Four major shoulder joints help to achieve a complex range of motion: the glenohumeral joint, the acromioclavicular joint, the scapulothoracic joint, and the sternoclavicular joint. Joints are where 2 or more bones meet. While the shoulder is often referred to as a singular joint, it is technically made up of 4 joints. The shoulder is essential to arm movement and therefore critical to most everyday activities, such as driving and cooking.
A healthy shoulder allows the arms to move up and down, side-to-side, forward and backward, and to perform reaching movements. Articular cartilage is a slippery, strong, and flexible material. It has 2 functions:. Articular cartilage is often thinner in the shoulder than it is in weight-bearing joints, such as the knees and hips. The damage and loss of articular cartilage is called osteoarthritis.
The glenohumeral joint and acromioclavicular joint are susceptible to this and other types of arthritis. Your rotator cuff is made up of muscles and tendons that keep the ball head of your humerus upper arm bone in your shoulder socket. It also helps to raise and rotate your arm.
Supraspinatus : This holds your humerus in place and keeps your upper arm stable. It also helps life your arm. Infraspinatus : The is the main muscle that lets you rotate and extend your shoulder like reaching into the back seat of your car. Teres Minor : This is the smallest rotator cuff muscle. Subscapularis : This holds your upper arm bone to your shoulder blade and helps you rotate your arm towards you. It can also happen if you fall on your arm or try to lift something heavy.
Tendinitis: is inflammation or irritation of a tendon that attaches to a bone. It causes pain in the area just outside the joint. Tendinitis can often be the first occurrence before a tear. Bursitis: is when the bursa a small sac filled with fluid that protects your rotator cuff gets irritated.
The shoulder muscles are responsible for maintaining the widest range of motion of any joint in your body. This flexibility is also what makes the shoulder prone to instability and injury. Muscles, tendons, and ligaments combine to keep your arm bone in your shoulder socket. They also protect the main shoulder joint, the glenohumeral. About eight shoulder muscles attach to the shoulder blade scapula , upper arm humerus , and collar bone clavicle. Many other muscles play a part in stabilizing and guiding the shoulder and its movements.
There are about 20 muscles supporting the shoulder and allowing it to turn and rotate in many directions. Another four muscles comprise the shoulder rotator cuff :. Each muscle and muscle group plays a role in supporting your shoulder and allowing the wide range of motion of your arms and shoulder. The four muscles of your rotator cuff keep the head of your upper arm bone, the humerus, from popping out of the socket of the shoulder blade.
According to the American Academy of Orthopedic Surgeons , most shoulder injuries involve the muscles, ligaments, and tendon, not the bones. Sometimes shoulder pain can be referred pain , which results from an injury to your neck or another place. