An orthosis apparatus comprising: a thermoformable first shell member and an opposed thermoformable second shell member, the first shell member having a first front edge and an opposite first back edge, and the second shell member having a second front edge and an opposite second back edge; wherein a front zipper assembly joined to and selectively closing the respective first and second front edges (38, 68) as by a front first zipper strip affixed at the first front edge and a front second zipper strip affixed at the second front edge; and a back zipper assembly joined to and selectively closing the respective first and second back edges (40, 70) as by a back first zipper strip affixed at the first back edge and a back second zipper strip affixed at the second back edge; whereby the apparatus is configured so that heat activation of the apparatus allows for conformable placement of the first and second shell members (30, 60) about a body part of a patient that is to be immobilized; whereby selective closure of the front and back zipper assemblies (90, 100) joins the first and second shell members (30, 60) along the respective first and second front and back edges (38, 68, 40, 70) to install the apparatus about the body part of the patient; whereby the apparatus is configured so that cooling of the apparatus causes the first and second shell members (30, 60) to take a set conforming to the body part of the patient; whereby selective opening of one or both of the front and back zipper assemblies (90, 100) separates the first and second shell members (30, 60) along one or both of the respective first and second front and back edges (38, 68, 40, 70) to uninstall and allow removal of the apparatus from the body part of the patient, at least a portion of one of the front and back zipper assemblies (90, 100) allowing for selective hinging of the set first and second shell members (30, 60) for ease of removal and replacement of the apparatus in use. a thermoformable first shell member and an opposed thermoformable second shell member, the first shell member having a first front edge and an opposite first back edge, and the second shell member having a second front edge and an opposite second back edge; wherein a front zipper assembly joined to and selectively closing the respective first and second front edges (38, 68) as by a front first zipper strip affixed at the first front edge and a front second zipper strip affixed at the second front edge; and a back zipper assembly joined to and selectively closing the respective first and second back edges (40, 70) as by a back first zipper strip affixed at the first back edge and a back second zipper strip affixed at the second back edge; whereby the apparatus is configured so that heat activation of the apparatus allows for conformable placement of the first and second shell members (30, 60) about a body part of a patient that is to be immobilized; whereby selective closure of the front and back zipper assemblies (90, 100) joins the first and second shell members (30, 60) along the respective first and second front and back edges (38, 68, 40, 70) to install the apparatus about the body part of the patient; whereby the apparatus is configured so that cooling of the apparatus causes the first and second shell members (30, 60) to take a set conforming to the body part of the patient; whereby selective opening of one or both of the front and back zipper assemblies (90, 100) separates the first and second shell members (30, 60) along one or both of the respective first and second front and back edges (38, 68, 40, 70) to uninstall and allow removal of the apparatus from the body part of the patient, at least a portion of one of the front and back zipper assemblies (90, 100) allowing for selective hinging of the set first and second shell members (30, 60) for ease of removal and replacement of the apparatus in use.