Analysis of an unexplored group of sagittal deformity patients: low pelvic tilt despite positive sagittal malalignment

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.

Machine-learning models for the prediction of ideal surgical outcomes in patients with adult spinal deformity

Aims

Adult spinal deformity (ASD) surgery can reduce pain and disability. However, the actual surgical efficacy of ASD in doing so is far from desirable, with frequent complications and limited improvement in quality of life. The accurate prediction of surgical outcome is crucial to the process of clinical decision-making. Consequently, the aim of this study was to develop and validate a model for predicting an ideal surgical outcome (ISO) two years after ASD surgery.

Methods

We conducted a retrospective analysis of 458 consecutive patients who had undergone spinal fusion surgery for ASD between January 2016 and June 2022. The outcome of interest was achievement of the ISO, defined as an improvement in patient-reported outcomes exceeding the minimal clinically important difference, with no postoperative complications. Three machine-learning (ML) algorithms - LASSO, RFE, and Boruta - were used to identify key variables from the collected data. The dataset was randomly split into training (60%) and test (40%) sets. Five different ML models were trained, including logistic regression, random forest, XGBoost, LightGBM, and multilayer perceptron. The primary model evaluation metric was area under the receiver operating characteristic curve (AUROC).

Results

The analysis included 208 patients (mean age 64.62 years (SD 8.21); 48 male (23.1%), 160 female (76.9%)). Overall, 42.8% of patients (89/208) achieved the ideal surgical outcome. Eight features were identified as key variables affecting prognosis: depression, osteoporosis, frailty, failure of pelvic compensation, relative functional cross-sectional area of the paraspinal muscles, postoperative sacral slope, pelvic tilt match, and sagittal age-adjusted score match. The best prediction model was LightGBM, achieving the following performance metrics: AUROC 0.888 (95% CI 0.810 to 0.966); accuracy 0.843; sensitivity 0.829; specificity 0.854; positive predictive value 0.806; and negative predictive value 0.872.

Conclusion

In this prognostic study, we developed a machine-learning model that accurately predicted outcome after surgery for ASD. The model is built on routinely modifiable indicators, thereby facilitating its integration into clinical practice to promote optimized decision-making.

Associations between NCLBP, spinal sagittal alignment and age groups: a cross-sectional cohort study

PURPOSE

Nonspecific chronic low back pain (NCLBP) is one of the most common manifestations of degenerative spondylitis. It affects many patients of all ages and seriously interferes with quality of life. However, the associations between NCLBP, sagittal alignment and age remain unclear. We aimed to investigate the typical features of sagittal alignment in individuals with NCLBP and to discuss the relationships between age and these NCLBP-related changes in sagittal alignment.

METHODS

We measured the sagittal parameters of patients with NCLBP and investigated their sagittal alignment and compensatory mechanisms by comparing them with those of asymptomatic individuals.

RESULTS

A total of 905 elderly patients (≥ 50 years old) and 1296 young patients (< 50 years old) were included. An analysis of sagittal parameters revealed that elderly patients with NCLBP had a smaller lumbar lordosis (LL, p = 0.001) and a greater T1 pelvic angle (TPA, p < 0.001). Age was significantly correlated with the TPA (rs = 0.549, p < 0.001) and pelvic tilt (PT, rs = 0.471, p < 0.001). The AUC value of the TPA was 0.782 (95% CI 0.764 to 0.799).

CONCLUSIONS

Although decreased lumbar lordosis is the most typical sagittal feature in patients with NCLBP, there are still differences in sagittal alignment between different ages. Compared with young patients, elderly patients with NCLBP more commonly present with a decompensated pattern of the anterior inclination of the trunk as the main sagittal alignment abnormality. TPA is more predictive than LL for the diagnosis of geriatric NCLBP.

The role of supine imaging in assessing failure of pelvic compensation and its impact on surgical outcomes in patients with adult spinal deformity

AIMS

This study aims to investigate the impacts of failure of pelvic compensation (FPC), as determined by variations in spinopelvic alignment during the transition from the supine to the upright position, on surgical outcomes in patients with adult spinal deformity (ASD).

METHODS

A total of 125 ASD patients who underwent posterior correction surgery with a minimum follow-up of two years were enrolled. Radiographic outcomes, including thoracic kyphosis, lumbar lordosis, sacral slope (SS), pelvic tilt (PT), pelvic incidence, T1-pelvic-angle and sagittal vertical axis (SVA), were measured on lateral whole-spine radiographs. Postoperative realignment was assessed using the sagittal age-adjusted score (SAAS). Patient-reported outcomes were collected through Scoliosis Research Society-22R (SRS-22R) questionnaire, alongside data on minimum clinically important difference (MCID) achievement. The incidence of proximal junctional kyphosis (PJK) following surgery was also recorded. Based on the calculated minimum detectable change of SS, FPC was defined as the change in SS of less than 3.9° between supine and upright positions. Patients were divided into the pelvic compensation (PC) cohort and the FPC cohort.

