Sacropelvic fixation: techniques and complications

A biomechanical study on bilateral SAI annular fixation in the treatment of unilateral Denis Ⅱ sacral fractures

PURPOSE

To investigate the biomechanical properties of bilateral SAI annular internal fixation in the treatment of unilateral Denis type Ⅱ sacral vertical fracture, so as to provide a reference for clinical practice.

METHODS

The finite element approach was utilized to simulate the Denis type Ⅱ fracture of the right sacral (the entire fracture through the sacral foraminarum) as well as the fracture of the upper and lower ramus of the right pubic bone, which represents unilateral vertical instability of the pelvic ring. The posterior pelvic ring was fixed using three different methods: lumbopelvic fixation and S1 transsacral screw (LPF-S1), bilateral S1AI annular fixation and S2 transsacral screw (BS1AI-S2), bilateral S2AI annular fixation and S1 transsacral screw (BS2AI-S1), and the anterior pelvic ring was fixed with pubic ramus screws. Six different loading methods are used to simulate six conditions: standing, forward bending, left flexion, right flexion, left rotation and right rotation. The maximum Von Mises stress of the implant, the vertical displacement of the upper surface of the sacral, and the relative intrafragmentary displacement (RID) of the observation point on the anterior surface of the sacral were recorded and analyzed.

RESULTS

The maximum Von Mises stress of the implant in the three fixed models did not exceed the maximum yield stress of the titanium alloy under different motion conditions in the finite element model. The descending order from high to low was LPF-S1, BS1AI-S2, and BS2AI-S1. The RID of each observation point on the anterior surface of the sacral and the vertical displacement of the upper surface of the sacral were both lower in the BS2AI-S1 group than in the LPF-S1 group and the BS1AI-S2 group. In the standing, forward flexion, left flexion, right flexion, and left rotation conditions, the LSD test results indicated a statistically significant difference in the mean RID of observation points between the BS2AI-S1 and BS1AI-S2 groups (p < 0.05), but not in the LPF-S1 group. In the condition of right rotational motion, there was no statistically significant difference in the mean RID between the three groups (p > 0.05).

CONCLUSION

The biomechanical stability of the fixation of Denis type II sacral fractures was satisfactory in the LPF-S1, BS1AI-S2, and BS2AI-S1 groups, with the BS2AI-S1 group exhibiting the maximum level of stability. Bilateral SAI annular internal fixation is a viable alternative to the fixation of vertical sacral fractures, as it does not impair the lumbar spine's mobility and accomplishes satisfactory biomechanical stability.

Feasibility and intra-operative accuracy of robotic-guided stacked S1AI and S2AI screw placement

BACKGROUND

Pelvic fixation with S1 and S2 sacral alar-iliac screws (S1 & S2 AIs) in a stacked configuration can help to offset the exceedingly large forces across the lumbosacral junction in long spinal fusion constructs extending to the sacrum. Traditionally, these modalities of pelvic fixation have been heavily reliant on fluoroscopy and other intraoperative imaging for safe insertion through the sacral alar, the sacroiliac joint and into the narrow corridor of the wing of the ilium. However, recently, computer-assisted robotic guidance and its intraoperative re-registration function has allowed for safe and accurate placement, and intraoperative accuracy assessment of S1 & S2 AIs while minimizing additional radiation associated with fluoroscopic-guidance.

OBJECTIVE

To review and report our experience with, and assess the intraoperative accuracy and feasibility of, robotic-guided S1AI and S2AI screws inserted in a stacked bedrock configuration as part of instrumented constructs aimed to achieve spinopelvic fusion.

STUDY DESIGN / SETTING

Retrospective Cohort study.

OUTCOME MEASURES

We evaluated the number of sacral spinopelvic fixation screws successfully implanted under robotic guidance and the deviation of the achieved screw trajectories from the pre-operatively planned trajectories. The presence and orientation of sacral alar-iliac cortical screw breaches and other intra- or postoperative complications directly related to placement of the stacked S1AI or S2AI implants were also evaluated.

METHODS

We included all patients that underwent posterior instrumented spinal fusion up to the pelvis under computer-assisted robotic guidance with open bilateral sacroiliac joint fixation and fusion using S1 & S2 AIs from June 2022 to December 2024. Patients were excluded if the pelvic fixation was not applied in a stacked bedrock configuration. Patient demographics, intra-operative technical errors, complications and other surgical parameters, and any post-operative complications were reviewed and recorded. The data was collected from clinical charts in the electronic medical records system, radiologic images from PACS, and surgical details from operative notes. We also obtained intraoperative secondary registration images for assessment of accuracy, interpreted as the deviation (mm) of the achieved trajectories from the preoperatively planned trajectories in the coronal and sagittal planes, from the robotic planning software system.

RESULTS

51 patients (32 F & 19 M), mean age 66 (34-80) years, underwent placement of S1AI and S2AI screws under computer-assisted robotic guidance in a stacked bedrock configuration. The most common primary indication for instrumented spinopelvic fusion in these cases was scoliosis (degenerative scoliosis = 26, idiopathic scoliosis = 8), followed in descending order by degenerative spondylolisthesis [10] and kyphosis [7]. Robotic guidance was successful in all 204 screws (4 screws per patient). There was no significant difference in the length of implants inserted on either side of the pelvis, however, the mean length of the S1 AIs (80 mm) was significantly shorter than the S2 AIs (90 mm) [p = 0.005]. The overall mean accuracy in all planes was 2.05 ± 1.97 mm; larger values of proximal deviation were associated with similarly larger values of distal deviation. The mean deviation of the revision screws was greater (3.5 ± 2.16) than that of newly inserted screws (1.72 ± 1.30) [p-value = 0.003]. There were no complications directly related to the robotic-guided placement of the screws. 11 iliac cortical breaches - 5 each through the lateral and medial cortices, and one through the inferior cortex - were identified in 10 patients on post-operative CT images but with no further clinical consequences as they only invaded the bulk masses of the surrounding mm.

CONCLUSION

Robotic-guided placement of S1 and S2 AI implants in a stacked bedrock configuration for spinopelvic fixation and fusion is feasible with clinically acceptable results. Secondary registration and intra-operative accuracy assessment of screw placement may help to avoid the need for revision surgery related to misplacement of these implants.

Sacral Alar-Iliac (SAI) screw diameter is not associated with pelvic fixation failure for neuromuscular scoliosis patients

PURPOSE

Determine if Sacral Alar-Iliac (SAI) screw diameter is associated with pelvic fixation failure in pediatric patients with neuromuscular scoliosis (NMS) treated with posterior spinal fusion (PSF).

METHODS

NMS patients from a single institution who underwent PSF with bilateral SAI screw fixation from 2010 to 2021 were retrospectively reviewed. Clinical parameters, SAI screw sizes, and radiographic outcomes were analyzed. Patients with greater or less than two SAI screws, > 21 years old, or with < 2 years of radiographic follow-up were excluded.

RESULTS

142 patients had 284 SAI screws placed. Mean(± SD) age was 13.6 ± 2.7 years. Preoperative curve magnitude averaged 84.3 ± 29.1°. Mean patient weight was 36.4 ± 14.1kg and BMI was 18 ± 5.1. Radiographic follow-up averaged 4.6 ± 2.0 years. Most screws (234/284,82.4%) were < 8.5 mm and 7.5 mm screws were most frequently used (158/248,55.6%). Mean screw diameter was 7.4 ± 0.7 mm. Patients with greater age, weight, and BMI trended towards larger screws. Three patients had five screw complications (1 screw fracture and 4 set screw dislodgments). One screw fracture (1/284,0.4%;7.5 mm diameter) and contralateral set screw dislodgement occurred in a patient at 14 months but was not revised. One patient who had bilateral set screws dislodge 3 months after PSF underwent revision. The remaining patient was asymptomatic and was observed. Screw diameter was not associated with risk of postoperative complications (p = 0.245).

CONCLUSION

SAI screw fracture is rare after PSF in pediatric patients with NMS. Contrary to pelvic fixation in adults, smaller diameter SAI screws, which may be optimal in patients with smaller anatomy, were not associated with increased risk of screw failure.

LEVEL OF EVIDENCE

III.

Historical Perspectives on the Evolution of Spino-Pelvic Fixation and its Implications on Clinical Care A Narrative Review

STUDY DESIGN

Broad narrative review.

OBJECTIVES

To review and summarize the evolution of spinopelvic fixation (SPF) and its implications on clinical care.

METHODS

A thorough review of peer-reviewed literature was performed on the historical evolution of sacropelvic fixation techniques and their respective advantages and disadvantages.

RESULTS

The sacropelvic junction has been a long-standing challenge due to a combination of anatomic idiosyncrasies and very high biomechanical forces. While first approaches of fusion were determinated by many material and surgical technique-related limitations, the modern idea of stabilization of the lumbosacral junction was largely initiated by the inclusion of the ilium into lumbosacral fusion. While there is a wide spectrum of indications for SPF the chosen technique remains is defined by the individual pathology and surgeons' preference.

CONCLUSION

By a constant evolution of both instrumentation hardware and surgical technique better fusion rates paired with improved clinical results could be achieved.

Do Iliac Screws Placed Close to the Sciatic Notch Have Greater Pullout Strength?

BACKGROUND AND OBJECTIVES

Optimal iliac screw position in relation to the sciatic notch remains unknown. In 12 cadavers undergoing S2 alar-iliac (S2AI) screw placement, we tested the pullout strength of screws placed in proximity to the sciatic notch (≤5 mm) vs farther away from the sciatic notch (>5 mm).

