Spine deformities, such as idiopathic scoliosis and kyphosis (also known as “hunchback”), are characterized by an abnormal curvature in the spine. The children with these spinal deformities are typically advised to wear a brace that fits around the torso and hips to correct the abnormal curve. Bracing has been shown to prevent progression of the abnormal curve and avoid surgery; however, the underlying technology for bracing has not fundamentally changed in 50 years.
While bracing can retard the progression of abnormal spine curves in adolescents, current braces impose a number of limitations due to their rigid, static, and sensor-less designs. In addition, users find them uncomfortable to wear and can suffer from skin breakdown caused by prolonged excessive force. Moreover, the inability to control the correction provided by the brace makes it difficult for users to adapt to changes in the torso over the course of treatment, resulting in diminished effectiveness.
The Robotic Spine Exoskeleton (RoSE) may solve most of these limitations and lead to new treatments for spine deformities. The RoSE is a dynamic spine brace that looks at in-vivo measurements of torso stiffness and characterizes the three-dimensional stiffness of the human torso. Earlier studies used cadavers, which by definition don't provide a dynamic picture. The RoSE measures and modulates the position or forces in all six degrees-of-freedom in specific regions of the torso.
The RoSE consists of three rings placed on the pelvis, mid-thoracic, and upper-thoracic regions of the spine. The motion of two adjacent rings is controlled by a six-degrees-of-freedom parallel-actuated robot. Overall, the system has 12 degrees-of-freedom controlled by 12 motors (Figure 1). The RoSE can control the motion of the upper rings with respect to the pelvis ring or apply controlled forces on these rings during the motion. The system can also apply corrective forces in specific directions while still allowing free motion in other directions.
Eight healthy male subjects and two male subjects with spine deformities participated in the pilot study, which was designed to characterize the three-dimensional stiffness of their torsos. The RoSE was used to control the position/orientation of specific cross-sections of the subjects’ torsos while simultaneously measuring the exerted forces/moments. The results showed that the three-dimensional stiffness of the human torso can be characterized using the RoSE, and that the spine deformities induce torso stiffness characteristics significantly different from the healthy subjects. Spinal abnormal curves are three-dimensional; hence, the stiffness characteristics are curve-specific, and depend on the locations of the curve apex on the human torso.
The design of the system was based on principles used in conventional spine braces, i.e., to provide three-point loading at the curve apex using the three rings to snugly fit on the human torso (Figure 2). In order to characterize the three-dimensional stiffness of the human torso, the RoSE applies six unidirectional displacements in each DOF of the human torso, at two different levels, while simultaneously measuring the forces and moments.
While this first study used a male brace designed for adults, a brace for girls has been designed, as idiopathic scoliosis is 10 times more common in teenage girls than boys. Directional difference in the stiffness of the spine may help predict which children can potentially benefit from bracing and avoid surgery.