Tendonitis affecting the Achilles tendon in a 55-year-old man with osteoarthritis affecting the middle area of the foot (the midfoot). Osteoarthritis is a joint disease aggravated by mechanical stress. Symptoms include joint pain, stiffness and swelling. Achilles tendinitis, the inflammation of the Achilles tendon, can be caused by overstretching, traumatic injury and obesity. If the inflammation is not treated and the tendon rested and allowed to heal.