METHODS

A biomechanical, cadaver-based study was performed on 12 cadavers undergoing bilateral S2AI screw insertion. The position of the S2AI screw regarding the sciatic notch was dichotomized as ≤5 mm from the sciatic notch on the right side and >5 mm on the left side, confirmed using c-arm fluoroscopy. The primary outcome was the pullout strength of the screw (N). Secondary outcomes were stiffness (N/mm), yield force (N), and work to failure (N mm). Ischial tuberosity was embedded into polymethyl methacrylate and secured to a custom 3-axis vise grip mounted to a 14.5-kN load cell. Pullout testing was performed at 5 mm/min. Force and displacement data were collected at 100 Hz and evaluated using MATLAB. The Mann-Whitney test was performed.

RESULTS

Of 24 S2AI screws, 3 screws could not be tested because of cement-bone interface failure. A positive though nonsignificant trend of screw pullout strength was found for screws close to the notch compared with those farther from the notch (861.8 ± 340.7 vs 778.7 ± 350.8 N, P = .859). Similarly, screws close to the notch demonstrated a higher trend of stiffness (149.4 ± 145.4 vs 111.34 ± 128.2 N/mm, P = .320) and force to yield (806.9 ± 352.0 vs 618.6 ± 342.9 N, P = .455). Conversely, screws farther from the notch had a higher but similarly nonsignificant area under the force-displacement curve (10 867.0 ± 9565.0 vs 14 196.6 ± 9578.3 N mm, P = .455), which might be due to excess sheer/translation force that could not be reliably quantified.

CONCLUSION

Although placing S2AI screws ≤5 mm of the sciatic notch provided stronger fixation in 3 of 4 biomechanical testing categories, these results were not statistically significant. Therefore, placing S2AI screws ≤5 mm of the sciatic notch did not provide stronger fixation.

Treatment Strategies in the Osteoporotic Spine

This article reviews the appropriate assessment and management of osteoporotic compression fractures and discusses the implications of osteoporosis on initial patient evaluation, medical optimization for surgery, selection of instrumentation, and surgical technique. Adverse outcomes associated with osteoporosis are discussed. Failure to appropriately evaluate, optimize, and treat spine patients with osteoporotic bone can lead to disastrous complications. Weakened bone can lead to implant failure through cage subsidence and screw pullout, as well as, peri-implant fractures, failure of deformity correction, and proximal kyphosis. These risks must be taken into account when considering operative interventions in these patients.

Can We Rely on Prophylactic Two-Level Vertebral Cement Augmentation in Long-Segment Adult Spinal Deformity Surgery to Reduce the Incidence of Proximal Junctional Complications?

Background and Objectives: Proximal junctional kyphosis (PJK) and failure (PJF), the most prevalent complications following long-segment thoracolumbar fusions for adult spinal deformity (ASD), remain lacking in defined preventive measures. We studied whether one of the previously reported strategies with successful results-a prophylactic augmentation of the uppermost instrumented vertebra (UIV) and supra-adjacent vertebra to the UIV (UIV + 1) with polymethylmethacrylate (PMMA)-could also serve as a preventive measure of PJK/PJF in minimally invasive surgery (MIS). Materials and Methods: The study included 29 ASD patients who underwent a combination of minimally invasive lateral lumbar interbody fusion (MIS-LLIF) at L1-2 through L4-5, all-pedicle-screw instrumentation from the lower thoracic spine to the sacrum, S2-alar-iliac fixation, and two-level balloon-assisted PMMA vertebroplasty at the UIV and UIV + 1. Results: With a minimum 3-year follow-up, non-PJK/PJF group accounted for fifteen patients (52%), PJK for eight patients (28%), and PJF requiring surgical revision for six patients (21%). We had a total of seven patients with proximal junctional fracture, even though no patients showed implant/bone interface failure with screw pullout, probably through the effect of PMMA. In contrast to the PJK cohort, six PJF patients all had varying degrees of neurologic deficits from modified Frankel grade C to D3, which recovered to grades D3 and to grade D2 in three patients each, after a revision operation of proximal extension of instrumented fusion with or without neural decompression. None of the possible demographic and radiologic risk factors showed statistical differences between the non-PJK/PJF, PJK, and PJF groups. Conclusions: Compared with the traditional open surgical approach used in the previous studies with a positive result for the prophylactic two-level cement augmentation, the MIS procedures with substantial benefits to patients in terms of less access-related morbidity and less blood loss also provide a greater segmental stability, which, however, may have a negative effect on the development of PJK/PJF.

Connecting the S2 alar-iliac screw head to the satellite rod for surgical correction of degenerative sagittal imbalance

PURPOSE

The S2AI screw technique has several advantages over the conventional iliac screw fixation technique. However, connecting the S2AI screw head to the main rod is difficult due to its medial entry point. We introduce a new technique for connecting the S2AI screw head to a satellite rod and compare it with the conventional method of connecting the S2AI screw to the main rod.

METHODS

Seventy-four patients who underwent S2AI fixation for degenerative sagittal imbalance and were followed up for ≥ 2 years were included. All the patients underwent long fusion from T9 or T10 to the pelvis. The S2AI screw head was connected to the satellite rod (SS group) in 43 patients and the main rod (SM group) in 31 patients. In the SS group, the satellite rod was placed medial to the main rod and connected by the S2AI screw and domino connectors. In the SM group, the main rod was connected directly to the S2AI screw head and supported by accessory rods. Radiographic and clinical outcomes were evaluated in both groups.

RESULTS

There were no significant differences in postoperative complications, including proximal junctional failure, proximal junctional kyphosis, rod breakage, screw loosening, wound problems, and infection between the two groups. Furthermore, the correction power of sagittal deformity and clinical results in the SS group were comparable to those in the SM group.

CONCLUSION

Connecting the S2AI screw to the satellite rod is a convenient method comparable to the conventional S2AI connection method in terms of radiological and clinical outcomes.

Pelvic Fixation Construct Trends in Spinal Deformity Surgery

Purpose

Although many techniques exist, spinopelvic fixation continues to present challenges in the management of adult spinal deformity. Shear forces, complex anatomy, and bone quality are common reasons why spine surgeons continue to explore options for fixation.

Methods

A retrospective chart reviewed of patients receiving pelvic fixation for adult spinal deformity over a 12-year period was conducted. Patients were divided into 3 cohorts based on date of surgery: (1) 2010 to 2013, (2) 2014 to 2017, and (3) 2018 to 2021. Pelvic fixation constructs in the study included traditional iliac screws, stacked S2-alar-iliac (S2AI screws), and triangular titanium implants.

Results

Of the 494 patients with multiple implant constructs who met the inclusion criteria for this study, patients undergoing pelvic fixation surgery who received at least 2 implants increased by approximately 5% every 4 years (90.2%, 94.6%, 99.1% respectively). Over the 12-year span, the implementation of the S2AI screw grew 120%.

Conclusion

At our institution, there is a trend toward using multiple bilateral implant constructs for pelvic fixation, with nearly a tenfold percentage increase between the most recent cohorts. These include iliac screws with S2AI screws, multiple stacked S2AI screws, and S2AI screws used in conjunction with triangular titanium implants in hopes to decrease implant failure.

S2 Alar Screw Insertion Accuracy and Factors Associated With Screw Loosening and Lumbosacral Nonunion

OBJECTIVE

To investigate S2 alar screw (S2AS) accuracy and factors associated with S2AS loosening and lumbosacral nonunion.

METHODS

We retrospectively reviewed patients who underwent lumbosacral fusion surgery with S2AS addition under fluoroscopy. S2AS loosening and lumbosacral nonunion were analyzed using a 1-year postoperative computed tomography. S2AS insertion accuracy was originally classified as accurate, short, anterior perforation, lateral perforation, and sacroiliac joint (SIJ) deviation among lateral perforation. Clinical data including sex, age, body mass index, fused segments, fusion procedure, primary or revision surgery, Japanese Orthopedic Association scores and complications were collected. Factors associated with S2AS loosening and lumbosacral nonunion were analyzed.

RESULTS

A total of 37 patients (74 screws, age: 63.78 ± 13.57 years, female/male: 14/23 patients, body mass index: 23.11 ± 2.53, fused segments: 1-4 levels, revision: 38%) were included. S2AS loosening and lumbosacral nonunion were observed in 18 screws (13%) and 8 patients (22%) respectively. Only 35 screws (47%) were inserted accurately in our classification. Short, lateral perforation, and anterior perforation were observed in 14 screws (19%), 22 screws (30%), and 3 screws (4.1%). SIJ deviation was seen in 15 screws (20%) Factors associated with S2AS loosening were older age (P = 0.038), fusion levels (P = 0.011), and SIJ deviation (P < 0.001). S2AS loosening affects S1 pedicle screw (S1PS) loosening (P = 0.001). Furthermore, S2AS loosening is a risk factor for lumbosacral nonunion (P = 0.046).

CONCLUSIONS

S2AS insertion under fluoroscopy is inaccurate. S2AS loosening induces S1PS loosening and lumbosacral nonunion. Surgeons should avoid deviating to SIJ, especially in older patients and relatively longer fusion.

Bilateral dual iliac screw pelvic fixation for adult spinal deformity: a case report of a superior gluteal artery pseudoaneurysm secondary to aberrant iliac screw trajectory

PURPOSE

To present a case of a pseudoaneurysm of a branch of the left superior gluteal artery (SGA) secondary to lateral wall perforation from an iliac screw and its subsequent evaluation and management.

METHODS

Case report.

RESULTS

A 67-year-old female with a history of degenerative flatback and scoliosis and pathological fractures of T12 and L1 secondary to osteodisciitis underwent a single0stage L5-S1 ALIF and T9-pelvis posterior instrumented fusion with bilateral dual iliac screw fixation, revision T11-S1 decompression, and T12 and L1 irrigation and debridement and partial corpectomies. During the operation, non-pulsatile bleeding was encountered after creating an initial trajectory for the more proximal of the two left iliac screws. While the initial post-operative course was benign, the patient was readmitted for hypotension and anemia. Computed tomography of the abdomen/pelvis demonstrated a pseudoaneurysm (2.3 cm × 2.1 cm × 2.3 cm) of a branch of the left SGA. Diagnostic angiogram confirmed a pseudoaneurysm off of one of the branches of the left SGA. Endovascular embolization using multiple coils resulted in a complete cessation of blood flow in the pseudoaneurysm. At 2 years follow-up, no symptoms suggestive of recurrence of the pseudoaneurysm were reported.

CONCLUSIONS

A pseudoaneurysm of a branch of the left superior gluteal artery as a result of lateral wall perforation from an aberrantly placed iliac screw during an adult spinal deformity operation involving dual screw pelvic fixation is reported. Prompt recognition, multidisciplinary collaboration, and appropriate intervention were key in achieving a successful outcome and preventing further morbidity.

Correlation Between Rod Fracture and Shear Stress: A Novel Parameter

BACKGROUND

We sought to assess the accuracy of a novel parameter proportional to the rod shear stress (RSS) in identifying patients at risk of rod fracture (RF) after surgery for correction of adult spinal deformity.

METHODS

We performed a retrospective medical record review of patients aged ≥18 years treated for adult spinal deformity between 2004 and 2014 with ≥24 months of follow-up. The primary outcome was RFs identified radiographically. Patient weight (w), number of instrumented levels (N), and minimum rod diameter (d) were recorded and used to calculate the RSS parameter (RSS=Nwd2). Receiver operating characteristic curves were produced and the area under the curve (AUC ± 95% confidence interval [CI]) was calculated to compare this parameter's discriminative accuracy to that of its constituent variables. The sensitivity, specificity, and likelihood ratios (LRs) were calculated.

RESULTS

A total of 28 RF-positive and 154 RF-negative patients were included. The average age was 59.2 ± 9.6 years, and 93.4% were women. The RSS parameter produced the greatest AUC (0.73 ± 0.11). At an RSS cutoff of 30.1, it achieved a sensitivity of 71.4% and specificity of 71.4% (LR, 2.5; 95% CI, 1.8-3.5). The number of instrumented levels produced the next-greatest AUC (0.65 ± 0.12), with a sensitivity of 78.6% and specificity of 50.0% at a cutoff of 15 (LR, 1.6; 95% CI, 1.2-2.0).

CONCLUSIONS

The RSS is calculated using easily obtainable information and shows potential as a tool for predicting patient-specific risk of RF after spinal fusion. The number of instrumented levels also correlates strongly with the occurrence of RFs and is not significantly less accurate than the RSS. A larger sample size and prospective validation would be useful in determining with greater confidence which parameter is superior for predicting RFs after spinal fusion.

L4 fixation is not necessary in L5-Iliac spinopelvic fixation after trauma, but coadjutant transilio-transsacral fixation is

INTRODUCTION

Spinopelvic dissociation (SPD) is a severe injury characterized by a discontinuity between the spine and the bony pelvis consisting of a bilateral longitudinal sacral fracture, most of the times through sacral neuroforamen, and a horizontal fracture, usually through the S1 or S2 body. The introduction of the concept of triangular osteosynthesis has shown to be an advance in the stability of spinopelvic fixation (SPF). However, a controversy exists as to whether the spinal fixation should reach up to L4 and, if so, it should be combined with transiliac-transsacral screws (TTS).

OBJECTIVE

The purpose of this study is to compare the biomechanical behavior in the laboratory of four different osteosynthesis constructs for SPD, including spinopelvic fixation of L5 versus L4 and L5; along with or without TTS in both cases.

MATERIAL AND METHODS

By means of a formerly described method by the authors, an unstable standardized H-type sacral fracture in twenty synthetic replicas of a male pelvis articulated to the lumbar spine, L1 to sacrum, (Model: 1300, SawbonesTM; Pacific Research Laboratories, Vashon, WA, USA), instrumented with four different techniques, were mechanically tested. We made 4 different constructs in 5 specimen samples for each construct. Groups: Group 1. Instrumentation of the L5-Iliac bones with TTS. Group 2. Instrumentation of the L4-L5-Iliac bones with TTS. Group 3. Instrumentation of L5-Iliac bones without TTS. Group 4: Instrumentation of L4-L5-Iliac bones without TTS.

RESULTS AND CONCLUSIONS

According to our results, it can be concluded that in SPD, better stability is obtained when proximal fixation is only up to L5, without including L4 (alternative hypothesis), the addition of transiliac-transsacral fixations is essential.

Metastatic renal cell carcinoma of the lumbar spine with long posterior instrumented fusion and repetitive dislodgement of the set screws of the S2 alar-iliac screw

Background

S2 alar-iliac screws (S2AIS) are widely used to anchor the pelvis to a lumbar fusion. Here, we report a patient who experienced repetitive dislodgement of the set screws of the S2AIS following a posterior instrumented fusion.

Case Description

A 68-year-old male presented with an L3 metastasis and L2-L3 subluxation attributed to renal cell cancer. Following an L2-L5 posterior decompression and T9-pelvic fusion utilizing bilateral S2AIS fixation, the set screws of the S2AIS repeatedly dislodged, requiring two additional operations. The final surgery required multiple anchors to the ilium and provided adequate fixation until the patient's expiration.

Conclusion

The set screw fixing force was weaker than the fixing force of the S2AIS; multiple iliac anchors effectively salvaged this condition.

Skip Fusion With Sacral-Alar-Iliac Screw Fixation for Pelvic Ring and Lumbar Fractures: A Case Report

Pelvic ring fractures are associated with high-energy trauma and high mortality owing to critical blood loss and concomitant injuries. If there is a concurrent lumbar fracture, the postoperative range of motion will be limited owing to the increased fusion range. Here, we report a case in which skip fusion with sacral-alar-iliac screw fixation was effective as a minimally invasive procedure for treating pelvic ring and lumbar fractures.

The Lumbosacral Fractional Curve in Adult Degenerative Scoliosis

Spine surgeons are often faced with a profoundly difficult challenge in surgically treating adult degenerative scoliosis. Deformity correction surgery is complicated by the difficulty in offering extensive surgical corrections to the elderly, complication-prone population it commonly affects. As spine surgeons attempt to offer minimally invasive solutions to this disease process, the need for fusion of the fractional curve at L4, L5, and S1 may be discounted. A treatment strategy to identify, address, and treat the fractional curve with either open or minimally invasive techniques can lead to improved patient outcomes and decrease revision rates in this complicated pathologic process.

Pelvic Fixation With a Quad-Rod Technique Using S2 Alar Iliac and Medialized Entry Iliac Screws for Long Fusion Constructs

PURPOSE

Patients with adult spinal deformity (ASD) may have risk factors for nonunion and subsequent instrumentation failure. This study reviews a novel surgical technique for a quad-rod construct to the pelvis using both S2 alar iliac (S2AI) screw fixation and medialized entry iliac screw fixation as described through three separate cases and a review of the literature.

METHODS

This technique facilitates alignment of the construct and rod insertion into the tulip heads. The medialized iliac screw technique also avoids the potential soft-tissue complications of the conventional iliac screw bolt given that it is deeper and has more soft-tissue coverage.

RESULTS

Three cases performed by the most senior author (V.A.) in which this novel technique was used are presented in this report along with clinical and radiographic images to educate the reader on appropriate execution of this technique. A review of the existing literature regarding pelvic fixation techniques for ASD was also done.

CONCLUSION

Quad-rod augmentation of long thoracolumbar spinal constructs with two independent SI anchoring points is potentially an effective technique to increase lumbar sacral construct rigidity, thereby promoting fusion rates and decreasing revision rates. The described technique provides spine surgeons with an additional tool in their armamentarium to treat patients with complex ASD.

Modified unilateral iliac screw fixation with partial reduction in the treatment of high-grade spondylolisthesis at L5/S1 in adult patients: introduction of key technique, report of clinical outcomes and analysis of spinopelvic parameters

BACKGROUND

Management of high-grade spondylolisthesis (HGS) remains challenging. Spinopelvic fixation such as iliac screw (IS) was developed to deal with HGS. However concerns regarding constructs prominence and increased infection-related revision surgery have complicated it's use. We aim to introduce the modified iliac screw (IS) technique in treating high-grade L5/S1 spondylolisthesis and it's clinical and radiological outcomes.

METHODS

Patients with L5/S1 HGS who underwent modified IS fixation were enrolled. Pre- and postsurgical upright full spine radiographs were obtained to analyze sagittal imbalance, spinopelvic parameters, pelvic incidence-lumbar lordosis mismatch (PI-LL), slip percentage, slip angle (SA), and lumbosacral angle (LSA). Visual analogue scale (VAS), Oswestry disability index (ODI) were evaluated pre- and postoperatively for clinical outcomes assessment. Estimated blood loss, operating time, perioperative complications and revision surgery were documented.

