelvic fixation, namely, spinal deformity in cases requiring long segment fusion, pelvic obliquity, pseudarthrosis at the lumbosacral junction, infection or osteolytic tumors, and pathologic fractures. The classical iliac screws should be contained within the iliac bone but have some disadvantages: excessive soft tissue dissection needed for accurate insertion, screw prominence with patient discomfort, and usually, a side connector is needed to connect the iliac screws to the rest of the construct. Lumbopelvic fixation by insertion of S2 alar-iliac (S2AI) screws was recently described to overcome these disadvantages. In this study, the authors present the initial results for the evaluation of lumbopelvic fixation through the insertion of S2AI screws in 19 consecutive patients operated in the neurosurgery department at Alexandria University.ObjectiveThe aim of the study was to evaluate the efficacy and complications of lumbopelvic fixation through the use of S2 alar-iliac screws.MethodsThe authors conducted a retrospective cohort study of data collected from the database of patients who underwent lumbopelvic fixation through the insertion of S2AI screws from 2016 to 2019 at a single institution.ResultsThere were 19 patients indicated for lumbopelvic fixation, operated by modern instrumentation systems using lumbar pedicle screws and S2 alar-iliac screws. There were 14 females and 5 males. The mean age at the time of the operation was 38.6 ± 19.4 years with a range from 11 to 65 years. There was a total of 37 S2AI screws, screw diameter was 7mm in all cases regardless of age, and the length of the screws ranged from 50 mm in a young female patient (11 years) to 90 mm in an old male patient (60 years). Two screws were inserted per patient except in one case with congenital scoliosis due to the bad bone quality and the multiple iatrogenic wrong paths. Postoperative VAS score for back pain was greatly improved in all patients after the first 6 months of follow-up from 8 ± 1.5 to 3.5 ± 1.2 (paired t-test = 11.182, P<0.001). All patients had a good spinal range of motion to maintain normal daily activities without any significant restrictions after the first 3 months of follow-up. Immediate postoperative radiological follow-up had revealed 2 cases of posterior pelvic breaches and one case with anterior pelvic breach but without clinical manifestations with no need for revision. Two cases of unilateral screw breakout were observed after the first 6 months of follow-up. Removal of screws after the first 6 months was done in one patient with spondylodiscitis due to the unresolved infection and screw pullout.ConclusionThe insertion of S2AI screws is an effective technique for lumbopelvic fixation with a relatively low rate of complications. Pelvic breaches are the commonest complications encountered during the insertion of S2AI screws, although no significant clinical morbidities were reported.

Robotic-assisted percutaneous iliac screw fixation for destructive lumbosacral metastatic lesions: an early single-institution experience.

Robotic-assisted surgery is becoming more widely applied in surgical subspecialties due to its intraoperative and postoperative advantages such as minimally invasive approach, reduced blood loss, shorter hospital stay, and decreased incidence of postoperative complications. However, robotic devices were only recently introduced in the field of spinal surgery. Specifically, percutaneous approaches involving computer-assisted image guidance are relatively new in iliac screw fixation. Previous methods focused on the use of S2-alar-iliac (S2AI) screw fixation which allows for pelvic fixation without a need for side connectors. However, for patients with destructive lesions of the sacrum, placement of these S2AI screws may not be feasible. The purpose of this technical note is to illustrate the implementation of robotic-assisted percutaneous iliac screw fixation in two cases which allows for minimally invasive attachment to the proximal lumbar screws without a side connector and eliminates a potential source of instrumentation failure. Robotic-assisted percutaneous iliac screw fixation was performed on two patients. The robotics system was used to merge the fluoroscopic images with intraoperative computed tomography (CT) images to plan the trajectories for placement of bilateral pedicle and iliac screws. Intraoperative CT scan was again performed to confirm proper placement of all screws. Rods were then engaged bilaterally with the pedicle and iliac screws without the use of side connectors. The patients did not experience immediate postoperative complications and had stable hardware at one-month follow-up. Our cases demonstrate the surgical efficiency of robotic-assisted lumbo-iliac instrumentation which obviates the need to use a side connector, which is commonly used in iliac fixation. This eliminates a step, which can reduce the possibility of instrumentation failure. Robotic-assisted percutaneous iliac screw fixation is a safe and feasible technique to improve operative and clinical outcomes in complex spinal instrumentation surgeries.

Different distal fixation anchors in lumbosacral spinal deformities associated with sacral agenesis: which one is better?

