Reciprocal Changes in the Whole-Body Following Realignment Surgery in Adult Spinal Deformity

Ideal Lumbar Lordosis Correction in Patients With Adult Spinal Deformity Without Adversely Impacting Pelvic Tilt and Pelvic Incidence Minus Lumbar Lordosis: A Study of 426 Cases

STUDY DESIGN

Retrospective study.

OBJECTIVES

To determine the ideal pelvic incidence (PI)-lumbar lordosis (LL) range to prevent pelvic tilt (PT) undercorrection while avoiding PI-LL overcorrection following adult spinal deformity (ASD) surgery.

SUMMARY OF BACKGROUND

PI-LL and PT are the important sagittal parameters to be restored to an adequate range by surgery. Ideal PI-LL target without causing PI-LL overcorrection and PT undercorrection has not been documented.

METHODS

We included patients with ASD undergoing ≥5-level fusion, including the sacrum. Receiver operating characteristic (ROC) curve analysis was performed to calculate the lower limit of the ideal PI-LL without causing PI-LL overcorrection and the upper limit of the ideal PI-LL without causing PT undercorrection. The calculated ideal PI-LL was validated in terms of proximal junctional kyphosis and failure (PJK and PJF) rates and clinical outcomes. Analyses were performed according to age subgroups (below 70 and 70 yr or above).

RESULTS

In total, 426 patients were included in the study. Female patients were predominant (85.4%), with a mean age of 69.8 years. The lower limits of PI-LL were calculated as 4.9° for all patients, 2.3° for patients aged below 70 years, and 7.9° for patients aged 70 years or above. Meanwhile, the upper limits of PI-LL were calculated as 12.7° for all patients, 12.5° for patients aged below 70 years, and 13.3° for patients aged 70 years or above. There were no significant differences in the PJK and PJF rates among the new three PI-LL groups. Clinical outcomes were significantly better in patients with the ideal PI-LL group than those in patients with overcorrection or undercorrection groups for all age groups.

CONCLUSIONS

The ideal PI-LL correction target without adversely impacting PT and PI-LL was calculated at 2.3° to 12.5° for patients aged below 70 years and 7.9° to 13.3° for patients aged 70 years or above. These guideline parameters may help ensure optimal clinical outcomes without increasing the risk of PJK/F.

The role of the lower extremity on patient's cone of economy: an innovative approach

PURPOSE

To evaluate the effect of the lower extremities on cone of economy (CoE) calculations as well as to propose a novel assessment of seated balance using traditional CoE measurements.

METHODS

36 controls and 82 degenerative lumbar disease (LD) patients, (38 patients with unilateral radiculopathy (UR), 44 patients with neurogenic claudication (NC) with bilateral symptoms), were enrolled in the study. Functional balance tests were performed and recorded by 3D motion capture in both the standing (Romberg) and seated positions. Balance effort and CoE dimensions were calculated.

RESULTS

The lower extremities exert a significant impact on balance, as reflected in the total head (UR: 20.9, NC: 31.5 vs. H: 10.0 cm, p < 0.015), pelvis (UR: 73.2, NC: 110.0 vs. H: 36.4 cm, p < 0.002) and CoM (UR: 17.1, NC: 18.7 vs. H: 4.6 cm, p < 0.001) sway differences observed between LD patients and healthy controls. Significant differences in CoE dimensions were observed as captured by sagittal head (UR: 2.8 vs. H: 0.9 cm, p = 0.014) and pelvis (UR: 2.8 vs. H: 1.4 cm, p = 0.019) range of sway (RoS) and coronal pelvic RoS (UR: 1.1, NC: 1.1 vs. H: 0.6 cm, p < 0.012) between LD patients and healthy controls.

CONCLUSION

This study first provides a novel standardized means of isolating and quantifying the role of the lower extremity on the CoE in patients with LD, which highlights how spinal pathologies may directly impact and/or contribute to compensatory mechanisms in this region. As evidenced by 18.0-93.2 cm of total sway and 1.1-2.8 cm RoS, the lower extremities account for a significant amount of balance effort and CoE dimensions.

Anterior column realignment better restores sagittal alignment but carries higher risk of mechanical failures than lateral lumbar interbody fusion in patients with degenerative sagittal imbalance

BACKGROUND OF CONTEXT

Anterior column realignment (ACR), a modified lateral lumbar interbody fusion (LLIF), is an emerging, less invasive technique that allows greater lordosis correction by releasing anterior longitudinal ligament. However, long-term results have been poorly documented with regard to mechanical failure, such as proximal junctional kyphosis (PJK) and rod fracture (RF), and clinical outcomes.

PURPOSE

To compare the outcomes, primarily mechanical failure, in patients with degenerative sagittal imbalance (DSI) treated with ACR versus LLIF alone.

STUDY DESIGN/SETTING

Retrospective study.

PATIENT SAMPLE

Patients ≥60 years of age; severe DSI defined by pelvic incidence (PI) - lumbar lordosis (LL) ≥20°; performance of ≥2-level LLIF; and ≥5 total fused levels including the sacrum.

