A biosynthetic limb is a prosthetic limb made for patients who have lost limbs through injury or disease. The limb can replace the functionality of the original one in terms of both sensation and movement although it requires both physiotherapy and counseling for this to be achieved. There are some instances where biosynthetic limbs have failed, not due to the limb itself but due to neural trauma in the wound of the damaged limb, which will hinder the bio-electric signals required for the synthetic muscles to function as with a "real" limb.
Nog was given a biosynthetic leg in 2375 to replace the left leg that he lost during a critical mission on AR-558. (DS9: "The Siege of AR-558") He had difficulty with adjusting to his new leg but it was found that the problem was neither his body nor the biosynthetic leg but rather a psychological problem, which was later resolved. (DS9: "It's Only a Paper Moon")