The sitting vs standing spine

Evaluating Variations in Spinopelvic Parameters from Sitting to Standing: A Comparative Analysis of 1447 Older Adults Across Age, BMI, and Gender Subgroups

Background/Objectives: Sagittal spinal alignment goals for adult spinal deformity (ASD) surgery are predominantly derived from standing radiographs, despite the biomechanical relevance of sitting posture. Existing studies on sitting alignment involve young, healthy cohorts, which poorly represent ASD patients. This study assessed posture-dependent changes in spinopelvic parameters, including pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), and lumbar lordosis (LL), and examined how age, BMI, and gender influence these changes. Methods: In this retrospective cohort study, sitting and standing lateral radiographs of 1447 patients were evaluated. Spinopelvic parameters were measured, and changes (ΔPI, ΔPT, ΔSS, and ΔLL) were calculated. Multiple regression analysis was used to determine associations between these changes and age, BMI, and gender. Results: All parameters differed significantly between positions (p < 0.001); PT and PI increased in sitting (ΔPT = -19.20°; ΔPI = -4.52°), while SS and LL increased in standing (ΔSS = 14.67°; ΔLL = 18.44°). Older age correlated with increased ΔPT (p < 0.001) and ΔPI (p = 0.049) but reduced ΔLL and ΔSS (p < 0.001). Higher BMI was associated with decreased ΔPI, ΔPT, and ΔLL (p < 0.001, 0.003, and 0.025). Females showed greater ΔPT (p = 0.013) but smaller ΔPI, ΔSS, and ΔLL (p = 0.043, <0.001, and 0.001). Conclusions: Spinopelvic parameters vary significantly between sitting and standing positions, affected by age, BMI, and gender. The observed PI change suggests SIJ involvement, highlighting the need for posture-specific and demographic-adjusted alignment goals in ASD surgery to optimize outcomes.

The importance of the posterior osteoligamentous complex of the lumbar spine: dogma changing biomechanical insights

BACKGROUND

During full flexion of the spine, the paraspinal muscles are largely inactive. This suggests that passive structures like the posterior osteoligamentous complex (POLC), consisting of interspinous and supraspinous ligaments and the spinous processes, play a key role in spinal stability and protection of the spinal column. The POLC, however, is often resected or damaged during spinal decompression surgeries, whereas the biomechanical implications of this resection or damage are not yet fully understood.

METHODS

A stepwise reduction study was performed on three fresh frozen cadaveric torsi (aged 30-78 years) using a custom setup which only allows sagittal plane motion. After preloading and locking in full flexion, the posterior lumbar structures were gradually resected in the following order: Skin, fascia, musculature, facet joints, ligamentum flavum, posterior ligamentous complex, and posterior longitudinal ligaments. Load cells measured force increase on the fixation frame after each resection step.

RESULTS

The load increased sequentially with each resection, demonstrating load transfer from the passive structures onto the fixation frame. The POLC, including the supraspinous and interspinous ligaments at L2-L5, accounted for 69 - 74% of the measured passive load resistance in full flexion, representing the largest contribution. Facet joints with their capsules contributed 10-18%, while muscular contributions were negligible (< 2%).

CONCLUSION

The experiment indicates that the POLC is the primary passive stabilizer of the fully flexed lumbar spine. Surgical resection of this structure can redistribute loads and increase stresses on remaining spinal tissues, potentially leading to spinal instability, accelerated degeneration, and poor clinical long-term outcomes.

Impact of Standing and Sitting Postures on Spinal Curvature and Muscle Mechanical Properties in Young Women: A Photogrammetric and MyotonPro Analysis

BACKGROUND This study aimed to evaluate the effect of standing and sitting positions on spinal curvatures evaluated using projection moire and muscle tone and stiffness using the MyotonPRO hand-held device in young women. MATERIAL AND METHODS Thirty-three healthy women, aged 21 to 23 years, volunteered in the study. We used the projection moire method to examine spinal curvatures in both positions and the MyotonPRO device to measure the tone and stiffness of muscles in 3 regions. We evaluated the effects of positions (standing vs sitting), regions (cervical, thoracic, and lumbar), and side factor (right vs left) using multivariate analysis. RESULTS The sitting position significantly decreased the lumbosacral and thoracolumbar angles (P<0.001), but had no effect on the superior thoracic angle. Muscle tension and stiffness were the highest (P<0.001) in the cervical region and did not differ between positions (P>0.05) in this region. We found significantly higher muscle tone and stiffness in the thoracic and lumbar regions during sitting than during standing (P<0.001). There was symmetry in the muscle tone and the stiffness between the right and left sides of the spine. CONCLUSIONS The sitting posture decreased lumbosacral and thoracolumbar angles but increased muscle tension and stiffness in the lumbar and thoracic regions only. The symmetry of muscle tone and transverse stiffness in both positions was the normative value. This study provides insight into the adaptive physiological changes in spinal curvature and muscle mechanical properties in young women and serves as an important reference point for clinical studies of women.

