This Clinical Investigation (CI) is performed to clinically test and verify the safety and benefits of a bidirectional interface into the human body that allows permanent and reliable communication using implanted electrodes. These electrodes will provide long-term stable bioelectric signals for an improved control of artificial limbs. The bidirectional interface is based, and requires, the clinically established implant system for bone-anchored prostheses named Osseointegrated Prostheses for the Rehabilitation of Amputees (OPRA). The feasibility of the device was initially proven through a proof-on-concept patient who has used the system without any adverse events for more than three years.