Rod fractures after multi-rod constructs in adult spinal deformity patients fused to the sacrum/pelvis: where do they occur and why?

PURPOSE: (1) To describe the use of multi-rod constructs (MRCs) in adult spinal deformity (ASD) surgery, (2) to report rod fractures occurring at MRC sites, and (3) to evaluate risk factors for rod fractures. METHODS: A single-center, retrospective cohort study was conducted of patients undergoing ASD surgery with these inclusion criteria: minimum 2-year follow-up, MRCs used, ≥ 10-level fusion, and fused to sacrum/pelvis. The primary outcome was rod fracture. Univariate/multivariate logistic regression was performed controlling for age, kickstand rod usage, number of rods across the lumbosacral junction (LSJ), and the amount of coronal/sagittal Cobb correction. RESULTS: Among 57 patients undergoing ASD surgery with MRCs, mean age was 60 ± 11 years. With respect to MRCs, 32 (56%) patients had 3 rods, 18 (32%) had 4, and 7 (12%) had 5. Rods crossing the LSJ were most often three (63%), followed by four (25%) and five (5%) rods. Nine (16%) patients experienced rod fractures with eight (89%) patients having no more than three rods crossing the LSJ. A coronal correction > 30 mm was more often seen in patients with rod fracture (p = 0.030), while an SVA correction > 50 mm was not significantly different (p = 0.608). Multivariate logistic regression revealed that the amount of coronal correction was significantly associated with rod fracture (OR 1.03, 95% CI 1.01-1.07, p = 0.044), as was achieving a coronal correction > 30 mm (OR 7.72, 95% CI 1.17-51.10, p = 0.034), with no association between the amount of sagittal correction obtained and rod fracture. CONCLUSION: This study found that greater coronal correction was associated with an increased odds of rod fracture. We suggest adding at least four rods across the LSJ cephalad to the interbody fusions to avoid rod fractures in these high demand areas. LEVEL OF EVIDENCE: III.

Incidence, mechanism, and protective strategies for 2-year pelvic fixation failure after adult spinal deformity surgery with a minimum six-level fusion.

OBJECTIVE: The purpose of this study was to determine the incidence, mechanism, and potential protective strategies for pelvic fixation failure (PFF) within 2 years after adult spinal deformity (ASD) surgery. METHODS: Data for ASD patients (age ≥ 18 years, minimum of six instrumented levels) with pelvic fixation (S2-alar-iliac [S2AI] and/or iliac screws) with a minimum 2-year follow-up were consecutively collected (2015-2019). Patients with prior pelvic fixation were excluded. PFF was defined as any revision to pelvic screws, which may include broken rods across the lumbosacral junction requiring revision to pelvic screws, pseudarthrosis across the lumbosacral junction requiring revision to pelvic screws, a broken or loose pelvic screw, or sacral/iliac fracture. Patient information including demographic data and health history (age, sex, BMI, smoking status, American Society of Anesthesiologists score, osteoporosis), operative (total instrumented levels [TIL], three-column osteotomy [3CO], interbody fusion), screw (iliac, S2AI, length, diameter), rod (diameter, kickstand), rod pattern (number crossing lumbopelvic junction, lowest instrumented vertebra [LIV] of accessory rod[s], lateral connectors, dual-headed screws), and pre- and postradiographic (lumbar lordosis, pelvic incidence, pelvic tilt, major Cobb angle, lumbosacral fractional curve, C7 coronal vertical axis [CVA], T1 pelvic angle, C7 sagittal vertical axis) parameters was collected. All rods across the lumbosacral junction were cobalt-chrome. All iliac and S2AI screws were closed-headed tulips. Both univariate and multivariate analyses were performed to determine risk factors for PFF. RESULTS: Of 253 patients (mean age 58.9 years, mean TIL 13.6, 3CO 15.8%, L5-S1 interbody 74.7%, mean pelvic screw diameter/length 8.6/87 mm), the 2-year failure rate was 4.3% (n = 11). The mechanisms of failure included broken rods across the lumbosacral junction (n = 4), pseudarthrosis across the lumbosacral junction requiring revision to pelvic screws (n = 3), broken pelvic screw (n = 1), loose pelvic screw (n = 1), sacral/iliac fracture (n = 1), and painful/prominent pelvic screw (n = 1). A higher number of rods crossing the lumbopelvic junction (mean 3.8 no failure vs 2.9 failure, p = 0.009) and accessory rod LIV to S2/ilium (no failure 54.2% vs failure 18.2%, p = 0.003) were protective for failure. Multivariate analysis demonstrated that accessory rod LIV to S2/ilium versus S1 (OR 0.2, p = 0.004) and number of rods crossing the lumbar to pelvis (OR 0.15, p = 0.002) were protective, while worse postoperative CVA (OR 1.5, p = 0.028) was an independent risk factor for failure. CONCLUSIONS: The 2-year PFF rate was low relative to what is reported in the literature, despite patients undergoing long fusion constructs for ASD. The number of rods crossing the lumbopelvic junction and accessory rod LIV to S2/ilium relative to S1 alone likely increase construct stiffness. Residual postoperative coronal malalignment should be avoided to reduce PFF.