OUTCOME MEASURES

Mechanical failure such as PJK and RF; radiographic results; clinical outcomes METHODS: Enrolled patients were divided into two groups, based on whether their anterior reconstruction was accomplished with ACR or LLIF alone: ACR and LLIF groups. Mechanical failures were compared between the two groups as a composite outcome including PJK and /or RF. PJK was defined as proximal junctional angle (PJA) >28° and Δ PJA >22°. Only RFs developing at the level with corresponding procedures (ACR or LLIF) were included in the analysis. Logistic regression was performed to compare the relative risk of mechanical failure between the ACR and LLIF groups. The radiographic and clinical outcomes were also compared between the groups.

RESULTS

The final study cohort consisted of 210 patients. The mean age was 69.6 years, and there were 190 females (90.5%). There were 124 patients in the ACR group and 86 patients in the LLIF group. Perioperative changes for all sagittal parameters were significantly greater in the ACR group than in the LLIF group. Overall mechanical failure rates were significantly higher in the ACR group than in the LLIF group (32.3% vs 14.0%, p=.003). Multivariate regression analysis with adjusting potential confounders revealed that ACR carried a significantly higher risk of mechanical failure than LLIF (Odds ratio=5.6, 95% confidence interval=2.0-15.6, p<.001). The final clinical outcomes were worse in the ACR group than in the LLIF group.

CONCLUSION

ACR restored the sagittal malalignment more powerfully than did LLIF. However, compared to the LLIF, ACR was associated with a greater risk of mechanical failures and revision surgery. The final clinical outcomes in the ACR group were inferior to those in the LLIF group. Therefore, ACR should be left as a last resort for the cases where it is expected that an adequate correction cannot be achieved using LLIF alone. If ACR has to be performed, it is necessary to establish feasible surgical strategies to avoid mechanical failures.

Are Surgical Outcomes Different According to Baseline Balance Status in Elderly Patients with Degenerative Sagittal Imbalance?

STUDY DESIGN

This is a retrospective study.

OBJECTIVE

We sought to compare surgical outcomes according to baseline balance statuses in elderly patients with degenerative sagittal imbalance (DSI).

SUMMARY OF BACKGROUND

Although optimal sagittal correction has been emphasized for good surgical outcomes, the effect of the state of preoperative balance on surgical outcomes has been adequately described at present.

METHODS

Patients aged 60 years and above with DSI who underwent ≥5-level fusion to the sacrum were included. Among them, only those who postoperatively achieved the optimal age-adjusted pelvic incidence (PI) - lumbar lordosis (LL) target were included in this study. Study participants were divided into two groups according to their preoperative sagittal vertical axis (SVA): compensatory balance (SVA <5 cm, group CB) and decompensation (SVA ≥5 cm, group D). Comparisons between the two groups were performed using the χ 2 test or Fisher exact test for categorical variables and the independent t -test or Wilcoxon rank-sum test for continuous variables.

RESULTS

A total of 156 patients whose postoperative sagittal alignment matched the age-adjusted PI-LL target constituted the study cohort. There were 59 patients in group CB and 97 patients in group D. Mean follow-up duration was 50.0 months after surgery. Immediate postoperatively, sacral slope and SVA were significantly greater in group D than in group CB. At the last follow-up, the SVA was significantly greater in group D than in group CB (43.6 vs. 22.7 mm), while no significant differences were found in other sagittal parameters. The Oswestry disability index and Scoliosis Research Society -22 scores at the last follow-up were significantly worse in group D than in group CB.

CONCLUSION

The SVA tended to experience less correction postoperatively, with evidence of further deterioration during follow-up in group D than in group CB. This suboptimal correction of SVA may contribute to the inferior clinical outcomes encountered in group D relative to group CB. Therefore, we recommend correction of PI-LL as close as possible to the lower limit of the suggested PI-LL target range in patients with evidence of preoperative decompensation.

How Does Spino-Pelvic Fixation Affect Post-Operative Compensatory Mechanisms in Adult Spinal Deformity?

STUDY DESIGN

Retrospective single-center multi-surgeon cohort study.

OBJECTIVES

Compare the post-operative changes in the compensatory mechanisms of the sagittal balance according to the type of pelvic fixation: S2-Alar-iliac screws (S2AI) vs iliac screws (IS) in patients with Adult spine deformity (ASD).

METHODS

ASD patients who underwent spino-pelvic fixation and remained with a PI-LL >10° mismatch post-operatively were included. Pre-operative and 1-year-follow-up PI, Lumbar lordosis (LL), pelvic tilt (PT), sacral slope (SS), thoracic kyphosis (TK), femur obliquity angle (FOA), knee flexion angle (KFA) and ankle flexion angle (AFA) were analyzed on EOS imaging. Patients were categorized based on their pelvic fixation type (S2AI vs IS), and the pre-operative to 1-year-post-operative changes (ΔX°) in the compensatory mechanisms were compared between groups.

RESULTS

Patients with S2AI (n = 53) and those with IS (n = 26) screws were comparable at baseline. ΔSS averaged 9.87° in the S2AI compared to 13.2° in the IS (P = .001), whereas the ΔKFA reached 6.01° in the S2AI as opposed to 3.06° in the IS (P = .02). The ΔPT was comparable between both groups (6.35°[S2AI group] vs 5.21°[ISgroup], P = .42). ΔTK, ΔLL, ΔFOA and ΔAFA were comparable between both groups.

