A young swimmer comes to the sports clinic complaining of a very sore shoulder. He was running at the pool, slipped on some wet concrete, and tried to catch himself with his outstretched hand. He landed on his outstretched hand and has not been able to move his shoulder since. The nurses notices a length discrepancy between his two arms. The nurse suspects:

A. A tear in the rotator cuff usually results in pain and limited range of motion, but it doesn't typically cause a length discrepancy in the arms. B. Also known as frozen shoulder, this condition is characterized by limited range of motion but would not cause a discrepancy in arm length. C. While joint effusion involves fluid accumulation and can cause pain and swelling, it doesn't cause arm length discrepancy or the sudden inability to move the shoulder. D. A dislocated shoulder often results in an obvious deformity, such as a length discrepancy between the arms, and could prevent movement due to pain.