RESULTS

From Jan 2018 to March 2020, 32 patients (15 males) with mean age of 58.66 ± 7.77 years were included. The mean follow-up period was 49 months. The mean operation duration was 171.67 ± 36.66 min. At the last follow-up: (1) the VAS and ODI score were significantly improved (p < 0.05), (2) PI increased by an average of 4.3°, the slip percent, SA and LSA were significantly improved (p < 0.05), (3) four patients (16.7%) with global sagittal imbalance recovered a good sagittal alignment, PI-LL within ± 10° was observed in all patients. One patient experienced wound infection. One patient underwent a revision surgery due to pseudoarthrosis at L5/S1.

CONCLUSION

The modified IS technique is safe and effective in treating L5/S1 HGS. Sparing use of offset connector could reduce hardware prominence, leading to lower wound infection rate and less revision surgery. The long-term clinical affection of increased PI value is unknown.

Safe Optimal Tear Drop View for Spinopelvic Fixation Using a Three-Dimensional Reconstruction Model of the Pelvis

Background

Spinopelvic fixation (SPF) has been a challenge for surgeons despite the advancements in instruments and surgical techniques. C-arm fluoroscopy-guided SPF is a widely used safe technique that utilizes the tear drop view. The tear drop view is an image of the corridor from the posterior superior iliac spine to the anterior inferior iliac spine (AIIS) of the pelvis. This study aimed to define the safe optimal tear drop view using three-dimensional reconstruction of computed tomography images.

Methods

Three-dimensional reconstructions of the pelvises of 20 individuals were carried out. By rotating the reconstructed model, we simulated SPF with a cylinder representing imaginary screw. The safe optimal tear drop view was defined as the one embracing a corridor with the largest diameter with the inferior tear drop line not below the acetabular line and the lateral tear drop line medial to the AIIS. The distance between the lateral border of the tear drop and AIIS was defined as tear drop index (TDI) to estimate the degree of rotation on the plane image. Tear drop ratio (TDR), the ratio of the distance between the tear drop center and the AIIS to TDI, was also devised for more intuitive application of our simulation in a real operation.

Results

All the maximum diameters and lengths were greater than 9 mm and 80 mm, respectively, which are the values of generally used screws for SPF at a TDI of 5 mm and 10 mm in both sexes. The TDRs were 3.40 ± 0.41 and 3.35 ± 0.26 in men and women, respectively, at a TDI of 5 mm. The TDRs were 2.26 ± 0.17 and 2.14 ± 0.12 in men and women, respectively, at a TDI of 10 mm.

Conclusions

The safe optimal tear drop view can be obtained with a TDR of 2.5 to 3 by rounding off the measured values for intuitive application in the actual surgical field.

Modified Iliac Screw in Lumbopelvic Fixation After Sacral Tumor Resection: A Single-Center Case Series

BACKGROUND

Traditional iliac screw, S2-alar iliac screw, and modified iliac screw are the 3 common techniques for lumbopelvic fixation. The application of the modified iliac technique in sacral spinal tumors has been rarely reported.

OBJECTIVE

To report the feasibility and safety of modified iliac screws after sacral tumor resection and their preliminary clinical outcomes.

METHODS

Twenty-seven patients who underwent sacral tumor resection with modified iliac screw fixation between August 2017 and August 2021 at our center were clinically and radiographically evaluated.

RESULTS

A total of 59 iliac screws were inserted by freehand according to the anatomic landmarks. The mean operation time was 207 minutes (range, 140-435 minutes). The average estimated blood loss was 1396 mL (300-4200 mL). Computed tomography scans showed that 2 (3.4%) screws penetrated the iliac cortex, indicating a 96.6% implantation accuracy rate. There were no iatrogenic neurovascular or visceral structure complications observed. The mean minimal distances from the screw head to the skin were 24.9 and 25.8 mm on the left and right sides, respectively. The mean minimal distances from the screw head to the horizontal level of the posterior superior iliac spine were 7.9 and 8.3 mm on the left and right sides, respectively. Two patients (7.4%) underwent reoperation for wound infection. At the latest follow-up, no patient had complications of screw head prominence, pseudarthrosis, or instrument failure.

CONCLUSION

The modified iliac screw is characterized by its minimal invasiveness and simplicity of placement. It is an ideal alternative for lumbopelvic fixation after sacral tumor resection.

Avoiding Spinal Implant Failures in Osteoporotic Patients: A Narrative Review

STUDY DESIGN

Narrative review.

OBJECTIVES

With an aging population, the prevalence of osteoporosis is continuously rising. As osseous integrity is crucial for bony fusion and implant stability, previous studies have shown osteoporosis to be associated with an increased risk for implant failure and higher reoperation rates after spine surgery. Thus, our review's purpose was to provide an update of evidence-based solutions in the surgical treatment of osteoporosis patients.

METHODS

We summarize the existing literature regarding changes associated with decreased bone mineral density (BMD) and resulting biomechanical implications for the spine as well as multidisciplinary treatment strategies to avoid implant failures in osteoporotic patients.

RESULTS

Osteoporosis is caused by an uncoupling of the bone remodeling cycle based on an unbalancing of bone resorption and formation and resulting reduced BMD. The reduction in trabecular structure, increased porosity of cancellous bone and decreased cross-linking between trabeculae cause a higher risk of complications after spinal implant-based surgeries. Thus, patients with osteoporosis require special planning considerations, including adequate preoperative evaluation and optimization. Surgical strategies aim towards maximizing screw pull-out strength, toggle resistance, as well as primary and secondary construct stability.

CONCLUSIONS

As osteoporosis plays a crucial role in the fate of patients undergoing spine surgery, surgeons need to be aware of the specific implications of low BMD. While there still is no consensus on the best course of treatment, multidisciplinary preoperative assessment and adherence to specific surgical principles help reduce the rate of implant-related complications.

Comparative Clinical Efficacy and Safety of Sacral-2-Alar Iliac Screw Versus Iliac Screw in the Lumbosacral Reconstruction of Spondylodiscitis

OBJECTIVE

This study aimed to evaluate the clinical efficacy and safety of S2-alar-iliac (S2AI) and iliac screw (IS) techniques in treating lumbosacral spondylodiscitis.

METHODS

Between January 2020 and January 2022, 28 patients suffering from lumbosacral spondylodiscitis underwent lumbosacral fixation and were divided into the IS group (14 patients) and the S2AI group (14 patients). Surgical details, demographic characteristics, preoperative and postoperative Oswestry Disability Index, visual analog scale, and complications were analyzed.

RESULTS

Twenty-eight patients were included in this study, including 14 patients treated with IS and 14 patients treated with S2AI. The 2 groups were similar in sex, age, follow-up period, total drainage volume, hospitalization stay, and fusion time. (P > 0.05) The estimated blood loss and surgical time of S2AI during surgery were significantly lower than those of IS. (P < 0.05) The visual analog scale and Oswestry Disability Index scores significantly improved in both groups from preoperative to the last follow-up. Sacroiliac joint pain was found in both groups in the follow-up period, but the incidence was not significantly different (P = 0.663). Compared with the IS approach, the incidence of symptomatic screw prominence was lower in the S2AI group, but the difference was not significant. (P = 0.088).

CONCLUSIONS

S2AI, as well as IS techniques, can achieve promising results for reconstructing lumbosacral stability in spondylodiscitis. In addition, the S2AI technique can also reduce surgical trauma and operation time.

Sacropelvic fixation

The sacropelvis is not only an anatomically complex region but also a biomechanically unique zone transferring axial weights via the transitional lumbosacral junction and the pelvic girdle to the lower appendicular skeleton. When the sacral instrumentation alone is insufficient to achieve stability and solid arthrodesis across the lumbosacral junction, as in long-segment fusions, high-grade spondylolisthesis, deformity corrections, complex sacral/lumbosacral injuries, and neoplasms, sacropelvic fixation is indicated. Many modern sacropelvic fixation modalities outperform historical modalities, especially the conventionally open and percutaneous iliac and S2-alar-iliac screw (S2AI) fixation techniques. Novel screw insertion technologies such as navigation and robotics and modern screw designs aim to maximize the accuracy of screw placement and minimize complications. This review addresses the anatomy and biomechanics of the sacropelvic region as well as the indications, evolution, advantages, and disadvantages of various past and contemporary techniques of lumbosacral and sacropelvic fixation.

Catastrophic acute failure of pelvic fixation in adult spinal deformity requiring revision surgery: a multicenter review of incidence, failure mechanisms, and risk factors

OBJECTIVE

There are few prior reports of acute pelvic instrumentation failure in spinal deformity surgery. The objective of this study was to determine if a previously identified mechanism and rate of pelvic fixation failure were present across multiple institutions, and to determine risk factors for these types of failures.

METHODS

Thirteen academic medical centers performed a retrospective review of 18 months of consecutive adult spinal fusions extending 3 or more levels, which included new pelvic screws at the time of surgery. Acute pelvic fixation failure was defined as occurring within 6 months of the index surgery and requiring surgical revision.

RESULTS

Failure occurred in 37 (5%) of 779 cases and consisted of either slippage of the rods or displacement of the set screws from the screw tulip head (17 cases), screw shaft fracture (9 cases), screw loosening (9 cases), and/or resultant kyphotic fracture of the sacrum (6 cases). Revision strategies involved new pelvic fixation and/or multiple rod constructs. Six patients (16%) who underwent revision with fewer than 4 rods to the pelvis sustained a second acute failure, but no secondary failures occurred when at least 4 rods were used. In the univariate analysis, the magnitude of surgical correction was higher in the failure cohort (higher preoperative T1-pelvic angle [T1PA], presence of a 3-column osteotomy; p < 0.05). Uncorrected postoperative deformity increased failure risk (pelvic incidence-lumbar lordosis mismatch > 10°, higher postoperative T1PA; p < 0.05). Use of pelvic screws less than 8.5 mm in diameter also increased the likelihood of failure (p < 0.05). In the multivariate analysis, a larger preoperative global deformity as measured by T1PA was associated with failure, male patients were more likely to experience failure than female patients, and there was a strong association with implant manufacturer (p < 0.05). Anterior column support with an L5-S1 interbody fusion was protective against failure (p < 0.05).

