Abstract:

Objective　To investigate the factors influencing the adjustment function of PI on spinal sagittal balance in normal subject.　Methods　106 normal subjects were selected to perform a full standing spinal lateral radiograph including spine, pelvis and both hip joints from January 2008 to June 2008 in our outpatient department. The radiographs were digitized and 5 sagittal parameters were measured on lateral radiographs: pelvic incidence, sacral slope, pelvic tilt, lumbar lordosis and thoracic kyphosis, followed by the statistic analysis.　Results　106 cases of normal subjects were separately divided into 38 cases, belonging to high SS/lower PT, with the mean value of PI and LL of （50.85±10.01）° and（ 49.41±9.84）°respectively and the regression equation of LL=0.571PI+20.395 ; 68 cases, belonging to lower SS/high PT, with the mean value of PI and LL of （49.14±12.00）° and （39.17°±10.98）° respectively and the regression equation of LL=0.531PI+13.079°. The two groups demonstrated interclass positive correlation and linear regression between PI and SS, PT and LL, SS and LL respectively, while significant difference of SS, PT and LL between the two groups was showed except for that of PI.　Conclusions　(1)LL can't be concluded only by PI for the influence of pelvic posture.（2）Under the same PI, the more anteverted pelvis, the more large LL, otherwise, the more large PI, the more large LL under the same pelvic posture. 

Key words: Pelvic incidence, Pelvic posture, Sacral slope, Lumbar lordosis, Thoracic kyphosis, Sagittal balance