RESULTS

Eighty-eight patients were categorized into the PC cohort and 37 into the FPC cohort. Postoperatively, patients with FPC exhibited significantly lower PT (22.44° vs. 28.57°, p <.001) and higher SVA (57.49 mm vs. 32.57 mm, p =.008) than PC patients. Additionally, the SRS-22R subtotal score was lower in the FPC group (3.68 vs. 3.89, p =.035), and the proportion of MCID achievement in SRS-22R was significantly reduced (45.95% vs. 65.91%, p =.038). While the incidence of PJK was higher in FPC patients, this difference was not significant (40.54% vs. 29.55%, p =.232). Correcting to SAAS matching standard was associated with a reduced risk of PJK (OR 6.50, 95%CI 1.18-35.84) and increased likelihood of achieving MCID (OR 4.50, 95%CI 1.05-19.22) in ASD patients with FPC.

CONCLUSION

ASD patients with preoperative FPC are more likely to experience worse patient-reported outcomes and a higher incidence of mechanical complications following corrective surgery. To optimize surgical outcomes in these patients, individualized preoperative planning aligned with the SAAS criteria may be particularly beneficial.

The Role of Pelvic Compensation in Sagittal Balance and Imbalance: The Impact of Pelvic Compensation on Spinal Alignment and Clinical Outcomes Following Adult Spinal Deformity Surgery

BACKGROUND AND OBJECTIVES

The Scoliosis Research Society (SRS)-Schwab system does not include a pelvic compensation (PC) subtype, potentially contributing to gaps in clinical characteristics and treatment strategy for deformity correction. It also remains uncertain as to whether PC has differing roles in sagittal balance (SB) or imbalance (SI) status. To compare radiological parameters and SRS-22r domains between patients with failed pelvic compensation (FPC) and successful pelvic compensation (SPC) based on preoperative SB and SI.

METHODS

A total of 145 adult spinal deformity patients who received deformity correction were analyzed. Radiographic and clinical outcomes were collected for statistical analysis. Patients were classified into 4 groups based on the median value of PT/PI ratio (PTr) and the cutoff value of SB. Patients with low PTr and high PTr were defined as FPC and SPC, respectively. Radiographic and clinical characteristics of different groups were compared.

RESULTS

Patients with SPC exhibited significantly greater improvements in lumbar lordosis, pelvic tilt, PTr, and T1 pelvic angle as compared to patients with FPC, irrespective of SB or SI. No apparent differences in any of SRS-22r domains were observed at follow-up when comparing the SB-FPC and SB-SPC patients. However, patients with SI-SPC exhibited significantly better function, self-image, satisfaction, and subtotal domains at follow-up relative to those with SI-FPC. When SI-FPC and SI-SPC patients were subdivided further based on the degree of PI-LL by adjusting for age, the postoperative function and self-image domains were significantly better in the group with overcorrection of PI-LL than undercorrection of PI-LL in SI-FPC patients. However, no differences in these SRS-22r scores were observed when comparing the subgroups in SI-SPC patients.

CONCLUSION

Flexible pelvic rotation is associated with benefits to the correction of sagittal parameters, irrespective of preoperative SB or SI status. However, PC is only significantly associated with clinical outcomes under SI. Patients with SI-FPC exhibit poorer postoperative clinical outcomes, which should be recommended to minimize PI-LL.

Alignment considerations in degenerative spinal conditions: A narrative review

Background

With an aging population, degenerative spinal diseases are contributing significantly to the healthcare's burden. Spinal alignment in the context of adult spinal deformities has become an important domain of research.

Methods

We conducted a narrative review of the latest considerations in spinal alignment within the context of degenerative spinal conditions, discussed current strategies for morphological assessment and finally identified potential areas for future research.

Results

This review reported that degenerative spinal conditions lead to a complex disruption of spinal alignment. It also highlighted the importance of spino-pelvic alignment with specific attention to compensatory mechanisms that occur in response to spinal deformities. Emerging technologies including Artificial Intelligence and epigenetics are showing promises in terms of patient care.

Conclusions

Understanding spinal alignment in degenerative conditions underscores the importance of dynamic and individualized assessments. Future research should integrate emerging technologies along with traditional clinical practices in order to optimize patient outcomes and minimize complications for patients suffering from degenerative spinal diseases.

Identification and impact of failure of pelvic compensation in patients with adult spinal deformity

BACKGROUND CONTEXT

Previous research has identified a specific subtype known as failure of pelvic compensation (FPC) in patients with adult spinal deformity (ASD). However, the criteria for assessing FPC remain inconsistent, and its impacts on spinal sagittal alignment and health-related quality-of-life (HRQoL) scores remain unclear.

PURPOSE

To propose a novel criterion for identifying FPC based on variations in spinopelvic alignment during the transition from the supine to upright position and to evaluate the effects of FPC on patients' spinal sagittal alignment and HRQoL scores.

STUDY DESIGN/SETTING

Retrospective cross-sectional study.

PATIENT SAMPLE

Patients with ASD from a monocenter database.

