S2 Alar-iliac Screws Research Articles

Friday, September 28, 2018 10:30 AM–12:00 PM abstracts: deformity: technical factors: 170. Comparison of three lumbopelvic fixation techniques in long fusion to the sacrum in osteoporotic adult spinal deformity patients (>60 years): clinical and radiological outcomes

BACKGROUND CONTEXT Iliac screw techniques provide additional biomechanical stabilization to S1 in long fusion to the sacrum. Recently S2 Alar iliac screw (S2AI) fixation became more popular than traditional iliac screw (TIS) (entry point posterior superior iliac spine), and distal iliac screw (DIS) (entry point posterior inferior iliac spine) due to the lower implant profile and need for less extensive soft tissue dissection. S2AI fixes the sacroiliac (SI) joint differently from TIS and DIS. PURPOSE This study aimed to compare the clinical and radiologic outcomes between TIS, DIS and S2AI fixation in osteoporotic adult spinal deformity patients. STUDY DESIGN/SETTING Retrospective. PATIENT SAMPLE A total of 158 adult spinal deformity patients. OUTCOME MEASURES ODI questionnaire was evaluated for clinical outcome. METHODS A total of 158 (103f, 55m) adult spinal deformity patients pts who underwent long fusion to the sacrum with three different iliac screw techniques (TIS, DIS, S2AI) were reviewed. Radiologic parameters were compared between preop and f/up standing x-rays. Hospital charts and f/up CT scans were used to compare the screw lengths, diameters, and implant related complications including S1 and iliac screw loosening, rod breakage, sacroiliac joint dissociation (SID), surgical site infections (SSI) and hematoma. ODI scores were compared for clinical assessment. RESULTS A total of 54 patients had TIS, 51 patients had DIS, 53 patients had S2AI fixation. Mean ages were 67, 71, 68; mean f/up was 54.2 (24–174) months, respectively. Iliac screw lengths were 85mm, 90mm, 105mm; diameters were 9.0mm, 8.5mm, 9.5mm for TIS, DIS, S2AI, respectively. There were seven patients (12.9%) in TIS, six patients (11.7%) in DIS & three patients (5.6%) in S2AI with implant related complications. One patient (1.8%) in TIS and one patient (1.9%) in DIS group showed SID (TIS=1, DIS=1, S2AI=0). Postop hematoma was detected in 14 patients (8.8%) (TIS=4, DIS=7, S2AI=3) and SSI developed in two patients (1.2%) (TIS=1, DIS=1, S2AI=0). ODI scores improved in all groups. CONCLUSIONS All techniques provided sufficient stability for lumbosacral fusion in adult spinal deformity patients. S2 Alar iliac screw technique showed lower implant related complication rates when compared to both iliac screw techniques. Traditional iliac screwand Distal iliac screw had higher rates of hematoma and surgical site infections due to extensive soft tissue dissection compared to S2 Alar iliac screw. S2 Alar iliac screw does not lead to sacroiliac joint dissociation as it provides stability by fixing the sacroiliac joint.

Anatomic Parameters for Instrumentation of the Sacrum and Pelvis: A Systematic Review of the Literature.

Introduction:Multiple cadaver and radiographic analyses have been performed to define the surgical anatomy of the sacrum and pelvis. We provide a comprehensive review of this information, creating an accurate anatomic guide for practice and research.Methods:A systematic review was performed to identify publications citing sacral or iliac morphometric parameters based on cadaver or radiographic anatomy.Results:A total of 780 abstracts were evaluated. Fifty-six articles were included for final review and grouped into four sections: (1) bone density, (2) bony corridors, (3) screw length and trajectory, and (4) neurovascular and alimentary anatomy.Conclusion:A systematic analysis of the radiographic and gross anatomic features of the sacrum has yet to be published. This review includes details on the spatial arrangement of the S1 and S2 pedicle screws, sacroiliac screws, iliac screws, S2 alar iliac screws, and pelvic neurovascular anatomy. The study can be referenced by clinicians for sacral dissection, implant application, and ongoing advances in orthopaedic research.Study Design:Systematic reviewLevel of Evidence:Level IV

The posterior superior iliac spine and sacral laminar slope: key anatomical landmarks for freehand S2-alar-iliac screw placement.

