Sacral Alar Iliac Research Articles

Implantation of S1AIS has priority as a sacroiliac joint fixation technique.

The sacral alar-iliac screw (SAIS) fixation technique has evolved from spinopelvic fixation which originated from S2AIS to sacroiliac joint fixation, with more reports regarding its application of S2AIS than S1AIS. However, there is a lack of comparative evidence to determine which technique is superior for sacroiliac joint fixation. This study aimed to determine which of the screws was superior in terms of implantation safety and biomechanical stability for sacroiliac joint fixation. CT data of 80 normal pelvises were analyzed to measure the insertable range, trajectory lengths and widths of both S1AIS and S2AIS on 3D reconstruction models. Φ 6.5mm and 8.0mm screws were implanted on the left and right sides of fifty 3D printed pelvic models respectively to observe for breach of screw implantation. Ten synthetic pelvis models were used to simulate type C Tile injuries, and divided into 2 groups with an anterior plate and posterior fixation using one S1AIS or S2AIS on each side. The stiffness and maximum load of the plated and fixated models were measured under vertical loading. The trajectory lengths and widths of the S1AIS and S2AIS were similar (p > 0.05) and there was no breach for Φ 6.5mm SAIS. However, both the insertable range and trajectory length on the sacral side of S2AIS (234.56 ± 10.06mm2, 40.97 ± 2.81mm) were significantly less, and the breach rate of the posterior lateral cortex of the Φ 8.0mm S2AIS (46%) was significantly higher than the S1AIS (307.55 ± 10.42 mm2, 42.16 ± 3.06mm, and 2%, p < 0.05). The stiffness and maximum load of S2AIS were less than S1AIS but the difference was not statistically significant (p > 0.05). S1AIS and S2AIS have similar screw trajectories and stability. However, S1AIS has a larger insertable range, less breach of the posterior lateral sacral cortex and longer trajectory length on the sacral side than S2AIS, which indicates S1AIS has higher implantation safety and a trend of better mechanical performance over S2AIS for sacroiliac joint fixation. Furthermore, S2AIS with an excessively large diameter should be used with caution for sacroiliac joint fixation.

Distal sacral nerve roots severed by a fragility fracture of the sacrum: a case report

BackgroundOwing to the aging population, fragility fractures of the pelvis are occurring more frequently. Fixation of the fracture and stabilization of the pelvic ring usually provide good clinical results. A case of distal sacral nerve roots severed by a fragility fracture of the sacrum is presented.Case presentationA 62-year-old Japanese woman with schizophrenia with low back pain, gait disorder, dysuria, and fecal incontinence presented to an emergency department, and plain X-rays showed no findings. She also complained of dysuria, and neurogenic bladder and cystitis were diagnosed. One month later, she was admitted to a psychiatric hospital for exacerbation of schizophrenia. In hospital, she had a urethral catheter inserted and spent 3 months in bed. She was referred to our orthopedic department because a gait disorder was discovered after her mental condition improved and she was permitted to walk. On examination, she could not walk and had decreased sensation from the buttocks to both posterior thighs and around the anus and perineum. Manual muscle testing of her lower limbs showed mild weakness of about 4 in bilateral flexor hallucis longus and gastrocnemius, and bilateral Achilles tendon reflexes were lost. Her anal sphincter did not contract, and urinary retention continued after urethral catheter removal. Imaging examinations showed an H-shaped sacral fracture consisting of a transverse fracture with displacement of the third sacral vertebra and vertical fractures of the bilateral sacral wings, with severe stenosis of the spinal canal at the site of the transverse fracture. The patient was diagnosed as having bladder and rectal dysfunction due to a displaced, unstable sacral fracture. First to third sacral laminectomy and alar–iliac fixation using percutaneous pedicle screws and sacral alar–iliac screws were then performed. The bilateral distal sacral nerve roots (S3, S4, S5) were completely severed at the second to third sacral levels, but bilateral second sacral nerve roots were not compressed from the bifurcation to the sacral foramen. Postoperatively, bladder and rectal dysfunction remained, but the low back pain was alleviated. Two weeks postoperatively, she could walk with a walker and was discharged. Three months after the operation, bone fusion of the fracture was observed.ConclusionsIn cases of bladder–rectal dysfunction with low back pain, the possibility of sacral fracture should be considered, and computed tomography, magnetic resonance imaging, and X-ray examinations should be performed. Even sacral fractures without displacement require attention because they can cause serious injury in the event of a nerve root being severed if not diagnosed early and given appropriate treatment.