OUTCOME MEASURES

Radiographic measures, including thoracic kyphosis (TK), lumbar lordosis (LL), sacral slope (SS), pelvic tilt, pelvic incidence (PI), and sagittal vertical axis (SVA), were measured on lateral whole-spine radiographs. LL and SS were also measured on reconstructed lumbar computed tomography images in the sagittal view taken in the supine position. The relative functional cross-sectional area (rFCSA) of paraspinal muscles was evaluated via lumbar magnetic resonance imaging. HRQoL measures, encompassing visual analog scale for back pain (VAS-BP), Oswestry Disability Index (ODI), and Scoliosis Research Society-22R (SRS-22R), were collected.

METHODS

A total of 154 patients were enrolled. Based on the calculated minimum detectable change of SS, FPC was defined as the change in SS of less than 3.4° between supine and upright positions. Patients were divided into 3 groups: sagittal balance with pelvic compensation (SI-PC), sagittal imbalance with pelvic compensation (SI-PC), and sagittal imbalance with failure of pelvic compensation (SI-FPC). Radiographic parameters and HRQoL scores were compared among the groups.

RESULTS

Thirty-six patients were categorized into the SB-PC group, 87 into the SI-PC group, and 31 into the SI-FPC group. Patients with low PI and small paraspinal muscles rFCSA were more prone to experiencing FPC accompanied by severe sagittal imbalance. The SI-FPC group exhibited less TK and a larger SS than the SI-PC group exhibited and had a similar SVA as that of the SI-PC group. Additionally, they displayed worse VAS-BP, ODI, SRS-function, and SRS-22 total scores than the SB-PC group displayed.

CONCLUSIONS

In patients with ASD, an inherently low pelvic compensatory reserve and a high fatty infiltration in paraspinal muscles are pivotal factors contributing to FPC. Compared with SI-PC patients, SI-FPC patients demonstrate a thoracic-dominant compensatory pattern for sagittal malalignment. In addition, these patients experienced more severe pain and functional decline than the SB-PC patients experienced.

Primary Pelvic Anteversion: Definition, Relevance, and History After Surgery for Adult Spine Deformity

STUDY DESIGN

Retrospective analysis of prospectively collected data.

OBJECTIVE

To identify the best definition of primary anteverted pelvis in the setting of adult spine deformity (ASD), and to investigate whether this is a pathologic setting that requires surgical correction.

SUMMARY OF BACKGROUND DATA

While pelvic retroversion has been thoroughly investigated, pelvic anteversion (AP) is a far lesser discussed topic. Four different AP definitions have been proposed, and AP has been described as a normal or pathologic entity by different authors.

MATERIALS AND METHODS

All patients consulting for ASD at the five participating sites were included. First, the four definitions of AP were compared with descriptive statistics (anatomic method-Pelvic Tilt <0°; Relative Pelvic Version method-RPV >5°; Roussouly method-Pelvic Incidence (PI)<50° and Sacral Slope (SS)>35°); low PT method-PT/PI <25th percentile). Second a subgroup analysis among operated AP patients with a two-year follow-up was performed. Complication rate, radiographic parameters, and clinical scores (ODI, SF-36) were compared in a multivariate analysis between patients who did and did not maintain an AP at the 2-year follow-up.

RESULTS

A total of 1163 patients were available for the first analysis. The RPV method seemed to be the most appropriate to define AP in ASD patient. For the second analysis, data on 410 subjects were available, and most of them were young adults with idiopathic scoliosis that did not require pelvic fixation. AP patients who maintained an AP after ASD surgery presented comparable radiographic and clinical outcomes to the patients who presented a normoverted/retroverted pelvis after surgery.

CONCLUSIONS

According to the results of the presented study, the RPV method is the most appropriate to define primary AP, which is not a pathologic condition and is most often observed in young adults with idiopathic scoliosis. Anteverted pelvis does not require direct surgical correction in this patient group.

Influence of pelvic tilt correction on PJK occurrence after adult spinal deformity surgery

INTRODUCTION

Many risk factors for proximal junctional kyphosis (PJK) have been reported in the literature, especially sagittal alignment modifications, but studies on pelvic tilt (PT) variations and its influence on PJK are missing. Aim of this study was to analyze the influence of pelvic tilt correction, after long fusion surgery for ASD patients, on PJK occurrence.

METHODS

A monocentric retrospective study was conducted on prospectively collected data, including 76 patients, operated with fusion extending from the thoraco-lumbar junction to the ilium. Radiologic parameters were measured on fullspine standing radiographs preoperatively, postoperatively (<6 months) and at latest follow-up (before revision surgery or >2 years). All parameters were analyzed comparing patients with PJK (group "PJK") and without PJK (group "no PJK"). A further analysis compared patients with low (PT/PI<25th percentile, LowPT group) and high (PT/PI>75th percentile, HighPT group) preoperative pelvic tilt.

RESULTS

« PJK » patients had a greater lumbar lordosis and thoracic kyphosis correction (p=0,03 et <0,001 respectively) compared to the "no PJK" patients. Pelvic tilt was significantly lower postoperatively in the "PJK" group (p=0,03). Patients from the HighPT PJK group were significantly more corrected than patients from the HighPT noPJK group (p=0,003).

