In Vitro Method for Quantifying the Effectiveness of the Longitudinal Arch Support Mechanism of a Foot Orthosis

The purpose of this investigation was to develop a technique to quantify the effectiveness of the longitudinal arch support mechanism of a foot orthosis. The experimental model was based on the following principle of foot biomechanics: as the foot is subjected to a load, a proportion of the load is experienced as tension by the plantar aponeurosis. A differential variable reluctance transducer was implanted into the plantar aponeuroses of cadaveric lower limb feet through which the strain was calculated in three conditions, specimen barefoot, specimen with shoe, and specimen with shoe and orthosis. Each donor limb was mounted in an electromechanical test machine that applied a load of 900 N to the tibia. Time, load, and strain data were collected and analysed at four load levels (225, 450, 675, 900 N). In addition the measurements and test design were evaluated for reliability. Strain in the plantar aponeurosis decreased significantly in the specimen with shoe and orthosis compared to the specimen with shoe only. There was a significant increase in the time to load data in the specimen with shoe and orthosis condition in contrast to the barefoot measurements. There were no significant differences in strain between the barefoot tests and those of the shoe, indicating that the shoe tested provided minimal support to the foot's longitudinal arch. RELEVANCE: One of the most common foot pathologies that patients seek medical attention for is plantar fasciitis. The primary cause of this condition is excessive tension in the plantar aponeurosis. A foot orthosis is often prescribed for treatment, relying on its longitudinal arch support mechanism to relieve the strain in the plantar aponeurosis. Quantifying the amount of strain experienced by the plantar aponeurosis is needed to identify how effective foot orthoses are in providing support to the foot's longitudinal arches. Such information is of importance to the medical practitioner who is involved with orthotic clinical recommendations. The described method will also be useful to bioengineers concerned with the arch support component of running shoes.