The elbow can not straighten and pain may have the following reasons: First, arthritis of elbow joint, when the elbow joint has degeneration, there can be the formation of elbow bone spurs and severe pain, then there can be elbow joint activity limitation, especially the elbow joint can not be straightened, this time, we should carry out the X-ray examination at an early stage, to early diagnosis and early treatment. Secondly, synovial chondromatosis, synovial chondromatosis can appear cartilaginous change of synovial membrane in the elbow joint and free body, which can lead to the elbow can’t be straightened, and can be accompanied by pain symptoms, then we should take the X-ray film of the elbow joint and the MRI at an early stage for early diagnosis and early treatment.