The S2-alar-iliac (S2AI) screw is an increasingly popular method for spinopelvic fixation. The technique of freehand S2AI screw placement has been recently described. The purpose of this study was to demonstrate, through a CT imaging study of patients with spinal deformity, that screw trajectories based on the posterior superior iliac spine (PSIS) and sacral laminar slope result in reliable freehand S2AI trajectories that traverse safely above the sciatic notch. Fifty consecutive patients (age ≥ 18 years) who underwent primary spinal deformity surgery were included in the study. Simulated S2AI screw trajectories were analyzed with 3D visualization software. The cephalocaudal coordinate for the starting point was 15 mm cephalad to the PSIS. The mediolateral coordinate for the starting point was in line with the lateral border of the dorsal foramina. The cephalocaudal screw trajectory was perpendicular to the sacral laminar slope. Screw trajectories, lengths, and distance above the sciatic notch were measured. The mean sagittal screw angle (cephalocaudal angulation) was 44.0° ± 8.4° and the mean transverse angle (mediolateral angulation) was 37.3° ± 4.3°. The mean starting point was 5.9 ± 5.8 mm distal to the caudal border of the S1 foramen. The mean screw length was 99.9 ± 18.6 mm. Screw trajectories were on average 8.5 ± 4.3 mm above the sciatic notch. A total of 97 of 100 screws were placed above the sciatic notch. In patients with transitional lumbosacral anatomy, the starting point on the lumbarized/sacralized side was 3.4 mm higher than on the contralateral unaffected side. The PSIS and sacral laminar slope are two important anatomical landmarks for freehand S2AI screw placement.

Is S1 Alar Iliac Screw a Feasible Option for Lumbosacral Fixation?: A Technical Note.

Nonunion at the lumbosacral junction is a classic complication of long construct and deformity corrections. Iliac fixations have been extensively studied in the literature and have demonstrated superior biomechanical proprieties and lower complication rates. S2 alar iliac screws address the drawbacks of classical iliac screws but demonstrate similar biomechanical advantage. The main aim of this paper was to describe the S1 alar iliac (S1AI) screw fixation technique while evaluating our early results. S1AI screw fixation technique has the advantage of being able to achieve pelvic fixation without dissection to the S2 pedicle entry and is therefore a viable option for salvage of a failed S1 promontory screw.

Neurovascular Relationships of S2AI Screw Placement: Anatomic Study

The S2 alar-iliac (S2AI) screw is a modification of the traditional iliac fixation technique and has surgical and biomechanical benefits. However, there are significant regional neurovascular structures along the path of such screws. Therefore the current anatomic study was performed to better elucidate these relationships. Using fluoroscopy, S2AI screws were placed in 2 adult cadavers through a standard posterior midline exposure. The screw insertion point was placed 10 mm lateral to a line bisecting the S1 and S2 foramina, adjacent to the sacroiliac joint. Using 30- to 40-degree lateral angulation from the midline and 20- to 30-degree caudal angulation, a pedicle probe was directed toward the anterior inferior iliac spine. The final trajectory was positioned to sit 1-2 cm superior to the greater sciatic foramen. Lastly, the screws and surrounding bone were drilled in order to visualize both lateral and medial neurovascular relationships. Removing the bone around the S2AI-screw illustrated the close relationship to the medial (internal) neurovascular structures including the obturator nerve, lumbosacral trunk, sacral plexus and, specifically, the S1 ventral ramus and iliac vein and artery. By removing the outer cortex of the ilium, the close relationship to the superior gluteal artery, vein, and nerve was observed. In addition, we were able to identify the proximity to the iliopsoas muscle and internal iliac vessels. A comprehensive knowledge of the surrounding neurovascular anatomy relevant to S2AI screw placement can decrease patient morbidity and allow spine surgeons to better diagnose potential postoperative complications.

