For external fixation of patella fracture cast, the length should be measured first. Nowadays, the casts currently used in hospitals are medical polymer plaster splints, which come in three models, large, medium and small. Generally, the medium size cast can be used for patella fracture. Two medium-sized casts are cut to length and soaked and positioned with the lower extremity in the straight position, preferably with the assistance of someone to lift the leg during the soaking process. A physician’s assistant is needed to assist in dragging out the cast, taking a plaster bandage, a regular bandage, and an elastic bandage. The cast is wrapped around the limb in a loose and tight manner. When the cast is dry, the cast is complete and the knee needs to be flexed 5-10 degrees during the drying process to prevent discomfort due to hyperextension.