acromioclavicular

Your shoulder joint is composed of three bones: the clavicle (collarbone), the scapula (shoulder blade), and the humerus (upper arm bone). Your shoulders are the most movable joints in your body. They can also be unstable because the ball of the upper arm is larger than the shoulder socket that holds it. To remain in a stable or normal position, the shoulder must be anchored by muscles, tendons, and ligaments.

Because your shoulder can be unstable, it can be easily injured. Common problems include:

• Sprains and strains
• Dislocations
• Separations
• Tendinitis
• Bursitis
• Torn rotator cuffs
• Frozen shoulder
• Fractures (broken bones)
• Arthritis

Health care providers diagnose shoulder problems by using your medical history, a physical exam, and imaging tests.

Often, the first treatment for shoulder problems is RICE. This stands for Rest, Ice, Compression, and Elevation. Other treatments include exercise and medicines to reduce pain and swelling. If those don't work, you may need surgery.

NIH: National Institute of Arthritis and Musculoskeletal and Skin Diseases