CONCLUSION

Through the analysis of 76 patients, we showed that pelvic tilt did not seem to play a role in the setting of PJK after ASD surgery. Decreasing PT after surgery could be an element to watch out for in patients with PJK risk factors.

Association of radiological severity of hip involvement with clinical characteristics and sagittal spinopelvic balance in patients with ankylosing spondylitis

INTRODUCTION

This is the first study to analyze the associations between the radiological severity of hip involvement with clinical characteristics and sagittal spinopelvic balance in patients with ankylosing spondylitis (AS).

METHOD

We evaluated 182 patients with AS who were referred to outpatient clinics. Patient demographic data and clinical and radiographic parameters were collected. Patients were divided into three groups based on the Bath Ankylosing Spondylitis Radiology Hip Index. Clinical characteristics and spinopelvic parameters acquired by a low-dose biplanar imaging system were evaluated among these groups.

RESULTS

Patients with more severe hip involvement were older and had longer disease duration and diagnostic delay, with lower Harris Hip Score (p < 0.001) and 12-item Short Form Health Survey Physical Component Score (p < 0.001) and higher Bath Ankylosing Spondylitis Disease Activity Index (p = 0.030) and Functional Index (p < 0.001). Patients with more severe hip involvement had significantly higher sacroiliac grade (p < 0.001) and higher modified Stoke Ankylosing Spondylitis Spinal Score (p < 0.001). Patients with moderate and severe hip involvement had similar lumbar lordosis and spino-sacral angle, whereas patients with severe hip involvement had lower pelvic tilt, pelvic femoral angle, higher sacral slope, and sagittal vertical axis.

CONCLUSIONS

The severity of hip involvement is associated with physical function and is not consistent with the severity of spinal involvement. Severe hip involvement impairs the ability to retrovert the pelvis to accommodate the sagittal deformity, and spinopelvic parameters should be concretely evaluated in preoperative counseling of patients with AS waiting for total hip arthroplasty. Key Points • The severity of hip involvement in patients with AS is associated with physical function. • Severe hip involvement impairs the ability to retrovert the pelvis to accommodate the sagittal deformity.

Effects of dynamic and rigid implantation on biomechanical characteristics of different sagittal alignment lumbar after single- or double-level spinal fixations: a finite-element modeling study

BACKGROUND

Although it is critical to understand the accelerated degeneration of adjacent segments after fusion, the biomechanical properties of the spine have not been thoroughly studied after various fusion techniques. This study investigates whether four Roussouly's sagittal alignment morphotypes have different biomechanical characteristics after different single- or double-level spinal fixations.

METHODS

The parametric finite element (FE) models of Roussouly's type (1-4) were developed based on the radiological data of 625 Chinese community population. The four Roussouly's type models were reassembled into four fusion models: single-level L4-5 Coflex fixation model, single-level L4-5 Fusion (pedicle screw fixation) model, double-level Coflex (L4-5) + Fusion (L5-S1) model, and double-level Fusion (L4-5) + Fusion (L4-5) model. A pure moment of 7.5 Nm was applied to simulate the physiological activities of flexion, extension, lateral bending and axial rotation.

RESULTS

Both single-level and double-level spinal fixation had the greatest effect on lumbar range of motion, disc pressure, and annulus fibrosis stress in flexion, followed by lateral bending, extension, and axial rotation. In all models, the upper adjacent segment was the most influenced by the implantation and bore the most compensation from the fixed segment. For Type 2 lumbar, the L4-L5 Coflex effectively reduced the disc pressure and annulus fibrosis stress in adjacent segments compared to the L4-L5 Fusion. Similarly, the L4-L5 Coflex offered considerable advantages in preserving the biomechanical properties of adjacent segments for Type 1 lumbar. For Type 4 lumbar, the L4-L5 Coflex did not have superiority over the L4-L5 Fusion, resulting in a greater increase in range of motion at adjacent segments in flexion and extension. The difference between the two fixations was not apparent in Type 3 lumbar. Compared to the single-level Fusion, the changes in motion and mechanics of the lumbar increased after both the double-level Coflex + Fusion and Fusion + Fusion fixations, while the differences between two double-level fixation methods on adjacent segments of the four lumbar models were similar to that of the single-level fixation.

CONCLUSION

Type 3 and Type 4 lumbar have good compensatory ability and therefore allow for a wider range of surgical options, whereas surgical options for small lordotic Type 1 and Type 2 lumbar are more limited and severe.

A Complement Type to SRS-Schwab Adult Spinal Deformity Classification: The Failure of Pelvic Compensation

STUDY DESIGN

Retrospective review.

OBJECTIVE

To determine characteristics of patients with adult spinal deformity (ASD) who showed failed pelvic compensation even with significant sagittal imbalance.

BACKGROUND

Patients who show failed pelvic compensation despite significant sagittal imbalance reportedly present distinct clinical outcomes. However, to our knowledge, no study has clearly defined or characterized this subgroup of patients with ASD.