CONCLUSION

The type of pelvic fixation impacts significantly the post-operative compensatory mechanisms in patients with ASD. Patients with S2AI screws are more likely to compensate their remaining post-operative PI-LL mismatch through their knees and less likely through their pelvis compared to patients with IS, despite similar changes in PT. This could be explained by an increased SI joint laxity in ASD patient and the lower resistance of the iliac connectors to the junctional mechanical stresses, allowing for sacro-iliac joint motion in patients with IS.

Automated measurement of pelvic parameters using convolutional neural network in complex spinal deformities: overcoming challenges in coronal deformity cases

BACKGROUND CONTEXT

Accurate and consistent measurement of sagittal alignment is challenging, particularly in patients with severe coronal deformities, including degenerative lumbar scoliosis (DLS).

PURPOSE

This study aimed to develop and validate an artificial intelligence (AI)-based system for automating the measurement of key sagittal parameters, including lumbar lordosis, pelvic incidence, pelvic tilt, and sacral slope, with a focus on its applicability across a wide range of deformities, including severe coronal deformities, such as DLS.

DESIGN

Retrospective observational study.

PATIENT SAMPLE

A total of 1,011 standing lumbar lateral radiographs, including DLS.

OUTCOME MEASURE

Interclass and intraclass correlation coefficients (CC), and Bland-Altman plots.

METHODS

The model utilizes a deep-learning framework, incorporating a U-Net for segmentation and a Keypoint Region-based Convolutional Neural Network for keypoint detection. The ground truth masks were annotated by an experienced orthopedic specialist. The performance of the model was evaluated against ground truth measurements and assessments from two expert raters using interclass and intraclass CC, and Bland-Altman plots.

RESULTS

In the test set of 113 patients, 39 (34.5%) had DLS, with a mean Cobb's angle of 14.8°±4.4°. The AI model achieved an intraclass CC of 1.00 across all parameters, indicating perfect consistency. Interclass CCs comparing the AI model to ground truth ranged from 0.96 to 0.99, outperforming experienced orthopedic surgeons. Bland-Altman analysis revealed no significant systemic bias, with most differences falling within clinically acceptable ranges. A 5-fold cross-validation further demonstrated robust performance, with interclass CCs ranging from 0.96 to 0.99 across diverse subsets.

CONCLUSION

This AI-based system offers a reliable and efficient automated measurement of sagittal parameters in spinal deformities, including severe coronal deformities. The superior performance of the model compared with that of expert raters highlights its potential for clinical applications.

Postsurgical outcomes differ according to baseline sagittal alignment status even in patients achieving adequate correction relative to age-adjusted alignment target for adult spinal deformity

BACKGROUND CONTEXT

Baseline severities of sagittal malalignment and degrees of pelvic compensation may affect postsurgical outcomes differently after adult spinal deformity (ASD) surgery, even if the patients achieved optimal correction of sagittal malalignment.

PURPOSE

To investigate whether postsurgical outcomes vary according to baseline sagittal alignment and pelvic compensation status in patients achieving adequate correction relative to age-adjusted alignment target in ASD surgery.

STUDY DESIGN/SETTING

Retrospective study PATIENT SAMPLE: Patients who underwent ≥ 5-level fusion to the pelvis for ASD; achieved matched correction relative to age-adjusted pelvic incidence (PI)-lumbar lordosis (LL); and completed ≥ 2-year follow-up.

OUTCOME MEASURES

Radiographic results, mechanical failures, and clinical outcomes METHODS: Patients were divided into three groups based on baseline sagittal vertical axis (SVA) and pelvic tilt (PT)/PI ratio (median value of PT/PI ratio = 0.61): Group A (SVA < 5 cm), Group B (SVA ≥ 5 cm and PT/PI ratio <0.61, and Group C (SVA ≥ 5 cm and PT/PI ratio ≥ 0.61). Radiographic results, mechanical failures, and clinical outcomes were compared among the three groups.

RESULTS

A total of 153 patients were included in the study. They were predominantly female (89.5%), with a mean age of 68.3 years. The mean follow-up duration was 49.0 months. There were 50 patients in group A (SVA < 5cm), 53 in group B (SVA ≥ 5cm and low PT/PI), and 50 in group C (SVA ≥ 5cm and high PT/PI). No significant differences were observed in all radiographic parameters at six weeks. At the last follow-up, the PI-LL was comparable among the three groups; however, the SVA was significantly greater in groups B and C than in group A (46.5mm and 46.9mm vs. 31.5mm, p=.039). The PT at the last follow-up was significantly lower in group B than in group A and C (22.4° vs. 26.0° and 28.2°, respectively, p=.001). The rates of mechanical failure and subsequent revision surgery and did not differ among the groups. The final clinical outcomes were comparable among the three groups.

CONCLUSIONS

This study revealed that patients in groups B and C were likely to have a suboptimal sagittal alignment status at the last follow-up compared with those in group A. Tailored approaches considering patient's baseline alignment and compensatory status are recommended to optimize the final sagittal alignment status.

