First dynamic spine brace—the robotic spine exoskeleton—characterises spinal deformities

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The robotic spine exoskeleton consists of two six-degrees-of-freedom parallel-actuated modules connected in series, each with six actuated limbs.

Designed by Columbia Engineers, the robotic spine exoskeleton (RoSE) is the first device to take in vivo measurements of torso stiffness and to characterise the three dimensional stiffness of the human torso. RoSE could lead to new treatments for children with spinal deformities such as idiopathic scoliosis and kyphosis, according to lead investigators of the study, published online in the journal IEEE Transactions of Neural Systems and Rehabilitation Engineering.

Developed in Agrawal’s robotics and rehabilitation (ROAR) laboratory, 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. 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 spinal deformities participated in the pilot study, which was designed to characterise the three-dimensional stiffness of their torsos. The researchers used the RoSE to control the position and orientation of specific cross sections of the subjects’ torsos while simultaneously measuring the exerted forces and moments.

The results showed that the three-dimensional stiffness of the human torso can be characterised using the RoSE and that the spinal 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.

Sunil Agrawal (Columbia Engineering and Department of Rehabilitation and Regenerative Medicine, Columbia University, New York, USA), the study’s principal investigator, comments, “To our knowledge, there are no other studies on dynamic braces like ours. Earlier studies used cadavers, which by definition do not provide a dynamic picture. The RoSE is the first device to measure and modulate the position or forces in all six degrees-of-freedom in specific regions of the torso. This study is foundational and we believe will lead to exciting advances both in characterising and treating spine deformities.”

Spinal deformities, such as idiopathic scoliosis and kyphosis, are characterised by an abnormal curvature in the spine. Children with these spinal deformities are typically advised to wear a brace that fits around the torso and hips to correct the abnormal curve, and this technique has been shown to prevent progression of the abnormal curve and so avoid surgery. The underlying technology for bracing has not fundamentally changed in the last 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, and sensor-less designs. Users have reported finding 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.

David P. Roye (Department of Pediatric Orthopedic Surgery, Columbia University Irving Medical Center, New York Presbyterian Morgan Stanley Children’s Hospital, New York, USA), co-principal investigator of the study, says, “Our results open up the possibility for designing spine braces that incorporate patient-specific torso stiffness characteristics. Our findings could also lead to new interventions using dynamic modulation of three-dimensional forces for spine deformity treatment.”

Lead author Joon-Hyuk Park (Army Research Lab, Aberdeen, UK), who worked on this research as a PhD student and as a team member at Agrawal’s ROAR laboratory, adds, “We built upon the 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. In order to characterise the three-dimensional stiffness of the human torso, the RoSE applies six unidirectional displacements in each degree-of-freedom 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, Agrawal and his team have already designed a female brace as idiopathic scoliosis is 10 times more common in teenage girls than boys. The team is actively recruiting girls with scoliosis in order to characterise how torso stiffness varies due to such a medical condition.

“Directional difference in the stiffness of the spine may help predict which children can potentially benefit from bracing and avoid surgery,” says Agrawal.

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