Design and preliminary evaluation of a microprocessor controlled ankle-knee prosthetic system for above knee amputees. Knee and Ankle adaptations to stairs and slopes Bonnet X. 1 , Djian F. 1 , Drevelle X. 2 , Villa C. 3 , Pillet H. 3 1 R&D Department, PROTEOR, Dijon, France, xavier.bonnet@proteor.com 2 INI-CERAH, Créteil - Woippy, France, xavier.drevelle@invalides.fr 3 LBM, Arts et Métiers ParisTech, Paris, France, helene.pillet@ensam.eu Abstract- In spite of significant technical improvements on prosthetic components, the above knee amputees continue to report some difficulties for ambulation during outdoor displacements. Some of these difficulties could be attributed to the lack of ankle adaptations. A prototype of a microprocessor- controlled ankle-knee prosthetic system that mimics various adaptations observed for asymptomatic people was designed and evaluated in slopes and stairs with one above knee amputee. Compared to conventional designs, the prototype allows an increase of ankle range of motion during both the stance phase and the swing phase. The patient reported an increase of comfort and safety in slopes and stairs using this prototype. Keywords : prosthetic design, microprocessor control, knee ankle, amputation 1. INTRODUCTION Prosthetic knees and feet design has benefited from important technical improvements in the last decades. Microprocessor-controlled prosthetic knees have improved the safety and the functional outcomes of above knee amputee and became the standard of care in above knee prosthetics [1]. The control of the stance knee flexion improved walking ability of above knee amputees both during stairs [2] and slopes descent [3]. In spite of these active engineering developments on prosthetic components, the patients continue to report some difficulties for ambulation, emphasized during outdoor displacements [4]. Some of these difficulties could be attributed to the lack of ankle adaptations to multimodal locomotion. In the literature, some authors highlighted this lack of adaptations in stairs [2] and slopes [5]. Thus, in stairs, step-by – step descent is made possible by placing the prosthetic foot on the edge of the step allowing the progression of the tibia during stance [6]. This strategy would be a consequence of the lack of mobility of the ankle also observed in slopes [5], resulting from the fixed stiffness of conventional prosthetic feet. Some microprocessor-controlled prosthetic ankles are now available for both below knee and above knee amputees. In particular, some designs allow an ankle movement during the swing phase. By increasing toe clearance, they reduce the risk of falling and allow adjustment of ankle position according to the slope [7]. Other designs including hydraulic devices were proposed to adapt the ankle resistance during the stance phase according to the terrain [8]. Motorized design proposed by Herr et al. could combine the ankle adaptations during both swing and stance phases of gait [9]. Lastly, motorized ankle-knee systems were developed by the Vanderbilt University allowing motorized adaptations of both the knee and the ankle [10]. Compared to below knee amputees, the design of a prosthetic ankle for above knee amputees should more critically fit the following criteria: limited weight, reduced adaptation time, no critical detection errors and control of the knee and the ankle by the user. The objective of the study was to design and evaluate a microprocessor-controlled ankle-knee system able to mimic various adaptations observed for asymptomatic people in slopes and stairs. 2. MATERIAL AND METHODS Estimation of physiologic ankle stiffness in different situations A control group was formed with 30 asymptomatic subjects. Motion capture of 54 markers placed on the patient according to the protocol described by Pillet [11] was made with an optoelectronic system Vicon at 100 Hz. In the same time, ground reaction forces and moments were acquired using two AMTI force plates at 100 Hz. Acquisitions were made in 3 situations of daily living simulated using instrumented devices: level ground,