Tendonitis is mostly caused by repetitive, minor impact on the affected area, or from a sudden more serious injury. Arthritis is a condition that causes pain and inflammation in joints. While tendonitis affects tendons, arthritis affects the cartilage that connects bones in a joint. Unlike tendonitis, which tends to heal faster, arthritis is usually a long-term condition that develops as one gets older. Whether it is tendonitis or arthritis, getting an accurate diagnosis and early treatment are important in relieving discomfort and improving joint movement. Do consult with an orthopaedic surgeon for professional medical advice on your tendonitis or arthritis condition.