S2 alar-iliac screwing assisted by an individualized navigation template

Objective To evaluate the accuracy and feasibility of S2 alar-iliac screwing assisted by an individualized navigation template in clinic. Methods Five patients underwent S2 alar-iliac screwing from March 2015 to July 2017. They were 2 men and 3 women, aged from 41 to 61 years (average, 54.8 years). After their preoperative CT scan data of the pelvis were used for 3D reconstruction, their individualized navigation templates were designed, 3D printed and used to assist the implantation of S2 alar-iliac screws. After operation, their postoperative CT data were reviewed and reconstructed using software Mimics. The caudal angulation on the sagittal plane (sagittal angle, SA), lateral angulation on the transverse plane (transverse angle, TA), horizontal distance to the median sacral crest (horizontal distance, HD), and vertical distance to the first posterior sacral foramen's inferior margin (vertical distance, VD) of the screws were measured and compared with the corresponding values in the preoperative design. Results In the 5 patients, altogether 10 S2 alar-iliac screws were implanted through the sacroiliac joint without piercing the iliac bone cortex. There were no significant differences between the preoperative design and postoperative measurements in terms of SA (32.22°±5.57° versus 31.95°±5.78°), TA (42.59°±4.55° versus 42.21°±5.29°), HD (5.04±0.40 mm versus 5.00±0.41 mm) or VD (19.58±1.49 mm versus 19.54±1.12 mm) (P>0.05). Conclusion In the adult pelvic fixation, the S2 alar-iliac screwing can be assisted by an individualized navigation template to achieve high accuracy in implantation. Key words: Pelvis; Sacroiliac joint; Pelvimetry; 3D printing technology; Navigation template

Biomechanical characterization of three iliac screw fixation techniques: A finite element study

We aim to characterize the biomechanical properties of a modified iliac screw fixation method compared with the classic iliac screw fixation and the S2 alar iliac screw (S2AI) fixation using a FEM.A three-dimensional, non-linear FEM of lumbosacral spine and pelvis (L1-pelvis) was modified to simulate 3 different iliac screw fixations based on posterior screw fusion. The peak von Mises stress (PVMS) values of the iliac screws in the 3 different iliac screw fixations were recorded in during flexion/extension/axial rotation/lateral bending. The interaction stress which arose between the screw head and the shaft of iliac screws, was also measured for each case.The PVMS values of the 3 different iliac screw fixation techniques were lower than the fatigue strength levels under physiological loadings. PVMS of iliac screws was observed in the screw shaft for S2AI, in the screw neck for the modified iliac screw technique, and in the offset connectors of the classic iliac screw technique. The interaction between the screw head and the neck was compressed in modified iliac screw fixation technique. On the other hand, distraction force was observed in the S2AI technique between the screw head and the screw shaft.This FEM study supports our previous clinical results, which found that the modified iliac screw fixation technique can be an effective alternative sacropelvic fixation technique comparable to the classic iliac screw and the S2AI technique.

The Accurate Free-hand Placement of S2 Alar Iliac (S2AI) Screw.

Achieving an osseous fusion across the lumbosacral spine is still challenging in spine surgery. For the long multisegmental fusion surgery, it is crucial to build a robust and substantial foundation, which sometimes necessitates the distal spinal fixation to the pelvis. The pelvic fixation technique involves advancing the screw through the alar, thereby providing more purchase across the sacroiliac joint and into the ilium. The S2 alar iliac screws can obtain immediate stability and proper biomechanical strength of constructs. Here we demonstrated our experience of how to place the S2 alar iliac screw accurately as well as some pitfalls and pearls of this technique.

The Free-Hand Technique for S2-Alar-Iliac Screw Placement: A Safe and Effective Method for Sacropelvic Fixation in Adult Spinal Deformity.

Spinopelvic fixation is an integral part of achieving solid fusion across the lumbosacral junction, especially in deformity procedures requiring substantial correction or long-segment constructs. Traditional S2-alar-iliac (S2AI) screw-placement techniques utilize fluoroscopy, increasing operative time and radiation exposure to the patient and surgeon. We describe a novel free-hand technique for S2AI screw placement in patients with adult spinal deformity. We reviewed the records of 45 consecutive patients who underwent spinopelvic fixation performed with use of S2AI screws by the senior surgeon and various fellows or residents over a 12-month period (2015 to 2016). In each case, the S2AI screws were placed utilizing a free-hand technique without fluoroscopic or image guidance. Screw position and accuracy were assessed by intraoperative O-arm imaging and analyzed using 3-dimensional interactive manipulation of computed tomography images. A total of 100 screws were placed, 51 by the senior surgeon and 49 by trainees. The mean patient age was 57.4 ± 12.7 years at the time of surgery; 37 (82.2%) of the patients were female. Preoperative diagnoses included adult idiopathic scoliosis (n = 19), adult degenerative scoliosis (n = 15), flatback syndrome (n = 2), fixed sagittal imbalance (n = 6), and distal junctional kyphosis (n = 3). Five (5%) of the screws were placed with moderate to severe cortical breaches, all of which perforated the pelvis posteriorly, with no clinically notable neurovascular or visceral complications. The breach rate did not differ significantly between the senior surgeon and trainees. The free-hand technique for S2AI screw placement, when performed in a standardized manner, was demonstrated to be safe and reliable in constructs requiring spinopelvic fixation. The accuracy of screw placement relies on visible and palpable anatomic landmarks that obviate the need for intraoperative fluoroscopy or image guidance, potentially reducing operative time and radiation exposure. Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