CONCLUSIONS

Acute catastrophic failures involved large-magnitude surgical corrections and likely resulted from high mechanical strain on the pelvic instrumentation. Patients with large corrections may benefit from anterior structural support placed at the most caudal motion segment and multiple rods connecting to more than 2 pelvic fixation points. If failure occurs, salvage with a minimum of 4 rods and 4 pelvic fixation points can be successful.

S2 alar-iliac screw versus traditional iliac screw for spinopelvic fixation: a systematic review of comparative biomechanical studies

PURPOSE

To review and compare biomechanical properties between S2 alar-iliac (S2AI) screws and traditional iliac screws for spinopelvic fixation.

METHODS

A systematic review was performed according to PRISMA guidelines. All clinical, cadaveric, and finite-element model (FEM) studies that compared the biomechanical properties between S2AI screws and traditional iliac screws were included. Study methodological quality for cadaveric studies were analyzed using the Quality Appraisal for Cadaveric Studies (QUACS) scale.

RESULTS

Eight studies (4 cadaveric, 4 FEM) analyzing 58 S2AI screws and 48 traditional iliac screws were included. According to QUACS, the overall methodological quality was "moderate to good" for all four cadaveric studies. All four cadaveric studies found no difference in biomechanical stiffness, screw toggle, rod strain, and/or load-to-failure between the S2AI screws and traditional iliac screws for spinopelvic fixation. All four FEM studies found that S2AI screws were associated with lower implant stresses compared to traditional iliac screws.

CONCLUSIONS

There is moderate biomechanical evidence to suggest that there is no significant difference in stability and stiffness between S2AI screws and traditional iliac screws for spinopelvic fixation. However, there is some evidence to support that the placement of S2AI screws may have lower implant stresses on the overall lumbosacral instrumentation compared to traditional iliac screws.

Multiple Points of Pelvic Fixation: Stacked S2-Alar-Iliac Screws (S2AI) or Concurrent S2AI and Open Sacroiliac Joint Fusion with Triangular Titanium Rod

Sacropelvic fixation is a continually evolving technique in the treatment of adult spinal deformity. The 2 most widely utilized techniques are iliac screw fixation and S2-alar-iliac (S2AI) screw fixation^1-3. The use of these techniques at the base of long fusion constructs, with the goal of providing a solid base to maintain surgical correction, has improved fusion rates and decreased rates of revision⁴.

Description

The procedure is performed with the patient under general anesthesia in the prone position and with use of 3D computer navigation based on intraoperative cone-beam computed tomography (CT) imaging. A standard open posterior approach with a midline incision and subperiosteal exposure of the proximal spine and sacrum is performed. Standard S2AI screw placement is performed. The S2AI starting point is on the dorsal sacrum 2 to 3 mm above the S2 foramen, aiming as caudal as possible in the teardrop. A navigated awl is utilized to establish the screw trajectory, passing through the sacrum, across the sacroiliac (SI) joint, and into the ilium. The track is serially tapped with use of navigated taps, 6.5 mm followed by 9.5 mm, under power. The screw is then placed under power with use of a navigated screwdriver.Proper placement of the caudal implant is vital as it allows for ample room for subsequent instrumentation. The additional point of pelvic fixation can be an S2AI screw or a triangular titanium rod (TTR). This additional implant is placed cephalad to the trajectory of the S2AI screw. A starting point 2 to 3 mm proximal to the S2AI screw tulip head on the sacral ala provides enough clearance and also helps to keep the implant low enough in the teardrop that it is likely to stay within bone. More proximal starting points should be avoided as they will result in a cephalad breach.For procedures with an additional point of pelvic fixation, the cephalad S2AI screw can be placed using the previously described method. For placement of the TTR, the starting point is marked with a burr. A navigated drill guide is utilized to first pass a drill bit to create a pilot hole, followed by a guide pin proximal to the S2AI screw in the teardrop. Drilling the tip of the guide pin into the distal, lateral iliac cortex prevents pin backout during the subsequent steps. A cannulated drill is then passed over the guide pin, traveling from the sacral ala and breaching the SI joint into the pelvis. A navigated broach is then utilized to create a track for the implant. The flat side of the triangular broach is turned toward the S2AI screw in order to help the implant sit as close as possible to the screw and to allow the implant to be as low as possible in the teardrop. The navigation system is utilized to choose the maximum possible implant length. The TTR is then passed over the guide pin and impacted to the appropriate depth. Multiplanar post-placement fluoroscopic images and an additional intraoperative CT scan of the pelvis are obtained to verify instrumentation position.

Alternatives

The use of spinopelvic fixation in long constructs is widely accepted, and various techniques have been described in the past¹. Alternatives to stacked S2AI screws or S2AI with TTR for SI joint fusion include traditional iliac screw fixation with offset connectors, modified iliac fixation, sacral fixation alone, and single S2AI screw fixation.

Rationale

The lumbosacral junction is the foundation of long spinal constructs and is known to be a point of high mechanical strain^5-7. Although pelvic instrumentation has been utilized to increase construct stiffness and fusion rates, pelvic fixation failure is frequently reported^8,9. At our institution, we identified a 5% acute pelvic fixation failure rate over an 18-month period¹⁰. In a subsequent multicenter retrospective series, a similar 5% acute pelvic fixation failure rate was also reported¹¹. In response to these findings, our institution changed its pelvic fixation strategies to incorporate multiple points of pelvic fixation. From our experience, utilization of multiple pelvic fixation points has decreased acute failure. In addition to preventing instrumentation failure, S2AI screws are lower-profile, which decreases the complication of implant prominence associated with traditional iliac screws. S2AI screw heads are also more in line with the pedicle screw heads, which decreases the need for excessive rod bending and connectors.The use of the techniques has been described in case reports and imaging studies^12-14, but until now has not been visually represented. Here, we provide technical and visual presentation of the placement of stacked S2AI screws or open SI joint fusion with a TTR above an S2AI screw.

Expected Outcomes

Pelvic fixation provides increased construct stiffness compared with sacral fixation alone^15-17 and has shown better rates of fusion⁴. However, failure rates of up to 35%^8,9 have been reported, and our own institution identified a 5% acute pelvic fixation failure rate¹⁰. In response to this, the multiple pelvic fixation strategy (stacked S2AI screws or S2AI and TTR for SI joint fusion) has been more widely utilized. In our experience utilizing multiple points of pelvic fixation, we have noticed a decreased rate of pelvic fixation failure and are in the process of reporting these findings^18,19.

Important Tips

The initial trajectory of the caudal S2AI screw needs to be as low as possible within the teardrop, just proximal to the sciatic notch.The starting point for the cephalad implant should be 2 to 3 mm proximal to the S2AI screw tulip head. This placement provides enough clearance and helps to contain the implant in bone.More proximal starting points may result in cephalad breach of the TTR.The use of a reverse-threaded Kirschner wire helps to prevent pin backout while drilling and broaching for TTR placement.If malpositioning of the TTR is found on imaging, removal and redirection is technically feasible.

Acronyms and Abbreviations

S2AI = S2-alar-iliacTTR = triangular titanium rodCT = computed tomographyAP = anteroposteriorOR = operating roomSI = sacroiliacDRMAS = dual rod multi-axial screwK-wire = Kirschner wireDVT = deep vein thrombosisPE = pulmonary embolism.

Clinical utility of minimally invasive posterior internal fixation within the pelvic ring using S2 alar iliac screws for unstable pelvic ring fracture

INTRODUCTION

Posterior internal fixation for unstable pelvic ring fractures is often associated with complications, including pelvic hemorrhage and gluteal necrosis. Pelvic ring fixation using the S2 alar iliac screw (SAIS) without fixation of the lumbosacral vertebrae may have potential as a novel, minimally invasive technique for treating unstable pelvic ring fractures. The present study compared clinical outcomes in patients who underwent SAIS fixation within the pelvic ring with a historical control group of patients who underwent conventional trans-iliac plate fixation for the treatment of unstable pelvic ring fractures.

MATERIALS AND METHODS

Thirty-two patients diagnosed with unstable pelvic fractures with sacral fracture or sacroiliac joint fracture dislocation were retrospectively evaluated. Eight consecutive patients underwent trans-iliac plate fixation from April 2012 to March 2015, and 24 consecutive patients underwent SAIS fixation from April 2015 to February 2020. Rates of soft tissue complications, intraoperative blood loss, and intraoperative blood transfusion volume were compared in these two groups.

RESULTS

Mean intraoperative blood loss was significantly lower in patients who underwent SAIS fixation than in those who underwent trans-iliac plate fixation (141.0 ml vs 315.0 ml; P = 0.027), although there were no between-group differences in intraoperative blood transfusion volume (0.0 ml vs 140 ml; P = 0.105), incidence rate of soft tissue complications (4.2% vs 0%; P = 1.000), and operation time (88.5 min vs 93.0 min; P = 0.862). Bone healing was confirmed in all patients who underwent SAIS fixation without dislocation of the fracture site, whereas one patient who underwent trans-iliac plate fixation experienced a dislocation of the fracture site during follow-up (0% vs 12.5%; P = 0.250).

CONCLUSIONS

SAIS fixation reduces intraoperative blood loss and ensures bone healing without major complications, including dislocation of the fracture site. SAIS fixation may therefore be an alternative, minimally invasive method of treating unstable pelvic fractures.

