Rotator Cuff Tendinitis or Tear: This condition is the most common cause of shoulder pain and limited mobility, especially in individuals who perform repetitive overhead activities or have experienced trauma to the shoulder. The rotator cuff muscles and tendons play a crucial role in lifting the arm, and their injury can significantly impair this function.

Adhesive Capsulitis (Frozen Shoulder): Characterized by stiffness and pain in the shoulder joint, adhesive capsulitis can severely limit the range of motion, including the ability to lift the arm. It often occurs after a period of immobility or in association with other medical conditions like diabetes.
Shoulder Impingement Syndrome: This condition occurs when the tendons of the rotator cuff muscles become irritated or inflamed as they pass under the acromion, leading to pain and difficulty lifting the arm.
Bursitis: Inflammation of the bursae, the fluid-filled sacs that cushion the joints, can cause pain and limit movement, especially if the subacromial or subdeltoid bursae are affected.

Axillary Nerve Injury or Compression: Damage to the axillary nerve can lead to weakness of the deltoid muscle and potentially sensory loss over the lateral shoulder. Missing this diagnosis could result in permanent weakness or sensory deficits if not addressed promptly.
Brachial Plexus Injury: An injury to the brachial plexus, a network of nerves that conducts signals from the spinal cord to the shoulder and arm, can cause severe and potentially permanent neurological deficits, including paralysis of the arm.
Thoracic Outlet Syndrome: Compression of the nerves and/or blood vessels that pass into the arm through the thoracic outlet can cause pain, numbness, and weakness in the arm, and if not recognized, could lead to chronic disability.

Osteonecrosis of the Humeral Head: A condition where the blood supply to the humeral head is interrupted, leading to bone death. It can cause severe shoulder pain and limited mobility but is less common than other causes of shoulder pain.
Tumors (Bone or Soft Tissue): Although rare, tumors affecting the shoulder region can cause pain and limited mobility. Early diagnosis is crucial for effective treatment and prognosis.
Infection (Septic Arthritis or Osteomyelitis): Infections of the shoulder joint or bone can cause severe pain, swelling, and limited mobility. Prompt recognition and treatment are essential to prevent long-term damage.