Musculoskeletal strain: This is the most common cause of arm and elbow pain, often resulting from overuse, injury, or poor posture. The pain can be acute or chronic and may be accompanied by stiffness and limited mobility.

Tennis elbow (lateral epicondylitis): A condition characterized by pain on the outer part of the elbow, often caused by repetitive strain on the forearm extensors. It's common in individuals who frequently use their wrists and forearms in a twisting motion.
Golfer's elbow (medial epicondylitis): Similar to tennis elbow but affects the inner part of the elbow, caused by strain on the forearm flexors. It's more common in individuals who engage in activities that involve gripping and twisting motions.
Cubital tunnel syndrome: A condition that involves pressure or stretching of the ulnar nerve, which can cause pain, numbness, and tingling in the arm and hand, especially in the ring and little fingers.
Radial head fracture: A break in one of the bones of the elbow joint, often caused by a fall onto an outstretched hand. It can cause pain on the outside of the elbow and may limit forearm rotation.

Myocardial infarction (heart attack): Although less common, pain in the left arm can be a symptom of a heart attack, especially if accompanied by chest pain, shortness of breath, or other cardiac symptoms. It's crucial to consider this diagnosis, especially in individuals with risk factors for cardiovascular disease.
Thoracic outlet syndrome: A condition where the nerves and/or blood vessels between the neck and shoulder are compressed, leading to pain in the shoulder, arm, and hand, along with numbness, tingling, and weakness.
Brachial plexus injury: An injury to the network of nerves that conducts signals from the spinal cord to the shoulder, arm, and hand, which can cause severe pain, numbness, and paralysis of the arm.

Osteochondritis dissecans: A joint condition in which a piece of cartilage, along with a thin layer of the bone beneath it, comes loose from the end of a bone because of inadequate blood supply. It can cause pain and swelling in the affected joint.
Bone tumors: Both benign and malignant tumors can cause arm pain, although they are much less common than other causes.
Infectious causes (e.g., osteomyelitis, septic arthritis): Infections of the bone or joint can cause severe pain, swelling, and redness, and are considered medical emergencies.
Neurological conditions (e.g., multiple sclerosis, peripheral neuropathy): Certain neurological diseases can cause arm pain, numbness, and weakness, often with a more complex and widespread symptom profile.