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

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

Dynamic change of pelvic incidence after long fusion to pelvis with S2-alar-iliac screw: a 2-year follow-up study.

INTRODUCTION: Pelvic incidence (PI) is a key morphological parameter that reflects the relation between the sacrum and iliac wings. It is well accepted that PI remains constant after reaching maturity. However, recent studies indicated that PI might be altered after lumbosacral fusion. Additionally, it remains uncertain on the long-term influence of long fusion to pelvis with S2-alar-iliac screw on PI in patients with adult spinal deformity (ASD). STUDY DESIGN: A retrospective study. OBJECTIVE: To investigate whether and how PI would change during the follow-up in ASD patients who underwent S2AI fixation and to identify factors associated with the change in PI. METHODS: We retrospectively reviewed all ASD patients who underwent spinal surgery using S2AI screws between November 2014 and January 2017 at our institution. Patients with minimum follow-up of two years were included. The following sagittal radiographic parameters were measured: PI, Lumbar lordosis (LL), pelvic tilt (PT), PI-LL, sagittal vertical axis (SVA) at pre-op, post-op and 2-year follow-up. According to the changes in PI at immediate post-operation, patients were classified into two groups; Group A: Changes of PI less than or equal 5° and Group B: Changes of PI greater than 5°. RESULTS: A total of 82 ASD patients (Group A: 32, Group B: 50; mean age of 53.5 ± 12.6 years) with a mean follow-up period of 30.2 ± 9.2 months were included in this study. At immediate post-operation, Group A showed no significant change in PI (45.7° ± 11.4° to 45.3° ± 11.2°, p = 0.749); while Group B had a significant decrease in PI (51.6° ± 14.5° to 40.9° ± 14.0°, p < 0.001). At the last follow-up, 48% patients (24/50) in Group B had a significant increase in PI (32.8° ± 6.4° to 45.8° ± 11.2°, p < 0.001). Intergroup analysis showed that ΔPI, post-op PI, post-op PT and age were significantly different between both groups. In addition, pre-op PI, post-op PI, post-op PT, post-op PI-LL were significantly correlated with ΔPI at last follow-up. Also, logistic regression analysis showed that post-op PI was the associated risk factor (OR = 0.865, p = 0.024) for PI-LL mismatch. CONCLUSION: Our study showed that PI decreased in more than half of ASD patients immediately after spinal surgery using S2AI screws. Approximately 48% of them were able to recover during the 2-year follow-up. Lower pre-op PI, post-op PI and PT were found to be strongly associated with the return of PI. Thus, these current findings indicated that patients with a high PI at pre-operation should not be over-corrected to avoid PI-LL mismatch postoperatively.

Intraoperative imaging and navigated spinopelvic instrumentation: S2-alar-iliac screws combined with tricortical S1 pedicle screw fixation.

PURPOSE: The present study aimed to assess the feasibility, safety and accuracy of navigated spinopelvic fixation with focus on S2-alar-iliac screws (S2AIS) and tricortical S1 pedicle screw implantation with the use of high-resolution three-dimensional intraoperative imaging and real-time spinal navigation. METHODS: Patients undergoing navigated intraoperative CT-based spinopelvic stabilization between January 2016 and September 2019 were included. Pelvic fixation was achieved by implantation of S2AIS or iliac screws (IS). S1 screws were implanted with the goal of achieving tricortical purchase. In all cases, instrumentation was performed with real-time spinal navigation and intraoperative screw positioning was assessed using intraoperative computed tomography (iCT), cone-beam CT (CBCT) and robotic cone-beam CT (rCBCT). Screw accuracy was evaluated based on radiographic criteria. To identify predictors of complications, univariate analysis was performed. RESULTS: Overall, 52 patients (85%) received S2AIS and nine patients (15%) received IS instrumentation. Intraoperative imaging and spinal navigation were performed with iCT in 34 patients, CBCT in 21 patients and rCBCT in six patients. A total number of 10/128 (7.8%) iliac screws underwent successful intraoperative correction due to misalignment. Tricortical purchase was successfully accomplished in 58/110 (53%) of the S1 screws with a clear learning curve in the course of time. S2AIS implantation was associated with significantly fewer surgical side infection-associated surgeries. CONCLUSIONS: Real-time navigation facilitated spinopelvic instrumentation with increasing accuracy of S2AIS and tricortical S1 screws. Intraoperative imaging by iCT, CBCT or rCBCT permitted screw assessment with the chance of direct navigated revision of misplaced iliac screws to avoid secondary screw revision surgery.

