It is an inflammation and swelling of a tendon, especially in the wrist and typically caused by repetitive movement.

it is an infection of the synovial fluid.

Tenosynovitis is an inflammation of the myelin sheath surrounding the tendon. It can be caused by an infection of the tissues either of the tendon, sheath or of the synovial fluid, and is often accompanied by or associated with tendonitis. Symptoms are very similar to tendonitis, including pain in the articulation, limited range of motion, point tenderness and crepitus. Common causes are repetitive strain injury due to new activities or increased use, infection due to open wound in the area of the tendon and sheath, impact directly to the tendon and sheath which causes hematoma and swelling. Treatment is the same as that for tendonitis. It includes rest, immobilization and antiinflammatory medications. Cold can be used to reduce swelling in rest periods, and upon resuming activities heat can be applied to increase perfusion and subsequently lubrication in the affected limb. Activities should be gradually increased to a comfortable level according to the amount of pain in the joint, and stopped if the condition persists or worsens. Medical attention should be sought if there is obvious deformity, numbness or tingling distal to the injury, if the limb is pale or cold, if the pain is severe or if the condition does not improve after three days of rest.