A cast for use in limiting movement of the hand to promote healing of an injured body part includes a water hardenable orthopaedic blank for mounting on the forearm, preferably with a thumb hole, and an outrigger, also impregnated with water hardenable material, secured to the blank for holding the thumb or fingers against movement. This construction minimizes irritation of the web between the thumb and forefinger and reduces discomfort and trauma caused by chafing and pressure.