Grasping the Future: Advances in Powered Upper Limb Prosthetics

In the USA there have been many initiatives to develop advanced arm/hand prostheses in the light of the casualties seen in the wars in Iraq and Afghanistan. In this chapter the issues involved in some of these designs is presented as well as an overview of some of the more high profile prosthetic system development efforts.

Prosthetic management of partial hand amputation poses many challenges to prosthetists and other treating professionals. Partial hand amputations have been challenging to fit with externally powered devices due to the limited space available for prosthetic mechanisms. It has long been the goal of prosthesis designers to mimic as many of the six commonly referenced grasp patterns as possible. With the commercial introduction of individually powered fingers exciting possibilities for fitting externally powered finger prostheses that can replicate various hand postures is now feasible. Powered fingers have allowed individuals with partial hand absence to regain some of the dynamic and conformable grasp functions they lost. This chapter will present a general overview of prosthetic options available for partial hand prostheses with specific focus on externally powered fingers.

Recent findings in clinical neurophysiology show that the cortical representation of an amputated hand is not so largely affected, as once thought, by critical rearrangements, and that central and peripheral neural connections somehow maintain their functions. These findings paved the way towards the exploitation of cortical and peripheral residual functions by neural interfaces for hand prosthesis control. In the present study, a young male amputee has been implanted with four intraneural multielectrodes, two in the median and two in the ulnar stump nerves. During the next four weeks, these electrodes were used with the double purpose of recording neural signals (for the extraction of subject’s motor intentions to be performed by the robotic hand prosthesis) and eliciting sensory feedback through proper electrical stimulation (pulses frequency and duty cycle). Recorded neural signals were mapped in real-time onto three actions of the robotic hand through an amplitude on the best matching channel threshold method, while, thanks to an AI classifier trained offline, was achieved an 85% accuracy. Recorded peripheral nerves activity was then compared with the cortical activity over the missing hand motor area. By performing the classification of the motor intention over the peripheral signals solely during a time window compatible with the transmission delay of the motor command from the cortex, identified as an event related desynchronization of the EEG rhythm, the classification rate approached 100% of success. The study also aimed at investigating possible neurorehabilitative effects of the re-acquired stream of data to/from the missing limb and the continuative use of a high-interactive hand prosthesis. Results show that training for robotic hand control and for sensory perception produced a normalization in the electroencephalographic activation pattern and a reorganization of the motor cortical maps as evaluated via TMS, with restriction of the cortical overrepresentation of muscles proximal to the stump. In parallel, a clinical improvement of phantom limb pain has been observed, that recognizes in the correction of the aberrant plasticity in its anatomical substrate.

Assessment tools are vital in measuring the outcomes of any practice or procedure. In the development and use of a prosthetic limb, this can be divided into three areas; the basic functions of the design, activities the limb is used for, and the amount the user actually employs the hand in everyday life. Each area is distinct and different and it needs different tools designed specifically for each area in order to reliably measure these outcomes. The development of these tools must include means to make sure the tool measures what the tester thinks it measures and makes sure that such measurements are consistent across time and between testers. Once a consistent set of tools is developed it allows clinicians to discuss and compare devices, training methods and solutions. It also allows investigation of different designs.

Currently, the emphasis is on the basic practical measurements of function, activity and participation. This uses simple methods based on observation, timing or questionnaires to measure the use of simple prostheses. With newer designs of multifunction hands and microprocessor controllers being introduced, there are more varied control methods for the different hands. This requires more sophisticated methods to measure the impact of the new designs. These new methods include the measurement of the motions of the body and upper limbs with optical methods, and looking at measuring the cognitive load that controlling such hands impose on the user. To allow simple comparisons between users, the tasks and methods have to be constrained. This creates more artificial activities which may themselves be too artificial to tell the observer what they need to know, so the choice of activity is a balance between realistic tasks and reliable results.

The scenario of upper-limb prosthetics is rapidly changing: innovative solutions are “moving out” from laboratories to be used by patients in the every-day-life. In particular, prosthetic hands are facing major changes, with the availability of multi-grip options. While these new technologies are potentially effective for patients, they are surely more expensive and complex in terms of mechanics, electronics and cosmetic covering, i.e. aspects that also determine an increase of maintenance costs. Since it is important to provide patients with effective components while keeping costs under control, technology assessment is crucial. In this framework, the aim of this Chapter is to provide an overview of some evaluation tools that were set-up at Centro Protesi INAIL to gain insight into the psychosocial and biomechanical aspects of upper-limb amputees using high-tech prostheses. A case study reporting the application of these tools is also presented, regarding a patient using the Otto-Bock Michelangelo hand. Results highlighted an increased satisfaction with the new multi-grip hand and, remarkably, the new prosthesis triggered a higher level of embodiment, with a mindchanging in the use the previous hand as well. Thanks to pleasant appearance and functional features of Michelangelo, the patient started to assume more natural gestures and postures also with the traditional myoelectric hand, reporting this different way of thinking the prosthesis as “a fundamental step for an amputee”. Regarding the biomechanical assessment, the shoulder biomechanics was positively influenced by the availability of the lateral grip and by the overall hand shape, which allowed the patient to approach cylindrical and coin-shaped objects in a more natural way, limiting the shoulder compensatory movements. Overall, the assessment tools that we set-up provided a valid contribution for the systematic analysis of the changes taking place in the amputee due to the use of new technologies. The broad on-the-field experimentation will ultimately prove the validity of the approach.

After introductory considerations on the main functional and design differences between anthropomorphic hands conceived as robotic end effectors or as prostheses, this chapter presents two topics related to advances in robotic hand design that seem transferable to prosthetic hands, in order to increase their functional capability yet coping with specific constraints like simplicity, lightweight, cost effectiveness, robustness, etc. The development of a bio-inspired robotic hand, called UB Hand IV, based on an endoskeletal articulated structure, actuated by tendons and covered by a soft dermal-epidermal layer is briefly illustrated, in order to show the potential of its design solutions to be transferred into prosthetic hands. The first part of the chapter presents alternative design approaches for articulated joints and finger structures based on purposely designed compliant hinges. The basic problem of compliant hinges adoption in robotic structures, that is the limitation of secondary compliance effects, is analyzed and considerations about comparative metrics are proposed. Two hinge morphologies which show promising features are critically compared and pros and cons the production of fully integral fingers with compliant joints are discussed. The second part reports on the development of thin soft covers for robotic (and prosthetic) hands capable of strictly mimicking the actual compliance of human finger pulps. A design method, called by the authors Differentiated Layer Design (DLD), is reviewed and its potential for application on both robotic and prosthetic devices is underlined. Conclusions summarize the main aspects that encourage the transfer of the described results from the world of robots to that of human portable devices.

This contribution deals with a particular type of robotic systems, i.e. exoskeletons or wearable systems. With respect to conventional robots, exoskeletons present the main feature of being wearable and, consequently, always in contact with the human operator during operative conditions. The design and control of exoskeletons must then necessarily take into account this condition, not only for safety issues, but also in terms of transparency for user’s movement and fidelity in the generation of torques/forces to the operator. The experience of the PERCeptual RObotics laboratory of Scuola Superiore Sant’Anna in the design of exoskeletons is presented, by addressing the description of developed robotic exoskeletons. Implications for the usage of exoskeleton systems in the simulation of grasping in Virtual Environments are discussed, with an analysis of the issues associated to the test of myoelectric control of prostheses in Virtual Environments.