Effect of pelvic fixation on ambulation in children with neuromuscular scoliosis.

BACKGROUNDThe effect of posterior spinal fusion (PSF) incorporating the pelvis on an ambulatory patient’s ability to mobilize after the fusion is not well understood. AIMTo see whether a posterior spinal fusion with pelvic fixation using iliac or sacral alar iliac screws in ambulatory neuromuscular scoliosis (NMS) patients influences postoperative ambulatory ability.METHODSA retrospective review of all patients with NMS that underwent PSF with fixation incorporating the pelvis between January 1, 2012 and February 29, 2019. A total of 118 patients were eligible, including 11 ambulatory patients. The primary outcome was the maintenance of ambulatory status postoperatively. Secondary outcomes included postoperative curve magnitude, pelvic obliquity, and complications, comprising infections, instrumentation failure, and any unplanned returns to the operative room.RESULTSThe ambulatory function was maintained in all 11 ambulatory NMS patients. One patient had an improvement in functional status with equipment-free ambulation postoperatively. An average postoperative follow-up was 19 mo. The overall complication rate was 19.4% (n = 23) with no significant differences between the groups in infection (P = 0.365), hardware failure (P = 0.505), and reoperation rate (P = 1.0). Ambulatory status did not affect complication rate (P = 0.967).CONCLUSIONSpinal fusion to the pelvis in ambulatory patients with NMS provides effective deformity correction without the reduction in ambulatory capabilities.

Sacral-Alar-Iliac (SAI) Fixation in Children With Spine Deformity: Minimum 10-Year Follow-Up.

Sacral-alar-iliac (SAI) screws are utilized to achieve pelvic fixation in spine deformity patients. The primary purpose of this study is to investigate the long-term outcomes of pediatric patients with scoliosis treated with posterior spinal fusion and SAI fixation at 10-year clinical and radiographic follow-up. We reviewed the clinical and radiographic records of patients aged 18 years or below treated for scoliosis with posterior spinal fusion using SAI fixation. Pelvic obliquity and the major coronal curve were determined at the preoperative visit and 6-week, 1-year, 5-year, and 10-year postoperative visits. SAI screw-specific data collected included screw dimensions, rate of screw revision, pain at the SAI screw sites, presence of lucency >2 mm around the screw, screw loosening or breaking, and deep surgical site infections. Ninety-seven of 151 patients (75%) were included. The average age at index surgery was 13.5±3.1 years, and the most common diagnosis was cerebral palsy (67%). The mean duration of follow-up was 11±3 years. The mean pelvic obliquity measured 20±8.0 degrees preoperatively, and 8.7±4.0 degrees at the 10-year follow-up. There were no significant difference in pelvic obliquity when comparing the 10-year follow-up visit with the 6-week postoperative follow-up. Average screw dimensions were 8.4×68.8 mm. By the 10-year follow-up, 4 patients (4%) had at least 1 SAI screw-related complication. Of these patients, 2 (2%) had pain at 1 SAI screw, 4 (4%) had lucency around the screw, and 3 (3%) had broken or loose screws. Two (2%) required SAI screw revision because of late deep wound infection, and underwent exchange with a longer screw. There were no intrapelvic protrusions, vascular, or neurological complications. SAI screws are a safe and effective method for pelvic fixation in children with spinal deformity. The outcomes at ≥10 years are satisfactory, with low rates of long-term complications and excellent postoperative correction and subsequent maintenance of coronal curvature and pelvic obliquity over time. Level IV.

Pelvic Osteotomy in Patients With Previous Sacral-Alar-Iliac (SAI) Fixation.

