Healthy Shoulder

Understanding how your shoulder works

Your shoulder is a ball-and-socket joint made up mainly of two bones. The ball portion of the joint is part of the upper arm bone (humerus), and the socket portion is part of the shoulder blade. The ball fits into the socket, allowing the shoulder to move. The surfaces of the ball and socket bones are smooth and covered with a protective tissue called cartilage. The cartilage prevents direct contact between these bones and allows them to move smoothly over each other, without friction or wear on the bone surfaces.

Osteoarthritic Shoulder


When osteoarthritis (OA) affects the shoulder, the cartilage cushioning the bones softens and wears away, causing the bones to grind against one another. That grinding causes pain when moving your arm/shoulder. You can feel it when you pull on a doorknob, pick up a book or even when you raise your arm. Eventually, friction causes the bone surfaces to wear down.

Although osteoarthritis is more common among people over 50 years old, people of any age can have OA due to previous injury, overuse of the joints or obesity. Osteoarthritis is the most common type of arthritis and affects an estimated 27 million Americans.1

Symptoms2 of osteoarthritis include:

  • Joint aching and soreness
  • Pain, especially following activity
  • Stiffness after periods of rest
  • Swelling of the affected joint

Proximal humeral fracture

A proximal humeral fracture is just the medical name for a broken shoulder. Specifically, it means a fracture of the upper arm bone at the shoulder joint. This injury is especially common among people 50 or older who suffer from osteoporosis. Osteoporosis causes bones to become more fragile over time, making them vulnerable to fractures caused by falls or direct blows, like a car accident.


Rotator cuff arthropathy

The rotator cuff is a group of muscles and tendons that holds the shoulder together and helps to stabilize it and give it strength. Rotator cuff arthropathy is a combination of two types of damage—not only has the cartilage been damaged or worn away, the rotator cuff tendon that connects the muscle to the bone has also been severely worn or torn.

  1. Osteoarthritis. U.S. Department of Health & Human Services.

  2. Handout on Health: Osteoarthritis. National Institute of Arthritis and Musculoskeletal and Skin Diseases.
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