Skeletal abnormalities and cerebral palsy often lead to abnormal walking patterns. But changing where muscles attach to bones alters the way the muscles work across the joint, and in turn, alters the patient's gait. However, it is difficult to understand the complex mechanical dynamics and predict the best attachment points. This uncertainty can lead to multiple surgeries that are difficult and painful, especially for children, who make up most of these patients.

The recent LifeMOD Biomechanical Modeler from Biomechanics Research Group Inc. (BRG), San Clemente, Calif., (lifemodeler.com) works inside MSC.Adams to develop individual human models from libraries of skeletal geometry, muscles, joints, and motion. The software gives doctors a new way to prepare for surgery. Previously, they might experiment on cadavers, but those cannot provide repeatable results and may not provide accurate information because of tissue damage. And clinical studies of patients with similar conditions are limiting because of widely varying physical parameters.

MRI data lets the software generate a personalized model that helps eliminate multiple surgeries. Modeling begins by creating body segments of, for example, the pelvis, shank, thigh, and foot. Standard geometry for these bones is extracted from the software's bone and joint library. A surgeon then “arranges” various muscle-attachment points to make the model walk and sit as the patient does.

The musculoskeletal model of a human can be used to determine the necessary muscle forces for moving a leg in a required pattern. After changing attachment locations of the gluteus medius muscle to correct a gait, doctors repeat the simulation and examine loads on surrounding muscles.

The software creates mechanical joints using kinematic joint elements and passive torque elements. Passive torque elements stabilize the joints. The software can also draw from its library of muscles for the entire body. These idealizations include data on physiological cross-section areas which are scaled based on patient size and act between two bone-attachment points.

Doing this helps doctors understand how location changes the muscle force, and the forces in surrounding muscles. Moving the attachment also changes the way a muscle effects a joint. If a new attachment reduces the force, it has to be taken up by all other muscles. As a result, the surgeon can determine an optimal attachment position. The simulations lead to more effective surgical procedures, fewer revisions, higher patient satisfaction, and an improve quality of life.