There are 12 thoracic vertebrae in the upper back (a.k.a. the thoracic spine), which are labeled T1 to T12. There are two types of joints that connect these vertebrae: facet joints (on either side of the spine) and discs (in the center of the spine). These joints support the body’s weight and allow the spine to move. Near these joints are nerves that can sustain damage or become irritated when the discs or facet joints are injured. Nerve irritation or damage at the T4 level can cause pain and numbness in the upper arm, upper back, and, in some cases, the neck. The pain may come on suddenly following injury, or may worsen with time as stiffness in the affected area becomes more severe. While the symptoms are usually only present on one side, pain does sometimes occur on both sides. Additionally, the affected person may feel pain in the shoulder blade, ribs, or chest. The affected person may experience muscle spasms and reduced mobility around the joint. The pain may become worse with movement, sitting for extended periods of time, coughing or sneezing, or performing tasks that require putting the hands in front of the body (e.g., driving or ironing). Injury in this area often results from poor posture or from excessive bending, lifting, arching, or twisting movements. It also can occur following trauma. While most patients with this condition can recover completely with physical therapy, the recovery time will vary.