Adult spinal deformity patients undergoing total hip arthroplasty experience higher hip dislocation rates than those with normal spinal alignment. The traditional Lewinnek safe zone does not account for spinopelvic variation such as pelvic retroversion. To address this, three patient-specific normative zones for acetabular anteversion were defined. A multicenter retrospective analysis of 146 adult spinal deformity patients and 47 asymptomatic controls was performed using three-dimensional biplanar radiograph reconstructions to measure spinopelvic alignment and acetabular orientation. Normative Zone 1, for patients not undergoing spinal realignment, was delineated by the 95% confidence interval limits: minimum anteversion = 0.3182 × pelvic tilt +2.947 and maximum anteversion = 0.3317 × pelvic tilt +25.823. Normative Zone 2, for patients following spinal realignment, was based on pelvic incidence: minimum anteversion = 0.0682 × pelvic incidence +9.7749 and maximum anteversion = 0.0698 × pelvic incidence +21.5218. Normative Zone 3, intended for cases with uncertain spinal correction plans, was defined as the intersection of Zones 1 and 2, yielding a narrower target anteversion range. These zones enable patient-specific cup placement that accounts for existing or planned spinal alignment, with the potential to reduce dislocation risk. Clinical Significance: This study provides acetabular cup orientation tailored to each patient's spinopelvic alignment and surgical plan, potentially reducing dislocation rates in spinal malalignment patients.

Lower limbs can play a major compensating role for sagittal malalignment; however, little is known about the different types of compensation. This study aimed to identify different patterns of lower limb compensation and to determine which parameters may affect the recruitment of knee flexion versus hip extension. This study included adult spinal deformity (ASD) patients with full-body X-rays in erect position from a multicentric prospective database. All parameters were measured at baseline: demographics, clinical scores and radiographic parameters: pelvic parameters, pelvic incidence-lumbar lordosis (PI-LL) mismatch, T1 pelvic angle (TPA), sacro-femoral angle (SFA), knee flexion angle (KA), ankle dorsi-flexion angle (AA), pelvic shift (PSh), hip and knee osteoarthritis (OA) grade. A K-means cluster analysis was conducted to identify patterns of lower limb compensation based on SFA and KA. The optimal number of clusters was determined using the silhouette score. The different parameters were then compared across clusters. 871 ASD patients were included, of whom 66.9

STUDY DESIGN:Retrospective radiographic study of a multicentric prospective database. OBJECTIVE:This study aimed to analyze lumbar lordosis (LL) proximal and distal arcs relationships with spinopelvic parameters and determine how their distribution varies with pelvic incidence (PI). SUMMARY OF BACKGROUND DATA:LL is a key component of sagittal spinal alignment, yet its definition and assessment remain debated. Recent evidence suggests LL is not a uniform curvature but a complex structure with proximal and distal arcs exhibiting possibly distinct biomechanical roles. METHODS:This study included 642 healthy volunteers (mean age: 37.6±16.3) with full-body stereoradiographs, without spinal deformities. Maximum LL was assessed (LLmax), measured between thoracolumbar inflexion vertebra upper endplate and sacral plateau. Correlations between proximal lordosis (LLprox, measured between thoracolumbar inflexion vertebra upper endplate and lumbar apex upper endplate), distal lordosis (LLdist, measured between lumbar apex upper endplate and sacral plateau) and spinopelvic parameters were sought. Subjects were stratified into five PI groups to determine lordosis distribution variation with PI regarding angle and number of vertebrae included in curvature. RESULTS:LLdist strongly correlated with pelvic parameters, particularly sacral slope (SS, r=-0.83, P<0.001) and PI (r=-0.54, P<0.001), but not with thoracic alignment. LLprox correlated with both pelvic and thoracic parameters, including SS (r=-0.31, P<0.001) and thoracic kyphosis (r=-0.35, P<0.001). As PI increased, the contribution of LLdist to LLmax rose from 55±12% to 66±8% (P<0.001), while the number of vertebrae in the distal arc increased from 1.52±0.50 to 2.32±0.59 (P<0.001). Consequently, LLprox's proportional contribution to LLmax decreased, despite a stable vertebral extent. CONCLUSION:LL comprises two functionally distinct arcs: a pelvic-driven distal arc and a proximal arc influenced by overlying alignment and pelvic parameters. As PI increases, LL distal arc becomes preponderant. These findings advocate for a segmental approach in clinical assessment and surgical planning, emphasizing the need to consider both arcs independently. LEVEL OF EVIDENCE:3.

