The knee joint became stiffer after receiving a sodium hyaluronate injection.

　　"Injection" generally refers to an intramuscular or intra-articular shot. Sodium hyaluronate plays a role in nourishing cartilage, lubricating joint surfaces, and relieving stress on the joint, thereby promoting repair of knee joint cartilage, inhibiting inflammation, and alleviating pain. Many conditions causing knee swelling and pain can be treated with sodium hyaluronate injections. If a patient experiences increased stiffness after receiving sodium hyaluronate injection, it may be due to poor drug tolerance, excessive number of injections, intra-articular infection, improper injection technique, or drug allergy, all of which require symptomatic treatment. The specific causes are analyzed as follows:

　　1. Poor drug tolerance

　　Sodium hyaluronate injection may irritate soft tissues, leading to knee pain and stiffness. Applying a warm towel for local heat application may help.

　　2. Excessive number of injections

　　If a patient receives sodium hyaluronate injections over a prolonged period, it may significantly affect the knee joint, potentially causing sensations of soreness, swelling, and stiffness. This condition usually resolves within a few days; if symptoms persist, prompt medical evaluation is recommended.

　　3. Intra-articular infection

　　Severe joint inflammation or actual infection within the knee joint may lead to stiffness and pain. If infection results in joint effusion, therapeutic knee arthrocentesis may be required. In such cases, medical consultation is advised.

　　4. Improper injection technique

　　If sodium hyaluronate is inadvertently injected into the synovium rather than the joint cavity, it may cause knee pain or stiffness. Symptoms can be managed under physician guidance with medications such as diclofenac sodium sustained-release capsules or celecoxib capsules.

　　5. Drug allergy

　　If a patient is allergic to sodium hyaluronate, discomfort such as knee pain and stiffness may occur. It is recommended that patients take antiallergic medications such as desloratadine tablets or levocetirizine hydrochloride dispersible tablets as directed by a physician.

　　If increased stiffness occurs after sodium hyaluronate injection into the knee joint, it is advisable to observe for two days. If symptoms do not improve, timely medical evaluation is necessary. During treatment, avoid spicy and irritating foods and ensure adequate rest.