IN VIVO AND IN VITRO TESTING OF SHOE HEEL INSERT PROPERTIES; A COMPARATIVE STUDY

Shoe heel inserts (SHI) are a common method of conservative treatment for various painful disorders like degenerative joint diseases (DJD) and overuse injuries. They are also used to enhance exercise performance in athletes. There is little in the literature to guide orthopaedic practitioners in relation to optimum material for these SHI. The current study examines properties of three different kinds of off-the-shelf SHI in terms of their performance, endurance and cost. The material properties of inserts were tested on a universal material testing machine (UTM) before and after mechanical degradation (MD) that was performed by a purpose built repetitive loading machine (RLM) under compression and shearing forces. The results of material tests were augmented through subject tests by a pressure sensitive insole system, Pedar®. The data provided evidence that MD, simulating a normal walking distance of 100 to 130 Km, deteriorated the performance of all inserts tested in the current study. There were significant changes in the stiffness and elastic hysteresis of inserts and they were less efficient in cushioning heel areas. The SHI were responsible for putting more pressure under the lateral metatarsal heads. The SHI may be effective in symptomatic relief of painful DJD and overuse injuries but should be used cautiously in diabetic patients. Acknowledgements: The authors would like to acknowledge Mr. Ian Christie and Mr. Sadiq Nasir for their assistance. The study was funded by Institute of Motion Analysis and Research. The authors have no financial or personal relationships with the companies whose products were evaluated in this work.