BACKGROUND CONTEXT:Recently, functional evaluation using 3D gait analysis (3DGA) proved to predict health-related quality-of-life (HRQOL) scores better than static radiographic evaluation in adult spinal deformity (ASD). However, 3DGA provides multiple parameters that can be a burden to interpret by nonexperts. A recent study showed that the dynamic pelvic tilt (dPT), the forward projection of the head and thorax (dODHA) and walking step length (SL) are the most representative gait kinematics in ASD patients. PURPOSE:To determine whether reducing kinematic parameters to only these 3 key parameters would still predict HRQOL outcomes in ASD based on machine learning (ML) random forest regression model. STUDY DESIGN:Single-center prospective study. PATIENT SAMPLE:A total of 197 patients with ASD and 57 control subjects. OUTCOME MEASURES:Self-report measures: SF36 with the physical and mental components (PCS & MCS), Oswetry Disability Index (ODI), Beck's depression inventory (BDI) and Visual analogue scale (VAS) for pain. Physiologic measures: low-dose full-body biplanar Xrays with 3D skeletal reconstructions. Functional measures: full-body 3D gait analysis during walking. Prediction accuracy: random forest regression ML model. METHODS:All subjects underwent low-dose full-body biplanar Xrays with 3D skeletal reconstructions (with the calculation of spino-pelvic and global alignment parameters), full-body 3DGA during walking (with the calculation of full-body joint kinematic parameters), and completed HRQOL questionnaires: SF36 with the physical and mental components (PCS&MCS), ODI, BDI and VAS for pain. A random forest regression machine learning model was used to predict HRQOL scores in 4 simulations: (Sim-1) X-ray parameters (spinopelvic and global alignment); (Sim-2) Key-kinematic parameters (dPT, dODHA and SL); (Sim-3) X-ray parameters and dPT, dODHA and SL; (Sim-4) All-kinematic parameters. The prediction accuracy and root mean squared error (RMSE) were evaluated using a 10-fold cross-validation and compared between simulations. The same methodology was applied on a subset of 30 ASD patients followed (6 months to 2 years) after medical, orthopedic and surgical treatment. RESULTS:Simulations 1, 2, 3 and 4 had a median accuracy of 82, 85, 86 and 86%, respectively. Simulations 2, 3 and 4 had comparable accuracies of prediction for all HRQOL scores and higher predictions compared to Simulation 1 (ie, accuracy for PCS=86±3 vs 90±2, 91±3% and 91±3% for simulations 1, 2, 3 and 4 respectively, p<.05). Similar results were obtained for the 30 follwed-up ASD patients. CONCLUSIONS:Head and pelvis kinematics and step length are sufficient to predict HRQOL scores, even postoperatively, with higher accuracies than classic spinopelvic and global alignment parameters. While the latter play an integrating role in the surgical planning of ASD patients, coupling radiographic to only 3 key functional parameters would be optimal to provide a complete assessment and postoperative follow-up. Future technologies should focus on capturing these 3 parameters alone to allow surgeons to easily access functional assessment, bypassing the complexity of the complete gait analysis process.

