Numerous conditions can cause severe left-sided rib cage and shoulder pain. According to the American Academy of Orthopaedic Surgeons, most shoulder problems involve soft tissue damage or damage to the muscles, ligaments and tendons in and around the shoulder. Left-sided shoulder problems are often associated with left-sided rib cage problems and vice versa. Pain in one of these areas could cause pain in the others. In some cases, however, problems outside the shoulder and rib cage can cause pain in these areas.
Myocardial infarction, also known as a heart attack, can cause severe left-sided rib cage and shoulder pain. A myocardial infarction occurs when a blood clot obstructs the flow of blood through a coronary artery, which is a blood vessel that transports blood to the heart. In some cases, reduced circulation to the heart can damage or destroy heart muscle tissue. Certain risk factors can increase the likelihood of myocardial infarction, including the type of food a person eats, how much exercise a person gets and the way in which a person deals with stress. Common signs and symptoms associated with a myocardial infarction include left-sided chest, rib cage and shoulder pain; jaw pain; shortness of breath; sweating; fainting; nausea and vomiting; and a feeling of impending doom. MayoClinic.com states that diabetics and people with elevated blood pressure are more likely to experience a myocardial infarction.
A dislocated shoulder can cause excruciating left-sided rib cage and shoulder pain. The AAOS states that, because of its great mobility, the shoulder joint is one of the body's easiest joints to dislocate. A dislocated joint occurs when one of the bones that helps form the joint slips out of its usual position. Although the shoulder joint can dislocate in almost any direction, most dislocations occur on the anterior, or front, side of the shoulder, causing the head of the humerus, or arm, bone to slip forward and down out of the joint. The shoulder joint can be partially dislocated or completely dislocated, depending on the cause and the severity of the dislocation. Common signs and symptoms associated with a shoulder dislocation include swelling, numbness, weakness and bruising on the affected side. In some cases, especially cases that involve ligament, tendon or nerve damage, shoulder dislocations can cause intense shoulder pain on the involved side. Because trauma is a common cause of dislocation, other injuries, including rib cage injuries, may also be present.
Fractured ribs can cause severe left-sided rib cage and shoulder pain. A fractured rib may be caused by chest trauma from a fall, a motor vehicle accident or a contact sports injury. Rib cage trauma can cause cracked ribs or ribs that are broken in two or more pieces. If the rib is broken in two or more pieces, a jagged edge of bone could harm major blood vessels and internal organs, notes MayoClinic.com. Common signs and symptoms associated with fractured ribs include excruciating pain when taking a deep breath, pain in the affected area that is worse when the injury site is pressed, and pain that is worse when bending or twisting the torso. Because trauma is one of the principal causes of fractured ribs, other injuries, including serious shoulder injuries, may also be present.