Mechno-arms were cybernetic arms meant to replace organic hands and arms, that could have been in the most varied ways, including cut by lightsaber blades. This way, the host would not be impaired by the lack of a limb, and could continue to perform the same functions, benefiting from the fact that the mechno-limbs were stronger than the original organic members. After Count Dooku cut off the arm of Anakin Skywalker during the First Battle of Geonosis, he began using a mechno-arm.
Luke Skywalker had one (covered over in synthetic skin so it would look like more realistic) grafted to his wrist after Darth Vader severed his hand during the Duel on Cloud City. However, by 34 ABY, this synthetic skin had been removed, exposing the cybernetic extremity underneath.