Study design. Multicentric prospective study. Objective. This study aimed to analyze lumbarized transitional vertebra (LTV) impact on spinal alignment, according to Castellvi grade, particularly regarding lumbar lordosis (LL) magnitude and distribution. Summary of Background Data. Few data is available regarding sagittal alignment in patients with LTV. Methods. Only healthy volunteers aged above 18 years with full-body biplanar radiograph were included. In case of LTV, the sixth lumbar vertebra was named “L0”, between T12 and L1. Pelvic and acetabular parameters, thoracic, cervical and global alignment were analyzed. LL was assessed through maximum, proximal and distal according to thoracolumbar inflection point and apex location as well as with fixed vertebrae: L1-S1, L1-L4 and L4-S1. Castellvi I and II were considered low-grade and Castellvi III and IV as high-grade LTV. Comparisons between the three groups (No, low-grade and high-grade) were performed, before and after matching on pelvic incidence (PI). Results. This study included 713 subjects (50.6% F, mean age: 37.5±16.2). 10.1% (n=72) presented transitional vertebra, of which 22 with lumbarization, 13 low-grade and 9 high-grade. PI was greater in LTV subjects. LLmax increased from -59.7±11.0° in No-LSTV subjects to -67.5±19.4° in high-grade LTV, mainly through proximal arc measured both through L1-L4 and LLprox. Lumbar apex was more cranial in LTV subjects: 5.9% in L3 in No-lumbarization cohort versus 53.9% and 44.4% respectively in low-grade and high-grade. A decreased lordosis in the transitional segment was partially compensated for by a steeper increase of LL above L5 in both LTV groups. After matching, LTV subjects presented lesser maximum lordosis than No-LTV subjects, driven by lesser distal lordosis, more anterior global alignment with greater T1PA and greater pelvic retroversion. Conclusions. Lumbarization individuals present decreased distal lordosis and a more cranial lumbar apex resulting in a more anteriorly tilted global sagittal alignment. Pelvic and spinal alignment parameters normative values are provided for LTV subjects.

To evaluate instability during gait and their determinants in ASD patients. 123 ASD patients and 42 controls underwent biplanar radiographs with calculation of spinopelvic and global alignment parameters, and performed 3D gait analysis to calculate full-body kinematics. They all filled the SF-36 with its physical component (PCS). The frontal and sagittal Center of Mass-Center of Pressure (CoM-CoP) angles were calculated during the gait cycle. Patients were classified as ASD-unstable or ASD-stable based on the corridor of normality of the CoM-CoP angle. Kinematics, radiographic parameters and PCS were compared between groups. All ASD patients had a normal CoM-CoP angle in the sagittal plane. 38 ASD were classified as unstable in the frontal plane and 85 as stable (14 ± 3° vs 8 ± 2° resp., p < 0.001). While the 2 groups had a similar pelvic incidence (PI = 53°), ASD-unstable patients had an increased SVA (69 vs 20 mm), and global tilt (GT: 33 vs 24°, all p < 0.05), compared to ASD-stable. The frontal Cobb was similar between the 2 groups (Cobb = 17°). ASD-unstable also had an increased sagittal kinematic ODHA (10 vs 6°), and a decreased normalized step length (0.30 vs 0.34, both p < 0.05). They also had a decreased PCS (33 vs 37). ASD patients with increased global sagittal malalignment (SVA GT) appear to have increased frontal instability during gait. Frontal instability during gait was associated with kinematic limitations in the sagittal plane and deterioration in quality of life. Future work will focus on changes in gait stability in ASD patients after corrective spinal malalignment surgery.

Study Design. Retrospective study of a multicentric prospective database. Objective. This study aimed to determine, in a cohort of healthy volunteers, the impact of sacralized lumbosacral transitional vertebra (LSTV) on spinal alignment according to its grade, particularly regarding lumbar lordosis magnitude and distribution, and the implications for spinopelvic parameters measurement. Summary of Background Data. There is little data regarding spinopelvic alignment assessment in LSTV patients. Methods. This study included healthy volunteers with full-body stereoradiographs in free-standing position aged over 18. Castellvi grade, pelvic parameters (measured on S1 and L5), L1-S1 lumbar lordosis (LL), and segmental lordosis for each disc and vertebral body, thoracic kyphosis, cervical lordosis, lower limb, and global alignment parameters were assessed. Castellvi I and II were considered as low-grade and Castellvi III and IV as high-grade LSTV. Alignment parameters between no-LSTV, low-grade, and high-grade LSTV were compared. Propensity score matching was used to match PI in No-LSTV and low-grades. Spinopelvic parameters measured on S1 in the no-LSTV group and on L5 in the high-grades were compared. Results. Seven hundred thirteen subjects were included, of whom 23 low-grades and 27 high-grades. The mean pelvic incidence was 51.0 +/- 11.0 degrees, and the mean age was 37.5 +/- 16.2 years. LL distribution was different between groups, with an apex and inflexion point significantly higher in high grade (P<0.001). Kyphosis in the LSTV segment was compensated for by a steeper increase of LL above L5 in the high-grades. Low-grades and PI-matched no-LSTV presented similar alignment parameters. There were minor differences in parameters measured on S1 in no-LSTV and no L5 in high-grades. Conclusions. Subjects with low-grade LSTV present similar alignment as PI-matched no-LSTV subjects and S1 should be taken as reference to measure spinopelvic parameters. High-grade LSTV subjects have kyphotic L5-S1 segment with more cranial lumbar apex and thoracolumbar inflexion point. In these subjects, spinopelvic parameters should be measured on L5.

