gms | German Medical Science

Objectives: The loss of a hand is a traumatizing experience that can comprise an individual capability to interact intuitively with his environment. The state-of-the-art (SoA) functional replacement for the lost limbs are myoelectric prostheses. Their overall mechanical design and dexterity have improved over the last decades, but unfortunately, users have not profited greatly from these advances because of inherent limitations of the SoA myoelectric control interface (challenging, inefficient control and low bandwidth). Specifically, interesting aspect of daily activities such as bimanual interactions have been neglected by the prosthetic research community. Namely, when performing bimanual interactions with an object, voluntary movements of one limb are often involuntary altered when another movement has to be carried out simultaneously by the contralateral limb.

Methods: The system builds upon the SoA two-channel myoelectric control and utilizes two additional sensors: inertial measurement units (IMU) that measure velocity and orientation of both limbs. The system processes the user's movements in real-time and classifies them either as unilateral or bilateral. If the system detects synchronous movements of both limbs, it will adjust the prosthesis automatically to follow the orientation of the sound limb to assist it appropriately (e.g., for carrying and balancing a tray with both hands). The aperture is controlled via the SoA control as usual. The system has been evaluated on two able-bodied subjects and compared to the SoA in terms of performance and workload (Figure 1 [Fig. 1]).

Results and conclusion: The experiment consisted of two unilateral and two bimanual object interaction tasks in a randomized order. Results show that the novel control interface allows the user to complete the task 26% faster on average, while reducing their perceived workload (data obtained using NASA-TLX questionnaire).

The developed system addresses until now neglected, yet important prosthesis application scenarios, i.e. bimanual interactions. This novel, simple, yet robust, SoA extension showed that performance gain and workload reductions are possible for bimanual interaction tasks. These promising results will be (re)evaluated in clinical studies on transradial amputees (Table 1 [Tab. 1]).