Incidence and Risk Factors of Recurrent Proximal Junctional Failure in Adult Spinal Deformity Surgery

STUDY DESIGN

Retrospective cohort study.

OBJECTIVES

This study aimed to examine the incidence and risk factors for recurrent proximal junctional failure (R-PJF) in adult spinal deformity (ASD) surgery.

METHODS

Among 482 patients receiving ≥ five-level fusion to the pelvis for ASD, 60 patients who underwent fusion extension surgery for PJF were included in the study cohort. R-PJF was defined as the performance of re-revision surgery after revision surgery for PJF. Various clinical and radiographic variables were compared between no R-PJF and R-PJF groups. Stepwise multivariate logistic analysis was performed to identify the risk factors for R-PJF.

RESULTS

Of the 60 patients, there were 51 women (85.0%) and 9 men (15.0%) with a mean age of 72.4 ± 6.7 years. The mean fusion length at the index surgery was 7.3 ± 1.6 levels and an average of 4.1 ± 1.3 levels was extended during the revision surgery. Among them, R-PJF developed in 17 patients (28.3%). Multivariate analysis revealed that overcorrection relative to age-adjusted pelvic incidence (PI) - lumbar lordosis (LL) at the index surgery and high total sum of proximal junctional kyphosis severity scale (PJKSS) at the revision surgery were significant risk factors for R-PJF development. The cutoff value for the PJKSS sum was calculated as 8.5 points.

CONCLUSIONS

R-PJF was developed in 17 patients (28.3%). PI-LL overcorrection should be avoided during the index surgery to mitigate the R-PJF. In addition, timely surgical intervention is required in patients with PJF, considering that the PJF severity tends to increase over time.

Risk Factors for Recurrent Proximal Junctional Failure Following Adult Spinal Deformity Surgery: Analysis of 60 Patients Undergoing Fusion Extension Surgery for Proximal Junctional Failure

BACKGROUND

Despite numerous studies identifying risk factors for proximal junctional failure (PJF), risk factors for recurrent PJF (R-PJF) are still not well established. Therefore, we aimed to identify the risk factors for R-PJF following adult spinal deformity (ASD) surgery.

METHODS

Among 479 patients who underwent ≥5-level fusion surgery for ASD, the focus was on those who experienced R-PJF at any time or did not experience R-PJF during a follow-up duration of ≥1 year. PJF was defined as a proximal junctional angle (PJA) ≥28° plus a difference in PJA ≥22° or performance of revision surgery regardless of PJA degree. The patients were divided into 2 groups according to R-PJF development: no R-PJF and R-PJF groups. Risk factors were evaluated focusing on patient, surgical, and radiographic factors at the index surgery as well as at the revision surgery.

RESULTS

Of the 60 patients in the final study cohort, 24 (40%) experienced R-PJF. Significant risk factors included greater postoperative sagittal vertical axis (OR = 1.044), overcorrection relative to age-adjusted pelvic incidence-lumbar lordosis (PI-LL; OR = 7.794) at the index surgery, a greater total sum of the proximal junctional kyphosis severity scale (OR = 1.145), and no use of the upper instrumented vertebra cement (OR = 5.494) at the revision surgery.

CONCLUSIONS

We revealed that the greater postoperative sagittal vertical axis and overcorrection relative to age-adjusted pelvic incidence-lumbar lordosis at the index surgery, a greater proximal junctional kyphosis severity scale score, and no use of upper instrumented vertebra cement at the revision surgery were significant risk factors for R-PJF.

CLINICAL RELEVANCE

To reduce the risk of R-PJF after ASD surgery, avoiding under- and overcorrection during the initial surgery is recommended. Additionally, close assessment of the severity of PJF with timely intervention is crucial, and cement augmentation should be considered during revision surgery.

LEVEL OF EVIDENCE: 3

Radiological Spinopelvic Parameters Can Be Risk Factors for Early Total Hip Replacement After Spine Fusion

BACKGROUND

Interest in the correlation between the spinopelvic complex and its radiographic parameters in early total hip arthroplasty has been increasing. This study investigated whether radiological spinopelvic parameters are risk factors for early total hip replacement (THR) within 1 year of spinal fusion surgery. The primary research question focused on identifying specific spinopelvic changes that may lead to early THR.

METHODS

We retrospectively analyzed patients who underwent lumbar spinal fusion between 2016 and 2021. The patients were divided into 2 groups: patients who underwent early THR (n = 35) and patients who did not (n = 213). Spinopelvic parameters, including pelvic incidence (PI), sacral slope (SS), pelvic tilt, lumbar lordosis, thoracolumbar kyphosis (TLK), sagittal vertical axis, and thoracic kyphosis (TK), were measured before and after surgery. The statistical analyses included inverse probability of treatment weighting, independent t tests, χ 2 tests, and logistic regression analyses.

RESULTS

A total of 248 patients were included in the study. The pre- and postoperative TLK and TK angles were significantly smaller in the early THR group than in the late THR group. Increases in the PI and SS after surgery were significant risk factors. The use of interbody fusion techniques was associated with a higher rate of early THR. The difference in the PI minus lumbar lordosis before and after surgery was also significantly correlated with early THR.