S2 alar-iliac screw loosening as a preventive factor for hip joint osteoarthritis after adult spinal deformity surgery: a case-control study.

PURPOSE: This study aimed to evaluate the progression of hip pathology and risk factors after ASD surgery. METHODS: This case-control study enrolled 123 patients (246 hips); seven hips underwent hip arthroplasty were excluded. We measured the center-edge (CE) angle, joint space width (JSW), and Kellgren-Lawrence (KL) grade. We defined a CE angle˂25° as developmental dysplasia of the hip (DDH). We evaluated S2 alar-iliac (AI) screw loosening at final follow-up. RESULTS: The annual decrease in the JSW was 0.31 mm up to 1 year, and 0.13 mm after 1 year (p = 0.001). KL grade progression occurred in 24 hips (10.0%; group P), while no progression occurred in 215 (90.0%; group N) hips. Nonparametric analysis between groups P and N revealed that significant differences were observed in sex, DDH, KL grade, ratio of S2AI screw fixation at baseline, and ratio of S2AI screw loosening at final follow-up. Multiple logistic regression analysis revealed that DDH (p = 0.018, odds ratio (OR) = 3.0, 95%CI = 1.2-7.3), baseline KL grade (p < 0.0001, OR = 37.7, 95%CI = 7.0-203.2), and S2AI screw fixation (p = 0.035, OR = 3.4, 95%CI = 1.1-10.4) were significant factors. We performed sub-analysis to elucidate the relationship between screw loosening and hip osteoarthritis in 131 hips that underwent S2AI screw fixation. Non-loosening of the S2AI screw was a significant factor for KL grade progression (p < 0.0001, OR = 8.9, 95%CI = 3.0-26.4). CONCLUSION: This study identified the prevalence and risk factors for the progression of hip osteoarthritis after ASD surgery. Physicians need to pay attention to the hip joint pathology after ASD surgery.

Surgical strategy of lumbopelvic instrumentation in the treatment of lumbosacral tuberculosis: S2-alar-iliac screws vs iliac screws.

The objective of this study was to evaluate the feasibility and clinical outcomes of S2-alar-iliac (S2AI) and iliac screw (IS) techniques in the lumbopelvic reconstruction of lumbosacral tuberculosis patients. From January 2014 to August 2016, 26 patients with lumbosacral tuberculosis attending the 8th Medical Centre of Chinese PLA General Hospital were included in this retrospective study. The subjects were divided into two groups based on the lumbopelvic fixation type (16 patients in the S2AI group, 10 patients in the IS group). The operation time, blood loss, length of hospitalisation, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP) level, visual analogue scale (VAS), Oswestry Disability Index (ODI), ambulatory status, and 36-Item Short-Form Health Survey (SF-36) scores of the patients in two groups were recorded and compared. In addition, surgical complications were collected and analysed. The operation time and intraoperative blood loss were significantly lower in the S2AI group than that in the IS group (P < .05). Compared with preoperative data, postoperative data showed significant improvement in ESR, CRP level, ODI scores, VAS scores, ambulatory status, and SF-36 (P < .05), but there was no significant difference in remission degree between the two groups. Compared with IS group, The S2AI group had significantly lower rates of symptomatic screw prominence (P < .05). Both the IS and S2AI fixation techniques can achieve satisfactory outcomes for the restoration of lumbosacral stability of lumbosacral tuberculosis. Furthermore, compared to the traditional IS fixation technique, the S2AI fixation technique can shorten operation time and reduce surgical trauma for the treatment of lumbosacral tuberculosis.

Comparative radiological outcomes and complications of sacral-2-alar iliac screw versus iliac screw for sacropelvic fixation.

