Technologies related to tumid implants and pumps are generally described. In some examples, a tumid implant device may comprise an enclosed sack membrane adapted to fit between bones in a joint. Articulation of the joint may cause a first layer of the membrane to move through a first boundary section into a second layer of the membrane, while the second layer moves through a second boundary section into the first layer. A working fluid may be disposed inside the sack membrane, and a reservoir may optionally be coupled to the membrane via a gate. The working fluid may be expelled from the sack membrane into the reservoir, and may re-enter the sack membrane from the reservoir in response to changes in pressure in the joint. The working fluid may be conducted into the reservoir or sack membrane by a pump, and several artery pump designs are disclosed.