Neuromusculoskeletal Interface for Bionic Arms: A Randomized Crossover Study

In the past decade, progress has been made in creating stronger, more capable prosthetic devices, with improved control. Similar improvements have been made in prosthesis suspension, which is a critically important factor in both comfort and function of a prosthetic device. While skin-fit suction sockets were considered the state of the art for many years, custom-rolled silicon and instrumented gel-liners are now becoming more common, as they provide improved comfort. However, these approaches still require use of an external socket worn on the residual limb.

The Osseoanchored Prostheses for the Rehabilitation of Amputees (OPRA) implant system (Integrum AB, Mölndal, Sweden) uses osseointegration (OI) (i.e., a metal implant is placed in the residual bone, which then grows into and integrates with the implant) to provide mechanical attachment of the prosthesis to the skeleton in the residual limb, thus eliminating the need for a socket.

However, obtaining electromyographic (EMG) control signals to enable myoelectric control of a prosthesis, whether it is attached through OI or a conventional socket, requires placement of surface electrodes over residual limb muscles, which has many practical limitations. Surface EMG signals are a complex blend of all local muscle activations and as such have low fidelity. It is difficult to isolate EMG signals from large surface muscles, and it is impossible to separate out signals from small or deep muscles. In addition, surface EMG signals are contaminated by several sources of noise, including ambient electromagnetic interference, motion artifact, and even electrocardiogram signals.

The limitations of surface electrodes may be overcome by surgically implanting the electrodes into the residual limb and placing them directly onto/into the tissue of the target muscle so that the EMG can be recorded directly at the source with improved signal to noise ratio and without disturbances from the external environment. Typically, such an approach would require skin-penetrating leads to convey the EMG signals from the implanted electrodes to the outside of the body to enable myoelectric prosthesis control, making it unsuitable as a permanent solution.

However, in the e-OPRA (electronic OPRA) device, the percutaneous interface of the OPRA Implant is utilized as a conduit for the wired communication between the inside and the outside of the body, eliminating the need for permanent skin penetrating leads and enabling a permanent solution for myoelectric prosthesis control using implanted electrodes. The e-OPRA system (which is not yet commercially available) developed by Integrum AB (Mölndal, Sweden), is built on decades of developing the OPRA system (which is commercially available).