A patient-specific multibody kinematic model for representation of the scoliotic spine movement in frontal plane of the human body

Multibody models of scoliotic spine have shown great promise in planning scoliosis surgery by providing predictive information concerning the surgery outcome. To provide good predictive information, it is important that the kinematic models underlying the movement of the spine models would be personalized to give good estimates of the spine in different positions, which is lacking in the existing literature. This paper aims to develop a patient-specific multibody kinematic model of the scoliotic spine to represent its movement in frontal plane of the human body. The model is an open-chain mechanism comprising rigid links interconnected with rotary joints. To represent the movement, the mechanism lays on the spine curve and estimates the curve and the location and orientation of vertebrae. To personalize the mechanism for a patient, a minimization problem is defined to give the number of the links and their length by using X-rays of different spine positions. The feasibility and capabilities of our patient-specific model are tested by using the data from preoperative X-rays of five positions of 10 AIS (adolescent idiopathic scoliosis) patients; three of the X-rays are routine in scoliosis standard care. The mechanism is personalized to each patient by using the three routine X-rays, and it is used to estimate all the five positions. Root-mean-square-errors (RMSE) of the curve, location, and orientation are 2e–5 mm, 0.27 mm, and 0.25°, respectively. The small RMSEs imply that our kinematic model is capable of estimating the scoliotic spine positions in the frontal plane and thus of describing the scoliotic spine movement in this plane. Our personalization using X-rays of three spine positions helps to set better values for the kinematic parameters (such as the length of the links) for more accurate estimates of the spine in the frontal plane.