Robotic exoskeleton can help correct spinal deformities

Scientists have developed a dynamic, robotic exoskeleton that can help correct spinal deformities, while eliminating the rigidity of conventional braces. Spine deformities, such as idiopathic scoliosis and kyphosis (also known as "hunchback"), are characterised 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.

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. 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.

Researchers from Columbia University in the US have invented a new Robotic Spine Exoskeleton (RoSE) that may solve most of these limitations and lead to new treatments for spine deformities. The RoSE is a dynamic spine brace that enabled the team to conduct the first study that looks at in vivo measurements of torso stiffness and characterises the 3D stiffness of the human torso. "To our knowledge, there are no other studies on dynamic braces like ours. Earlier studies used cadavers, which by definition don't provide a dynamic picture," said Sunil Agrawal, professor at Columbia.

"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," Agrawal said. The study, published in the journal IEEE Transactions of Neural Systems and Rehabilitation Engineering, may lead to exciting advances both in characterising and treating spine deformities, he said.

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 spine deformities participated in the pilot study, which was designed to characterise the 3D stiffness of their torsos. The researchers used the RoSE, 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 3D stiffness of the human torso can be characterised 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. "Our results open up the possibility for designing spine braces that incorporate patient-specific torso stiffness characteristics," said David P Roye, a spine surgeon at the Columbia University. "Our findings could also lead to new interventions using dynamic modulation of three-dimensional forces for spine deformity treatment," Roye said.

While this first study used a male brace designed for adults, researchers have also designed a brace for girls 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.