There are two reasons why hot compresses should not be applied after the injection of sodium vitrate: first, after the injection of sodium vitrate, if the hot compresses are applied for too long, the sodium vitrate may become denatured and lose its normal efficacy, which will not be able to lubricate the joint and protect the joint cartilage; second, after the injection of sodium vitrate, there will be a pinhole on the skin surface of the knee joint, and the skin barrier of the knee joint will be weak at this pinhole, so when hot compresses are applied, there will usually be local sweating of the knee joint, which may contaminate the pinhole and lead to skin and soft tissue infection at the pinhole, and in serious cases, bacteria may enter the joint cavity through the pinhole and the needle channel to cause septic infection of the knee joint.