PURPOSE: To compare the outcomes of sacropelvic fixation (SPF) using sacral-2-alar iliac (S2AI) screw with SPF using iliac screw (IS). METHODS: A comprehensive search of PubMed, EMBASE, Cochrane Central Register of Controlled Trials and Scopus was performed for comparative studies between S2AI and IS for SPF. Two independent investigators selected qualified studies and extracted data indispensably. With 95% confidence intervals (CI), the odds ratio (OR) was applied to dichotomous outcomes and standardized mean difference (SMD) was applied to continuous outcomes for each item. RESULTS: We included data from thirteen studies involving 722 patients (S2AI, 357 patients; IS, 365 patients). In the pediatric population, the S2AI group had a smaller pelvic obliquity (PO) than the IS group at final follow-up (SMD, - 0.38; 95% CI, - 0.72 to - 0.04). Patients who underwent S2AI screws showed reduced rates of re-operation (S2AI, 13%; IS, 28%), implant failure (S2AI, 12%; IS, 26%) [screw loosening (S2AI, 8%; IS, 20%); screw breakage (S2AI, 2%; IS, 12%)], implant prominence (S2AI, 2%; IS, 14%), pseudarthrosis (S2AI, 3%; IS, 15%), wound infection (S2AI, 8%; IS, 22%) and less blood loss (S2AI, 2035.4 ml; IS, 2708.4 ml). CONCLUSION: Radiological outcomes indicate an effective maintenance of the correction and arrest of progression of deformity by S2AI, which is equal or better than IS. SPF with S2AI screw has obviously lower incidence of postoperative complications and less blood loss. Given these advantages, the S2AI screw seems to be a beneficial alternative to IS.

Can pelvic incidence change after spinal deformity correction to the pelvis with S2-alar-iliac screws?

PURPOSE: Pelvic incidence (PI) is assumed to be fixed, yet studies have reported PI changes after long fusions to the pelvis. In a cohort of ASD patients undergoing surgery with S2-alar-iliac (S2AI) screws, we sought to: (1) report the magnitude of PI changes, and (2) evaluate subsequent pelvic parameter changes. METHODS: A retrospective case series of ASD patients undergoing surgical correction with S2AI screw placement and sagittal cantilever correction maneuvers was conducted. Patients were categorized based on preoperative PI: High-PI (H-PI) (PI ≥ 60°); Normal-PI (N-PI) (60° > PI > 40°); Low-PI (L-PI) (PI ≤ 40°). PI was measured preoperatively and immediately postoperatively. A significant PI change was established a priori at ≥ 6.0. PI, pelvic tilt (PT), lumbar lordosis (LL), and PI-LL mismatch were analyzed. RESULTS: In 68 patients (82.3% female, ages 22-75 years), the average change in PI was 4.6° ± 3.1, and 25 (36.8%) had a PI change ≥ 6.0° with breakdown as follows: H-PI 12 (66.7%) patients, 9 (25.87%) patients, and 4 (33.3%) patients. Of 25 patients with PI changes, 10 (14.7%) had a PI increase and 15 (22.1%) had a PI decrease. Significant improvements were seen in PT, LL, PI-LL mismatch in all patients with a PI change ≥ 6.0°, in addition to both subgroups with an increase or decrease in PI. CONCLUSIONS: PI changes of ≥ 6.0° occurred in 36.8% of patients, and H-PI patients most commonly experienced PI changes. Despite PI alterations, pelvic parameters significantly improved postoperatively. These results may be explained by sacroiliac joint laxity, S2AI screw placement, or aggressive sagittal cantilever techniques.

Innovative sacropelvic fixation using iliac screws and triangular titanium implants.

