Tendonitis is an inflammation or irritation of a tendon that occurs as a result of aging, overuse or injury. A tendon is the flexible cord of tissue that connects muscles to bones. This condition occurs often in the tendons of the foot and ankle.  Symptoms of tendonitis usually involve pain, tenderness and swelling in the affected area. This pain is usually worse with movement and increased activity. Many cases of tendonitis can be treated simply through rest, immobilization and anti-inflammatory pain medication. However, you should seek treatment if symptoms interfere with daily activities. More severe cases may also benefit from corticosteroid injections, physical therapy or surgery. Untreated tendonitis can lead to chronic symptoms or rupturing of the tendon, so it is important to take proper care when treating this condition.