S2 Alar-Iliac Screw Insertion: Technical Note with Pictorial Guide.

The S2 alar-iliac (S2AI) screw is a modification of the iliac fixation technique using the space between the neuroforamina of S1 and S2 as an insertion point to fix the sacrum to the ilium. To our knowledge, an anatomic review of the S2AI technique has not been described and the insertion point is vague and angles differ in reports from the literature. The purpose of the current anatomic illustration is to provide step-by-step techniques with fluoroscopic imaging to help confirm the safe placement of S2AI screws. The procedure was performed on the left and rights sides of a fresh, frozen, and thawed predissected male cadaver in a surgical training facility through a standard posterior midline exposure for placement of the S2AI screws. All screws were placed by a fellowship-trained spine surgeon and an attending spine surgeon. The specimen was placed prone, and a midline incision begun at the L4 or L5 spinous process. Using the anteroposterior and inlet views, the S1 dorsal sacral foramen, the S1 endplate, and the sacroiliac joint can be identified. The insertion point is 10 mm laterally between the S1 and S2 foramina and near to the sacroiliac joint. Aim toward the anterior inferior iliac spine is ensured by using a 30°-40° lateral angulation in the transverse plane and 20°-30° caudal angulation in the sagittal plane depending on the sacral angulation. Using lateral fluoroscopy, the acetabulum and greater sciatic notch can be identified and screw misplacement can be avoided. The screw length is measured and is usually between 60 and 90 mm (8- to 9-mm diameter). An elevator is used to identify the outer sacral cortex. Anteroposterior, obturator-outlet, and teardrop views are used to ensure correct screw insertion. Fluoroscopic guidance is crucial for optimal S2AI screw placement. Using the described technique allows a safe and correct insertion of the S2AI screw.

Subcrestal Iliac-Screw: A Technical Note Describing a Free Hand, In-line, Low Profile Iliac Screw Insertion Technique to Avoid Side-connector Use and Reduce Implant Complications.

Case-series. To report our modified iliac-screw insertion technique and its clinical outcomes. Iliac-screws are one of the preferred methods for modern spinopelvic-fixation. However, the technique is not without complications, predominantly because of iliac-screw head prominence, leading to pain and revisions. Conventional iliac-screw entry point is sited superficially at the posterior-superior-iliac-spine (PSIS) contributing to screw-head prominence. We propose a more low-profile, subcrestal entry point that is more medial and inferior to the PSIS at the medial wall of the iliac crest, lying underneath the crest but above the sacroiliac joint. This position keeps the screw-head low profile and in-line with proximal instrumentation to ease rod engagement. Ten consecutive patients who underwent spinal deformity correction surgery using the modified iliac-screw entry point fixations were enrolled. Clinical, radiological, and surgical parameters were reviewed. Five males and five females with average age of 66 years and average follow up of 29 months were reviewed. Mean preoperative Cobb angle and C7-SVA were 32.1° and 10.3 cm, respectively. Surgical indication was progressive deformity and neurogenic claudication in eight cases and fracture in two cases. Twenty noncannulated, polyaxial iliac-screws with median dimension of 7.5 x 75 mm were inserted free hand. Bilateral S1 screws were used in all except two cases. Only five out of 16 iliac-screws with concomitant S1 screws needed side-connectors. At the last follow up only one iliac-screw head was felt to be prominent but without pain in a Parkinson's patient. None of the 10 patients had cases of revision, breakages, or sacroiliac pain. Subcrestal iliac-screw insertion is feasible, safe, and has the potential to reduce screw-head complications and avoid the use of side-connectors, lowering construct complexity and cost. The technique has the advantage of both the low-profile S2 alar iliac screw and the ease of free-hand insertion of the traditional iliac-screw. 4.

