Relationship between trunk muscle forces, static and dynamic postural malalignment in patients with adult spinal deformity

Patients with Adult spinal Deformity (ASD) are known to have a deteriorated quality of life (QOL). Severe spinal deformity can develop into postural malalignment caused by a forward shift of the trunk and head. Recent studies have shown that sagittal malalignment in patients with ASD can affect joints and segments’ kinematics during daily life activities [1,2]. On the other hand, ASD patients are known to present with muscular degeneration [3]. However, it is still unknown how trunk muscle’s weakness can affect ASD postural alignment in static position and during daily life activities. To investigate the relationship between muscle forces, radiographic parameters, joint kinematics during daily activities, and QOL scores in ASD. 25 ASD & 19 controls underwent biplanar radiographs in both standing and sitting positions with the calculation of 3D classic spinopelvic and postural alignment parameters (i.e: SVA plumbline between C7 and posterior corner of the sacrum; ODHA angle between line joining odontoid process and middle of hip axis with the vertical). Movement analysis was performed during walking, sit-to-stand, and stair ascent-descent with the calculation of 3D joint and segment kinematics. Participants filled out QOL questionnaires (SF-36 with both physical and mental components, Oswestry Disability Index ODI). The strength of the following muscle groups was measured using a hand-held dynamometer: trunk extensors, flexors, and right & left lateral flexors. ASD were divided into 2 groups based on the age-normalized strength of trunk extensors compared to controls: ASD-normal extensors and ASD-weak extensors (having strength