MATERIALS AND METHODS

We examined 126 patients who underwent reconstructive spinal surgery for ASD between September 2016 and September 2020. Radiographic spinopelvic parameters were assessed. The patients were divided into four quadrant groups based on the two axes of pelvic tilt/pelvic incidence (PT/PI) and the sagittal vertical axis (SVA) with reference to the population median values (0.68 and 147.5 mm, respectively). Patients with low PT/PI and high SVA were considered to have failed pelvic compensation, and they were compared with other patient groups.

RESULTS

Patients with failed pelvic compensation (low PT/PI and high SVA) had worse clinical outcomes than those with successful pelvic compensation (high PT/PI and high SVA) at one year after surgery. Regarding radiographic outcomes, patients with failed pelvic compensation showed a significantly larger postoperative SVA even after correcting the PI-lumbar lordosis mismatch was corrected to a comparable range with the group of successful pelvic compensation. Notably, patients with failed pelvic compensation showed larger cross-sectional areas of the psoas and back extensor muscles than those with successful pelvic compensation. This suggests that failure of pelvic compensation did not occur because of back muscle weakness, which implies another underlying pathophysiology, including neurological origin.

CONCLUSION

Compared with patients with successful pelvic compensation, those with failed pelvic compensation showed lower postoperative improvements in clinical and radiographic outcomes. Therefore, it is important to consider pelvic compensation when planning surgical correction of deformities. Distinct surgical approaches, including overcorrection of the PI-lumbar lordosis mismatch or global sagittal alignment, should be attempted to ensure postoperative symptom improvement.

Biomechanical comparative analysis of effects of dynamic and rigid fusion on lumbar motion with different sagittal parameters: An in vitro study

Background: Although the management of the lumbar disease is highly dependent on the severity of the patient’s condition, optimal surgical techniques to reduce the risk of adjacent degeneration disease (ADS) remain elusive. Based on in vitro biomechanical tests of the cadaver spine, this study aimed to comparatively analyze the kinematic responses of the spine with dynamic and rigid fixations (i.e., Coflex fixation and posterolateral fusion) after single-or double-level lumbar fusion in daily activities.

Methods: Six human lumbar specimens (L1-S1) were selected for this experiment, and the sagittal parameters of each lumbar specimen were measured in the 3D model. The specimens were successively reconstructed into five groups of models: intact model, single-level L4-5 Coflex fixation model, single-level L4-5 Fusion (posterior pedicle screw fixation) model, double-level L4-5 Coflex + L5-S1 Fusion model; and double-level L4-5 Fusion + L5-S1 Fusion model. The pure moment was applied to the specimen model to simulate physiological activities in daily life through a custom-built robot testing device with an optical tracking system.

Results: For single-level lumbar fusion, compared to the traditional Fusion fixation, the Coflex dynamic fixation mainly restricted the extension of L4-L5, partially retained the range of motion (ROM) of the L4-L5 segment, and reduced the motion compensation of the upper adjacent segment. For the double-level lumbar fixation, the ROM of adjacent segments in the Coflex + Fusion was significantly decreased compared to the Fusion + Fusion fixation, but there was no significant difference. In addition, PT was the only sagittal parameter of the preoperative lumbar associated with the ROM under extension loading. The Coflex fixation had little effect on the original sagittal alignment of the lumbar spine.

Conclusion: The Coflex was an effective lumbar surgical technique with a less altering kinematic motion of the lumbar both at the index segment and adjacent segments. However, when the Coflex was combined with the fusion fixation, this ability to protect adjacent segments remained elusive in slowing the accelerated degradation of adjacent segments.

Biomechanical responses of human lumbar spine and pelvis according to the Roussouly classification

Background

Few studies have analyzed the different biomechanical properties of the lumbar with various morphological parameters, which play an important role in injury and degeneration. This study aims to preliminarily investigate biomechanical characteristics of the spine with different sagittal alignment morphotypes by using finite element (FE) simulation and in-vitro testing.

Methods

According to the lumbar-pelvic radiographic parameters of the Chinese population, the parametric FE models (L1-S1-pelvis) of Roussouly’s type (1–4) were validated and developed based on the in-vitro biomechanical testing. A pure moment of 7.5 Nm was applied in the three anatomical planes to simulate the physiological activities of flexion, extension, left-right lateral bending and left-right axial rotation.

Results

The sagittal configuration of four Roussouly’s type models had a strong effect on the biomechanical responses in flexion and extension. The apex of the lumbar lordosis is a critical position where the segment has the lowest range of motion among all the models. In flexion-extension, type 3 and 4 models with a good lordosis shape had a more uniform rotation distribution at each motor function segment, however, type 1 and 2 models with a straighter spine had a larger proportion of rotation at the L5-S1 level. In addition, type 1 and 2 models had higher intradiscal pressures (IDPs) at the L4-5 segment in flexion, while type 4 model had larger matrix and fiber stresses at the L5-S1 segment in extension.

Conclusion

The well-marched lordotic type 3 lumbar had greater stability, however, a straighter spine (type 1 and 2) had poor balance and load-bearing capacity. The hypolordotic type 4 model showed larger annulus fiber stress. Therefore, the sagittal alignment of Roussouly’s type models had different kinetic and biomechanical responses under various loading conditions, leading to different clinical manifestations of the lumbar disease.