How common is acute pelvic fixation failure after adult spine surgery? A single-center study of 358 patients.

OBJECTIVE: There is a paucity of literature on pelvic fixation failure after adult spine surgery in the early postoperative period. The purpose of this study was to determine the incidence of acute pelvic fixation failure in a large single-center study and to describe the lessons learned. METHODS: The authors performed a retrospective review of adult (≥ 18 years old) patients who underwent spinal fusion with pelvic fixation (iliac, S2-alar-iliac [S2AI] screws) at a single academic medical center between 2015 and 2020. All patients had a minimum of 3 instrumented levels. The minimum follow-up was 6 months after the index spine surgery. Patients with prior pelvic fixation were excluded. Acute pelvic fixation failure was defined as revision of the pelvic screws within 6 months of the primary surgery. Patient demographics and operative, radiographic, and rod/screw parameters were collected. All rods were cobalt-chrome. All iliac and S2AI screws were closed-headed screws. RESULTS: In 358 patients, the mean age was 59.5 ± 13.6 years, and 64.0% (n = 229) were female. The mean number of instrumented levels was 11.5 ± 5.5, and 79.1% (n = 283) had ≥ 6 levels fused. Three-column osteotomies were performed in 14.2% (n = 51) of patients, and 74.6% (n = 267) had an L5-S1 interbody fusion. The mean diameter/length of pelvic screws was 8.5/86.6 mm. The mean number of pelvic screws was 2.2 ± 0.5, the mean rod diameter was 6.0 ± 0 mm, and 78.5% (n = 281) had > 2 rods crossing the lumbopelvic junction. Accessory rods extended to S1 (32.7%, n = 117) or S2/ilium (45.8%, n = 164). Acute pelvic fixation failure occurred in 1 patient (0.3%); this individual had a broken S2AI screw near the head-neck junction. This 76-year-old woman with degenerative lumbar scoliosis and chronic lumbosacral zone 1 fracture nonunion had undergone posterior instrumented fusion from T10 to pelvis with bilateral S2AI screws (8.5 × 90 mm); i.e., transforaminal lumbar interbody fusion L4-S1. The patient had persistent left buttock pain postoperatively, with radiographically confirmed breakage of the left S2AI screw 68 days after surgery. Revision included instrumentation removal at L2-pelvis and a total of 4 pelvic screws. CONCLUSIONS: The acute pelvic fixation failure rate was exceedingly low in adult spine surgery. This rate may be the result of multiple factors including the preference for multirod (> 2), closed-headed pelvic screw constructs in which large-diameter long screws are used. Increasing the number of rods and screws at the lumbopelvic junction may be important factors to consider, especially for patients with high risk for nonunion.

Worse Preoperative Disability is Predictive of Improvement in Disability After Complex Adult Spinal Deformity Surgery.