Study Design. Retrospective study of a multicentric prospective database. Objective. This study aimed at describing the relative contribution of vertebral bodies versus discs to lumbar lordosis, and its variation with age and pelvic incidence. Summary of Background Data. While studies sought to determine the physiological magnitude and distribution of lumbar lordosis, data regarding its anatomical composition is lacking. Methods. This study included healthy volunteers with full-body stereoradiographs in free-standing position, without lumbosacral transitional vertebra or age under 18. The following parameters were analyzed: age, sex, pelvic incidence (PI), lumbar lordosis (LL). Posterior heights and sagittal Cobb angles between upper and lower endplate for each lumbar disc and each vertebral body were measured from L1 to S1. Ratios of contribution to LL were calculated for each disc and vertebral body. The cohort was divided into four age groups and four PI groups. Results. 645 subjects were included, mean age was 37.6±16.3, 51% of females. There was a significant decrease in total lumbar disc lordosis with age (−48.9±9.7° to −42.9±10.2°), occurring in lower LL. Vertebral bodies were significantly more kyphotic in Seniors than Youngs (−8.9±8.4° vs. −5.0±9.4°, P=0.03), driven by a significant increase in kyphosis of L1 and L2 bodies. Vertebral body contribution to LL significantly increased between groups as PI increased, from a median of 8.0% to 20.5% (P<0.001). This decrease in disc contribution in favor of vertebral bodies mainly took place in lower LL. Conclusion. This study highlights the importance of vertebral contribution to lumbar lordosis, ranging from 8 to 21% among PI groups. Lumbar lordosis decreased with aging through decreased disc lordosis in the lower lumbar spine and increased body kyphosis in the upper lumbar spine. These results may help surgeons in the assessment of sagittal alignment and the selection of operative technique to achieve surgical correction.

Adolescent Idiopathic Scoliosis (AIS) is classically evaluated through static X-rays and health-related quality of life questionnaires that do not reflect the functional limitations of patients during daily life activities, such as walking. The aim was to investigate kinematic strategies in non-operated AIS with different types of curvature during walking using 3D gait analysis. 13 AIS with Lenke 5 (major Cobb: 23 ± 8°), 30 AIS with Lenke 1 (major Cobb: 40 ± 14°) in addition to 24 controls underwent biplanar X-rays followed by 3D gait analysis. The kinematic parameters of the head, trunk, spinal segments, pelvis and lower limbs were compared between groups. AIS Lenke 5 had a lumbar segment bending while walking (T12L3-L3L5: 5 ± 7° vs. -3 ± 7° in controls) to the concave side of the scoliosis. They walked with an increased pelvic frontal mobility (12 ± 3° vs. 9 ± 3°) and internal rotation of the right foot (-2 ± 6° vs. -11 ± 8°; all p < 0.05). AIS Lenke 1 increased their thoracic lumbar segment bending to the concave and to the opposite side respectively (T6T9-T9T12: -4 ± 9° vs. 1 ± 4°; T12L3-L3L5: 8 ± 12° vs. -2 ± 7°). However, they tended to reduce their lumbo-pelvic mobility (7 ± 5° vs. 12 ± 5°; all p < 0.05). In response to their inherent lumbar stiffness and bending, AIS Lenke 5 patients tended to increase their pelvic frontal mobility and to develop a homolateral internal foot rotation, ensuring a dynamic alignment during gait. AIS Lenke 1, by producing opposite bending movement at the thoracic and lumbar segments, tended to reduce their lumbo-pelvic mobility and ensure coronal dynamic alignment.