Patients with neuromuscular disease are at high risk for developing hip dysplasia and scoliosis. The purpose of this study was to investigate the technical challenges and outcomes of pelvic osteotomy in patients with prior sacral-alar-iliac (SAI) fixation. We reviewed clinical and radiographic records of patients aged 18 years and below who underwent pelvic osteotomy after SAI fixation. We recorded technical challenges during the osteotomy, time from SAI fixation to osteotomy, type of osteotomy, migration index, and distance from the SAI screw to the acetabulum. A 2-sample Wilcoxon rank-sum test was used to assess the data. Nineteen patients were included. Technical challenges were defined as having greater intraoperative fluoroscopy times and noted difficult osteotomy in the operative report. The mean time from SAI fixation to pelvic osteotomy was 2.2±1.5 years. For all 12 Chiari osteotomies, the ilium could not be laterally displaced; however, medial displacement of the distal segment of the osteotomy allowed adequate coverage. All 7 Dega osteotomies were performed by cutting the cortex at the tip of the SAI screw. The screw improved proximal leverage and provided a strong buttress for bone graft. The mean migration index before pelvic osteotomy was 59±19%, and at most recent follow-up was 13±4%. Twelve patients, who had a noted complicated osteotomy, had SAI screws that were ≤1.87 cm ( P <0.01) from the acetabulum and significantly increased intraoperative fluoroscopy time (1.76 vs. 1.18 min, P <0.01). The presence of SAI screws may cause iliac osteotomies to be technically challenging if the tip of the SAI screw is ≤1.87 cm to the acetabulum. When initially implanting SAI screws in neuromuscular patients, surgeons should attempt to place screw tips ∼2 cm from the acetabulum in the event these patients require subsequent pelvic osteotomy. Level IV.

Innovation of Surgical Techniques for Screw Fixation in Patients with Osteoporotic Spine.

Osteoporosis is a common disease in elderly populations and is a major public health problem worldwide. It is not uncommon for spine surgeons to perform spinal instrumented fusion surgeries for osteoporotic patients. However, in patients with severe osteoporosis, instrumented fusion may result in screw loosening, implant failure or nonunion because of a poor bone quality and decreased pedicle screw stability as well as increased graft subsidence risk. In addition, revision surgeries to correct failed instrumentation are becoming increasingly common in patients with osteoporosis. Therefore, techniques to enhance the fixation of pedicle screws are required in spinal surgeries for osteoporotic patients. To date, various instrumentation methods, such as a supplemental hook, sublaminar taping and sacral alar iliac screws, and modified screwing techniques have been available for reinforcing pedicle screw fixation. In addition, several materials, including polymethylmethacrylate and hydroxyapatite stick/granules, for insertion into prepared screw holes, can be used to enhance screw fixation. Many biomechanical tests support the effectiveness of these augmentation methods. We herein review the current therapeutic strategies for screw fixation and augmentation methods in the surgical treatment of patients with an osteoporotic spine.

Sacral-Alar-Iliac (SAI) Fixation in Patients With Previous Pelvic Osteotomy.

This was a retrospective study. The purpose of this study was to investigate the technical challenges and outcomes of sacral-alar-iliac (SAI) fixation for scoliosis in patients who had previously undergone a pelvic osteotomy for hip dysplasia. Patients with neuromuscular disease are at high risk for developing hip dislocation and scoliosis. Surgical correction of one may affect the other. We reviewed the records of patients aged 18 years and below who underwent spinal fusion using SAI screws after having undergone a pelvic osteotomy, with ≥2-year follow-up. We recorded the SAI screw dimensions, time from osteotomy to SAI fixation, type of osteotomy, and any complications performing SAI fixation due to the pelvic osteotomy. Bivariate statistics were used to analyze the data with statistical significance defined as P -value <0.05. Thirty-two patients were included. The average age was 10.3±3.2 years at pelvic osteotomy and 13.5±3.4 years at SAI fixation. Most patients had cerebral palsy (87.5%) and a unilateral Dega osteotomy (78.1%). Average screw dimensions were significantly shorter on the side of the osteotomy (66 vs. 72 mm, P <0.05). SAI screw placement was technically challenging in 8 patients (25%), due to pelvic distortion from the pelvic osteotomy. The use of a curved awl helped to find the intracortical channel. No patients had complications due to the SAI screw, and there were no significant differences in pelvic obliquity and major coronal curve correction. Two patients (6.3%) had screw lucency >2 mm around the SAI screw on the side of the pelvic osteotomy but no clinical symptoms. SAI fixation in patients with previous pelvic osteotomy is technically challenging due to pelvic morphology and prior implants. Often, a shorter SAI screw is required on the side of the osteotomy. However, outcomes in this patient population are satisfactory, with no significant complications at a 2-year follow-up. Level IV.

Three-Dimensional Analysis of the Ideal Entry Point for Sacral Alar Iliac Screws.

