1. A device to change the distance between a first member of the human skeletal system and a second member of the human skeletal system, comprising: a flowable substance, wherein this substance is a liquid, gas, or gel; reservoir, wherein this reservoir contains the flowable substance wherein this reservoir is configured to be implanted into the human body, and wherein movement of a moving portion of this reservoir causes the flowable substance to flow; a turbine, wherein this turbine is configured to be implanted into the human body, and wherein this turbine is rotated by a flow of the flowable substance; a pair of thread-engaged members, wherein this pair of thread-engaged members is configured to be implanted into the human body, wherein rotation of a first thread-engaged member relative to a second thread-engaged member changes the distance that these members span together, and wherein changes in the distance that these members span together change the distance between a first member of the human skeletal system and a second member of the human skeletal system; and a gear sequence that transduces rotation of the turbine into rotation of a first thread-engaged member relative to a second thread-engaged member, wherein this gear sequence decreases the magnitude of rotational movement when transducing rotational movement from the turbine to the first thread-engaged member.