Unilateral S2 alar-iliac screws for spinopelvic fixation.

Background:This study compared the clinical complications, radiographic measurements of deformity, and quality of life outcomes for patients with de novo scoliosis undergoing thoracolumbar fusions for spinopelvic fixation (SPF) utilizing unilateral S2 alar-iliac (S2AI) screw or unilateral iliac bolt fixation.Methods:This retrospective review was performed in 29 patients who underwent SPF at one institution; 10 patients received unilateral S2AI screws, and 19 patients received unilateral iliac bolts. The following variables were studied: reoperation rates, pseudarthrosis, sacral insufficiency fracture, hardware prominence, infection, proximal junctional kyphosis (PJK), deformity correction (radiographs), windshield wipering, hardware fracture, and hardware removal. Outcomes were analyzed utilizing both the visual analog scale (VAS) and Oswestry Disability Index (ODI). The mean follow-up period was 27 months.Results:The reoperation rate for unilateral S2AI screws was 30% vs. 53% for unilateral iliac bolts (P = 0.43); reoperations were performed with a 1:5 ratio for infection, a 1:4 ratio for pseudarthrosis, and 1:1 a ratio for PJK comparing S2AI screws to iliac bolts, respectively.Conclusion:There were no significant differences in postoperative complications and reoperation rates between unilateral S2AI screws and unilateral iliac bolts utilized for SPF. For the S2AI screw group, there were no instances of hardware prominence or need for removal. The use of unilateral S2AI screws resulted in adequate fixation and comparably low complication rates.

Freehand S2 Alar-Iliac Screw Placement Using K-Wire and Cannulated Screw : Technical Case Series

ObjectiveAmong the various sacropelvic fixation methods, S2 alar-iliac (S2AI) screw fixation has several advantages compared to conventional iliac wing screw. However, the placement of S2AI screw still remains a challenge. The purpose of this study was to describe a novel technique of free hand S2AI screw insertion using a K-wire and cannulated screw, and to evaluate the accuracy of the technique.MethodsS2AI screw was inserted by free hand technique in sixteen consecutive patients without any fluoroscopic guidance. The gearshift was advanced to make a pilot hole passing through the sacroiliac joint and directing the anterior inferior iliac spine. A K-wire was placed through the pilot hole. After introducing a cannulated tapper along with the K-wire, a cannulated S2AI screw was installed over the K-wire.ResultsThirty-three S2AI screws were placed in sixteen consecutive patients. Thirty-two screws were cannulated screws, and one screw was a conventional non-cannulated screw. Thirty out of 32 (93.8%) cannulated screws were accurately positioned, whereas two cannulated screws and one non-cannulated screw violated lateral cortex of the ilium.ConclusionThe technique using K-wire and cannulated screw can provide accurate placement of free hand S2AI screw.

S2 Alar Iliac Fixation in Long Segment Constructs, a Two- to Five-Year Follow-up

Study DesignRetrospective review of patients having undergone S2 alar-iliac (S2AI) fixation for long fusions with a minimum two-year follow-up. ObjectivesTo report on fusion rates, complications, technique-specific complications of patients having undergone S2AI fixation. Summary of background dataSacropelvic fixation continues to be a challenge when performing long fusions to the pelvis. S2AI screws have been found to provide solid biomechanical fixation and have been found to have good clinical results in short-term follow-up for pediatric and adult patients. MethodsCases were retrospectively reviewed in patients who had placement of S2AI screws for long fusions with at least a two-year follow-up. Demographic data, complications, and reoperations were reviewed. Complications were broken into minor and major categories similar to previous series on pelvic fixation. ResultsThere were 86 cases identified. Minor and major complications occurred in 29% and 24% of patients, respectively, with the majority of minor complications being intraoperative dural tears. Revision surgery for all causes was performed in 23% of the cohort. Fusion rate at L5–S1 for patients without preoperative pseudarthrosis was 95.3%. Preoperative L5–S1 pseudoarthrosis was identified in 20 patients, 17 (95%) of these went onto fusion after one surgery. There was evidence of S2AI screw lucency in 10.4% of cases. However, the majority of these were asymptomatic. ConclusionsSacropelvic fixation using the S2AI technique provides safe, durable fixation with low rates of technique-specific complications and limited need for hardware removal. Complication rates in this series were similar to other series on long fusions to the pelvis. Additionally, fusion rates were high at L5–S1 for both patients with and without preoperative L5–S1 pseudarthrosis. It appears that the S2AI technique is a powerful option for patients with previous L5–S1 pseudarthrosis. Level of EvidenceLevel III.