Minimum 2-Year Analysis of S2-Alar-Iliac Screw Fixation for Adult Spinal Deformity

STUDY DESIGN

Retrospective cohort.

OBJECTIVE

Determine the rate and risk factors for S2AI screw-related pain after adult spinal deformity surgery with a minimum 2-year follow-up.

METHODS

A consecutive 83 spinal deformity patients undergoing surgical treatment between August 2015 and December 2017 with minimum 2-year follow-up for S2AI screw complication and screw-related pain were included. Linear regression was performed on various risk factors and postoperative S2AI screw-related pain. Subset analysis of 53 patients was performed on preoperative and postoperative SRS and ODI scores, operative data, and radiographic data.

RESULTS

The overall proportion of S2AI screw-related pain was 9.6%. An S2AI screw complication was identified radiographically in 10.8% of patients; among these, 22.2% experienced S2AI screw-related pain. 3.4% of all patients underwent S2A1 screw removal. The SRS, ODI, sagittal vertical axis (SVA), and coronal alignment scores/measurements improved following treatment in all patients. However, the mean difference for the pre and postoperative SRS function score (1.2 ± 0.5 vs 0.9 ± 0.8) and SVA (4.0 ± 4.9 cm vs 2.1 ± 4.8 cm) were higher for the pain group.

CONCLUSIONS

A minimum 2-year analysis of S2AI screw fixation in adult spinal deformity patients showed that 9.6% of patients experienced S2AI screw-related pain and 3.4% of patients had S2A1 screws removed. The size and the number of S2AI screws did not predict postoperative pain, nor were radiographic findings correlated with clinical outcomes. The patient outcome scores, coronal alignment, and SVA improved for all patients, but within the pain group there was an overall larger change in the SVA and SRS function score.

Freehand S2-Alar-Iliac Screw Placement Technique in Lumbosacral Spinal Tumors: A Preliminary Study

OBJECTIVE

S2-alar-iliac (S2AI) screw technique is widely used in spinal surgery, but it is rarely seen in the field of spinal tumors. The aim of the study is to report the preliminary outcomes of the freehand S2AI screw fixation after lumbosaral tumor resection.

METHODS

The records of patients with lumbosacral tumor who underwent S2AI screw fixation between November 2016 to November 2020 at our center were reviewed retrospectively. Outcome measures included operative time, blood loss, complications, accuracy of screws, screw breach, and overall survival. Mean ± standard deviation or range was used to present continuous variables. Kaplan-Meier curve was used to present postoperative survival.

RESULTS

A total of 23 patients were identified in this study, including 12 males and 11 females, with an average age of 47.3 ± 14.5 (range,15-73). The mean operation time was 224.6 ± 54.1 (range, 155-370 min). The average estimated blood loss was 1560.9 ± 887.0 (600-4000 ml). A total of 46 S2AI screws were implanted by freehand technique. CT scans showed three (6.5%) screws had penetrated the iliac cortex, indicating 93.5% implantation accuracy rate. No complications of iatrogenic neurovascular or visceral structure were observed. The average follow-up time was 31.6 ± 15.3 months (range, 13-60 months). Two patients' postoperative plain radiography showed lucent zone around the screw. One patient underwent reoperation for wound delayed infection. At the latest follow-up, eight patients had tumor-free survival, 11 had survival with tumor, and four died of disease.

CONCLUSION

The freehand S2AI screw technique is reproducible, safe, and reliable in the management of lumbosacral spinal tumors.

Rates of Loosening, Failure, and Revision of Iliac Fixation in Adult Deformity Surgery

STUDY DESIGN

Retrospective cohort review of a prospective multicenter database.

OBJECTIVE

Identify rates and variations in lumbopelvic fixation failure after adult spinal deformity (ASD) correction.

SUMMARY OF BACKGROUND DATA

Traditional iliac (IS) and S2-alar-iliac (S2AI) pelvic fixation methods have unique technical characteristics for their application, and result in varied bio-mechanical and anatomic impact. These differences may lead to variance in lumbopelvic fixation failure types/rates.

METHODS

ASD patients undergoing correction with more than five level fusion and pelvic fixation, separated by pelvic fixation type (IS vs. S2AI). Fixation fracture or loosening assessed radiographically (Figure 1). Multivariate logistic regression, accounting for significant confounders, was used to examine differences between the two groups for screw loosening/fracture, rod fracture, and revision surgery. Level of significance set at P< 0.05.

RESULTS

Four hundred eighteen of 1422 patients were included (IS = 287, S2AI = 131). The groups had similar age, body mass index (BMI), baseline comorbidities, number of levels fused (P>0.05), baseline health related quality of life measures (HRQLs) (short form survey-36, Oswestry Disability Index [ODI], Scoliosis Research Society [SRS-22], numeric rating scale [NRS] leg and back, P>0.05) and deformity (pelvic tilt [PT], pelvic incidence-lumbar lordosis [PI-LL], and sagittal vertical axis [SVA], P> 0.05). The IS group had more unilateral fixation versus S2AI (12.9% vs. 6%; P = 0.02). The overall lumbopelvic fixation failure rate was 23.74%. Pelvic fixation (13.4%) and S1 screw (2.9%) loosening was more likely with S2AI (odds ratio [OR] 2.63, P = 0.001; OR 6.05, P = 0.022). Pelvic screw (2.3%) and rod fracture (14.1%) rates similar between groups but trended toward less occurrence with S2AI (OR 0.47, P= 0.06). Revision surgery occurred in 22.7%, and in 8.5% for iliac fixation specifically, but with no differences between fixation types (P = 0.55 and P = 0.365). Pelvic fixation failure conferred worse HRQL scores (physical component score [PCS] 36.23 vs. 39.37, P= 0.04; ODI 33.81 vs. 27.93, P = 0.036), and less 2 years improvement (PCS 7.69 vs. 10.46, P = 0.028; SRS 0.83 vs. 1.03, P = 0.019; ODI 12.91 vs. 19.77, P = 0.0016).

CONCLUSION

Lumbopelvic fixation failure rates were high following ASD correction, and associated with lesser clinical improvements. S2AI screws were more likely to demonstrate loosening, but less commonly associated with rod fractures at the lumbopelvic region.

Sacroiliac Joint Degeneration After Lumbopelvic Fixation

STUDY DESIGN

Retrospective Study.

OBJECTIVES

Sacroiliac buttress screws (SBS) and S2 alar iliac screws (SAI) are used as distal screws in cases with long fusion to the pelvis. Distal fixation ends, whether exceeding the sacroiliac joint (SIJ), may affect postoperative degenerative changes in the SIJ. The aim of this study was to investigate SIJ degeneration after lumbosacral and lumbopelvic fixation, using SBS and SAI in degenerative spine diseases, respectively.

METHODS

This study included 70 patients aged ≥50 years with lumbosacral fusion (>3 levels). They were divided into 2 groups (SBS 20 and SAI 50 cases) based on the type of distal screws. Radiographical and clinical data were reviewed with a minimum 2-year follow-up. Radiographical SIJ degeneration was analyzed using computed tomography; clinical outcomes were evaluated using visual analog scale (VAS) and Japanese Orthopaedic Association Back Pain Questionnaire (JOABPEQ).

RESULTS

No significant differences were observed in patients' preoperative characteristics between the 2 groups. The incidence of SIJ degeneration, including osteophyte formation (30.0% and 8.0%, p = 0.03), intraarticular air (75.0% and 16.0%, p < 0.001), and subchondral cyst (20.0% and 2.0%. p = 0.02) in SBS and SAI groups, respectively, at the follow-up, was significantly higher in the SBS group. Although SIJ degenerative changes were significantly different between the SBS and SAI groups, there was no significant difference in VAS and JOABPEQ scores between the groups at 2 years post-surgery.

CONCLUSIONS

Lumbosacral fusion can cause SIJ degeneration, which is more frequent when SBS are used in fixation to the sacrum.

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.

Radiological Evaluation of Pelvic Morphology for S2 Alar-Iliac Screw Insertion in the Japanese Samples: A Retrospective Cohort Study

Introduction

S2 alar-iliac screw (S2AIS) insertion for lumbosacral fixation is becoming a common procedure for deformity surgeries. However, studies that have reported the anatomy and morphometric features of the pelvis for S2AIS insertion in the Japanese samples are scarce. This study aimed to elucidate the morphometric features of the pelvis regarding S2AIS insertion in the Japanese samples.

Methods

We used 60 computed tomography scans of the pelvis (30 men and 30 women). The entry point for the S2AIS was determined as 1-mm lateral and 1-mm distal to the S1 dorsal sacral foramen. We resliced the plane in which the pelvis was sectioned obliquely from this entry point to the anterior inferior iliac spine in the sagittal plane. We bilaterally placed the shortest and longest virtual S2AISs in this plane using a 4-mm margin. We analyzed the length, angle, and safety of the determined trajectory and compared these measurements according to sex and age.

Results

The median longest and shortest screw lengths were 108.1 and 103.3 mm, respectively. The median longest and shortest distances from the entry point to the sacroiliac joint were 31.2 and 28.2 mm, respectively. The median smallest and largest lateral angulations were 40.7° and 47.3°, respectively. The median angle range was 4.2°. The median caudal angulation was -2.8°. The median shortest and longest distances from the S2AISs to the acetabular roof were 23.5 and 27.4 mm, respectively. The median distance from the S2AISs to the sciatic notch was 23.1 mm. Assuming the insertion of screw with a diameter of 8 mm, S2AIS insertion was difficult in 32 of 120 (27%) screws because the dorsal cortex of the sacrum was damaged.

