Objective: Sway Back posture is one of the most common postural deformity.This study aimed to define Sway back posture prevalence and quantitatively meassure of the joints alignment in it.

Materials & Methods: In this cross sectional descriptive study The posture of 51 female students of Shahid Beheshti University of Medical Sciences at an average of 22.05±2.44 years was evaluated. First, subjects completed a general characteristics questionnaire. Scond, the amount of their pelvic sway was measured by a grid paper and plumb line. When the plumb line passed the more than 3cm posterior to mid point of ASIS (Anterior Superior Iliac Spine) - PSIS (Posterior Superior Jliac Spine) axis, the subjects were categorized in Sway back posture. Then with goniometer alignment of hip, knee and ankle joints were measured. Also, the pelvic inclination and kyphosis and lordosis angles were measured with a Pelvic Inclinometer and Flexicurve Ruler, respectively.

Results: The mean value of lordosis in Sway back posture group was greater than normal group (p = 0.004). Though the amount of kyphosis and anterior tilt were greater in Sway back posture than normal group, but did not show any significant difference between them (P>0.05). In Sway back posture group, the hip and knee joints tend to flexion. The ankle showed dorsiflexion which had a significant corelation with the pelvic sway. The prevalence of this deformity was 39.2% and was more common than other spinal deformities in young female subjects.

Conclusion: This study indicated that the prevalence of the Sway back posture in the population of our study is high (39.21%). Also, indicated that the lordose increased and the pelvic displaced to anterior without noticeable changing in alignment of the thorasic region, joint of lower extremity and pelvic inclination