BACKGROUND: 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.
OBJECTIVE: 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.
METHODS: Retrospective cross-sectional study.
METHODS: Patients with ASD from a monocenter database.
METHODS: 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.

BACKGROUND: Pelvic incidence (PI)-lumbar lordosis (LL) mismatch has a significant destabilizing effect on the center of gravity sway in the static standing position. However, the association between spinopelvic alignment and balance during gait in healthy volunteers is poorly understood.
OBJECTIVE: The degree of PI-LL mismatch and trunk anterior tilt in the static standing posture influences dynamic balance during gait.
METHODS: In this study, 131 healthy volunteers were divided into two groups: harmonious group (PI - LL ≤ 10°; n = 91) and unharmonious group (PI - LL > 10°; n = 40). A two-point accelerometer system was used for gait analysis; accelerometers were attached to the pelvis and upper trunk to measure acceleration in the forward-backward, right-left, and vertical directions so that sagittal (front-back) deviation width, coronal (right-left) width, and vertical width and their ratios were calculated. Measurements were compared between the two groups, and correlations between alignment and accelerometer data were examined.
RESULTS: The harmonious group showed a negative correlation between pelvic sagittal width and PI - LL, pelvic tilt (PT), and sagittal vertical axis (SVA) (correlation coefficient ρ = -0.42, -0.38, and -0.4, respectively), and a positive correlation between sagittal ratio and PI - LL (ρ = 0.35). The unharmonious group showed a positive correlation between pelvic sagittal width and PI and PT (ρ = 0.43 and 0.33, respectively) and between sagittal ratio and SVA (ρ = 0.32). The unharmonious group showed a positive correlation between upper trunk sagittal width and PI - LL and PT (ρ = 0.38 and 0.36, respectively).
CONCLUSIONS: The association between spinal alignment and gait parameters differs depending on the presence or absence of PI-LL mismatch. The degree of pelvic compensation and trunk anterior tilt during static standing were associated with unstable gait balance.

OBJECTIVE: To identify factors associated with T1 slope (T1S).
METHODS: A total of 215 patients over 18 years old who underwent whole-spine X-rays to evaluate lower back pain were enrolled in this study. T1S, pelvic tilt (PT), sacral slope (SS), pelvic incidence (PI), thoracic kyphosis (TK), lumbar lordosis (LL), cervical lordosis (CL), thoracolumbar kyphosis (TLK), and sagittal vertical axis (SVA) were measured. Patients were divided into balance, compensatory balance, thoracic compensation, and thoracic decompensation groups.
RESULTS: TK (p < 0.001), SVA (p < 0.001), and CL (p = 0.020) were significantly related to high T1S. The balance group had the smallest PT, largest SS and largest LL of the four groups (p < 0.001). The thoracic compensation group had the smallest TK of all groups (p < 0.001). There was no significant difference in T1S between the balance and thoracic compensation groups (p = 0.099). The thoracic decompensation group had a larger T1S than the balance group (p = 0.023).
CONCLUSIONS: Caudal spine segments had a sequential effect on cranial spine segments. T1S reflected the compensation ability of the spine. The absence of balance tended to increase the T1S. Pelvic posterior rotation and thoracic compensation were two crucial factors protecting against increased T1S in patients with ASD.

UNASSIGNED: 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.
UNASSIGNED: 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.
UNASSIGNED: 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).
UNASSIGNED: 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.

To analyze pelvic compensation during walking in patients with severe sagittal plane deformity by using motion analysis.
A total of 44 patients with sagittal plane deformity who were scheduled to undergo surgery were included. Motion analysis was performed 3 consecutive times during walking to estimate the anterior pelvic tilt (Ant-PT) angle, trunk kyphosis (TK) angle, and distance of the center of gravity (CoG) from the center of mass (CoM) of the pelvic segment, and hip and knee joint angles during gait. The patients were classified into Ant-PT+/Ant-PT-, TK+/TK-, and CoG+/CoG- groups according to the changes in Ant-PT angle, TK angle, and distance of the CoG from the CoM of the pelvic segment. Increases and decreases in the values of the variables from the first trial to the third trial were indicated with \"+\" and \"-\" signs, respectively.
The mean Ant-PT angle, TK angle, and distance of the CoG from the CoM of the pelvic segment increased progressively, and the differences in the values of these variables from the first to the third trials were statistically significant (P = 0.046, P = 0.004, and P = 0.007 for the Ant-PT angle, TK angle, and distance of the CoG from the CoM of pelvic segment, respectively). Among the 44 patients, 27 and 34 were classified into the Ant-PT+ and CoG+ groups, respectively. Older age and higher body mass index (BMI) were significantly associated with the Ant-PT+ group. The CoG+ group demonstrated a significantly higher height and weight than the CoG- group.
Higher BMI, height, and weight are risk factors for progressive worsening of dynamic sagittal imbalance. These slides can be retrieved under Electronic Supplementary Material.