STUDY DESIGN: Retrospective Cohort Study. OBJECTIVES: Few previous studies have examined the relationship between preoperative disability and patient outcomes after complex adult spinal deformity surgery. In this study, we hypothesized that patients with worse preoperative disability would be more likely achieve a clinically significant improvement in their symptoms after surgery. METHODS: Demographics, comorbidities, surgical data, and health related survey results were analyzed from a consecutive series of adults (≥18 years old) who underwent spinal deformity correction, instrumentation, and fusion. Patients included had 6 or more levels fused and their surgery performed at single institution between 2015 and 2018 with minimum 2 year follow up. RESULTS: A total of 108 patients met inclusion criteria. Bivariate analysis demonstrated the following as having a greater probability of reaching minimum clinically important difference (MCID) at 2 years postoperatively: >50th percentile Oswestry Disability Index (ODI) score (ODI >36), cardiac comorbidities, and use of pelvic fixation, pedicle subtraction osteotomy, and transforaminal lumbar interbody fusion. Conversely, baseline Scoliosis research society score (SRS) >50th percentile (SRS ≥62) and use of vertebral column resection (VCR) were significant predictors of not reaching MCID at 2 years. On logistic regression analysis, >50th percentile ODI score (ODI >36) was identified as the only independent predictor of achieving MCID. CONCLUSIONS: Patients with greater disability, independent of other preoperative or surgical factors, are more likely to have clinically significant improvement in their daily functioning after complex deformity surgery. For patients who undergo surgical intervention for severe or progressive deformity, including VCR, MCID might be an ineffective outcome measure.

Determining the relationship between preoperative mental health scores and postoperative outcomes in adult spinal deformity surgeries.

OBJECTIVE: The objective of this study was to examine the relationship between the mental health domain of the refined 22-item Scoliosis Research Society Outcome Questionnaire (SRS) and various postoperative outcome measures in the adult spinal deformity (ASD) population. Given the scale and involved nature of deformity surgery, some surgeons have proposed that preoperative mental health scores (MHSs) may assist in screening out poor surgical candidates. In this study, the authors aimed to further assess the SRS MHS as a preoperative metric and its association with postoperative outcomes and to comment on its potential use in patient selection and optimization for ASD surgery. METHODS: The authors conducted a retrospective study of 100 consecutive patients who had undergone primary or revision ASD surgery at a single academic institution between 2015 and 2019. Each patient had a minimum 2-year follow-up. Patients were categorized on the basis of their baseline mental health per the SRS mental health domain, with a score < 4 indicating low baseline mental health (LMH) and a score ≥ 4 indicating high baseline mental health (HMH). Baseline and follow-up SRS and Oswestry Disability Index scores, surgical procedures, lengths of stay, discharge locations, intraoperative or postoperative complications, and other outcome metrics were then compared between the HMH and LMH groups, as well as these groups stratified by an age ≤ 45 and > 45 years. RESULTS: Among patients aged ≤ 45 and those aged > 45, the LMH group had significantly worse baseline health-related quality-of-life (HRQOL) metrics in nearly all domains. The LMH group also had an increased median estimated blood loss (EBL; 1200 vs 800 ml, p = 0.0026) and longer average surgical duration (8.3 ± 2.8 vs 6.9 ± 2.6 hours, p = 0.014). Both LMH and HMH groups had significant improvements in nearly all HRQOL measures postoperatively. Despite their worse preoperative HRQOL baseline, patients in the LMH group actually improved the most and reached the same HRQOL endpoints as those in the HMH group. CONCLUSIONS: While patients with lower baseline MHSs may require slightly longer hospital courses or more frequent discharges to rehabilitation facilities, these patients actually attain greater absolute improvements from their preoperative baseline and surprisingly have the same postoperative HRQOL metrics as the patients with high MHSs, despite their poorer starting point. This finding suggests that patients with LMH may be uniquely positioned to substantially benefit from surgical intervention and improve their HRQOL scores and thus should be considered for ASD surgery to an extent similar to patients with HMH.