This is a virtual three-dimensional (3D) imaging study examining computed tomography (CT) data to investigate instrumentation placement. In this study, we aim to clarify the ideal entry point and trajectory of the sacral alar iliac (SAI) screw in relationship to the dorsal foramen at S1 and the respective nerve root. To the best of our knowledge, there is yet no detailed 3D imaging study on the ideal entry point of the SAI screw. Despite the evidence suggesting that the dorsal foramen at S1 is a landmark on the sacrum, the S1 nerve root disruption is a general concern during the insertion of SAI screws. No other study has been published examining the nerve root location at the S1and SAI screw insertions. Preoperative CT data from 26 patients pertaining to adult spinal deformities were investigated in this study. We applied a 3D image processing method for a detailed investigation. Virtual cylinders were used to mimic SAI screws. These were placed to penetrate the sacral iliac joint without violating the other cortex. We then assessed the trajectory of the longest SAI screw and the ideal entry point of SAI using a color mapping method on the surface of the sacrum. We measured the location of the nerve root at S1 in relation to the foramen at S1 and the sacral surface. As per the results of our color mapping, it was determined that areas that received high scores are located medially and caudally to the dorsal foramen of S1. The mean angle between a horizontal line and a line connecting the medial edge of the foramen and nerve root at S1 was 93.5°. The mean distances from the dorsal medial edge of the foramen and sacral surface to S1 nerve root were 21.8 mm and 13.9 mm, respectively. The ideal entry point of the SAI screw is located medially and caudally to the S1 dorsal foramen based on 3D digital mapping. It is also shown that this entry point spares the S1 nerve root from possible iatrogenic injuries.

Complication Profiles Associated with Sacral Alar Iliac Screw Fixation in Patients with Adult Spinal Deformity: A Comparative Analysis to the Conventional Iliac Screw Fixation

Objective: This study aimed to compare the radiographic and clinical outcomes between sacral alar iliac (SAI) screw fixation and conventional iliac (CI) screw fixation with a particular focus on the rate of reoperation, surgical site infection (SSI), sacroiliac joint pain, instrument failure, and screw prominence.Methods: Patients who underwent sacropelvic fixation in the authors’ institution from June 2011 to May 2017 were retrospectively investigated. Forty-three patients with SAI screw fixation and 25 with CI screw fixation were included. Preoperative patient and surgical characteristics and postoperative outcomes and complications were analyzed between the SAI and CI groups. Radiographic parameters were analyzed before and after surgery.Results: Lumbosacral fusion rates showed no statistically significant difference between the SAI group and CI groups (90.7% vs. 92.0%, p=0.878). The SAI group showed a significantly good result with regard to SSI compared to the CI group (0% vs. 16%, p=0.016), but had a significantly higher rate of distal screw fracture than the CI group (16.3% vs. 0%, p=0.042).Conclusion: The SAI screw fixation technique could achieve good outcomes of pain relief, deformity correction, and lumbosacral fusion rate with relatively lower complications such as the rates of reoperation, SSI, and screw prominence as compared to the CI screw fixation technique. However, distal instrument failure was observed more frequently in the SAI group, requiring further biomechanical studies.

Comparative Study of Bilateral Dual Sacral-Alar-Iliac Screws versus Bilateral Single Sacral-Alar-Iliac Screw for Adult Spine Deformities

To evaluate the feasibility of O-arm navigation of bilateral dual sacral-alar-iliac (SAI) screws compared with conventional bilateral single SAI and S1 pedicle screws for pelvic anchors in cases of adult spinal deformity. This retrospective, comparative study included 39 patients who underwent corrective fusion using SAI screws from T10 to the pelvis. Patients were divided into 2 groups according to the number of SAI screws placed during adult spinal deformity surgery: single SAI screw (group S, 17 cases) and dual SAI screws (group D, 22 cases). The incidence of rod breakage, proximal junctional kyphosis, screw loosening, reoperation, and global alignment in each group was estimated. Postoperative patient-reported outcomes were measured using the Oswestry Disability Index, Japanese Orthopaedic Association Back Pain Evaluation Questionnaire, and visual analog scale. The incidence of SAI screw loosening was significantly lower in group D than in group S (23% vs. 65%, P= 0.011). The rod breakage incidence was 0% and 12% in groups D and S, respectively (P= 0.17). There were no significant differences in the postoperative global alignment and clinical outcomes between the 2 groups. Dual SAI screws were associated with a significantly reduced incidence of screw loosening compared with single SAI screws. The bilateral dual SAI screws technique for pelvic anchors is feasible for the treatment of patients with adult spinal deformity.

