3-D steps up to decode mobility

STANFORD (US) — Researchers are using computer-generated 3-D simulations of how humans move to improve the lives of people with limited mobility.

A movement disorder can have many origins, such as a birth defect, spinal cord injury, or stroke. Rehabilitation scientists facilitate treatment of mobility disorders by studying the bodily cause of physical impairments and providing a scientific basis for therapies that can improve function.

The source of physical impairment is often hidden among the complex interactions of the nervous, muscle, and skeletal systems of the human body.

Simulating a patient’s movement in three-dimensional computer models can help uncover the source of the problem, whether it’s the size of a particular muscle or bone or the way these components perform.

Computer models also provide a visual platform on which to test whether surgery would improve mobility for a specific patient.

“People think about cancer and cardiovascular disease as the major problems associated with aging, but mobility is also very important, says Scott Delp, professor of bioengineering at Stanford University.

“When people lose mobility, it can be devastating to their mental and physical health. It’s a big challenge to figure out ways to maintain mobility as people age and restore mobility when people have physical disabilities.”

Delp is the director of a new research center funded by the National Institutes of Health that will be part of a national network of research centers to support and advance medical rehabilitation research.

Two years ago, Delp and his team introduced a free software program called OpenSim, a biomechanical research platform that simulates biological movement. The program combines data on muscle size and strength, joint motion, and recorded movements of a subject to produce a highly realistic simulation of a specific person’s maneuvering. The team is not focusing on using OpenSim to understand and treat movement disorders, including cerebral palsy.

Many children with cerebral palsy walk in a crouch-like pose, with their knees excessively bent. The cause of the crouch gait, which can be exhausting, painful and even debilitating, varies from patient to patient.

In some patients, the hamstring muscles are very tight and short and pull the knees bent. If the hamstrings are surgically lengthened, these patients may be able to straighten their legs and walk more easily. However, if that surgery is used on a patient who walks in a crouch gait for a different reason, the procedure could be ineffective or, worse, harmful.

By creating a computer model of a patient’s movements, researchers can non-invasively explore whether the surgery would be appropriate for a specific patient.

“If you make a simulation of a subject walking, we can tell you how long the hamstring muscles are during the motion and compare that to normal muscle,” says graduate student Katherine Steele.

Whether modeling cerebral palsy, stroke or prosthetics, the simulations created in OpenSim allow researchers to explore potential causes of mobility problems and run virtual tests of treatment options. The new center also will encourage researchers to share their models and build upon each other’s work.

The lack of a standard method for modeling movement had been an impediment to the rehabilitation science community.

“One of the biggest drawbacks of previous studies using simulations is that people cannot reproduce those results,” says Ayman Habib, who designed the graphical interface of OpenSim. “OpenSim solves that problem by providing a standard tool used by the entire field.”

A common platform that allows researchers to share their models, which can take years to build, will also propel rehabilitation research forward. The center will be responsible for curating a collection of movement models, ensuring scientists all over the world can share them.

If scientists develop a biomechanical model of the hand, for example, they can add it to the center’s database, making it available to anyone who might want to build on the work—by adding it to a model of a wrist or arm, for instance.

“Sharing models accelerates research because it’s so much effort to build and test each one of these biomechanical models,” says Delp.

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