Conclusions

Screw length and lateral angulation were similar to those in previous studies. Insertion difficulty occurred in 27% of screws.

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.

The relationship between S1 screw loosening and postoperative outcome in patients with degenerative lumbar scoliosis

Background

When choosing S1 as the lowest level of instrumentation, there are many complications may come out such as S1 screw loosening. Facing this problem, there has been various techniques for the protection of S1 screw including sacropelvic fixation, bicortical or tricortical insertion of S1 screw.

Objective

This study aimed to explore the risk factors for the S1 screw loosening, then to demonstrate the relationship between S1 screw loosening and postoperative outcome for patients with degenerative lumbar scoliosis (DLS).

Methods

Patients who underwent lumbosacral fixation for DLS were evaluated retrospectively. They were divided into two groups according to the S1 pedicle screw at the follow-up. Age, gender, bone mineral density, body mass index, history of smoking, the number of instrumented levels, comorbidities, complications and radiological parameters were collected. We established logistic regression analysis to determine independent risk factors for S1 screw loosening and multiple linear regression to identify whether S1 screw loosening would influence postoperative clinical outcome.

Results

S1 screw loosening rate was up to 41.0% (32/78). Patients were older in the S1 screw loosening group than those in the control group (P < 0.05). Compared with the control group, the rate of osteoporosis was higher in screw loosening group than that in the control group (P < 0.05). Older age and osteoporosis were independent risk factors for S1 screw loosening (P < 0.05). In the screw loosening group, the rate of hypertension was higher than that in the control group (P < 0.05). The relationship of S1 screw loosening and ODI was not significant in the multiple linear regression (P > 0.05). The clinical outcome was similar in the S1 screw loosening group and control group (P > 0.05).

Conclusion

Older age and osteoporosis are independent risk factors for the S1 screw loosening. Patients with complication of S1 screw loosening are not always along with worse clinical outcome. We should consider potential benefit, complications and medical cost when choosing the lowest instrumented vertebrae for patients with DLS.

Trends and Complications in Spinopelvic Fixation for Deformity for Spinal Surgeons in Early Independent Practice

STUDY DESIGN

Retrospective case series study.

OBJECTIVE

Evaluate trends and complications following posterior spinal instrumented fusion for deformity with/without pelvic fixation using the American Board of Orthopaedic Surgery Part II Oral Examination Candidate Case List data from 2008 to 2017.

SUMMARY OF BACKGROUND DATA

Complication rates for cases with pelvic fixation are widely reported in spine deformity literature but are typically derived from practices of senior surgeons. As surgical experience and clinical volume are shown to decrease complication rates, spine surgeons newly in practice may have higher risks of such events.

MATERIALS AND METHODS

Surgical cases submitted by candidates taking the American Board of Orthopaedic Surgery Part II Oral Examination between 2008 and 2017 with a self-designated sub-specialty of spine surgery were retrospectively reviewed. Mortality, readmission/reoperation data, and complications as reported by candidates were tracked over time. Bivariate testing and multivariable Poisson analyses, respectively, were used to assess complication rates and time-related trends.

RESULTS

A total of 37,539 cases were submitted between 2008 and 2017. Four hundred sixty-one cases (1.2%) were for deformity; of these, 60 cases included pelvic fixation (13% of deformity cases). For all deformity cases, we noted medical, surgical, and overall complication rates to be 17%, 22.3%, and 31.5%. Multivariable analyses demonstrated no difference in surgical/overall complication rates between spinopelvic and nonspinopelvic instrumented groups, but showed a consistently low number of cases using spinopelvic fixation over time.

CONCLUSIONS

Newly practicing spinal surgeons consistently performed low numbers of deformity cases with relatively high complication rates which remained stable over time.

The degenerative changes of the sacroiliac joint after S2 alar-iliac screw placement

OBJECTIVE

The goal of this study was to investigate clinical outcomes and risk factors for the progression of sacroiliac joint (SIJ) degeneration and bone formation after S2 alar-iliac screw (S2AIS) insertion.

METHODS

Using preoperative and follow-up CT scan findings (median follow-up 26 months, range 16-43 months), the authors retrospectively studied 100 SIJs in 50 patients who underwent S2AIS placement. The authors measured the progression of SIJ degeneration and bone formation after S2AIS insertion, postoperative new-onset SIJ pain, S2AIS-related reoperation, and instrumentation failures. Stepwise multivariate logistic regression modeling was performed to clarify the risk factors associated with the progression of SIJ degeneration.

RESULTS

Significant progression of SIJ degeneration was observed in 10% of the group with preoperative SIJ degeneration (p = 0.01). Bone formation was observed in 6.9% of joints. None of the patients with these radiographic changes had new-onset SIJ pain or underwent reoperation related to instrumentation failures. Multivariate logistic regression analysis revealed that preoperative SIJ degeneration (p < 0.01) and a young age at surgery (p = 0.03) significantly affected the progression of SIJ degeneration.

CONCLUSIONS

The progression of SIJ degeneration and bone formation neither led to major screw-related complications nor affected the postoperative clinical course during the median follow-up period of 26 months. Although S2AIS insertion is a safe procedure for most patients, the results of this study suggested that preoperative degeneration and younger age at surgery affected SIJ degeneration after S2AIS insertion. Further long-term observation may reveal other effects of S2AIS insertion on SIJ degeneration.

Intraoperative neuromonitoring during surgery for lumbar stenosis

The indications for neuromonitoring during lumbar stenosis surgery are defined by the risks associated with patient positioning, the approach, decompression of neural elements, deformity correction, and instrument implantation. The routine use of EMG and SEP alone during lumbar stenosis surgery is no longer supported by the literature. Lateral approach neuromonitoring with EMG only is also suspect. Lumbar stenosis patients often present with multiple co-morbidities which put them at risk during routine pre-surgical positioning. Frequently encountered morbid obesity and/or diabetes mellitus may play a role in monitorable and preventable brachial plexopathy after "superman" positioning or femoral neuropathy from groin pressure after prone positioning, for example. Deformity correction in lumbar stenosis surgery often demands advanced implementation of multiple neuromonitoring modalities: EMG, SEP, and MEP. Because the bulbocavernosus reflex detects the function of the conus medullaris and sacral somato afferent/efferent fibers of the cauda equina, it may also be recorded. The recommendation to record pedicle screw thresholds has become more nuanced as surgeon dependence on 3D imaging, navigation, and robotics has increased. Neuromonitoring in lumbar stenosis surgery has been subject mainly to uncontrolled case series; prospective cohort trials are also needed.

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.

Is L5/S1 interbody fusion necessary in long-segment surgery for adult degenerative scoliosis? A systematic review and meta-analysis

OBJECTIVE

There is no consensus regarding the best surgical strategy at the lumbosacral junction (LSJ) in long constructs for adult spinal deformity (ASD). The use of interbody fusion (IF) has been advocated to increase fusion rates, with additional pelvic fixation (PF) typically recommended. The actual benefit of IF even when extending to the pelvis, however, has not been vigorously analyzed. The goal of this work was to better understand the role of IF, specifically with respect to arthrodesis, when extending long constructs to the ilium.

METHODS

A systematic review of the PubMed and Cochrane databases was performed to identify the relevant studies in English, addressing the management of LSJ in long constructs (defined as ≥ 5 levels) in ASD. The search terms used were as follows: "Lumbosacral Junction," "Long Constructs," "Long Fusion to the Sacrum," "Sacropelvic Fixation," "Interbody Fusion," and "Iliac Screw." The authors excluded technical notes, case reports, literature reviews, and cadaveric studies; pediatric populations; pathologies different from ASD; studies not using conventional techniques; and studies focused only on alignment of different levels.

RESULTS

The PRISMA protocol was used. The authors found 12 retrospective clinical studies with a total of 1216 patients who were sorted into 3 different categories: group 1, using PF or not (n = 6); group 2, using PF with or without IF (n = 5); and group 3, from 1 study comparing anterior lumbar interbody fusion versus transforaminal lumbar interbody fusion. Five studies in group 1 and 4 in group 2 had pseudarthrosis rate as primary outcome and were selected for a quantitative analysis. Forest plots were used to display the risk ratio, and funnel plots were used to look at the risk of publication bias. The summary risk ratios were 0.36 (0.23-0.57, p < 0.001) and 1.03 (0.54-1.96, p = 0.94) for the PF and IF, respectively; there is a protective effect of overall pseudarthrosis for using PF in long constructs for ASD surgeries, but not for using IF.

CONCLUSIONS

The long-held contention that L5/S1 IF is always advantageous in long-construct deformity surgery is not supported by the current literature. Based on the findings from this systematic review and meta-analysis, PF with or without additional L5/S1 interbody grafting demonstrates similar overall construct pseudarthrosis rates. The added risk and costs associated with IF, therefore, should be more closely considered on a case-by-case basis.

The Simulation of Muscles Forces Increases the Stresses in Lumbar Fixation Implants with Respect to Pure Moment Loading

Simplified loading conditions such as pure moments are frequently used to compare different instrumentation techniques to treat spine disorders. The purpose of this study was to determine if the use of realistic loading conditions such as muscle forces can alter the stresses in the implants with respect to pure moment loading. A musculoskeletal model and a finite element model sharing the same anatomy were built and validated against in vitro data, and coupled in order to drive the finite element model with muscle forces calculated by the musculoskeletal one for a prescribed motion. Intact conditions as well as a L1-L5 posterior fixation with pedicle screws and rods were simulated in flexion-extension and lateral bending. The hardware stresses calculated with the finite element model with instrumentation under simplified and realistic loading conditions were compared. The ROM under simplified loading conditions showed good agreement with in vitro data. As expected, the ROMs between the two types of loading conditions showed relatively small differences. Realistic loading conditions increased the stresses in the pedicle screws and in the posterior rods with respect to simplified loading conditions; an increase of hardware stresses up to 40 MPa in extension for the posterior rods and 57 MPa in flexion for the pedicle screws were observed with respect to simplified loading conditions. This conclusion can be critical for the literature since it means that previous models which used pure moments may have underestimated the stresses in the implants in flexion-extension and in lateral bending.

