In order for our prosthetic design to allow our users to play volleyball at an accelerated level, we must pursue a strong methodological approach that encompasses the prominent issues our users typically face after above–elbow amputation. This will help ensure an increase in the range of function, capability, and quality of life for our users as they conduct their daily activities. Based on these requirements, we will prioritize demands based on importance to the user and the available material and technology we have access to.
Processing Capability
Volleyball games require each individual of a team to react in extremely short periods of time, while simultaneously executing complex motor functions such as: set, spikes, bumps, and overhead passes. These motions require refined motor control for the player to control the amount of force and the direction they want to move the ball in. For example, the overhead pass requires the wrist to be dorsiflexed (backward bending) followed by eccentrical contractions of the upper limbs followed by concentric contractions [13].
In addition, the spike begins with external rotations of the upper limb followed by extensions of the elbow and ending with the elbow prenoted [14]. These sequence of contractions of the muscles allow for a burst of energy that allows the player to project the ball at high velocities. As such, it is an upmost priority of our prosthesis to be capable of replicating complex motor functions. These demands push us to select a myoelectric prosthetic design as opposed to body powered or harnessed, as we can program functions and relay them using electromyographic (EMG) signaling to our prosthesis.
Mechanical capabilities of the design
In order for our design to properly replicate the motions associated with volleyball, our myoelectric prosthetic design must maximize EMG signaling transduction for our users.
A common issue with many current myoelectric prosthetic designs is the difficulty users experience when controlling their prosthesis, which can lead to total rejection of the prosthesis or damage of the opposing limb due to overuse. In order for us to avoid such issues, our design must take on two approaches: mechanical capabilities and user interface, which will be further discussed in the coming sections.
The fixation of our prosthesis to limb must ensure that we have placed the electrodes in the optimal positions on the remaining muscles of the remaining upper upper–limb stump which will allow for accurate readings of signals. This can be done by employing multi-channel detection systems that demonstrated extremely high classification rates of signals and also allows us to use less electrodes (12 maximum) which also reduce cost [15]. Our design must not only magnify signal detection but apply this information into movements. Current prostheses only allow for sequential control of limbs, meaning several different motions must be done in sequence for a desired action. However, due to the fast pace of volleyball and its unpredictable pace, our prosthesis must allow for simultaneous control of all joints. The programming of our prosthesis can be based on current Axon Bus Technology, whose prosthesis allow for simultaneous contractions of ligaments and joints. In unison with this demand, we must integrate capable electric drive motors that allow for rapid and responsive control of prosthesis.
Durability
In order to ensure extended use of our prosthesis and reduced need for repair and replacement, our prosthesis must be extremely durable. In unison, we must guarantee that the user’s range of function is not restricted as a result of the materials we used. This requires the correct selection of materials and design procedures from a wide variety of options. For example, our prosthesis requires supporting materials, which are located at the point of contact between prosthesis and stump. Their purpose is to prevent any painful or uncomfortable side effects that arise from contact between the two regions.
Typical materials used for this include poron and nickelplast which are extremely flexible and allow for increased range of movement. For the supporting body of the prosthesis, we must select a much more stiff, light weight and durable material. Titanium is perhaps one of the most common metals used for biomedical engineering devices due to its strength and corrosion resistance. Carbon fiber is a new and emerging material being used in prosthesis for its high strength, stiffness and lightweight, however it is costly to manufacture and difficult to design for each specific user dimension. Polymers such as polyethylene are used regularly in prosthetic designs for their flexibility and waterproof capabilities which help protect sensitive electronics and are primarily used in the joints. These materials must be specifically tailored for the user’s dimensions which entails an extensive amount of time and money resulting in high prices that many low-income families cannot afford. However, with current 3D Printing technology, it would be easier to design components of the prosthesis at cost–effective rates without compensating in reduced function. For example, researchers at Delft University of Technology had designed and evaluated a 3D-printed hand prosthesis which showed high levels of mechanical function capability, and it was able to perform various complex hand movements [16]. This would make our product more accessible to our targeted audience as we can reduce costs needed for producing the prosthesis [16].
Power Sustainability
Due to the intensive nature associated with volleyball, our prosthesis must have low power consumption that allows for whole day usage. The current market allows us to use lithium ion batteries quite easily. These batteries can last up to 1-3 days depending on the user usage and are capable of powering the vast electric motors used in current prostheses. They are also rechargeable and can be easily replaced if damaged, which allows easy maintenance. However, researches have been done on lithium metal pouch cells, that allows for us to configure the battery shape to the user’s prosthesis and reduction of materials which can lead to a bulkier and heavier design.
User Interface
Carefully selecting the mechanical aspects of our prosthesis is an important part for our design. However, to maximize user capability, we must train our users to improve their “EMG Skill”. Studies have indicated that by improving an individual’s ability to generate required EMG signals and their decision making though exercises and tests, they have an extended control over their myoelectric prosthesis as opposed to untrained users [17]. The training we will employ should replicate the movements and level of muscular arousal required to perform each move in volleyball.
Having our users familiarized to our product, will allow for them to perform at higher levels while playing volleyball [17]. The training we will employ should replicate the movements and level of muscular arousal required to perform each move in volleyball. Having our users familiarized to our product, will allow for them to perform at higher levels while playing volleyball.
Rehabilitation
Phantom limb pain continues to be a persisting issue associated with upper limb amputation. Our prosthesis should help play a role in the rehabilitation process many patients must go through, and it may hopefully prevent the need of drugs or electrotherapy for users that entails extensive medical costs. There are several methods in achieving this, the simplest being adequate fixation of prosthesis to limb, that may help restore limb kinematics that were disturbed by the sudden change in limb density and weight. Another method, employs somatosensory feedback by attaching a device on the users limb which sends electro cutaneous feedback to the residual limb, and has demonstrated to reduce phantom limb pain in tested patients [18]. Employing such techniques will help improve the quality of life for our users immensely [18].
By taking into several biological and mechanical aspects into our design, we may ensure that our prosthesis is capable of allowing our users to play volleyball at an elevated level.