The technique of S2-alar-iliac screw fixation: a literature review

The distal fixation in thoracolumbar deformity surgery can be challenging for spine surgeons. When isolated S1-pedicle screws are utilized as the sole distal fixation in long thoracolumbar posterior constructs, there is a high rate of failure, due to loosening, breakage, and pseudarthrosis. Unfortunately, with iliac screw fixation the entry point at the posterior superior iliac spine requires considerable soft tissue dissection and may potentially increase the likelihood of wound complications. S2-alar-iliac (S2AI) screw fixation technique was developed recently to provide increased fixation with a lower profile screw and rod construct. These screws can be inserted with percutaneous or free hand techniques. This fixation also has comparable biomechanical properties to the S1 iliac screw. This technique may provide advantages such as decreased rates of reoperation, surgical site infection, wound dehiscence and symptomatic screw prominence as compared to traditional iliac screw fixation. The purpose of this manuscript is to review the S2AI screw fixation literature including anatomy, technique, biomechanics, and clinical outcomes.

Accuracy of S2 Alar-Iliac Screw Placement Under Robotic Guidance

Study DesignCase series. ObjectivesTo determine the safety and feasibility of S2 alar-iliac (S2AI) screw placement under robotic guidance. Summary of Background DataSimilar to standard iliac fixation, S2AI screws aid in achieving fixation across the sacropelvic junction and decreasing S1 screw strain. Fortunately, the S2AI technique minimizes prominent instrumentation and the need for offset connectors to the fusion construct. Herein, we present an analysis of the largest series of robotic-guided S2AI screws in the literature without any significant author conflicts of interest with the robotics industry. MethodsTwenty-three consecutive patients who underwent spinopelvic fixation with 46 S2AI screws under robotic guidance were analyzed from 2015 to 2016. Screws were placed by two senior spine surgeons, along with various fellow or resident surgical assistants, using a proprietary robotic guidance system (Renaissance; Mazor Robotics Ltd., Caesara, Israel). Screw position and accuracy was assessed on intraoperative CT O-arm scans and analyzed using three-dimensional interactive viewing and manipulation of the images. ResultsThe average caudal angle in the sagittal plane was 31.0° ± 10.0°. The average horizontal angle in the axial plane using the posterior superior iliac spine as a reference was 42.8° ± 6.6°. The average S1 screw to S2AI screw angle was 11.3° ± 9.9°. Two violations of the iliac cortex were noted, with an average breach distance of 7.9 ± 4.8 mm. One breach was posterior (2.2%) and one was anterior (2.2%). The overall robotic S2AI screw accuracy rate was 95.7%. There were no intraoperative neurologic, vascular, or visceral complications related to the placement of the S2AI screws. ConclusionsSpinopelvic fixation achieved using a bone-mounted miniature robotic-guided S2AI screw insertion technique is safe and reliable. Despite two breaches, no complications related to the placement of the S2AI screws occurred in this series. Level of EvidenceLevel IV, therapeutic.

Comparison of S2-Alar and traditional iliac screw pelvic fixation for pediatric neuromuscular deformity

