A bed (A) has side rails (20, 22) and defines a patient supporting surface (38). A mounting assembly (B) includes a transverse member (50) which is clamped to the bed side rails and an upstanding post (58). A power module mounting bar (70) is slidably positioned on the upstanding post to be mounted thereto in a selectively adjustable vertical position and to be selectively swung about the axis of the post to a storage position. A power module (C) drives a shaft (98) through reciprocating angular displacement at a selectively adjustable speed and between selectively adjustable angular displacement limits. A patient joint flexing assembly (D) is connected with the power module shaft to flex a selected one of the patient's joints under motive force supplied by the power module. Commonly, a plurality of joint flexing assemblies are provided, each particularly adapted for flexing one of the patient's joints, such as a knee flexing assembly, an elbow flexing assembly, and the like. In the knee flexing assembly, a thigh supporting frame portion (174) and a calf supporting frame portion (176) are interconnected by a polycentric hinge (178). In a elbow flexing assembly, a wrist flexing mechanism (220) is provided for flexing the patient's wrist in coordination with flexing of the elbow.