246. Is the implant in bone? The accuracy of CT and fluoroscopic imaging for detecting malpositioned pelvic screw and SI fusion implants

Spine fusions to the pelvis have been associated with increased strain to the sacroiliac joint (SI) and possibly continued postoperative low back pain. To minimize this, concomitant SI joint fusion at the time of lumbopelvic fixation has been advocated. This requires concomitant placement of sacral alar iliac screws (S2AI) for lumbopelvic fixation and triangular titanium rods (TTR) for the SI joint fusion. Traditionally, surgeons have mostly relied on fluoroscopic images to confirm final implant position and patient safety after pelvic instrumentation, although computer tomography (CT) has also been used.We wanted to know which imaging modality, if any, was superior in helping to identify malpositioned implants during concomitant lumbopelvic fixation and SI joint fusion. We instrumented pelvic sawbones models with S2AI screws, TTR's, or both in the correct anatomic positions or malpositioned variants that led to known cortical breaches. Pelvic models were then imaged with fluoroscopy and CT, and the images assessed by blinded reviewers (spine surgeons and a musculoskeletal radiologist) for the presence of cortical breaches, the identity of the breached implant, and its direction. The responses of the blinded reviewers were then compared to the known position of the implants and Kappa coefficient calculated to determine agreement.We found that thorough evaluation of implant position with multiple fluoroscopic views (kappa 0.641) or CT imaging (kappa 0.906) allowed reviewers to assess implant position, identity, and breach direction.These findings suggest that intraoperative CT imaging allows surgeons to make the best decision regarding implant position prior to leaving the operating room, thus potentially improving patient safety and unplanned returns to the operating room.Level of Evidence: V.

Spinal Fusion with Sacral Alar Iliac Pelvic Fixation in Severe Neuromuscular Scoliosis.

We demonstrate how to perform posterior spinal fusion with SAI pelvic fixation in a patient with cerebral palsy. In correcting the scoliosis, we utilize the segmental 3-dimensional technique, which includes compression, distraction, transverse approximation to 1 rod at a time, and derotation around 2 rods. We also demonstrate SAI pelvic fixation with identification of the screw starting point on the lateral-caudal border of the first sacral foramen and trajectory toward the anterior inferior iliac spine. Nonoperative alternatives include bracing, trunk support, contouring of sitting surfaces (such as wheelchairs), and physical therapy to slow curve progression during growth periods and delay the need for surgical treatment3,4. Decision-making is shared with the family following education about the risks and benefits. Families who are satisfied with the function of the child at baseline should not be persuaded into pursuing surgical treatment. Neuromuscular scoliosis can include difficulty sitting secondary to increased pelvic obliquity, along with poor trunk control and balance. Surgical intervention is considered in patients with curves exceeding approximately 50°, as these curves will often continue to progress even after maturity5. In patients with neuromuscular scoliosis, indications for pelvic fixation include pelvic obliquity of >15°, poor control of the trunk as indicated by lack of independent sitting or standing, and location of the apex of the curve in the lumbar spine. SAI screws are utilized as a low-profile option for pelvic fixation to avoid implant prominence and an increased risk of skin breakdown and infection, which are associated with traditional sacroiliac screws2,6. Miyanji et al. reported quality outcomes in patients with cerebral palsy and Gross Motor Function Classification Scores of ≥41. In that study, caregivers completed a validated disease-specific questionnaire grading the health-related quality of life of the patient preoperatively and at 1, 2, and 5 years postoperatively. Complication data were prospectively collected for each patient and preoperative outcome scores were compared at each of the postoperative time points. Survey scores at 1, 2, and 5 years postoperatively were significantly higher compared with baseline preoperative values.Sponseller et al. compared the 2-year postoperative radiographic parameters of 32 pediatric patients who underwent SAI fixation and 27 patients who underwent pelvic fixation with the sacroiliac technique2. Among patients who underwent SAI fixation, the mean correction of pelvic obliquity was 20° ± 11° (70% correction) and the mean Cobb angle 42° ± 25° (67%). Among patients who underwent pelvic fixation with the sacroiliac technique, those values were 10° ± 9° (50%) and 46° ± 16° (60%), respectively. SAI screws provided significantly better pelvic obliquity correction (p = 0.002) but no difference in Cobb correction or complications compared with other traditional techniques. Family discussion prior to surgical treatment is paramount.Perform preoperative neurologic examination7.Examine the cranium carefully for a ventriculoperitoneal shunt or prior cranial reconstruction prior to cranial traction.Transcranial neuromonitoring may be useful. Use descending neural motor evoked potentials when no signals from transcranial monitoring are obtained8.Sink the SAI screw until it lines up with the S1 screw. Bury the SAI screw so it is not prominent.Measure rods longer in order to ensure adequate length for compression and distraction in correction of the pelvic obliquity.Use a T-square to verify adequate spinopelvic alignment9.Postoperatively, the use of incisional vacuum-assisted closure can decrease soiling in these patients. SAI = Sacral alar iliacCP = Cerebral palsyAIS = Adolescent idiopathic scoliosisSMA = Spinal muscular atrophyIONM = Intraoperative neuromonitoringGMFCS = Gross Motor Functional Classification SystemDNMEP = Descending neural motor evoked potentialTXA = Tranexamic acidFFP = Fresh frozen plasmaASIS = Anterior superior iliac spineAIIS = Anterior inferior iliac spinePJK = Proximal junctional kyphosis.

