Grades 1-4 correlate with injury levels. For example, a Grade 1 injury may be mild hyperextension, or minor tendon damage. For these injuries, orthoses made of rigid materials such as hard plastic are not needed. Therefore, Grade 1 orthoses are usually made of neoprene, which is lightly supportive and compressive but still allows freedom of movement.
Grade 2 and Grade 3 orthoses work in the same way. The more severe the injury, the more supportive the orthosis needs to be. Grade 2 uses a proven stabilization system of Velcro straps, which allows some mobility but stabilizes the joint in the direction that the strap is attached. For smaller animals, such as cats and Chihuahuas, Grade 2 can in some cases provide adequate stabilization even for a severe injury.
Grade 2.5 and Grade 3 use thermoplastic as a stabilizer. When the thermoplastic is molded on the patient after heating in hot water, it becomes completely rigid. Grade 3 is therefore used after surgery and more severe injuries, often instead of plaster. As the thermoplastic only covers half of the leg, the orthosis can be easily removed to check the skin, which is difficult to do with plaster. In addition, the orthosis can be reshaped to gradually return to a normal loading angle. Finally, the thermoplastic can be removed from the orthosis and the neoprene part used as a Grade 1 orthosis at a later stage of rehabilitation.
Grade 4 orthoses are also made of hard plastic, but are manufactured after a 3D scan of the body part. These orthoses can be fully immobilizing or equipped with joints or motion limiters. Motion limiters mean that you can lock the joint completely, allow a certain range of motion, or open up the joint to free movement. Grade 4 orthoses are often used conservatively (instead of surgery, for life) or post-operatively.