A 55-year-old woman was submitted to surgery to remove her left breast in which a malignant tumor had been found. Following the mastectomy, her recovery proceeded well, except that she noticed that she was experiencing weakness in her left shoulder and had considerable difficulty raising her left arm above her head, even two months after her surgery. Her husband also noticed that her left scapula seemed to protrude posteriorly to a greater extent than the one on her right side. This phenomenon is called a "winged scapula". Concerned, she went to see her doctor. She was referred to a neurologist, who performed electromyography (EMG) and nerve conduction studies to determine the source of the weakness.