Influence of Sagittal Lumbopelvic Morphotypes on the Range of Motion of Human Lumbar Spine: An In Vitro Cadaveric Study

Background: Although spinopelvic radiographs analysis is the standard for a pathological diagnosis, it cannot explain the activities of the spine in daily life. This study investigates the correlation between sagittal parameters and spinal range of motion (ROM) to find morphological parameters with kinetic implications. Methods: Six L1–S1 human lumbar specimens were tested with a robotic testing device. Eight sagittal parameters were measured in the three-dimensional model. Pure moments were applied to simulate the physiological activities in daily life. Results: The correlation between sagittal parameters and the ROM was moderate in flexion and extension, but weak in lateral bending and rotation. In flexion–extension, the ROM was moderately correlated with SS and LL. SS was the only parameter correlated with the ROM under all loading conditions. The intervertebral rotation distribution showed that the maximal ROM frequently occurred at the L5–S1 segment. The minimal ROM often appeared near the apex point of the lumbar. Conclusion: Sagittal alignment mainly affected the ROM of the lumbar in flexion and extension. SS and apex may have had kinetic significance. Our findings suggest that the effect of sagittal parameters on lumbar ROM is important information for assessing spinal activity.

Optimal Lumbar Lordosis Correction for Adult Spinal Deformity with Severe Sagittal Imbalance in Patients Over Age 60: Role of Pelvic Tilt and Pelvic Tilt Ratio

STUDY DESIGN

A retrospective study.

OBJECTIVES

The purpose of this study was to evaluate optimal and ideal target values of the spine balance correction in elderly patients with adult spinal deformity who were over the age of 60 years.

SUMMARY OF BACKGROUND DATA

The target values of the Scoliosis Research Society -Schwab classification to obtain satisfactory alignment and favorable outcomes are used in many spinal reconstruction surgeries. However, uniformly applying the Scoliosis Research Society-Schwab classification to all elderly patients aged 60 years or older showing sagittal malalignment may lead to several inconsistencies.

METHODS

This study included 121 patients (average age 70.5 yr and a minimum 2-yr follow-up) with adult spinal deformity who underwent long-segment fusion from T10 to sacrum. We used Pearson's correlation coefficient to analyze the relationship between clinical and radiographic parameters, and multilinear regression analysis and multivariate logistic regression model (backward elimination method) were conducted using the correlation factors of postoperative (Post) and last follow-up (Last) sagittal vertical axis to find the risk factors of Post sagittal imbalance.

RESULTS

Logistic regression analysis with the correlation factors of Post and Last sagittal vertical axis led to risk factors of Post sagittal imbalance, and after confirming the significance of each path, it was confirmed that the effects of pelvic incidence (PI)- lumbar lordosis (LL) and Post pelvic tilt ratio (PTr) were valid (P < 0.05). After using ROC curve, target value of PI-LL was 1.33, and that of PTr was 25.95%.

CONCLUSION

Through our study, the risk factors of Post sagittal imbalance were the Post value of PI-LL and that of PTr, and target value of PI-LL was <1.33 and that of PTr was <25.95%. These target values can be effective guidelines for spine surgeons who perform spine reconstruction surgeries for elderly patients with a pure sagittal imbalance based on Schwab's formula.Level of Evidence: 4.

Health insurance policy on surgical treatment of adult spinal deformity

Background: Recent burgeoning research on adult spinal deformity (ASD) has unveiled the benefits of surgical treatment and how to gain the benefits although these have only been around for 10 years.Current Concepts: During the last decade, the significance of pelvic incidence in the global spinal sagittal alignment and introductions of the Scoliosis Research Society-Schwab classification for ASD have been the guidelines of surgical treatment for ASD and the milestones for promising surgical results. However, one of the unsolved problems for the surgical treatment of ASD is the proximal junctional kyphosis, for which multifactorial causative factors have been suggested. Recent studies have focused on dynamic natures in patients with ASD during daily activities, which might be a clue for both prevention of proximal junctional kyphosis and a better level of surgical results. Even though a recent remarkable advancement for surgical treatment for ASD is present, the national guideline for reimbursement is still following the surgical indication for lumbar degenerative kyphosis published in 1988.Discussion and Conclusion: A significant gap exists between the national reimbursement guideline and generally held surgical indication for ASD surgery. Consequently, this huge gap raises trouble in both patients and surgeons. The patients with ASD cannot take an appropriate surgery for ASD, while the spine surgeons experience unreasonable adjustment of the cost by the Health Insurance Review and Assessment Service.

