Tendon sheath cysts present as a smooth, rounded mass on the ankle. In clinical practice, it is common to encounter patients who present with abnormal masses that are palpated or touched by the physician. Some are normal abdominal structures, while others suggest abnormalities or disease, and care should be taken to discern whether the problem is pathological or physiological. Smooth, rounded masses in the foot and ankle can occur at any age, mostly in youth and middle age, and more often in women than men. The cysts are slow growing, round and usually do not exceed 2 cm in diameter. they are also found suddenly. A few of them may recede on their own, or they may grow again. In some cases, except for the local swelling, there is no conscious discomfort, and sometimes there is mild pressure pain. Most cases have localized soreness or discomfort, which affects activities. 1.General symptoms Tenosynovial cysts can occur at any age, mostly in youth and middle age, more women than men. The cysts are slow growing, round, and generally do not exceed 2 cm in diameter, but are also found suddenly. A few of them may recede on their own, or they may grow again. In some cases, except for the local swelling, there is no conscious discomfort, and sometimes there is mild pressure pain. Most cases have local soreness or discomfort, which affects activities. 2.Local symptoms On examination, a round mass with smooth shape and clear boundary can be felt, and the surface skin can be pushed without adhesions. Most of the cysts have higher tension and tough masses, a few are soft, but all have cystic feeling. Ultrasound examination can help to determine the nature of the mass. (1) Tenosynovial cysts of the wrist: They occur mostly on the dorsal side of the wrist, with a few on the palmar side. The best site of occurrence is at the dorsal wrist joint capsule on the radial side of the common extensor tendon, followed by between the radial wrist flexor tendon and the long thumb extensor tendon. Tenosynovial cysts on the palmar side of the carpal joint sometimes need to be differentiated from radial artery aneurysms, and the radial artery, cephalic vein, and superficial branches of the radial nerve should be protected when removing the cyst there. Cysts can also occur in the flexor tendon sheath in the carpal tunnel, compressing the median nerve and triggering carpal tunnel syndrome. A few tendon sheath cysts can occur on the flexor tendon sheaths of the fingers far from the metacarpophalangeal joint, which are as hard as cartilage and the size of a grain of rice. (2) Tendon sheath cysts in the foot and ankle: There are 8 tendon sheaths in the foot and ankle: 3 anterior (anterior tibial tendon, long thumb tendon and long toe extensor tendon), 3 medial (posterior tibial tendon, long thumb flexor tendon and long toe flexor tendon), 1 lateral (long and short peroneal tendon), and 1 posterior (Achilles tendon). Dorsal tendon sheath cysts are more common and mostly originate from the tendon sheath of the long toe extensor tendon lateral to the dorsalis pedis artery. Tendon sheath cysts in the tarsal canal can compress the tibial nerve and are a cause of tarsal canal syndrome. Based on the medical history, general and local symptoms of clinical presentation, and ultrasound examination, the diagnosis can usually be established. Diagnosis: 1. A cystic mass with hemispherical shape, smooth surface and high tension appears on the dorsal side of the wrist, palmar side or dorsum of the foot, etc. 2. The mass grows slowly, with soreness or pain on pressure and a fixed base. 3.X-ray film shows no change of bone and joint. Differentiation of tendon sheath cyst from other bone diseases Tendon sheath cyst should be differentiated from giant cell tumor of tendon sheath, epidermoid cyst, lipoma, fibroma, rheumatoid arthritis, etc. When the cyst is more tense, the texture is harder but still elastic and cystic, and the mass is not mobile because it has a fixed tip. There is usually no pressure pain or light pressure pain. Seed cysts located on the metacarpal side of the proximal phalanges of the fingers are often mistaken for osteophytes because of the small, hard masses. Tenosynovial cysts that occur within the tendon can move with the movement of the tendon and when one end is pressed, the mass can move or expand toward the other end.