US Patent 7415381 Joint friction sensing

A system for determining an indication of animal joint mobility includes a mounting apparatus configured to hold a first condyle of the joint stationary in a position such that a second condyle of the joint can pivot about the joint, a pendulum configured to be coupled to the second condyle and configured such that a portion of a weight of the pendulum is disposed below a pivot axis of the joint such that the pendulum and second condyle can oscillate about the pivot axis, an angular displacement indicator associated with the pendulum, an angular displacement recorder configured to store indicia of the angular displacement, as indicated by the angular displacement indicator; of the pendulum over time, and a processor coupled to the angular displacement recorder and configured to use the angular displacement indicia to determine a first value associated with momentum decay of oscillations of the pendulum and to use the at least one value to determine a second value associated with a coefficient of friction of the joint.