Arthritis, tendinitis, rotator cuff injuries, broken bones and pinched nerves are possible causes of upper arm and shoulder pain, says Healthline. Some other causes include dislocation or separation of tendons and ligaments and spinal cord injuries.
Tendinitis of the rotator cuff causes pain when the tendons become inflamed due to keeping the shoulder in one position for long periods of time or repeatedly extending the arm over the head, explains Healthline. This mostly affects athletes who use the shoulder and upper arm a great deal, such as pitchers, swimmers and tennis players. Frozen shoulder and a torn rotator cuff are other injuries related to tendon problems. Tendons, muscles and ligaments stiffen, causing pain in the shoulder and limiting range of motion. If the tendons and muscles making up the rotator cuff become damaged or injured, a rotator cuff tear results, a painful condition that requires surgery or other medical intervention.
Tendinitis can also occur in the upper tendon of the biceps muscle, causing pain centered in the upper arm, according to the American Academy of Orthopaedic Surgeons. Biceps tendinitis begins with inflamed tendons that thicken over time, usually because of overhead activities and aging. This can lead to arthritis, tears in the glenoid labrum, the socket into which the arm bone fits, and shoulder instability.