Background ContextMany pelvic fixation options exist for posterior spinal fusion of pediatric neuromuscular scoliosis, including standard iliac screws (SISs) or a more recently introduced S2-Alar (S2A) technique. However, little data exist comparing the clinical and radiographic outcomes of these techniques. PurposeThis study aimed to dentify differences in clinical and radiographic outcomes for pediatric neuromuscular scoliosis patients treated with SIS or S2A pelvic fixation. Study Design/SettingThis was a retrospective cohort study at a pediatric orthopedic clinic. Patient SamplePatients aged 8–19 years undergoing posterior spinal fusion to the pelvis for neuromuscular scoliosis using SIS or S2A technique, with Gross Motor Function Classification System (GMFCS) Level 4 or 5 were included. Outcomes MeasuresPostoperative complication rates associated with pelvic fixation method were the outcome measures. MethodsCharts and radiographs were reviewed for demographics, intra- and postoperative course, levels of instrumentation, operative correction, and implant failure (IF). Postoperative complications were classified according to the Accordion scale. ResultsWe studied 50 patients (28 SIS, 22 S2A) aged 14.0±2.8 years and an average follow-up of 3.5±1.7 years. The average number of levels fused was 16.5±1.1 with an average curve correction of 48°±21° postoperatively. A significant difference in radiographic IF rates was noted between SIS and S2A groups (57% vs. 27%, p=.02). No difference was noted between groups for frequency or severity of postoperative complications, inclusive of wound infections. Subgroup analysis demonstrated equivalent IF rates when comparing the S2A group with the SIS group with cross-links. ConclusionsThe S2A group generally demonstrated improved rates of radiographic IF compared with the SIS group, but the rates became equivalent when a cross-link was added to an SIS construct. Further, no difference in postoperative complication rates were identified between SIS and S2A groups.

A novel technique for placement of sacro-alar-iliac (S2AI) screws by K-wire insertion using intraoperative navigation

Sacral-iliac fixation techniques may be indicated in the management of various lumbosacral pathologies including spinal degeneration, infection, tumour resection, fracture, pseudarthrosis, correction of spinal deformities involving long fusion constructs to the sacrum and cases with poor sacral fixation. There are a number of options for lumbosacral fixation each with their own advantages and disadvantages. Though S2-alar-iliac (S2AI) have demonstrated promising advantages over alternatives, the complex anatomy of the spinopelvic region demands precise insertion of the screws to create a biomechanically robust construct safely. As such, we present a novel technique of using intra-operative CT navigation and K-wires to establish and secure a planned trajectory, thereby ensuring solid spinopelvic fixation with S2AI screws. This was performed as part of a long fusion construct for correction of kyphosis deformity in a male patient.

Comparison Between S2-Alar-Iliac Screw Fixation and Iliac Screw Fixation in Adult Deformity Surgery: Reoperation Rates and Spinopelvic Parameters.

Study Design:Retrospective cohort study.Objective:The S2-alar-iliac (S2AI) technique has been described as an alternative method for pelvic fixation in place of iliac screws (ISs) in spinal deformity surgery. The objective of this study was to analyze the impact of S2AI screws on radiographical outcomes, including spinopelvic parameters.Methods:A retrospective review of 17 patients receiving ISs and 46 patients receiving S2AI screws for correction of adult spinal deformity between 2010 and 2015 with minimum 1-year follow-up was conducted. Patient data on postoperative complications, including reoperation rates and proximal junctional kyphosis (PJK), and radiographical parameters was collected and statistically analyzed.Results:With mean follow-up of 21.1 months, the overall reoperation rate was significantly lower in the S2AI group than in the IS group (21.7% vs 58.8%, P = .01), but the incidence of PJK was similar (32.6% vs 35.3%, P > .99). Moreover, the time to reoperation in the IS group was significantly shorter than in the S2AI group (P = .001), and the S2AI group trended toward a longer time to reoperation due to PJK (P = .08). There was a significantly higher change in pelvic incidence (PI) in the S2AI group (−6.0°) compared with the IS group (P = .001).Conclusions:Compared with the IS technique, the S2AI technique demonstrated a lower rate of overall reoperation, a similar rate of PJK, longer time to reoperation, and possible reduction in PI. Future studies may be warranted to clarify the mechanism of these results and how they can be translated into improved patient care.

Pelvic fixation: Biomechanics and complications

When extending a fusion construct to the sacrum in spinal deformity, there has long been difficulty in obtaining bony fusion at the L5-S1 level. This is due to a number of factors, including the altered morphology of the sacrum as compared to the lumbar vertebrae, adequate bone stock, and large cantilever forces at the lumbosacral junction, among others. This problem can be partially rectified by extending the construct to the pelvis, but even this does not result in a 100% fusion rate at the lumbosacral junction. The techniques currently used to fuse the spine to the pelvis primarily consist of iliac screws and S2 alar-iliac screws, but these techniques are not without complications. Here we review the biomechanics of pelvic fixation, techniques of these two screw types, and the complications associated with each.