Synchronous imaging of pelvic geometry and muscle morphometry: a pilot study of pelvic retroversion using upright MRI

This study investigated feasibility of imaging lumbopelvic musculature and geometry in tandem using upright magnetic resonance imaging (MRI) in asymptomatic adults, and explored the effect of pelvic retroversion on lumbopelvic musculature and geometry. Six asymptomatic volunteers were imaged (0.5 T upright MRI) in 4 postures: standing, standing pelvic retroversion, standing 30° flexion, and supine. Measures included muscle morphometry [cross-sectional area (CSA), circularity, radius, and angle] of the gluteus and iliopsoas, and pelvic geometry [pelvic tilt (PT), pelvic incidence (PI), sacral slope (SS), L3-S1 lumbar lordosis (LL)] L3-coccyx. With four volunteers repeating postures, and three raters assessing repeatability, there was generally good repeatability [ICC(3,1) 0.80-0.97]. Retroversion had level dependent effects on muscle measures, for example gluteus CSA and circularity increased (up to 22%). Retroversion increased PT, decreased SS, and decreased L3-S1 LL, but did not affect PI. Gluteus CSA and circularity also had level-specific correlations with PT, SS, and L3-S1 LL. Overall, upright MRI of the lumbopelvic musculature is feasible with good reproducibility, and the morphometry of the involved muscles significantly changes with posture. This finding has the potential to be used for clinical consideration in designing and performing future studies with greater number of healthy subjects and patients.

Spino-femoral muscles affect sagittal alignment and compensatory recruitment: a new look into soft tissues in adult spinal deformity

OBJECTIVE

To quantify muscle characteristics (volumes and fat infiltration) and identify their relationship to sagittal malalignment and compensatory mechanism recruitment.

METHODS

Female adult spinal deformity patients underwent T1-weighted MRI with a 2-point Dixon protocol from the proximal tibia up to the T12 vertebra. 3D reconstructions of 17 muscles, including extensors and flexors of spine, hip and knee, were obtained. Muscle volume standardized by bone volume and percentage of fat infiltration (Pfat) were calculated. Correlations and regressions were performed.

RESULTS

A total of 22 patients were included. Significant correlations were observed between sagittal alignment and muscle parameters. Fat infiltration of the hip and knee flexors and extensors correlated with larger C7-S1 SVA. Smaller spinal flexor/extensor volumes correlated with greater PI-LL mismatch (r =  - 0.45 and - 0.51). Linear regression identified volume of biceps femoris as only predictor for PT (R² = 0.34, p = 0.005) and Pfat of gluteus minimus as only predictor for SVA (R² = 0.45, p = 0.001). Sagittally malaligned patients with larger PT (26.8° vs. 17.2°) had significantly smaller volume and larger Pfat of gluteus medius, gluteus minimus and biceps femoris, but similar values for gluteus maximus, the hip extensor.

CONCLUSION

This study is the first to quantify the relationship between degeneration of spino-femoral muscles and sagittal malalignment. This pathoanatomical study identifies the close relationship between gluteal, hamstring muscles and PT, SVA, which deepens our understanding of the underlying etiology that contributes to adult spinal deformity.

An analysis of the interactions between the spine, pelvis, and lower limbs in asymptomatic adults with limited pelvic compensation

Background

The interactions between the spine, pelvis, and lower limbs are dynamic based on the "cone of economy" concept; thus, different global radiographic parameters could be regarded as reflections of different centers of gravity. We conducted this retrospective study to evaluate the offsets of different centers of gravity in asymptomatic populations and to investigate how the global sagittal alignment is supported.

Methods

The following parameters were measured: cervical lordosis, thoracic kyphosis (TK), lumbar lordosis (LL), pelvic incidence (PI), pelvic tilt (PT), the ratio between PT and PI (PT/PI), sacral slope, PI minus LL (PI-LL), the sagittal vertical axis (SVA), cranial SVA to ankle center (Cr-A), CrSVA to the femoral head center (Cr-FH), C2SVA to the femoral head center (C2-FH), pelvic translation (P. Shift), and knee angle (KA). Participants were divided into subgroups based on the PT/PI ratio. Mean values were compared using the t-test, and correlations were assessed using Pearson's coefficient.

Results

A total of 82 asymptomatic adults were enrolled. The average PT/PI in subgroup 1 was the smallest, showing that individuals in this group may have limited pelvic retroversion. No significant differences in Cr-FH, Cr-A, or C2-FH were found between subgroups (all P>0.1), implying that global alignment was well supported in each group. Specifically, C2-FH showed minor changes between subgroups (P=0.998), showing that C2-FH may be a target for sagittal compensation. There were positive correlations between PT/PI and both P. Shift and SVA (r=0.930 and r=0.606, respectively). However, Cr-FH, Cr-A, and C2-FH were not significantly correlated with P. Shift or PT/PI (all P>0.05). Weak correlations existed between Cr-A, Cr-FH, and age (all P>0.2).

Conclusions

This study revealed that the Cr-FH and C2-FH offsets are stable across the population and could be maintained by regulating only the sagittal spinal curvature when pelvic compensation is limited. Cr-FH is not affected by age in the asymptomatic population. Thus, the stable Cr-FH and C2-FH could provide references for surgeons during the surgical decision-making process in patients with adult spinal deformity with sagittal malalignment.

Mechanical complications in adult spinal deformity and the effect of restoring the spinal shapes according to the Roussouly classification: a multicentric study

PURPOSE

To evaluate the incidence of mechanical complications in patients with adult spine deformity (ASD) treated by restoring the normal shape according to the Roussouly classification.

