The causes of tendinitis usually fall into the following three categories: The first is acute injury, commonly referred to as tendon strain. The initial step is to stop any activity, followed by immobilization of the affected tendon area. Immobilization typically involves allowing the part to be completely relaxed, under no pressure, and is usually for a period of three weeks. The second cause is chronic overuse, which is the most common reason for tendinitis. It frequently occurs at sites of bony protrusions or where there is a tunnel, and this can easily lead to constrictive tendinitis. Treatment might start with rest, followed by non-steroidal anti-inflammatory drugs if rest is ineffective. Then, injection treatments are considered, typically around three times; symptoms or pain from tendinitis will significantly reduce or even disappear. If there is no improvement after three injections, a fourth should not be attempted, and surgical treatment to release the tendon and alleviate the constriction may be considered. The last cause is due to a purulent infection. This condition requires symptomatic treatment, initially with antibiotics, followed by cultures and sensitivity tests of the effusion. If the infection occurs adjacent to the tendon or in the tendon sheath, surgery might be necessary to perform drainage again. In summary, the treatment of tendinitis largely depends on the specific cause and involves different approaches.