The imaging study on the changes of sagittal parameters of different positional spine-pelvis in young Han men

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Objective To compare the spine-pelvic sagittal parameters of the healthy and young Han males in standing, erect sitting and natural sitting.Evaluate the effect of pelvic rotation on sagittal balance. Methods This was a cross-sectional study. Thirty-two volunteers were recruited from the graduate students of Nanjing Drum Tower Hospital from September 2017 to October 2017. All the volunteers were males, aged between 23 to 27 (24.8±1.6) years old, 171-185 (176.4±5.3) cm in height, 57.7-88.4 (69.5±8.6) kg in weight, and BMI 21.2-24.7 (22.5±2.3) kg/m2. EOS-X-ray imaging system was applied to all subjects, and vertical scanning method was adopted. Full-length images were scanned once, and standing position, erect sitting and natural sitting position were taken. Parameters were measured included thoracic kyphosis (TK), lumbar lordosis (LL), sacral slope (SS), pelvic incidence (PI), pelvic tilt (PT), sagittal vertical axis (SVA), T1 pelvic angle (TPA). Paired-samples T test was used to compare the changes of parameters in different positions, and Pearson correlation analysis was used to analyze the relationship between spinopelvic parameters. Results For 32 volunteers, in standing position, the average PI was 49.06°±6.22°, PT was 13.38°±6.06°, SS was 35.03°±2.32°, LL was -47.16°±7.64°, TK was 32.22°±9.74°, SVA was (3.29±13.64)mm, TPA was 9.47°±5.26°. In erect sitting position, the average PI was 48.22°±6.07°, PT was 29.06°±10.35°, SS was 18.84°±5.90°, LL was -26.38°±8.45°, TK was 31.78°±9.95°, SVA was (34.73±13.62)mm, TPA was 26.06°±8.71°. In natural sitting position, the average PI was 49.22°±6.20°, PT was 40.50°±10.42°, SS was 9.84°±4.87°, LL was -4.03°±6.14°, TK was 31.69°±9.73°, SVA was (63.37±13.70)mm, TPA was 49.66°±11.22°. Compared with the parameters of standing position, PT, SVA and TPA parameters of erect and natural sitting position increased, SS and LL parameters decreased. Compared with the parameters of erect sitting position: PT, SVA and TPA parameters of natural sitting position increased, SS and LL parameters decreased. The differences were statistically significant(all P values<0.05). Pearson correlation analysis results showed that: (1) In standing position, PI was correlated with PT, LL, TK and TPA. PT was correlated with LL, TK and TPA. LL was correlated with TK and TPA. TK was correlated with TPA. (2) In erect sitting position, PI was correlated with PT, SS, LL, TK and TPA. PT was correlated with SS, LL, TK and TPA. SS was correlated with LL, TK and TPA. LL was correlated with TK and TPA. TK was correlated with TPA. (3) In natural sitting position, PI was correlated with PT, SS, LL, TK and TPA. PT was correlated with SS, LL, TK and TPA. SS was correlated with LL, TK and TPA. LL was correlated with TK and TPA. Differences were statistically significant ( all P values<0.05). Conclusions In the process of from the standing position to the upright sitting position, the upright sitting position to the natural sitting position, Han people the LL of normal Han young men is decreasing and SVA, TPA are increasing.It indicates that SVA moves anteriorly and the pelvic rotates posteriorly. Some correlation between spinal parameters and pelvic parameters are also shown. The changing of pelvis can influence the sagittal alignment and balance of the spine. Key words: Spine; Pelvis; Spinopelvic parameters; Upright sitting; Natural sitting; Pelvic rotation; Sagittal alignment