METHODS

This is a retrospective multicentric study with a minimum follow-up of 2 years. Patients operated on with fusion for ASD (minimum performed fusion: L2 to sacrum) were included. Patients with a history of previous spinal fusion of more than three levels were excluded. Spinal and pelvic parameters were measured on the preoperative and the immediate postoperative follow-up. All mechanical complications were recorded.

RESULTS

A total of 290 patients met the criteria of inclusion with a minimum follow-up of 2 years. Mechanical complications occurred in 30.4% of the cohort. The most common complication was PJK with an incidence of 18% while nonunion or instrumentation failure (rod breakage, implant failure) occurred in 12.4%. 66% of the patients were restored to the normal shape according to the Roussouly classification based on their PI and had a mechanical complication rate of 22.5%, whereas the remaining 34% of patients had a complication rate of 46.8% (p < 0.001). The relative risk for developing a mechanical complication if the algorithm was not met was 3 (CI 1.5-4.3; p < 0.001) CONCLUSION: In the recent literature, there are no clear guidelines for ASD correction. Restoring the sagittal spinal contour to the normal shapes of Roussouly according to the PI could serve as a guideline for ASD treatment. Ignoring this algorithm has a threefold risk of increased mechanical complications. We recommend this algorithm for treatment of ASD.

LEVEL OF EVIDENCE

IV cross-sectional observational study. These slides can be retrieved under Electronic Supplementary Material.

Identifying Thoracic Compensation and Predicting Reciprocal Thoracic Kyphosis and Proximal Junctional Kyphosis in Adult Spinal Deformity Surgery

STUDY DESIGN

Retrospective analysis.

OBJECTIVE

To define thoracic compensation and investigate its association with postoperative reciprocal thoracic kyphosis and proximal junctional kyphosis (PJK) SUMMARY OF BACKGROUND DATA.: Adult spinal deformity (ASD) patients recruit compensatory mechanisms like pelvic retroversion and knee flexion. However, thoracic hypokyphosis is a less recognized compensatory mechanism.

METHODS

Patients enrolled in a multicenter ASD registry undergoing fusions to the pelvis with upper instrumented vertebra (UIV) between T9 and L1 were included. Patients were divided into those with postoperative reciprocal thoracic kyphosis (reciprocal kyphosis [RK]: change in unfused thoracic kyphosis [TK] ≥15°) with and without PJK and those who maintained thoracic alignment (MT). Thoracic compensation was defined as expected thoracic kyphosis (eTK) minus preoperative TK.

RESULTS

For RK (n = 117), the mean change in unfused TK was 21.7° versus 6.1° for MT (n = 102) and the mean PJK angle change was 17.6° versus 5.7° for MT (all P < 0.001). RK and MT were similar in age, body mass index (BMI), sex, and comorbidities. RK had larger preoperative PI-LL mismatch (30.7 vs. 23.6, P = 0.008) and less preoperative TK (22.3 vs. 30.6, P < 0.001), otherwise sagittal vertical axis (SVA), pelvic tilt (PT), and T1 pelvic angle (TPA) were similar. RK patients had more preoperative thoracic compensation (29.9 vs. 20.0, P < 0.001), more PI-LL correction (29.8 vs. 17.3, P < 0.001), and higher rates of PJK (66% vs. 19%, P < 0.001). There were no differences in preoperative health-related quality of life (HRQOL) except reciprocal kyphosis (RK) had worse Scoliosis Research Society questionnaire (SRS) appearance (2.2 vs. 2.5, P = 0.005). Using a logistic regression model, the only predictor for postoperative reciprocal thoracic kyphosis was more preoperative thoracic compensation. Postoperatively the RK and MT groups were well aligned. Both younger and older (>65 yr) RK patients had greater thoracic compensation than MT counterparts. The eTK was not significantly different from the postoperative TK for the RK group without PJK (P = 0.566).

CONCLUSION

The presence of thoracic compensation in adult spinal deformity is the primary determinant of postoperative reciprocal thoracic kyphosis and these patients have higher rates of proximal junctional kyphosis.

LEVEL OF EVIDENCE

3.

Focal disorders of the spine with compensatory deformities: how to define them

PURPOSE

In this paper, the authors propose classifying the epiphenomenon of spinal deformity in two different categories: structural deformity, when the main driver of the observed deformity is a fixed and stiff alteration of the spinal segments, and compensatory deformity, which includes cases where the observed deformity is due to focal abnormalities. This last category comprises, but is not limited to, spinal stenosis, spondylolisthesis, disc herniation, infection or tumor, hip disease or neurological disease (such as Parkinson's disease).

METHOD

Narrative review article.

RESULTS

We analyzed the focal diseases of the spine that may cause a compensatory deformity inducing adaptation in the unaffected part of the spine.

CONCLUSION

The compensatory mechanisms involved in adaptive deformity represent an attempt to maintain a global alignment, to escape from pain or to control body posture. These slides can be retrieved under Electronic Supplementary material.