CONCLUSIONS

Abnormal spinopelvic parameters, especially reduced TLK and TK angles and increased PI and SS, are risk factors for early THR.

CLINICAL RELEVANCE

Changes in spinopelvic parameters can lead to rapid hip joint destruction, which highlights the need for careful preoperative evaluation and postoperative monitoring of patients to prevent early THR.

LEVEL OF EVIDENCE: 3

Comparison of Surgical Burden, Radiographic and Clinical Outcomes According to the Severity of Baseline Sagittal Imbalance in Adult Spinal Deformity Patients

OBJECTIVE

To determine the clinical impact of the baseline sagittal imbalance severity in patients with adult spinal deformity (ASD).

METHODS

We retrospectively reviewed patients who underwent ≥ 5-level fusion including the pelvis, for ASD with a ≥ 2-year follow-up. Using the Scoliosis Research Society-Schwab classification system, patients were classified into 3 groups according to the severity of the preoperative sagittal imbalance: mild, moderate, and severe. Postoperative clinical and radiographic results were compared among the 3 groups.

RESULTS

A total of 259 patients were finally included. There were 42, 62, and 155 patients in the mild, moderate, and severe groups, respectively. The perioperative surgical burden was greatest in the severe group. Postoperatively, this group also showed the largest pelvic incidence minus lumbar lordosis mismatch, suggesting a tendency towards undercorrection. No statistically significant differences were observed in proximal junctional kyphosis, proximal junctional failure, or rod fractures among the groups. Visual analogue scale for back pain and Scoliosis Research Society-22 scores were similar across groups. However, severe group's last follow-up Oswestry Disability Index (ODI) scores significantly lower than those of the severe group.

CONCLUSION

Patients with severe sagittal imbalance were treated with more invasive surgical methods along with increased the perioperative surgical burden. All patients exhibited significant radiological and clinical improvements after surgery. However, regarding ODI, the severe group demonstrated slightly worse clinical outcomes than the other groups, probably due to relatively higher proportion of undercorrection. Therefore, more rigorous correction is necessary to achieve optimal sagittal alignment specifically in patients with severe baseline sagittal imbalance.

Transpedicular injection of rhBMP-2 with β-tricalcium phosphate to reduce the proximal junctional kyphosis after adult spinal deformity correction: preliminary study

The aim of this preliminary study was to assess the impact of injecting recombinant human bone morphogenetic protein-2 (rhBMP-2) with β-tricalcium phosphate (β-TCP) carrier into the uppermost instrumented vertebra (UIV) during surgery to prevent the development of proximal junctional kyphosis (PJK) and proximal junctional failure (PJF). The 25 patients from study group had received 0.5 mg rhBMP-2 mixed with 1.5 g β-TCP paste injection into the UIV during surgery. The control group consisted of 75 patients who underwent surgery immediately before the start of the study. The incidences of PJK and PJF were analyzed as primary outcomes. Spinopelvic parameters and patient-reported outcomes were analyzed as secondary outcomes. Hounsfield unit (HU) measurements were performed to confirm the effect of rhBMP-2 with β-TCP on bone formation at preoperative and postoperative at computed tomography. PJK and PJF was more occurred in control group than study group (p = 0.02, 0.29, respectively). The HU of the UIV significantly increased 6 months after surgery. And the increment at the UIV was also significantly greater than that at the UIV-1 6 months after surgery. Injection of rhBMP-2 with β-TCP into the UIV reduced PJK and PJF rates 6 months after surgery with new bone formation.

Gravity Line-Hip Axis Offset as a Guide for Global Alignment to Prevent Recurrent Proximal Junctional Kyphosis/Failure

BACKGROUND AND OBJECTIVES

Proximal junctional kyphosis/failure (PJK/F) is a potentially serious complication after adult spinal deformity (ASD) corrective surgery. Recurrent PJK/F is especially troublesome, necessitating fusion extension and occasionally resulting in irreversible neurological deficits. The gravity line (GL) offers valuable insights into global sagittal balance. This study aims to examine the postoperative GL-hip axis (GL-HA) offset as a critical risk factor for recurrent PJK/F.

METHODS

We retrospectively reviewed patients with ASD who had undergone revision surgery for initial PJK/F at a single academic center. Patients were categorized into 2 groups: nonrecurrent PJK/F group and recurrent PJK/F group. Demographics, surgical characteristics, preoperative and postoperative parameters of spinopelvic and global alignment, and the Scoliosis Research Society-22 scores were assessed. We examined these measures for differences and correlations with recurrent PJK/F.

RESULTS

Our study included 32 patients without recurrent PJK/F and 28 patients with recurrent PJK/F. No significant differences were observed in baseline demographics, operative characteristics, or Scoliosis Research Society-22 scores before and after surgery. Importantly, using a cutoff of -52.6 mm from logistic regression, there were considerable differences and correlations with recurrent PJK/F in the postoperative GL-HA offset, leading to an odds ratio of 7.0 (95% CI: 1.94-25.25, P = .003).

