Arm bending can not be straight for bone and joint disease, trauma, muscle strain, humeral epicondylitis related, for the cause of treatment. 1. Osteoarthritis: middle-aged and elderly people who can’t bend their arms straight may be osteoarthritis, osteophytes, intra-articular free bodies, mild patients can apply non-steroidal painkillers, such as nimesulide capsules, joint injection of sodium vitrate. For serious joint degeneration or free body can be arthroscopic cleaning or joint replacement surgery. 2. Trauma: If there is a trauma, the arm can not be bent straight, may be fracture or ligament damage, need to take elbow CT or MRI film to clarify the diagnosis, to take the plaster fixation or surgical repair. 3. Muscle strain: if you often carry heavy objects or do physical work will cause muscle strain around the elbow joint, can be relieved by hot compresses, massage, application of medication to relieve tendons and activate blood circulation, such as relaxing tendons and activating blood circulation tablets. 4. Epicondylitis of the humerus: If the pain on the outside of the elbow joint may be epicondylitis of the humerus, you can perform closed injection or shock wave physiotherapy. So arm bending can not straighten if through the rest did not get better need to go to the hospital to take pictures to check the cause of further treatment.