Standing balance and sagittal plane spinal deformity: analysis of spinopelvic and gravity line parameters.
METHODS
Prospective study of 131 patients and volunteers recruited for an analysis of spinal alignment and gravity line (GL) assessment by force plate analysis.


OBJECTIVE
To determine relationships between GL, foot position, and spinopelvic landmarks in subjects with varying sagittal alignment. Additionally, the study sought to analyze the role of the pelvis in the maintenance of GL position.


BACKGROUND
Force plate technology permits analysis of foot position and GL in relation to radiographically obtained landmarks. Previous investigation noted fixed GL-heel relationship across a wide age range despite changes in thoracic kyphosis. The pelvis as balance regulator has not been studied in the setting of sagittal spinal deformity.


METHODS
The 131 subjects were grouped by sagittal vertical axis (SVA) offset from the sacrum: sagittal forward (>2.5 cm), neutral (-2.5 cm <or= SVA <or= 2.5 cm), and sagittal backward (SVA <-2.5 cm). Simultaneous spinopelvic radiographs and GL measure were obtained. Offsets between spinopelvic landmarks, heel position, and GL were calculated. Group comparisons were made for all offsets to determine significance.


RESULTS
Aside from the offset T9-GL and GL-heels, all other offsets between spinopelvic landmarks and GL revealed significant differences (P < 0.001) across the 3 subject groups. However, with increasing SVA, the GL kept a rather fixed location relative to the feet. A correlation between posterior pelvic shift in relation to the heels with increasing SVA in this study population was confirmed (r = 0.6, P < 0.001).


CONCLUSIONS
Increasing SVA in standing subjects leads to a posterior pelvic shift in relation to the feet. However, no significant difference in GL-heel offset is noted with increasing SVA. It thus appears that pelvic shift (in relation to the feet) is an important component in maintaining a rather fixed GL-Heels offset even in the setting of variable SVA and trunk inclination.
NYU Hospital for Joint Diseases, New York, NY10010, USA. virginie.lafage@gmail.com
Virginie
V
Lafage
Frank
F
Schwab
Wafa
W
Skalli
Nicola
N
Hawkinson
Pierre-Marie
PM
Gagey
Stephen
S
Ondra
Jean-Pierre
JP
Farcy
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D005260:Female; D005528:Foot / Q000000981:diagnostic imaging; D006112:Gravitation; D006801:Humans; D007738:Kyphosis / Q000000981:diagnostic imaging / Q000503:physiopathology*; D008141:Lordosis / Q000000981:diagnostic imaging / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D010388:Pelvis / Q000000981:diagnostic imaging; D004856:Postural Balance / Q000502:physiology*; D011187:Posture / Q000502:physiology*; D011446:Prospective Studies; D011859:Radiography; D013131:Spine / Q000000981:diagnostic imaging