Adhesive Capsulitis (Frozen Shoulder): This condition is characterized by pain and stiffness in the shoulder joint, making it difficult to move. It is a common cause of shoulder pain and stiffness, especially in middle-aged individuals.

Rotator Cuff Tendinitis: Inflammation of the tendons surrounding the shoulder joint can cause pain and stiffness, especially with movement.
Rotator Cuff Tear: A tear in the rotator cuff tendons can cause pain, weakness, and stiffness in the shoulder.
Osteoarthritis: Wear and tear of the shoulder joint can cause pain and stiffness, especially in older adults.
Bursitis: Inflammation of the fluid-filled sacs (bursae) surrounding the shoulder joint can cause pain and stiffness.

Septic Arthritis: A bacterial infection of the shoulder joint can cause severe pain, stiffness, and swelling, and requires prompt antibiotic treatment.
Fracture: A broken bone in the shoulder or arm can cause severe pain and stiffness, and may require surgical intervention.
Thoracic Outlet Syndrome: Compression of the nerves and blood vessels in the thoracic outlet can cause pain, numbness, and stiffness in the shoulder and arm.
Referred Pain from the Cervical Spine: Pain from the neck can be referred to the shoulder, and underlying conditions such as herniated discs or spinal stenosis need to be ruled out.

Polymyalgia Rheumatica: An inflammatory condition that causes muscle pain and stiffness, especially in the shoulders and hips.
Rheumatoid Arthritis: An autoimmune condition that can cause joint pain and stiffness, including in the shoulder.
Tumors: Rarely, tumors such as osteosarcoma or metastatic cancer can cause shoulder pain and stiffness.
Infectious Diseases: Certain infections such as Lyme disease or tuberculosis can cause shoulder pain and stiffness, although these are rare causes.