Optimizing orthotic designs with FEA

Optimizing orthotic designs with FEA

by Dan Deitz, Associate Editor

Engineers are customizing finite-element-analysis software to support biomechanical designs that correct lower-limb abnormalities

Foot and ankle abnormalities traditionally have been corrected with an orthotic insert, which is worn for several weeks, then adjusted incrementally. By raising or lowering various areas of the feet, the inserts change the angle at which the foot hits the ground, easing pain and promoting proper muscle function.

Walk this way: Using leg and foot measurements plus the patient's age and weight, a customized version of ADAMS simulates his gait, with limbs displayed as realistic solid models or in skeletal form

Brent Konantz, president of Prothotics Corp. in Winnipeg, Manitoba, realized that orthotic-insert design was more of a craft based on trial and error than a science, and resolved to use computers to put orthotic design on a more scientific basis. He approached Mechanical Dynamics Inc. in Ann Arbor, Mich., whose Automatic Dynamic Analysis of Mechanical Systems (ADAMS) package simulates the motion of mechanical systems. ADAMS enables users to build a computer model of a mechanical system, simulate the action of its moving parts, and compute loads and forces on the components.

ADAMS was customized to simulate a patient's walking and running gait, using patient information gathered by a clinician. The software simulates the gait of the patient, compares it with a normal gait, and determines the orthotic required. Output includes animated graphic images and graphed data for the patient's present condition, the medical normal profile, and the predicted gait with inserts. Suggested orthotics can be overridden or modified by the clinician and the simulation rerun. The system also produces instructions for making the appliance on a numerically controlled milling machine.

A clinician with little or no computer training can enter data and interpret results easily, and the patient can usually wear the orthotic the same day. The software has been tested and verified and is now in use.

Konantz plans to license turnkey orthotic systems around the world. The hope is to replace manual measurements with signals from a force plate and MRI scans. Future software may also be able to "age" the model to investigate long-term effects.

The above was adapted from an article by Dan Deitz, Associate Editor. The full text may be found in the July 1997 issue of Mechanical Engineering magazine. © 1997 ASME International.© To obtain a copy of this issue, click here.