CONCLUSION

Postoperative GL-HA offset serves as a considerable risk factor for recurrent PJK/F in patients with ASD who have undergone revision surgery. Overcorrection, with GL-HA offset less than -5 cm, is associated with recurrent PJK/F. The instrumented spine tends to align the GL near the HA, even at the cost of proximal junction.

Narrative Review of Clinical Impact of Head-Hip Offset Following Adult Spinal Deformity Surgery

In adult spinal deformity (ASD) surgery, mechanical failure (MF) has been a significant concern for spine surgeons as well as patients. Despite earnest endeavors to prevent MF, the absence of a definitive consensus persists, owing to the intricate interplay of multifarious factors associated with this complication. Previous approaches centered around global spinal alignment have yielded limited success in entirely forestalling MF. These methodologies, albeit valuable, exhibited limitations by neglecting to encompass global balance and compensatory mechanisms within their purview. In response to this concern, an in-depth comprehension of global balance and compensatory mechanisms emerges as imperative. In this discourse, the center of gravity and the gravity line are gaining attention in recent investigations pertaining to global balance. This narrative review aims to provide an overview of the global balance and a comprehensive understanding of related concepts and knowledge. Moreover, it delves into the clinical ramifications of the contemporary optimal correction paradigm to furnish an encompassing understanding of global balance and the current optimal correction strategies within the context of ASD surgery. By doing so, it endeavors to furnish spine surgeons with a guiding compass, enriching their decision-making process as they navigate the intricate terrain of ASD surgical interventions.

Clinical Significance of Lordosis Orientation on Proximal Junctional Kyphosis Development in Long-Segment Fusion Surgery for Adult Spinal Deformity

OBJECTIVE

We sought to evaluate the clinical impact of lordosis orientation (LO) on proximal junctional kyphosis (PJK) development in adult spinal deformity surgery.

METHODS

This study included 152 patients who underwent low thoracic (T9-T12) to pelvis fusion and were followed up for ≥2 years. In the literature, 6 radiographic parameters representing LO were introduced, such as uppermost instrumented vertebra (UIV) slope, UIV inclination, UIV-femoral angle (UIVFA), thoracolumbar tilt, thoracolumbar slope, and lordosis tilt. Various clinical and radiographic factors including 6 LO parameters were investigated using logistic regression analysis to identify risk factors for PJK.

RESULTS

The mean age was 69.4 years, and 136 patients were females (89.5%). PJK developed in 65 patients (42.8%). Multivariate logistic regression analysis revealed that only small postoperative pelvic incidence (PI)-lumbar lordosis (LL) (odds ratio [OR] = 0.962, 95% confidence interval: 0.929-0.996, P = 0.030) and large UIVFA (OR = 1.089, 95% confidence interval: 1.028-1.154, P = 0.004) were significant for PJK development. UIVFA showed significantly positive correlation with pelvic tilt (CC = 0.509), thoracic kyphosis (CC = 0.384), and lordosis distribution index (CC = 0.223). UIVFA was also negatively correlated with sagittal vertical axis (CC = -0.371). However, UIVFA did not correlate with LL, PI-LL, or T1 pelvic angle.

CONCLUSIONS

LO significantly increases the risk of PJK development in ASD surgery. Multivariate analysis revealed that smaller postoperative PI-LL and greater UIVFA were significant risk factors for PJK. Surgeons should avoid undercorrection and overcorrection to prevent PJK development.

Proximal Junctional Failure after Corrective Surgery: Focusing on Elderly Patients with Severe Sagittal Imbalance

Background

Previous reports with proximal junctional failure (PJF) included relatively young patients or deformity without sagittal imbalance. The present study focused on the two well-known risk factors for PJF, old age and severe sagittal imbalance. With these high-risk patients, the present study aimed to identify a strategy that could prevent PJF and to investigate whether the degree of correction would really affect the PJF occurrence.

Methods

Patients who were ≥ 60 years of age and underwent long fusion (≥ 4) to the sacrum for severe sagittal imbalance (defined as pelvic incidence minus lumbar lordosis [PI-LL] ≥ 30°) were included. PJF was defined as a vertebral fracture at the uppermost instrumented vertebra (UIV) or UIV+1, failure of UIV fixation, myelopathy, or any need for proximal extension of fusion. Presumed risk factors were compared between the patients with and without PJF.

Results

Total 146 patients (mean age, 68.4 years) with preoperative mean PI-LL of 46.8° were included. PJF developed in 39 patients (26.7%) at a mean of 18.1 months after surgery. Multivariate analysis showed that osteoporosis (odds ratio [OR], 2.812; p = 0.019) and UIV located below T10 (OR, 3.773; p = 0.010) were significant risk factors for developing PJF. However, the degree of correction did not affect PJF occurrence.

Conclusions

The present study indicates that osteoporosis should be well corrected preoperatively and extending the fusion above T10 should be considered for severe imbalance in old patients. However, the amount of correction was not associated with PJF development.

Predictive factors for conversion from conservatively to surgically treatment osteoporotic thoracolumbar compression fractures based on sagittal parameters and magnetic resonance imaging features

PURPOSE

To investigate the relationship between sagittal plane characteristics of the spinal column and conservative treatment failure in acute osteoporotic spinal fractures (OSFs).

