From Halopedia, the Halo wiki
An artificial limb is a type of prosthesis that replaces a missing extremity, such as arms or legs. The type of artificial limb used is determined largely by the extent of an amputation or loss and location of the missing extremity. Artificial limbs may be needed for a variety of reasons where a body part is either missing from the body or is too damaged to be repaired, including disease, accidents, and congenital defects. A congenital defect can create the need for an artificial limb when a person is born with a missing or damaged limb. Prosthetics are however not needed in the event of an accident where only the nerves were damaged and not the extremities.
Unlike Kat's prosthetic arm which was permanent, Captain Ponder's was removable. In contrast to the more conventionally mechanical design of Kat's robotic arm, Captain Ponder's prosthetic operated based on artificial "musculature" of carbon-fiber weave. The fingers had joints made of titanium. The prosthetic arm sometimes made shooting difficult for the Captain. According to SSgt Avery Johnson, Captain Ponder's choice not to use a permanent prosthetic was unusual for an active duty soldier.
While military prosthetics are designed for practicality, civilian ones may be designed to mimic biological limbs in appearance. Despite this, their artificial nature is often not difficult to discern; for example, Eddie Underwood's prosthetic arm was said to be "fake pink".
In Halo: Reach, the player can purchase an artificial limb as part of one of several "chest" armor pieces for Noble Six; specifically, the Assault Sapper [R], Collar/Breacher [R] and HP/Parafoil [R] armor variants sport prosthetic limbs for the right arm, similar to Kat's.
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