title: Finding line of action of the force exerted on erect spine based on lateral bending test in personalization of scoliotic spine models.
abstract: In multi-body models of scoliotic spine, personalization of mechanical properties of joints significantly improves reconstruction of the spine shape. In personalization methods based on lateral bending test, simulation of bending positions is an essential step. To simulate, a force is exerted on the spine model in the erect position. The line of action of the force affects the moment of the force about the joints and thus, if not correctly identified, causes over/underestimation of mechanical properties. Therefore, we aimed to identify the line of action, which has got little attention in previous studies. An in-depth analysis was performed on the scoliotic spine movement from the erect to four spine positions in the frontal plane by using pre-operative X-rays of 18 adolescent idiopathic scoliosis (AIS) patients. To study the movement, the spine curvature was considered as a 2D chain of micro-scale motion segments (MMSs) comprising rigid links and 1-degree-of-freedom (DOF) rotary joints. It was found that two MMSs representing the inflection points of the erect spine had almost no rotation (0.0028° ± 0.0021°) in the movement. The small rotation can be justified by weak moment of the force about these MMSs due to very small moment arm. Therefore, in the frontal plane, the line of action of the force to simulate the left/right bending position was defined as the line that passes through these MMSs in the left/right bending position. Through personalization of a 3D spine model for our patients, we demonstrated that our line of action could result in good estimates of the spine shape in the bending positions and other positions not included in the personalization, supporting our proposed line of action.
authors.affiliation: Department of Mechanical Engineering, Faculty of Engineering, National University of Singapore, 1 Engineering Drive 2, Block EA, #02-17, Singapore, 117576, Singapore. athena@u.nus.edu.
authors.forename: Athena
authors.initials: A
authors.lastname: Jalalian
authors.affiliation: Department of Mechanical Engineering, Faculty of Engineering, National University of Singapore, 1 Engineering Drive 2, Block EA, #02-17, Singapore, 117576, Singapore.
authors.forename: Francis Eng Hock
authors.initials: FEH
authors.lastname: Tay
authors.affiliation: Department of Mechanical Engineering, Faculty of Engineering, National University of Singapore, 1 Engineering Drive 2, Block EA, #02-17, Singapore, 117576, Singapore.
authors.forename: Soheil
authors.initials: S
authors.lastname: Arastehfar
authors.affiliation: School of Engineering, Deakin University, Geelong, Australia.
authors.forename: Ian
authors.initials: I
authors.lastname: Gibson
authors.affiliation: Department of Orthopedic Surgery, National University of Singapore, Singapore, Singapore.
authors.forename: Gabriel
authors.initials: G
authors.lastname: Liu
mesh_terms: D000293:Adolescent; D001696:Biomechanical Phenomena; D002648:Child; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008297:Male; D008962:Models, Theoretical; D009068:Movement; D011187:Posture; D057285:Precision Medicine / Q000379:methods; D011859:Radiography; D015203:Reproducibility of Results; D012399:Rotation; D012600:Scoliosis / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D013131:Spine / Q000000981:diagnostic imaging / Q000502:physiology / Q000503:physiopathology*; D055815:Young Adult
keywords: Lateral bending test; Line of action; Multi-body model; Personalization; Scoliotic spine; Spine shape