METHODS

As a retrospective study of single-institute data, thoracolumbar OSF patients with similar propensities in terms of location of fractures and results of bone mineral density were analyzed. Among them, 43 patients (group I) who needed reconstructive surgical interventions and 39 patients (group II) who obtained successful treatment through conservative care were included. General demographic data, radiographic features of fractures, and magnetic resonance imaging (MRI) features of fractures were analyzed. To investigate the relationship between global sagittal alignment of the spine and occurrence of delayed complication following OSFs, radiological sagittal parameters were analyzed.

RESULTS

The number of cases requiring reconstructive surgery was significantly higher when the index vertebra showed diffuse or mid-portion bone marrow changes in MRI. In terms of sagittal parameters, pelvic incidence (group I 59.1° ± 11.9°, group II 54.6° ± 9.8°) and thoracolumbar angle (group I 26.5° ± 14.1°, group II 17.4° ± 11.2°) were significantly higher in group I. Logistic regression analysis showed that higher pelvic incidence (OR 1.09, 95% CI 1.01-1.18, p value < 0.05) and higher thoracolumbar angle (OR 1.09, 95% CI 1.02-1.17, p value < 0.05) were significant risk factors for delayed complications requiring reconstructive surgery following OSFs.

CONCLUSION

Delayed complications requiring reconstructive surgery following OSFs are related to sagittal plane parameters of the spine such as high pelvic incidences, in addition to previously known radiographic characteristics of fractures.

Machine Learning-Based Measurement of Regional and Global Spinal Parameters Using the Concept of Incidence Angle of Inflection Points

This study delves into the application of convolutional neural networks (CNNs) in evaluating spinal sagittal alignment, introducing the innovative concept of incidence angles of inflection points (IAIPs) as intuitive parameters to capture the interplay between pelvic and spinal alignment. Pioneering the fusion of IAIPs with machine learning for sagittal alignment analysis, this research scrutinized whole-spine lateral radiographs from hundreds of patients who visited a single institution, utilizing high-quality images for parameter assessments. Noteworthy findings revealed robust success rates for certain parameters, including pelvic and C2 incidence angles, but comparatively lower rates for sacral slope and L1 incidence. The proposed CNN-based machine learning method demonstrated remarkable efficiency, achieving an impressive 80 percent detection rate for various spinal angles, such as lumbar lordosis and thoracic kyphosis, with a precise error threshold of 3.5°. Further bolstering the study's credibility, measurements derived from the novel formula closely aligned with those directly extracted from the CNN model. In conclusion, this research underscores the utility of the CNN-based deep learning algorithm in delivering precise measurements of spinal sagittal parameters, and highlights the potential for integrating machine learning with the IAIP concept for comprehensive data accumulation in the domain of sagittal spinal alignment analysis, thus advancing our understanding of spinal health.

Predictors of Vertebral Endplate Fractures after Oblique Lumbar Interbody Fusion

BACKGROUND

Cage subsidence after oblique lumbar interbody fusion (OLIF) induces restenosis and adversely affects patient outcomes. Many studies have investigated the causes of subsidence, one of which is endplate fracture (EF). This study aimed to identify predictors of EF after OLIF.

METHODS

This retrospective study reviewed consecutive patients who underwent OLIF at a single institute between August 2019 and February 2022. A total of 104 patients were enrolled. The patients' demographic data and surgical details were collected through chart reviews. Radiographic variables were measured. Related variables were also analyzed using binomial logistic regression, dividing each group into those with versus without EF.

RESULTS

EF occurred at 30 of 164 levels (18.3%), and the binary logistic analysis revealed that sex (odds ratio [OR], 11.07), inferior endplate concave depth (OR, 1.95), disc wedge angle (OR, 1.22), lumbar lordosis (OR, 1.09), pelvic incidence (OR, 1.07), sagittal vertical axis (OR, 1.02), sacral slope (OR, 0.9), L3-4 level (OR, 0.005), and L4-5 level (OR, 0.004) were significantly related to EF.

CONCLUSIONS

OLIF in older Asian patients should be performed carefully after recognizing the high possibility of EF and confirming the factors that should be considered preoperatively.

Does the Amount of Correction of Sagittal Deformity Really Promote Proximal Junctional Kyphosis? Multivariate Analyses According to Uppermost Instrumented Vertebra Levels

BACKGROUND

The present study assumed that the effects of deformity correction amounts on proximal junctional kyphosis (PJK) development after long deformity surgery would vary according to uppermost instrumented vertebrae (UIV) levels. Our study was to reveal the association between the amount of correction and PJK according to UIV levels.

METHODS

Adult spinal deformity patients aged >50 years who underwent thoracolumbar fusion (≥4 levels) were included. PJK was defined by proximal junctional angles ≥15°. Presumed demographic and radiographic risk factors for PJK were evaluated including parameters regarding the correction amount such as postoperative change in lumbar lordosis and postoperative offset grouping, the value associated with age-adjusted pelvic incidence-lumbar lordosis mismatch. The patients were divided according to UIV levels of T10 or above (group A) and T11 or below (group B). Multivariate analyses were performed separately for both groups.