Novel Technique for Sacral-Alar-Iliac Screw Placement Using Three-Dimensional Patient-Specific Template Guide.

Introduction The sacral-alar-iliac (SAI) screw technique is becoming popular for sacropelvic fixation. However, appropriately placing SAI screws is technically demanding because of a narrow safe corridor and the risk of neurovascular/visceral injuries. Recently, a three-dimensional patient-specific template guiding technique for pedicle screw placement has been considered a promising method to improve accuracy and safety. The objective of the present study was to investigate the accuracy of SAI screw placement with a patient-specific template guide using cadaveric and prospective clinical pilot studies. Methods Three-dimensional planning of SAI screw placement, including entry point, screw trajectory, length, and diameter, was performed using a computer simulation software. Then, three-dimensional printed patient-specific template guides were created based on the plan. Firstly, a total of 12 SAI screws were placed for 6 cadaveric specimens using the guides. Next, in a prospective clinical trial, a total of 20 SAI screws were placed for 10 consecutively enrolled patients. The safety and accuracy of screw placement were analyzed using postoperative computed tomography by the evaluation of any cortical breach and measurement of screw deviations between the planned and actual screw positions. Results All the screws showed no perforation. In the cadaveric study, the mean horizontal and vertical deviations from the planned screw position at the entry point were 1.40±1.21 mm and 1.34±1.09 mm, respectively. The mean angular deviations in the sagittal and transverse planes were 1.68°±1.24° and 1.53°±1.06°, respectively. The results of the clinical study showed comparable accuracy with those of the cadaveric study, except for the vertical deviation at the entry point (p=0.048). Conclusions This is the first study to evaluate the feasibility and accuracy of using a patient-specific template guide for SAI screw placement. This technique could become an effective solution to achieve accurate screw placement.

Augmented Reality Navigated Sacral-Alar-Iliac Screw Insertion

Sacral-alar-iliac (SAI) screws are increasingly used for lumbo-pelvic fixation procedures. Insertion of SAI screws is technically challenging, and surgeons often rely on costly and time-consuming navigation systems. We investigated the accuracy and precision of an augmented reality (AR)-based and commercially available head-mounted device requiring minimal infrastructure. A pelvic sawbone model served to drill pilot holes of 80 SAI screw trajectories by 2 surgeons, randomly either freehand (FH) without any kind of navigation or with AR navigation. The number of primary pilot hole perforations, simulated screw perforation, minimal axis/outer cortical wall distance, true sagittal cranio-caudal inclination angle (tSCCIA), true axial medio-lateral angle, and maximal screw length (MSL) were measured and compared to predefined optimal values. In total, 1/40 (2.5%) of AR-navigated screw hole trajectories showed a perforation before passing the inferior gluteal line compared to 24/40 (60%) of FH screw hole trajectories (P < .05). The differences between FH- and AR-guided holes compared to optimal values were significant for tSCCIA with -10.8° ± 11.77° and MSL -65.29 ± 15 mm vs 55.04 ± 6.76 mm (P = .001). In this study, the additional anatomical information provided by the AR headset and the superimposed operative plan improved the precision of drilling pilot holes for SAI screws in a laboratory setting compared to the conventional FH technique. Further technical development and validation studies are currently being performed to investigate potential clinical benefits of the AR-based navigation approach described here. 4.

Combination of sacral-alar-iliac screw and cortical bone trajectory screw techniques for lumbosacral fixation: technical note.

