Disclosed is a prosthetic knee appliance having upper and lower leg elements with a single-axis, articulating joint therebetween controllable with an electric knee-lock mechanism. A tilt-switch located within the prosthetic knee can facilitate activation of the electric knee-lock to lock or unlock the joint when the lower leg element is in a pre-determined position. A remote control can provide external locking control of the articulating joint. A pressure switch can ensure that the free-knee is locked only when the lower leg element is sufficiently extended relative to the upper leg element. The mobility of a free-knee system combined with the stability of a straight-leg prosthesis can be advantageous for pre-ambulatory pediatric patients.