Durable Short Double-Flexure Type Orthotic Ankle Joint


We have developed two designs for durable double-flexure type ankle joints. Flexure elements, singly and in multiples, have been used for centuries to create hinges. The earliest hinges were of animal hides used for doors and lids. In recent times, plastic flexures have been used as a bridge between the thigh, calf, and foot sections of fracture orthoses. The designs, however, are unstable when subjected to varus, valgus, torsional, or longitudinal loading.

We have been developing and using short double-flexure orthotic joints since 1975. Our design adds torsional, varus, valgus, and compressive load stability not achievable with longer flexures. We designed a testing apparatus which simultaneously subjects four ankle-foot orthoses to service cycle repetitions to determine more quickly and objectively which designs and materials are most durable. The double-flexure design approach retains the lightweight and cosmetic advantages of plastic while providing several advantages as compared with the posterior leaf. Flexures can be located for full congruency of anatomic and orthotic joint axes. Desired ankle range of motion is almost totally free of resistance, while the degree of motion restraint can be controlled easily and precisely. Several thousand ankle-foot and knee-ankle-foot orthoses incorporate these ankle joints.

Gillette Children's Hospital, 200 East University Avenue, Saint Paul, MN 55101