Sacral agenesis (SA) is a rare congenital malformation of the spine. There has been a paucity of clinical research to investigate the surgical outcome of spinopelvic fixation in these patients. In this study, the authors aimed to evaluate the outcome of different distal fixation anchors in lumbosacral spinal deformities associated with SA and to determine the optimal distal fixation anchor. Patients with diagnoses of SA and lumbosacral scoliosis undergoing spinopelvic fixation with S1 screws, iliac screws, or S2-alar-iliac (S2AI) screws were analyzed. The main curve, coronal balance distance, and pelvic obliquity were compared at baseline, postoperatively, and during follow-up in three groups. The complications were also recorded. A total of 24 patients were included: 8 patients were stratified into group 1 (S1 screws), 9 into group 2 (iliac screws), and 7 into group 3 (S2AI screws). The main curves were well corrected postoperatively (p < 0.05) in all groups. Coronal balance showed a tendency of deterioration during follow-up in patients with S1 screws (from 18.8 mm to 27.0 mm). Regarding pelvic obliquity, patients with both iliac and S2AI screws showed significant correction (from 3.7° to 2.3° and from 3.3° to 1.6°). Implant-related complications were rod breakage in 3 patients and infection in 1 patient in group 2, and no implant-related complications were observed in group 3. There were 3 cases of unilateral S1 pedicle screw misplacement in group 1. Spinopelvic fixation is a safe and effective procedure that can achieve coronal correction in lumbosacral scoliosis associated with SA. Compared with S1 and iliac screws, S2AI screws as distal fixation anchors can achieve a more satisfactory correction with fewer implant-related complications.

Iliac Screw Fixation Revisited: Improved Clinical and Radiologic Outcomes Using a Modified Iliac Screw Fixation Technique.

A retrospective study. To describe the modified iliac screw (mILS) technique and compare it to other spinopelvic fixation techniques in terms of wound healing complications, hardware prominence, and failure. The traditional entry point of an iliac screw often causes postoperative gluteal pain from the prominent screw head. The use of an offset connector also adds a point of weakness to the construct. By choosing a different screw entry point offset connectors can be avoided, and the screw head itself is less prominent, thereby reducing postoperative discomfort. A retrospective analysis was performed of adult patients undergoing lumbopelvic fixation (LPF) between January 2014 and June 2019. Patients were grouped into 1 of 3 groups based on the technique of pelvic fixation: S2 alar-iliac (S2AI) screw, traditional iliac screw (tILS), and mILS. The primary outcome parameter was the minimal distance from screw head to skin. Secondary outcome parameters were instrumentation loosening/failure, adjacent level fractures, pseudoarthrosis, and medial or lateral iliac screw perforation. A total of 190 patients undergoing LPF were included in the following 3 groups: mILS group (n=113), tILS group (n=40), and S2AI group (n=37). The mean minimal distance from screw head to skin in the mILS group was 31.3 mm compared with 23.7 mm in the tILS group (P<0.00199). No statistically significant differences were found when comparing the 3 groups with respect to complications. The mILS group did not show any cases of prominent instrumentation and had the lowest rate of instrumentation failure. The mILS technique is an acceptable alternative for LPF, offering the benefits of iliac screw fixation while avoiding offset connectors and screw prominence complications associated with tILS. Level III.

Sacroiliac joint arthropathy in adult spinal deformity patients with long constructs to the pelvis

ObjectiveSacroiliac joint (SIJ) arthropathy is an increasingly recognized problem in adult spinal deformity patients undergoing long construct surgery. S2-alar-iliac (S2AI) screw instrumentation is thought to reduce morbidity from pelvic fixation in these patients. The goal of this study is to assess the overall incidence of SIJ arthropathy in patients with long constructs to the pelvis as well as compare SIJ outcomes of partially threaded (PT) versus fully threaded (FT) S2AI screws. MethodsData of eligible patients were collected from a prospectively maintained database with retrospective review of electronic records at an academic institution between 2016 and 2019. Results65 consecutive patients who underwent S2AI screw instrumentation (40 in PT group, 25 in FT group) were enrolled. The rate of postoperative SIJ pain was higher in the PT (52.5 %) compared to FT (32 %) group. There was a significantly shorter time-to-pain development in the PT compared to FT group (11.8 versus 20.1 months, respectively). Of those who developed SIJ pain in the PT group, the pain worsened in 80.9 % versus only 25 % of those in the FT group despite conservative treatment. Cox regression found the PT group more likely to develop SIJ pain at any point during follow-up compared to the FT group (Hazard Ratio = 7.308). SIJ fusion was not detected on imaging of any patient during follow-up. ConclusionFT S2AI screws are associated with better SIJ outcomes compared to PT screws. However, our data suggest that S2AI screw instrumentation is not sufficient to achieve fusion or prevent development of SIJ pain. Concurrent SIJ fusion may be necessary in patients with long constructs to prevent SIJ arthropathy.