The bulge on the outside of the ankle may be related to tendon sheath cysts, lipomas or osteophytes, etc., which need to be diagnosed after examination. 1. Tendon sheath cyst: it is a kind of disease caused by degeneration of connective tissue around the joint capsule, which may be caused by trauma, long-term strain injury, etc. The lesion site may have a pushable, non-adhesive lump, joint pain and discomfort and other symptoms. It occurs mostly in the wrist and foot, and is more common in women and diabetics. 2. Lipoma: It is a kind of benign tumor originated from adipose tissue, which may be related to high blood fat, heredity and so on. Usually there are one or more lumps with soft texture, clear boundary, smooth surface and easy to push. It usually does not affect the functional activities of the surrounding joints or tissues. 3. Osteomalacia: patients with osteomalacia in the ankle joint area are prone to degeneration, fracture or even peeling of the cartilage of the ankle joint, which may stimulate the synovial membrane inside the ankle joint, causing edema and proliferation of the synovial membrane, leading to increased exudate of fluids, and also visible swelling protruding from the ankle joint. In addition, the bulge on the outside of the ankle may also be caused by other diseases, which need to be examined before diagnosing and treating accordingly, and it is recommended to go to the hospital for examination and diagnosis in a timely manner.