Pelvic tilt (PT) is used as an indicator of pelvic version with increased values indicating retroversion and disability. The concept of using PT solely as an absolute numerical value can be misleading, especially for the patients with pelvic incidence (PI) values near the upper and lower normal limits. Relative pelvic version (RPV) is a PI-based individualized measure of the pelvic version. Relative pelvic version indicates the individualized spatial orientation of the pelvis relative to the ideal sacral slope as defined by the magnitude of PI.
The aim of this study was to compare RPV and PT for their ability to predict mechanical complications and their correlations with health-related quality of Life (HRQoL) scores.
A retrospective analysis of a prospectively collected data of adult spinal deformity patients was carried out. Mechanical complications (proximal junctional kyphosis or proximal junctional failure, distal junctional kyphosis or distal junctional failure, rod breakage, and implant-related complications) and HRQoL scores (Oswestry Disability Index [ODI], Core Outcome Measures Index [COMI], Short Form-36 Physical Component Summary [SF-36 PCS], and Scoliosis Research Society 22 Spinal Deformity Questionnaire [SRS-22]) were used as outcome measures.
Inclusion criteria were ≥4 levels fusion, and ≥2-year follow-up. Correlations between PT, RPV, PI, and HRQoL were analyzed using Pearson correlation coefficient. Pelvic incidence values and mechanical complication rates in RPV subgroups for each PT category were compared using one-way analysis of variance, Student t test, and chi-squared tests. Predictive models for mechanical complications with RPV and PT were analyzed using binomial logistic regressions.
A total of 222 patients (168 women, 54 men) met the inclusion criteria. Mean age was 52.2±19.3 (18-84) years. Mean follow-up was 28.8±8.2 (24-62) months. There was a significant correlation between PT and PI (r=0.613, p<.001), threatening the use of PT to quantify pelvic version for different PI values. Relative pelvic version was not correlated with PI (r=-0.108, p>.05), being able to quantify pelvic version for all PI values. Compared with PT, RPV had stronger partial correlations with ODI, COMI, SF-36 PCS, and SRS-22 scores (p<.05). Discrimination performance assessed by area under the curve, percentage accuracy in classification, true positive rate, true negative rate, and positive and negative predictive values was better for the model with RPV than for PT. For average PI sizes, the agreement between RPV and PT were moderate (0.609, p<.001), whereas the agreement in small and large PI sizes were poor (0.189, p>.05; -0.098, p>.496, respectively). When analyzed by RPV, each PT \"0,\" \"+,\" and \"++\" category was further divided into two or three distinct subgroups of patients having different PI values (p=.000, p=.000, and p=.029, respectively). Relative pelvic version subgroups within the same PT category displayed different mechanical complication rates (p=.000, p=.020, and p=.019, respectively).
Pelvic tilt may be insufficient or misleading in quantifying normoversion for the whole spectrum of PI values when used as an absolute numeric value in conjunction with previously reported population-based average thresholds of 20 and 30 degrees. Relative pelvic version offers an individualized quantification of ante-, normo-, and retroversion for all PI sizes. Schwab PT groups were found to constitute inhomogeneous subgroup of patients with different mean PI values and mechanical complication rates. Compared with PT, RPV showed a greater association with both mechanical complications and HRQoL.

Shortened hamstrings are likely to restrict the anterior pelvic tilt and induce a slumped posture due to the posterior pelvic tilt. This study was conducted to compare the effects of proprioceptive neuromuscular facilitation (PNF) stretching and modified anterior pelvic tilt taping (APTT) on hamstring shortness-associated pelvic compensation while executing seated double-knee extension. Male college students (28 healthy young adults; mean age: 21.4 ± 2.1 years) with hamstring shortness were recruited as study subjects and randomly assigned to either the PNF stretching group (control group) or the APTT group (experimental group). In all the subjects, changes in the movement distance of the centre of gluteal pressure (COGP) as well as rectus abdominis (RA) and semitendinosus (SEM) muscle activities were measured during seated double-knee extension while the respective intervention method was applied. Both groups showed significant decreases in COGP distance and RA muscle activity compared with their respective baseline values (p < 0.05), however, no significant changes were observed in SEM muscle activity. We can infer that not only a direct intervention on the hamstring, such as PNF stretching, but also a modified APTT-mediated pelvic intervention may be used as a method for reducing pelvic compensation induced by hamstring shortness.