RESULTS

The present study included 241 patients (74 for group A and 167 for group B). PJK developed in approximately half of all patients within an average of 5 years of follow-up. For group A, only body mass index (P = 0.002) was associated with PJK. No radiographic parameters were correlated. For group B, postoperative change in lumbar lordosis (P = 0.009) and offset value (P = 0.030) were significant risk factors for PJK development.

CONCLUSIONS

The correction amount of sagittal deformity increased the risk of PJK only in patients with UIV at or below T11. However, it was not associated with PJK development in patients with UIV at or above T10.

Introduction of a New Radiographic Parameter to Predict Proximal Junctional Kyphosis in Adult Spinal Deformity: UIVPTA (Uppermost Instrumented Vertebra-Pelvic Tilt Angle)

OBJECTIVE

To introduce a new sagittal parameter, uppermost instrumented vertebra-pelvic tilt angle (UIVPTA), and to determine the effects on the proximal junctional kyphosis (PJK) development in adult spinal deformity (ASD) surgery.

METHODS

Patients ≥ 60 years with ASD who underwent low thoracic spine to pelvis fusion with a minimum of 2-years of follow-up were included in this study. Two groups were created according to PJK development. Various clinical and radiographic factors were compared between PJK and non-PJK groups to identify the risk factors for PJK. Cutoff value of UIVPTA for PJK development was calculated using receiver operating characteristic curve according to different pelvic incidence groups. Linear regression analysis was performed to identify factors to affect UIVPTA.

RESULTS

One hundred fifity-one patients were included in this study. There were 135 female patients (89.4%). Mean age was 70.5 years. PJK developed in 65 patients (43.0%). Multivariate analysis showed that overcorrection relative to age-adjusted pelvic incidence (PI) minus lumbar lordosis (LL) (PI-LL) target and lower UIVPTA were independent risk factors for PJK. The cutoff value of UIVPTA for PJK development was calculated as 4.0° in patients with PI less than 45°, 9.5° in patients with PI between 45° and 60°, and 13.0° in patients with PI greater than 60°. Linear regression analysis showed that UIVPTA was positively affected by postoperative values of LL (coefficient = 0.505), PI-LL (coefficient = 0.674), and pelvic tilt (coefficient = 0.286).

CONCLUSION

Optimal correction within the age-adjusted PI-LL combined with keeping UIVPTA within optimal range is suggested for the prevention of PJK.

Reciprocal Changes Following Cervical Realignment Surgery

Over the last few decades, the importance of the sagittal plane and its contour has gained significant recognition. Through full-body stereoradiography, the understanding of compensatory mechanisms, and the concept of global balance and reciprocal change has expanded. There have been a few reports describing how cervical realignment surgery affects global spinal alignment (GSA) and global balance. Despite the research efforts, the concept of reciprocal change and global balance is still perplexing. Understanding the compensatory status and main drivers of deformity in a patient is vital because the compensatory mechanisms may resolve reciprocally following cervical realignment surgery. A meticulous preoperative evaluation of the whole-body alignment, including the pelvis and lower extremities, is paramount to appreciate optimal GSA in the correction of spinal malalignment. This study aims to summarize relevant literature on the reciprocal changes in the whole body caused by cervical realignment surgery and review recent perspectives regarding cervical compensatory mechanisms.

Clinical Impact and Correlations of Odontoid Parameters Following Multilevel Posterior Cervical Fusion Surgery

OBJECTIVE

C2 slope (C2S), a cervical parameter mathematically approximated as T1 slope minus cervical lordosis (T1S-CL), predicts functional improvement in cervical deformity patients. Nonetheless, C2S is a positional parameter based only on the horizontal axis. The current study aims to introduce novel odontoid parameters and establish their relationships with patient-reported health-related quality of life (HRQoL).

METHODS

Lateral plain radiographs of 32 adults who underwent multilevel posterior cervical fusion were analyzed. The odontoid parameters included odontoid incidence (OI), C2S, odontoid tilt (OT), and gravity line-C2 distance (GL-C2), while the cervical parameters were the Cobb angle at C0-1, C1-2, C0-2, C2-7, C2-7 sagittal vertical axis (cSVA), T1 slope, and T1S-CL. The range of motion (ROM) of the occipito-atlantoaxial complex was measured in flexion and extension plain radiographs. Scores on the Neck Disability Index (NDI) and visual analogue scale (VAS) for axial neck (VASn) and arm pain were measured.

RESULTS

Compared to asymptomatic subjects, patients had larger C2S, cSVA, and T1S-CL, and smaller OT. Preoperatively, OI was significantly correlated with the ROM of C1-2 (r = 0.37, p < 0.05) and C0-2 (r = 0.46, p < 0.01). OT and C2S had significant correlations with the C0-1, C1-2, and C0-2 angles, GL-C2, and T1S-CL. Postoperative NDI scores were significantly correlated with OI (r = -0.40, p < 0.05) and OT (ρ = -0.37, p < 0.05). VASn was significantly correlated with GL-C2 (r = -0.35, p < 0.05).

CONCLUSION

The odontoid parameters were significantly correlated with established cervical parameters and HRQoL measures. OI is a constant parameter representing the individual's compensatory reservoir at the upper cervical spine.