Lumbosacral fixation plays an important role in the management of devastating spinal pathologies, including osteoporosis, fracture, infection, tumor resection, and spinal deformities, which require long-segment fusion constructs to the sacrum. The sacral-alar-iliac (SAI) screw technique has been developed as a promising solution to facilitate both minimal invasiveness and strong fixation. The rationale for SAI screw insertion is a medialized entry point away from the ilium and in line with cranial screws. The divergent screw path of the cortical bone trajectory (CBT) provides a higher amount of cortical bone purchase and strong screw fixation and has the potential to harmoniously align with SAI screws due to its medial starting point. However, there has been no report on the combination of these two techniques. The objective of this study was to assess the feasibility of this combination technique. The subjects consisted of 17 consecutive patients with a mean age of 74.2 ± 4.7 years who underwent posterior lumbosacral fixation for degenerative spinal pathologies using the combination of SAI and CBT fixation techniques. There were 8 patients with degenerative scoliosis, 7 with degenerative kyphosis, 1 with an osteoporotic vertebral fracture at L5, and 1 with vertebral metastasis at L5. Fusion zones included T10-sacrum in 13 patients, L2-sacrum in 2, and L4-sacrum in 2. No patients required complicated rod bending or the use of a connector for rod assembly in the lumbosacral region. Postoperative CT performed within a week after surgery showed that all lumbosacral screws were in correct positions and there was no incidence of neurovascular injuries. The lumbosacral bone fusion was confirmed in 81.8% of patients at 1-year follow-up based on fine-cut CT scanning. No patient showed a significant loss of spinal alignment or rod fracture in the lumbosacral transitional region. This is the first paper on the feasibility of a combination technique using SAI and CBT screws. This technique could be a valid option for lumbosacral fixation due to the ease of rod placement with potential reductions in operative time and blood loss.

S3 Sacral-Alar Iliac Screw: A Salvage Technique for Pelvic Fixation in Complex Deformity Surgery

Sacral-alar iliac (SAI) screws constitute a relatively new technique for pelvic fixation. Since their initial description in 2007, SAI screws have gained wide popularity among the spine surgery community. In 2013, we first described the possibility of using both S1 and S2 SAI screws for pelvic fixation in revision surgeries for adult degenerative scoliosis. Although a previous radiological study has suggested the feasibility of S3 and S4 SAI screws, to the best of our knowledge, there has been no report in the literature on the clinical use of such techniques. In this brief technical note, we present the first clinical report of the use of S3 SAI screws as a salvage method for pelvic fixation in a patient with suboptimal anatomy that prevented proper placement of S1 and S2 SAI screws. We also discuss the recommended anatomical entry points and trajectory of such screws.

Pedicle screw instrumentation with or without pelvic fixation in neuromuscular scoliosis: Outcome and complications in a series of 37 patients with a minimum 2-year follow-up

ObjectiveNeuromuscular scoliosis (NMS) is often associated with rapid progressive spinal deformities. Indications, when to extend the instrumentation to the pelvis for pelvic obliquity are not generally accepted at this time. This study reports on the indications, surgical technique and results using pedicle screw instrumentation exclusively with or without pelvic fixation for spine fusion in patients with NMS. Patients and methodsThirty-seven NMS patients were treated with pedicle screw instrumentation (PSI) between 2007 and 2013 with a minimum follow-up of 24 months. The mean age at the time of operation was 14.91 ± 2.03 years (range, 11.17–18.58). Posterior spine fusion (PSF) was conducted in 33 patients; 4 patients underwent a combined anterior spinal release followed by PSF during one-stage surgery. Pelvic fixation was achieved by ilium screws combined with S-1 screws in 4 cases and by sacral-alar-iliac (SAI) technique by Sponseller in 9 cases, respectively. ResultsThe mean primary Cobb angle was 65.5° (range, 14–103°) and improved significantly to 19.8° (range, 1–50°, p < 0.001) after surgery and 20.5° (range, 3–57, p = 0.47) at 2 years FU, respectively. Besides, an improvement of pelvic obliquity and T1 tilt angle could be detected. Major complications occurred in 19% and minor complications in 32%. ConclusionPedicle screw fixation only for spine fusion in patients with NMS can be applied safely with reasonable complication rates. An excellent correction in all planes, a significant improvement of the pelvic obliquity and almost no loss of correction at 2 years FU were observed.

Morphometric measurement and applicable feature analysis of sacral alar-iliac screw fixation using forward engineering.