PURPOSE: Sacropelvic fixation is frequently used in combination with thoracolumbar instrumentation for the correction of severe spinal deformities. The purpose of this study was to explore the effects of the triangular titanium implants on the iliac screw fixation. Our hypothesis was that the use of triangular titanium implants can increase the stability of the iliac screw fixation. METHODS: Three T10-pelvis instrumented models were created: pedicle screws and rods in T10-S1, and bilateral iliac screws (IL); posterior fixation and bilateral iliac screws and triangular implants inserted bilaterally in a sacro-alar-iliac trajectory (IL-Tri-SAI); posterior fixation and bilateral iliac screws and two bilateral triangular titanium implants inserted in a lateral trajectory (IL-Tri-Lat). Outputs of these models, such as hardware stresses, were compared against a model with pedicle screws and rods in T10-S1 (PED). RESULTS: Sacropelvic fixation decreased the L5-S1 motion by 75-90%. The motion of the SIJ was reduced by 55-80% after iliac fixation; the addition of triangular titanium implants further reduced it. IL, IL-Tri-SAI and IL-Tri-Lat demonstrated lower S1 pedicle stresses with respect to PED. Triangular implants had a protective effect on the iliac screw stresses. CONCLUSION: Sacropelvic fixation decreased L5-S1 range of motion suggesting increased stability of the joint. The combination of triangular titanium implants and iliac screws reduced the residual flexibility of the sacroiliac joint, and resulted in a protective effect on the S1 pedicle screws and iliac screws themselves. Clinical studies may be performed to demonstrate applicability of these FEA results to patient outcomes.

Applicable safety analysis and biomechanical study of iliosacral triangular osteosynthesis.

BACKGROUND: The 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. METHODS: Pelvic 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. RESULTS: The 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. CONCLUSIONS: The 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.

Use of iliac screw associated with more correction of lumbar lordosis than S2-alar-iliac screw for adult spinal deformity.

BACKGROUND: To date, there is a paucity of reports clarifying the change of spinopelvic parameters in patients with adult spinal deformity (ASD) who underwent long segment spinal fusion using iliac screw (IS) and S2-alar-iliac screw (S2AI) fixation. METHODS: A retrospective review of consecutive patients who underwent deformity correction surgery for ASD between 2013 and 2017 was performed. Patients were divided into two groups based on whether IS or S2AI fixation was performed. All radiographic parameters were measured preoperatively, immediately postoperatively, and the last follow-up. Demographics, intraoperative and clinical data were analyzed between the two groups. Additionally, the cohort was subdivided according to the postoperative change in pelvic incidence (PI): subgroup (C) was defined as change in PI ≥5° and subgroup (NC) with change < 5°. In subgroup analyses, the 2 different types of postoperative change of PI were directly compared. RESULTS: A total of 142 patients met inclusion criteria: 111 who received IS and 31 received S2AI fixation. The IS group (65.6 ± 26°, 39.8 ± 13.8°) showed a significantly higher change in lumbar lordosis (LL) and upper lumbar lordosis (ULL) than the S2AI group (54.4 ± 17.9°, 30.3 ± 9.9°) (p < 0.05). In subgroup (C), PI significantly increased from 53° preoperatively to 59° postoperatively at least 50% of IS cohort, with a mean change of 5.8° (p < 0.05). The clinical outcomes at the last follow-up were significantly better in IS group than in S2AI group in terms of VAS scores for back and leg. The occurrence of sacroiliac joint pain and pelvic screw fracture were significantly greater in S2AI group than in IS group (25.8% vs 9%, p < 0.05) and (16.1% vs 3.6%, p < 0.05). CONCLUSIONS: Compared with the S2AI technique, the IS technique usable larger cantilever force demonstrated more correction of lumbar lordosis, and possible increase in pelvic incidence. Further study is warranted to clarify the clinical impaction of these results.

Long fusion to the pelvis with S2-alar-iliac screws can induce changes in pelvic incidence in adult spinal deformity patients: analysis of predictive factors in a retrospective cohort.

PURPOSE: To verify whether pelvic incidence (PI) would change in adult spinal deformity (ASD) patients who underwent long instrumentation using S2-alar-iliac (S2AI) screws and to identify factors associated with the change in PI. METHODS: We retrospectively reviewed all patients who underwent spinal surgery using S2AI screws between November 2014 and January 2017 at our institution. Patients aged 20 years or above with available radiographs were included. According to the change in PI, patients were divided into two groups, group C: PI variance reached 5 or more degrees postoperatively and group NC: PI changed less than 5°. RESULTS: A total of 47 patients (3 males, 44 females; mean age, 52.47 ± 15.80 years) were included in this study. PI significantly decreased from 51.25° ± 14.80° to 40.43° ± 14.23° in group C (n = 26), with a mean change in 11.52° ± 6.17° (P < 0.05), but changed from 47.00° ± 13.18° to 46.57° ± 13.71° in group NC without statistical significance. Intergroup analysis showed that change in PI, preoperative PI-LL, preoperative LL, preoperative SVA, and postoperative PT were significantly different between both groups. Correlation analysis showed that the change in PI and preoperative LL and PI were significantly associated. The formula provided by the regression analysis was ΔPI = - 3.108 - 0.11PreLL + 0.211PrePI. CONCLUSIONS: Our study showed that PI decreased in 55% of ASD patients after spinal surgery using S2AI screws. Greater preoperative PI-LL mismatch and PI, as well as lumbar kyphosis, were associated with postoperative change in PI. These slides can be retrieved under Electronic Supplementary Material.

