Slipping rib syndrome, which may also be known as Tietze's syndrome, is considered to be somewhat uncommon. It occurs when the ligaments that hold the ribs in place become weak. This weakness may cause the ribs to slip out of place. Because it is uncommon and several symptoms may mimic other medical conditions, it may be difficult to get a diagnosis at first. It's important to look at all symptoms and medical tests available to help confirm a diagnosis.