Abstract: An apparatus for use in bracing or exercising a knee joint in a manner that allows bending of the joint only along a predetermined path which approximates the natural bending of the joint. On at least one side of the joint are upper and lower struts that run along and are attached to the upper and lower leg and are attached to one another near the joint by a connecting mechanism which includes a set of linkage arms and telescoping elements that allow the struts to pivot relative to one another along the prescribed pivot line. The amount of joint flexing or extension is adjustable by use of spacers placed in the telescoping portions or by the activation of a releasable lock. The apparatus may be used as a brace or, alternatively, may be used with or without a cycling mechanism to flex and extend the joint.