Lateral knee pain can be due to knee synovitis, lateral meniscus injury, lateral wear of the patellar articular surface, and lateral interphalangeal wear of the knee. 1. Knee synovitis: Knee synovitis is usually a sterile inflammatory disease caused by knee sprains and multiple intra-articular injuries. Depending on the nature, it can generally be divided into tumor synovitis of the knee and non-tumor synovitis of the knee. Patients usually present with symptoms such as redness and swelling of the knee joint as well as pain on the outside of the knee. 2. Lateral meniscus injury: it may be caused by direct trauma to the lateral meniscus, or it may be caused by the long-term degeneration of the joint itself, which may also cause lateral meniscus injury. Lateral meniscus injury can also lead to lateral knee pain. 3. Patellar articular surface lateral wear: patellar articular surface lateral wear is a manifestation of joint degeneration, mostly seen in degenerative osteoarthritis of the knee joint, which will lead to lateral knee pain. 4. Knee lateral interphalangeal wear: some patients have valgus knee joints, which can lead to knee lateral interphalangeal wear and lateral knee pain when walking.