Differences in spinal postures and mobility among adults with Prader-Willi syndrome, essential obesity, and normal-weight individuals

Introduction

Spinal kinematics/motion are reported to be altered in adolescents and adults with essential obesity, while no information is available in patients with Prader-Willi syndrome so far. The aim of this study was to examine cross-sectionally the characteristics of spinal postures and mobility in 34 patients with PWS, in 35 age- and sex-matched adults with essential obesity, and in 37 normal-weight individuals.

Methods

Spinal posture and mobility were assessed using a radiation-free back scan, the Idiag M360 (Idiag, Fehraltorf, Switzerland). Differences in spinal posture and mobility between the three groups were determined using a two-way analysis of variance.

Results

Adults with Prader-Willi syndrome had greater thoracic kyphosis [difference between groups (Δ) = 9.60, 95% CI 3.30 to 15.60, p = 0.001], less lumbar lordosis (Δ = -6.50, 95% CI -12.70 to -0.30, p = 0.03) as well as smaller lumbar and hip mobility than those with normal weight.

Discussion

Although the characteristics of the spine in patients with Prader-Will syndrome appear to be similar to that found in subjects with essential obesity, Prader-Willi syndrome was found to influence lumbar movements more than thoracic mobility. These results provide relevant information about the characteristics of the spine in adults with Prader-Willi syndrome to be taken into careful consideration in the management of spinal conditions. These findings also highlight the importance of considering the musculoskeletal assessment of spinal postures and approaches targeting spinal and hip flexibility in adults with Prader-Willi syndrome.

Differences in spinal posture and mobility between adults with obesity and normal weight individuals

The aim of this study was to cross-sectionally investigate the relationships between obesity and spinal posture as well as mobility by comparing the spinal parameters between adults with obesity and normal-weight individuals. The spinal parameters were measured in 71 adults with obesity and 142 normal-weight individuals using a radiation-free back scan, the Idiag M360. Differences in spinal posture and movements between the two groups were determined using a two-way analysis of variance. Adults with obesity had greater thoracic kyphosis [difference between groups (Δ) = 6.1°, 95% CI 3.3°-8.9°, p < 0.0001] and thoracic lateral flexion (Δ = 14.5°, 95% CI 5.1°-23.8°, p = 0.002), as well as smaller thoracic flexion (Δ = 3.5°, 95% CI 0.2°-6.9°, p = 0.03), thoracic extension (Δ = 4.1°, 95% CI 1.1°-7.1°, p = 0.008), lumbar flexion (Δ = 10.4°, 95% CI 7.7°-13.5°, p < 0.0001), lumbar extension (Δ = 4.8°, 95% CI 2.2°-7.4°, p = 0.0003) and lumbar lateral flexion (Δ = 12.8°, 95% CI 9.8°-15.7°, p = < 0.0001) compared to those with normal weight. These findings provide relevant information about the characteristics of the spine in adults with obesity to be taken into careful consideration in the prescription of adapted physical activities within integrated multidisciplinary pathways of metabolic rehabilitation.

Differences in spinal posture and mobility between children/adolescents with obesity and age-matched normal-weight individuals

The aim of this study was to cross-sectionally explore the association of obesity with spinal posture and mobility, commonly associated with musculoskeletal problems, by comparing the spinal parameters between 90 obese and 109 normal-weight children and adolescents. A non-invasive electromechanical device, the Idiag M360 (Idiag, Fehraltorf, Switzerland), was used to measure the spinal parameters. An age-and-sex-adjusted two-way analysis of variance (ANOVA) was used to determine postural and mobility differences between the two groups. Children and adolescents with obesity had significantly greater thoracic kyphosis [difference between groups (Δ) = 13.0⁰, 95% CI 10.1⁰–15.8⁰, p < 0.0001] and thoracic extension (Δ = 6.5⁰, 95% CI 2.9⁰–11.6⁰, p = 0.005), as well as smaller mobility in thoracic flexion (Δ = 5.0⁰, 95% CI 1.2⁰–8.8⁰, p = 0.01), thoracic lateral flexion (Δ = 17.7⁰, 95% CI 11.6⁰–23.8⁰, p < 0.0001), lumbar flexion (Δ = 12.1⁰, 95% CI 8.7⁰–15.5⁰, p < 0.0001), lumbar extension (Δ = 7.1⁰, 95% CI 3.1⁰–12.2⁰, p = 0.003) and lumbar lateral flexion (Δ = 9.1⁰, 95% CI 5.5⁰–12.8⁰, p < 0.0001) compared to the normal-weight children and adolescents. These findings provide important information about the characteristics of the spine in children and adolescents with obesity and unique insights into obesity-related mechanical challenges that the spine has to withstand and strategies designed to improve spinal mobility in this young population.