To evaluate S1AI-S4AI screw channels with three-dimensional digital technology simulation analysis and to study the feasibility and applicable features of sacral alar-iliac screw fixation in adults. Forty (20 men and 20 women) normal adult's pelvic CT scan data sets were selected to reconstruct the three-dimensional pelvic model. The ideal S1AI-S4AI screw channels were simulated, followed by precise measurement of their parameters. The results showed that there were no significant differences in the transverse angles, sagittal angles, radiuses of the maximal inscribed circles, or lengths of the screw channels in S1AI-S2AI screws between genders (P > 0.05). In contrast, the radiuses of the maximal inscribed circles on the left and right, respectively, were 5.93 ± 1.02mm and 5.92 ± 1.04mm in males and 4.64 ± 0.98mm and 4.59 ± 0.95mm in females, and there was a significant difference in S3AI screws between genders (P < 0.05). With a radius of 2.50mm considered to be standard, there were 25 cases (62.5%) with an S4AI screw channel radius ≤ 2.50mm in 40 adults, and 15 cases (37.5%; 9 males and 6 females) with a radius > 2.50mm. Furthermore, the transverse angles, the sagittal angles, the lengths of the screw channels, and the radiuses of the maximal inscribed circles were significantly different between genders in 15 cases (P < 0.05). Only one maximum ideal screw can be placed on one side at a time. With a radius of 2.50mm considered to be standard, it is feasible to place S1AI-S3AI screws with a radius > 2.50mm in the entire adult population and S4AI screws with a radius > 2.50mm in some of the adult population. Furthermore, preoperative three-dimensional reconstruction and three-matic research software can effectively simulate the sacral alar-iliac screw channels, and they can provide accurate data for clinical applications.

A comprehensive biomechanical analysis of sacral alar iliac fixation: an in vitro human cadaveric model.

In BriefIn this in vitro investigation, we compared the multidirectional flexibility properties of sacral alar iliac fixation with conventional methods of sacral and sacroiliac fixation using nondestructive and destructive investigative methods. The study demonstrated that S1-2 sacral fixation alone significantly increases sacroiliac motion under all loading modalities, while sacral alar iliac fixation reduced motion in axial rotation at the sacroiliac joint and offers potential advantages of a lower instrumentation profile and ease of assembly compared to conventional sacroiliac screw instrumentation.

Comparison of Sacral-Alar-Iliac and Iliac-Only Methods of Pelvic Fixation in Early-Onset Scoliosis at 5.8 Years' Mean Follow-up

Study DesignRetrospective. ObjectiveCompare clinical outcomes in early-onset scoliosis (EOS) patients treated with sacral-alar-iliac (SAI) versus iliac-only methods of pelvic fixation at two years' minimum follow-up. Summary of Background DataPelvic fixation in EOS is challenged by poor bone, anchor migration, and displacement. The long-term outcomes of SAI fixation in EOS is unknown. MethodsWe retrospectively reviewed EOS patients in a single center from 2000 to 2017. Inclusion criteria were posterior spinal instrumentation with pelvic fixation before age 10 and 2 years' minimum follow-up. Clinical and radiographic data were analyzed using chi-squared and Student t tests (significance defined as p <.05). ResultsSeven subjects were included in the iliac-only fixation group (Galveston technique = 2, iliac screws = 5) and 17 in the SAI group. For the iliac-only group (mean follow-up = 6.8 years), pelvic obliquity improved from a mean of 18° at initial presentation to 11° at first instrumentation (p = .096), to 9° at end follow-up (p = .060), whereas the major curve improved correspondingly from a mean of 84° to 50° (p = .002) to 39° (p = .006). For the SAI group (mean follow-up = 5.5 years) at the same time points, pelvic obliquity improved from a mean of 25° to 6° (p <.001) to 5° (p <.001), whereas the major curve improved from a mean of 83° to 38° (p <.001) to 29° (p <.001). SAI fixation was associated with fewer complications (11 complications in 17 patients) compared to iliac-only fixation (10 complications in 7 patients) (p = .04). Neither method was associated with pelvic growth disturbances or neurologic deficits. ConclusionsIn EOS patients at 2 years' minimum (5.8 years' mean) follow-up, both SAI and iliac-only methods corrected major curve, only SAI fixation corrected pelvic obliquity, and neither was associated with pelvic growth disturbances. SAI fixation was also associated with fewer complications. These findings may be due to the length and direction of the SAI anchors and abutment on the iliac cortex. Level of EvidenceLevel III.