Understanding the normal anatomy of thoracic kyphosis (TK) in healthy subjects is essential for evaluating sagittal malalignment and planning the surgery accordingly. The aim of this study was to identify the proportion of thoracic kyphosis originating from disc versus vertebral body shape and to describe its variation according to age and thoracic kyphosis magnitude. This study was a retrospective review of a prospective multicenter database of healthy volunteers aged 18 years or older. Vertebral body and disc sagittal Cobb angles were measured at each level and summed within each of the 3 TK regions (Upper, Middle and Lower TK). Relative contributions of discs and vertebral bodies to Upper, Middle, Lower, and total TK were assessed in the whole cohort, and according to age and TK groups, after stratification. Finally, a multivariate analysis including age and TK magnitude was conducted. Among these 645 subjects, the mean age was 37.6 ± 16.3 years with 51

Background: Adults with spinal deformity (ASD) are known to have spinal malalignment, which can impact their quality of life and their autonomy in daily life activities. Among these tasks, ascending and descending stairs is a common activity of daily life that might be affected. Research question: What are the main kinematic alterations in ASD during stair ascent and descent? Methods: 112 primary ASD patients and 34 controls filled HRQoL questionnaires and underwent biplanar X-from which spino-pelvic radiographic parameters were calculated. Patients were divided into 3 groups: 44 with sagittal malalignment (ASD-Sag: PT > 25 degrees, SVA>5 cm or PI-LL>10 degrees), 42 with isolated thoracic hyperkyphosis (ASD-HyperTK: TK > 60 degrees), 26 with isolated frontal spine deformity (ASD-Front: Cobb>20 degrees). All participants underwent 3D motion analysis of the whole body while ascending and descending a stair step from which kinematic waveforms were extracted. Results: During stair ascent, ASD-Sag exhibited an increased thorax flexion (20 vs 5 degrees), a decreased lumbar lordosis L1L3-L3L5 (7 vs 14 degrees), and an increased ROM of lumbo-pelvic joint (15 vs 10 degrees, all p < 0.05), compared to controls. Similar compensations were shown while descending the stairstep. ASD-HyperTK had similar kinematic limitations as ASD-Sag but to a lesser extent. ASD-Front had normal kinematic patterns. PCS-SF36 correlated to thorax flexion (r = -0.45) and ODI was correlated to pelvic tilt ROM (r = 0.46). Discussion and conclusion: ASD subjects with sagittal malalignment tend to ascend and descend stairs with increased thorax flexion, making them more prone to falls. Compensation mechanisms occur at the head and lumbo-pelvic levels to maintain balance and avoid falling forward.

Spinopelvic alignment assessment needs to account for pelvic incidence (PI). This study aimed at providing normative values for commonly used parameters in whole-body alignment analysis based on PI. Multicentric prospective study. This study included healthy volunteers with full-body biplanar radiograph in free-standing position. All radiographic data were collected from 3D reconstructions: Sagittal vertical axis (SVA), T1 pelvic angle (TPA), spino-sacral angle (SSA), sagittal odontoid-hip axis angle (ODHA), pelvic parameters, sacro-femoral angle (SFA), knee flexion angle (KFA), ankle flexion angle (AA), Pelvic shift (PSh), lumbar lordosis (LL), thoracic kyphosis (TK) and cervical lordosis (CL). Population was divided into five groups according to PI. Normative values were described for each group. Linear regressions including age and PI provided prediction formulas for PT, TPA, SSA and SFA. 642 subjects were included. Mean age was 37.7 ± 16.3 years (range: 18–90). Mean PI in the cohort was 49.3 ± 9.5°. LL, PT, SFA, SSA and TPA correlated with PI and age. ODHA, TK, CL and the other lower limb parameters were not associated with PI. All normative values across PI groups are provided for segmental, regional and global alignment parameters. Prediction formulas were: PT=-12.7 + 0.38*PI + 0.14*Age, TPA=-16.9 + 0.34*PI + 0.15*Age, SSA = 109.8 + 0.58*PI-0.19*Age, and SFA = 173 + 0.39*PI + 0.11*Age. SSA, PT, TPA and SFA must be assessed according to patient’s PI. This study provides normative values for each PI group, and predictive formulas taking age and PI into account. PI cannot be used to define thoracic and cervical curvatures. II.

