Design and Qualitative Testing of a Prosthetic Foot with Rotational Ankle and Metatarsal Joints to Mimic Physiological Roll-over Shape

This paper presents the analysis, design, and preliminary testing of a prototype prosthetic foot for use in India. A concept consisting of a rigid structure with rotational joints at the ankle and metatarsal with rotational stiffnesses provided by springs is discussed. Because literature suggests that prosthetic feet that exhibit roll-over shapes similar to that of physiological feet allow more symmetric gait, the joint stiffnesses were optimized to obtain the best fit between the roll-over shape of the prototype and of a physiological foot. Using a set of published gait data for a 56.7 kg subject, the optimal stiffness values for roll-over shape that also permit the motion required for natural gait were found to be 9.3 N·m/deg at the ankle and 2.0 N·m/deg at the metatarsal. The resulting roll-over shape has an R2 value of 0.81 when compared with the physiological roll-over shape. The prototype was built and tested in Jaipur, India. Preliminary qualitative feedback from testing was positive enough to warrant further development of this design concept. INTRODUCTION Bhagwan Mahaveer Viklang Sahayata Samiti (BMVSS), based in Jaipur, India, is one of the world’s largest distributors of assitive devices [1]. In 2013, they distributed 24,000 of their prosthetic feet, the Jaipur Foot. The Jaipur Foot was designed ∗Address all correspondence to this author. in 1968 to meet the specific needs of persons with lower limb amputations living in India: it lasts 3-5 years in the field, can be used barefoot, allows users to squat, and costs approximately $10 USD [2]. A study comparing the Jaipur Foot to two different prosthetic feet available in the western market found that the Jaipur Foot allowed a the most natural gait [3]. However, the current foot is handmade, which is relatively costly in terms of both time and money, and causes quality to vary from foot to foot. The goal of this work is to create an upgraded replacement to the Jaipur Foot that meets the needs of the nearly one million persons with lower limb amputations living in India to replace the original Jaipur Foot [4]. Before manufacturability can be addressed, first the mechanism must be designed, tested, and iterated via proof of concept prototypes. Most prosthetic feet used in developing countries are solid ankle cushioned heel, or SACH, feet [5]. The SACH foot consists of a rigid structure, or keel, and a cushioned heel to provide shock absorption at heel strike. While inexpensive and robust, the SACH foot does not meet the needs of persons with lower limb amputations, particularly in India. The original motivation behind the design of the Jaipur Foot was that the solid ankle of SACH-type feet does not allow squatting, a critical requirement for most people in India [2]. In the past two decades, energy storage and return, or ESAR, feet have become a popular alternative to SACH feet in the western world. The human ankle is a net power generator over the Proceedings of the ASME 2015 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference IDETC/CIE 2015 August 2-5, 2015, Boston, Massachusetts, USA