Robotic-guided sacro-pelvic fixation using S2 alar-iliac screws: feasibility and accuracy.

PURPOSE: To review our experience with robotic guided S2-alar iliac (S2AI) screw placement. METHODS: We retrospectively reviewed patients who underwent S2AI fixation with robotic guidance. Screw placement and deviation from the preoperative plan were assessed by fusing preoperative CT (with the planned S2AI screws) to postoperative CT. The software's measurement tool was used to compare the planned vs. actual screw placements in axial and lateral views, at entry point to the S2 pedicle and at a 30 mm depth at the screws' mid-shaft, in a resolution of 0.1 mm. Medical charts were reviewed for technical issues and intra-operative complications. RESULTS: 35 S2AI screws were reviewed in 18 patients. The patients' mean age was 60 years. No intra-operative complications that related to the placement of S2AI screws were reported and robotic guidance was successful in all 35 screws. Post-operative CT scans showed that all trajectories were accurate. No violations of the iliac cortex or breaches of the anterior sacrum were noted. At the entry point, the screw deviated from the pre-operative plan by 3.0 ± 2.2 mm in the axial plane and 1.8 ± 1.6 mm in the lateral plane. At 30 mm depth, the screw deviated from the pre-operative plan by 2.1 ± 1.3 mm in the axial plane and 1.2 ± 1.1 mm in the lateral plane. CONCLUSIONS: Robotic guided S2AI screw placement is feasible and accurate. No screw malpositions or complications that related to the placement of S2AI screws occurred in this series. Larger studies are needed to assess the long-term clinical outcomes of robotic guided sacral-pelvic fixation.

S2 alar iliac screw placement under robotic guidance for adult spinal deformity patients: technical note.

PURPOSE: S2 alar-iliac (S2AI) screws are generally placed using an open approach, but have recently been shown to be implantable using a minimally invasive approach. Nevertheless, optimal screw positioning, even when supported by fluoroscopic guidance, is challenging in the complex anatomy of the sacral-pelvic area. This work presents our novel technique of S2AI sacropelvic fixation procedures performed with robotic guidance. METHODS: This was a single-center, retrospective, mini case-series of adult spinal deformity patients in need of sacropelvic fixation as part of a longer thoraco-lumbar fusion. The surgeon drilled a pilot hole through a robotic guide and then inserted a K-wire. A Jamshidi needle was placed over the K-wire and used to advance the pilot hole anterolaterally. RESULTS: Medical charts of four 60-70 year-old patients, who underwent robotic-guided insertion of S2AI screws in a minimally invasive approach were reviewed. Follow-up ranged between 10 and 13 months. Post-operative CTs and X-rays showed all eight trajectories were fully within the bone and accurately placed. Average surgery time per patient was 13 min with 5.3 s of fluoroscopy per screw. No intra- or post-operative complications occurred. CONCLUSIONS: Robotic-guidance with a Jamshidi needle technique was a safe and effective means for implanting S2AI screws in a minimally invasive approach.

S-1 and S-2-alar-iliac screw fixation via intraoperative navigation.

Adult deformity patients often require fixation to the sacrum and pelvis for construct stability and improved fusion rates. Although certain sacropelvic fixation techniques can be challenging, the availability of intraoperative navigation has made many of these techniques more feasible. In this video case presentation, the authors demonstrate the techniques of S-1 bicortical screw and S-2-alar-iliac screw fixation under intraoperative navigation in a 67-year-old female. This instrumentation placement was part of an overall T-10-pelvis construct for the correction of adult spinal deformity. The video can be found here: https://youtu.be/3HZo-80jQr8 .