Study design. Multicentric retrospective study of prospectively collected data. Objective. On the basis of normative data from a cohort of asymptomatic volunteers, this study sought to determine the rate of abnormal values of proximal junctional angles (PJA) in adult spinal deformity (ASD) surgery patients, and compare it with PJK rate. Summary of Background Data. Proximal junctional kyphosis (PJK) definition does not take the vertebral level into account. Patients and Methods. This study included 721 healthy volunteers and 824 ASD surgery patients with two-year postoperative follow-up. Normative values for each disc and vertebral body between T1 and T12 were analyzed, then normative values for PJA at each thoracic level were defined in the volunteer cohort as the mean +/- 2SD. PJA abnormal values at the upper instrumented vertebra (UIV) were compared with Glattes' and Lovecchio's definitions for PJK in the ASD population at two years. Results. Mean age was 37.7 +/- 16.3 in the volunteer cohort, with 50.5% of females. Mean thoracic kyphosis (TK) was -50.9 +/- 10.8 degrees. Corridors of normality included PJA greater than 20 degrees between T3 and T12. Mean age was 60.5 +/- 14.0 years in the ASD cohort, with 77.2% of females. Mean baseline TK was -37.4 +/- 19.9 degrees, with a significant increase after surgery (-15.6 +/- 15.3 degrees, P<0.001). There was 46.2% of PJK according to Glattes' versus 8.7% according to Lovecchio's and 22.9% of kyphotic PJA compared with normative values (P<0.001). Conclusion. This study provides normative values for segmental and regional alignment of thoracic spine, used to describe abnormal values of PJA for each level. Using level-adjusted PJA values allows a more precise assessment of abnormal proximal angles and question the definition for PJK.

BACKGROUND:Adult spinal deformity (ASD) is associated with muscles' degeneration that affects postural control and outcomes of an eventual corrective surgery. Evaluation of ASD is usually based on static radiographs and more recently on functional assessment. However, there has been limited exploration of muscle strength weakness in ASD. The aim was to investigate the relationship between trunk muscles' strength in ASD and its relationship with radiographic and kinematic alterations and quality-of-life decline. METHODS:28 ASD and 18 asymptomatic subjects underwent biplanar radiographs with 3D calculation of spino-pelvic and global postural parameters. 3D movement analysis of gait, sitting to standing and stair ascent, was studied allowing the calculation of head, trunk and lower limbs 3D kinematics. Participants filled out health related quality of life questionnaires. A single operator measured 4 times the strength of the trunk muscles, using a hand-held dynamometer, to assess measurements' reliability. ASD population was divided into two groups based on the strength of trunk extensors: ASD-weak extensors (N = 11 patients having trunk extensors strength0.94). On standing radiographs, the ASD-weak extensors group showed an increased positive sagittal malalignment compared to the other groups (SVA=61 mm vs ASD-normal extensors: 18 mm, controls: -4 mm, p < 0.001). This sagittal malalignment remained during movement (kinematic-SVA=223 mm vs ASD-normal extensors:178 mm, controls:138 mm, p < 0.001). Muscle strength weakness was correlated to the decline of quality-of-life scores (PCS-SF36: r = 0.48, VAS for pain: ρ=-0.39). CONCLUSIONS:This study showed that weak trunk extensors are associated with sagittal malalignment in static position, kinematic limitations during daily life activities and reduced quality of life scores. Future studies will investigate the effect of muscle strengthening on both static and dynamic alignment in ASD and their quality of life.