dynamic seating orthosis


seating orthosis

the need

People with spinal cord injuries often do not have the back musculature control to sit up after leaning forward in their adaptive equipment. Cross country skiers, mono-skiers, and wheelchair road racers in particular need to lean forward and then sit up a moment later while moving forward with speed.

assistive seating

dynamic seating orthosis

dynamic seating orthosis

the solution

Many such athletes have enough strength in their abdominal musculature to pull themselves forward against a counteracting spring force. This spring force can be used to help them return to an upright sitting position. A dynamic seating orthosis that supports the user in an upright position was designed to take advantage of this ability.

innovative seating design

Many adaptive recreational devices use custom molded orthotic seats that fit the user like a well-fitted boot. Early seating orthosis prototypes consisted of a molded plastic seat that rose from the buttocks to the upper torso. Flex points at the back were added to give the user more freedom of movement.

In a radical departure from this approach, the seating system was divided into two sections. The lower section consists of a seat shell that comes up to the L1 level of the athlete. The upper section grips the user from approximately T10 to T5 and is custom molded to fit the individual. One or two flexible fiberglass rods link the upper and lower sections. These rods are clamped to the lower seat shell at the back of the user and extend up into a plastic tube mounted to the back of the upper section. When the athlete leans forward, the fiberglass spring rods bend forward and slide through the upper support. Varying the thickness and flexibility of the spring rod varies the degree and direction of torso movement.

current status

Three configurations of the upper block system have been tested: one that allows only forward and backward movement, one that allows rotation of the upper body, and one that allows lateral flexion of the spine. The system was tested by Peter Axelson in his mono-ski while he was a member of the U.S. Disabled Ski Team.


This project was funded by Beneficial Designs, Inc. and Allen Siekman, Children’s Hospital at Stanford.