Technique and nuances of an S-2 alar iliac screw for lumbosacral fixation in patients with transitional and normal anatomy.

S-2 alar iliac (S2AI) screw fixation has recently been recognized as a useful technique for pelvic fixation. The authors demonstrate two cases where S2AI fixation was indicated: one case was a sacral insufficiency fracture following a long-segment fusion in a patient with a transitional S-1 vertebra; the other case involved pseudarthrosis following lumbosacral fixation. S2AI screws offer rigid fixation, low profile, and allow easy connection to the lumbosacral rod. The authors describe and demonstrate the surgical technique and nuances for the S2AI screw in a case with transitional S-1 anatomy and in a case with normal S-1 anatomy. The video can be found here: https://youtu.be/Sj21lk13_aw .

Modified iliac screw fixation: technique and clinical application.

BACKGROUND: A conventional iliac bolt and the S2 alar iliac screw fixation technique (S2AI) are commonly used sacropelvic fixation techniques. However, conventional iliac bolt technique requires a lateral connector and commonly has prominent screw head problems. S2AI reportedly has a high instrument failure rate. We aim to introduce a modified iliac screw fixation technique and to investigate its clinical application in adult patients. METHODS: The entrance site of the modified iliac screw fixation technique was 1 cm medial and 1 cm caudal from the posterosuperior iliac spine. From 2009 to 2015, ten adult patients underwent sacropelvic fixation with the modified iliac screw fixation technique in our spine clinic. A minimum 12-month clinical and radiographic follow-up was adopted. The mean follow-up period was 30.7 months (12-74 months). Mean number of fixation levels was 7.7 segments (5-10 segments). RESULTS: Postoperatively, the C7 plumb line (SVA) was significantly decreased (P = 0.04). Upon the last X-ray, SVA did not differ between postoperative and the last X-ray (P = 0.1). There was no breakage during our follow-up period. There was no prominent screw head. There were no cases requiring implant removal. CONCLUSIONS: The modified iliac screw fixation technique does not cause prominence in the sacral region, and does not require a lateral connector, both of which are necessary when using the classical iliac bolt technique. This technique also avoids the acute angle between the screw head and the shaft of the screw commonly seen in S2AI. The modified iliac screw fixation technique can be an effective alternative for sacropelvic fixation.

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

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

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

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

A New Approach to the Treatment of Sacroiliac Joint Pain and First Patient-Reported Outcomes Using a Novel Arthrodesis Technique for Sacroiliac Joint Fusion.

Purpose: To report the development of a new sacroiliac joint (SIJ) arthrodesis system that can be used for isolated fusion of the SIJ and, unlike known implant systems, in combination with lumbar instrumentation or as an alternative to existing sacropelvic fixation (SPF) methods, and the patient-reported outcomes in two cases. Materials and Methods: After a comprehensive review of 207 pelvic computed tomography (CT) datasets, an implant body was designed. Its shape was modeled based on the SIJ recess. A screw anchored in the ilium secures the position of the implant and allows connection to lumbar instrumentation. Two patients with confirmed SIJ syndrome underwent surgery with the anatomically adapted implant. They were evaluated preoperatively, 6 months, and 12 months postoperatively. Visual Analogue Scale (VAS), Oswestry Disability Index (ODI), Million Visual Analogue Scale (MVAS), Roland Morris Score (RMS), reduction of SIJ/leg pain, and work status were assessed. Bony fusion of the SIJ was evaluated by radiographs and CT 12 months after the procedure. Results: Analysis of pelvic CT data revealed a wedge-shaped implant body in four different sizes. In the two patients, VAS decreased from 88 to 33 points, ODI improved from 67 to 35%, MVAS decreased from 80 to 36%, and RMS decreased from 18 to 9 points 12 months after surgery. SIJ pain reduction was 80% and 90%, respectively. Follow-up CT and radiographs showed solid bony integration. Conclusion: The implant used takes into account the unique anatomy of the SIJ and also meets the requirements of a true arthrodesis. Initial results in two patients are promising. Biomechanical and clinical studies will have to show whether the considerable theoretical advantages of the new implant system over existing SIJ implants - in particular the possibility of connection to a lumbar stabilization system - and SPFs can be put into practice.

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

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