Abstract
Fixed Knee flexion deformity (FKFD) is a condition which restricts the extension of the lower limb. It is common in children with cerebral palsy (CP) due to tight hamstrings, creating developmental deformity in the tissues around the knees. Current treatment of the condition is through surgery, physiotherapy or with the use of orthotics for static progressive stretching (SPS). The purpose of an orthotics is to gently correct FKFD with the use of a brace and a distraction mechanism that extends the lower limb over time. We aim to realize a more optimal design of a distraction mechanism in the orthosis and understand the effect the design causes on the force distribution on the lower limb. With design considerations and available mechanisms in mind, a novel approach to a mediolateral placement of the distraction mechanism is explored. Dubbed as “crossbow”, the design combines a bicentric geared hinge and a lead screw to form a modular distraction mechanism. “crossbow” is tested against existing mechanisms to understand its viability. A duplicated physical model of the subject’s (male; femur length ~ 40cm; tibia length ~36cm) lower limb is fabricated. Model is rigged with sensors and has a lockable knee to simulate different angles of FKFD. Three parameters are tested: 1. Hinge design; 2. Position of distraction mechanism and; 3. Type of mechanism used. Our primary interest is in the force distribution across the lower limb. A bicentric hinge displays an improvement in normal force exerting on the limb as compared to simple hinge (p=0.05). Position of distraction mechanism is most optimal at the mediolateral sides of the brace compared posterior part of the brace (p=0.05) with higher pushing capabilities. This research hopes to display greater clarity in the effects of knee-ankle-foot orthosis (KAFO) design on the leg to allow better treatment to be proposed. A modular approach could streamline fabrication processes to increase availability of simpler KAFO for the children.