The posterior superior iliac rim screw as an adjunct to pelvic fixation in complex spinopelvic stabilization

BACKGROUND

Fixation to the ilium is a commonly used alternative or supplement to sacral fixation in complex spinopelvic reconstructions. This can be achieved with traditional posterior superior iliac spine or S2 alar-iliac screws. Posterior superior iliac rim screws may be considered to achieve or enhance pelvic fixation. The objective of this case series was to describe the use of and indications for posterior superior iliac rim screws.

METHODS

A retrospective review was performed of the medical records and radiographic data for three patients who underwent complex lumbosacral reconstructions involving the use of posterior superior iliac rim screws to enhance pelvic fixation. The cases included a 35-year-old with bilateral sacral fractures, a 43-year-old with extensive metastatic sarcoma to the sacrum, and a 48-year-old with multiple lumbar and pelvic fractures. An overview of the key surgical techniques is provided.

RESULTS

All three patients tolerated the procedure, without any unexpected post-operative complications or deficits. Radiographs at last follow-up showed stable fixation and no hardware issues.

CONCLUSIONS

The use of posterior superior iliac rim screws as an adjunct method of fixation in complex spinopelvic reconstructions is a feasible option that can be considered in the fixation armamentarium.

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

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

Multicenter assessment of outcomes and complications associated with transforaminal versus anterior lumbar interbody fusion for fractional curve correction

OBJECTIVE

Few studies have compared fractional curve correction after long fusion between transforaminal lumbar interbody fusion (TLIF) and anterior lumbar interbody fusion (ALIF) for adult symptomatic thoracolumbar/lumbar scoliosis (ASLS). The objective of this study was to compare fractional correction, health-related quality of life (HRQL), and complications associated with L4-S1 TLIF versus those of ALIF as an operative treatment of ASLS.

METHODS

The authors retrospectively analyzed a prospective multicenter adult spinal deformity database. Inclusion required a fractional curve ≥ 10°, a thoracolumbar/lumbar curve ≥ 30°, index TLIF or ALIF performed at L4-5 and/or L5-S1, and a minimum 2-year follow-up. TLIF and ALIF patients were propensity matched according to the number and type of interbody fusion at L4-S1.

RESULTS

Of 135 potentially eligible consecutive patients, 106 (78.5%) achieved the minimum 2-year follow-up (mean ± SD age 60.6 ± 9.3 years, 85% women, 44.3% underwent TLIF, and 55.7% underwent ALIF). Index operations had mean ± SD 12.2 ± 3.6 posterior levels, 86.6% of patients underwent iliac fixation, 67.0% underwent TLIF/ALIF at L4-5, and 84.0% underwent TLIF/ALIF at L5-S1. Compared with TLIF patients, ALIF patients had greater cage height (10.9 ± 2.1 mm for TLIF patients vs 14.5 ± 3.0 mm for ALIF patients, p = 0.001) and lordosis (6.3° ± 1.6° for TLIF patients vs 17.0° ± 9.9° for ALIF patients, p = 0.001) and longer operative duration (6.7 ± 1.5 hours for TLIF patients vs 8.9 ± 2.5 hours for ALIF patients, p < 0.001). In all patients, final alignment improved significantly in terms of the fractional curve (20.2° ± 7.0° to 6.9° ± 5.2°), maximum coronal Cobb angle (55.0° ± 14.8° to 23.9° ± 14.3°), C7 sagittal vertical axis (5.1 ± 6.2 cm to 2.3 ± 5.4 cm), pelvic tilt (24.6° ± 8.1° to 22.7° ± 9.5°), and lumbar lordosis (32.3° ± 18.8° to 51.4° ± 14.1°) (all p < 0.05). Matched analysis demonstrated comparable fractional correction (-13.6° ± 6.7° for TLIF patients vs -13.6° ± 8.1° for ALIF patients, p = 0.982). In all patients, final HRQL improved significantly in terms of Oswestry Disability Index (ODI) score (42.4 ± 16.3 to 24.2 ± 19.9), physical component summary (PCS) score of the 36-item Short-Form Health Survey (32.6 ± 9.3 to 41.3 ± 11.7), and Scoliosis Research Society-22r score (2.9 ± 0.6 to 3.7 ± 0.7) (all p < 0.05). Matched analysis demonstrated worse ODI (30.9 ± 21.1 for TLIF patients vs 17.9 ± 17.1 for ALIF patients, p = 0.017) and PCS (38.3 ± 12.0 for TLIF patients vs 45.3 ± 10.1 for ALIF patients, p = 0.020) scores for TLIF patients at the last follow-up (despite no differences in these parameters at baseline). The rates of total complications were similar (76.6% for TLIF patients vs 71.2% for ALIF patients, p = 0.530), but significantly more TLIF patients had rod fracture (28.6% of TLIF patients vs 7.1% of ALIF patients, p = 0.036). Multiple regression analysis demonstrated that a 1-mm increase in L4-5 TLIF cage height led to a 2.2° reduction in L4 coronal tilt (p = 0.011), and a 1° increase in L5-S1 ALIF cage lordosis led to a 0.4° increase in L5-S1 segmental lordosis (p = 0.045).

CONCLUSIONS

Operative treatment of ASLS with L4-S1 TLIF versus ALIF demonstrated comparable mean fractional curve correction (66.7% vs 64.8%), despite use of significantly larger, more lordotic ALIF cages. TLIF cage height had a significant impact on leveling L4 coronal tilt, whereas ALIF cage lordosis had a significant impact on restoration of lumbosacral lordosis. The advantages of TLIF may include reduced operative duration and hospitalization; however, associated HRQL was inferior and more rod fractures were detected in the TLIF patients included in this study.

ANATOMICAL STUDY OF THE IDEAL POSITIONING OF THE S2 ILIAC SCREW

ABSTRACT Objective: To evaluate the morphometry of the pelvis to determine the safe trajectory for the insertion of the S2-iliac screw, and to correlate it with studies reported in the literature for other populations. Method: The computed tomography (CT) pelvic exams of 36 Brazilian patients without congenital malformations, tumors, pelvic ring fractures or dysplasias were selected from the database of a radiological clinic. To define the ideal trajectory of the S2-iliac screw, the following variables were measured: 1- maximum sacroiliac screw length; 2- thickness of the iliac dipole for planning the choice of screw dimensions (length and diameter); 3 - distance between the insertion point of the iliac S2 screw and the posterior sacral cortex; 4 - angulation for insertion of the screw in the mediolateral direction, representing the angle formed between the “iliac line” and the anatomical sagittal plane; 5- Angulation for insertion of the screw in the craniocaudal direction. The Pearson's chi squared and student's t tests were used for statistical analysis. Results: The sample consisted of 36 patients, 50% (18/36) of whom were women. The mean age was 63.7 years, ranging from 23 to 96 years. All the pelvic morphometric variables analyzed presented values similar to those described in the literature for other populations. Conclusion: Prior evaluation of the tomography exams was important for preoperative planning, and there was a statistically significant difference between the sexes only in relation to the variables left craniocaudal and length of the left internal table. Level of evidence III; Observational cross-sectional study.

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

Background

Current literature on robot-assisted S2 alar-iliac (S2AI) screw placement shows favorable outcomes and screw accuracy; however, the data is limited by a few retrospective, single-surgeon studies. To the author's knowledge, this is the first multicenter study which evaluates the accuracy of robot-assisted S2AI screws.

Methods

Adult (≥18 years old) patients who underwent robot-assisted S2AI screw placement from 2017-2019 were reviewed. All surgeries used the same proprietary robotic guidance system, Mazor X (Mazor Robotics Ltd).

Results

A total of 65 screws were assessed in 31 patients. The mean follow-up ± standard deviation was 362±190 days (minimum was 90 days). The mean age was 61.1±11 years old, and 54.8% (n=17) of patients were female. Nearly half of the patients had a primary diagnosis of degenerative scoliosis (48.4%, n=15). Other diagnosis included pseudarthrosis (22.6%, n=7), degenerative disc disease (16.1%, n=5), and high-grade spondylolisthesis (12.9%, n=4). The mean length and diameter of screws were 84.6±6.1 mm and 8.4±0.7, respectively. The mean axial and sagittal angles were 50.0±6.3 and 24.0±10.5, respectively. The overall screw accuracy was 93.8% (n=61). There were four iliac cortex breaches (anterior =3, inferior 1) with a mean breach distance of 3.5±3.2. No statistically significant differences in screw length, diameter, axial angle, and sagittal angle were observed between screws with and without a breach. No intraoperative neurologic, vascular, or visceral complications from the S2AI screw were observed. No post-discharge wound complications, screw prominence issues, or revision of S2AI screws were observed during the study's follow-up period.

Conclusions

Robot-assisted S2AI screw placement was found to be safe and accurate in this multicenter study. This is largely attributed to the versatility of the robotic guidance software that allows for detailed and precise preoperative and intraoperative planning.

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.

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

OBJECTIVE

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.