A multi-phase orthopedic system for immobilizing a fractured limb, comprising: a sleeve formed of moisture-impervious material and sealable to prevent entry of moisture; a moldable splint positioned in the sleeve and sealed therein against entry of moisture until use, the splint comprising a substrate, a reactive system impregnated into or coated onto the substrate and remaining stable when maintained in substantially moisture-free conditions and hardening upon exposure to sufficient moisture to form a rigid, self supporting structure, and a removable cover enclosing the substrate along its length and forming a barrier between the substrate and a limb during an initial treatment phase during which the splint is worn by a patient on the limb; and an elongate removable wrap for retaining the splint on the limb during the initial treatment phase; characterized by: a removable cast for application to the limb during a subsequent treatment phase, and comprising: a cast body having an interior side and exterior side; and a flap carried by the cast body and movable between an open position, and a closed position overlying a part of the cast body to be applied to a treatment area of the limb, the flap adapted to cover and retain between the cast body and the flap the splint worn by the patient during the subsequent treatment phase in the same position as the location of the splint during the initial treatment phase; wherein the removable cover is configured to be removed from the substrate prior to placing the moldable splint between the flap and the cast body, so that in use during the subsequent treatment phase, the molded substrate of the splint, free from the removable cover, is covered and retained between the cast body and the flap, wherein the removable cast includes a plurality of straps (36, 38, 40) and complementary strap fastening rings (52, 54, 56) for being releasably positioned around the cast for securing the cast to the limb, wherein the cast includes a padding layer positioned on the cast to overlie a part of the cast body to be applied to the treatment area of the limb. a sleeve formed of moisture-impervious material and sealable to prevent entry of moisture; a moldable splint positioned in the sleeve and sealed therein against entry of moisture until use, the splint comprising a substrate, a reactive system impregnated into or coated onto the substrate and remaining stable when maintained in substantially moisture-free conditions and hardening upon exposure to sufficient moisture to form a rigid, self supporting structure, and a removable cover enclosing the substrate along its length and forming a barrier between the substrate and a limb during an initial treatment phase during which the splint is worn by a patient on the limb; and an elongate removable wrap for retaining the splint on the limb during the initial treatment phase; characterized by: a removable cast for application to the limb during a subsequent treatment phase, and comprising: a cast body having an interior side and exterior side; and a flap carried by the cast body and movable between an open position, and a closed position overlying a part of the cast body to be applied to a treatment area of the limb, the flap adapted to cover and retain between the cast body and the flap the splint worn by the patient during the subsequent treatment phase in the same position as the location of the splint during the initial treatment phase; a cast body having an interior side and exterior side; and a flap carried by the cast body and movable between an open position, and a closed position overlying a part of the cast body to be applied to a treatment area of the limb, the flap adapted to cover and retain between the cast body and the flap the splint worn by the patient during the subsequent treatment phase in the same position as the location of the splint during the initial treatment phase; wherein the removable cover is configured to be removed from the substrate prior to placing the moldable splint between the flap and the cast body, so that in use during the subsequent treatment phase, the molded substrate of the splint, free from the removable cover, is covered and retained between the cast body and the flap, wherein the removable cast includes a plurality of straps (36, 38, 40) and complementary strap fastening rings (52, 54, 56) for being releasably positioned around the cast for securing the cast to the limb, wherein the cast includes a padding layer positioned on the cast to overlie a part of the cast body to be applied to the treatment area of the limb.