Abstract: A gravity operated locking device and method of operation are disclosed for use with an orthotic brace of a type having upper and lower members hinged together for articulation of the brace with flexion and extension of a limb joint, the locking device comprising a housing adapted for ready attachment to or ready detachment from a portion of the brace, preferably the upper brace member, and forming a groove extending along the length of the housing for receiving a drop bolt tapered at its lower end for riding over and locking into engagement with a projecting stop surface on the lower brace member. The drop bolt is preferably formed with an elongated slot captured by a portion of an attachment means for the brace. The locking device may include an overriding lock for securing the brace in either a fixed, fully extended condition or free for articulation. With the overriding lock released, the drop bolt may be manually operated for selectively permitting either articulated or locked operation of the brace.