What is tendonitis?

Tendonitis, also spelled tendinitis, is an inflammation or irritation of a tendon. Chronic strain, overuse, or misuse of a tendon leading to a repetitive stress injury, or a serious acute injury can lead to weakness, tear, or swelling of the tendon tissue, resulting in pain and stiffness near the tendon. Tendonitis usually occurs in the elbow, hip, knee, shoulder, thumb, and wrist, but can occur anywhere there is a tendon.