permanently attached to the body (using osseointegration). An approach that is very useful is called arm rotation which is common for unilateral amputees which is an amputation that affects only one side of the body; and also essential for bilateral amputees, a person who is missing or has had amputated either both arms or legs, to carry out activities of daily living. This involves inserting a small permanent magnet into the distal end of the residual bone of subjects with upper limb amputations. When a subject rotates the residual arm, the magnet will rotate with the residual bone, causing a change in magnetic field distribution. EEG (electroencephalogram) signals, detected using small flat metal discs attached to the scalp, essentially decoding human brain activity used for physical movement, is used to control the robotic limbs. This allows the user to control the part directly. Robotic transtibial prostheses The research of robotic legs has made some advancement over time, allowing exact movement and control. Researchers at the Rehabilitation Institute of Chicago announced in September 2013 that they have developed a robotic leg that translates neural impulses from the user's thigh muscles into movement, which is the first prosthetic leg to do so. It is currently in testing. Hugh Herr, head of the biomechatronics group at MIT's Media Lab developed a robotic transtibial leg (PowerFoot BiOM). The Icelandic company Össur has also created a robotic transtibial leg with motorized ankle that moves through algorithms and sensors that automatically adjust the angle of the foot during different points in its wearer's stride. Also there are brain-controlled bionic legs that allow an individual to move his limbs with a wireless transmitter. Prosthesis design The main goal of a robotic prosthesis is to provide active actuation during gait to improve the biomechanics of gait, including, among other things, stability, symmetry, or energy expenditure for amputees. There are several powered prosthetic legs currently on the market, including fully powered legs, in which actuators directly drive the joints, and semi-active legs, which use small amounts of energy and a small actuator to change the mechanical properties of the leg but do not inject net positive energy into gait. Specific examples include The emPOWER from BionX, the Proprio Foot from Ossur, and the Elan Foot from Endolite. Various research groups have also experimented with robotic legs over the last decade. Central issues being researched include designing the behavior of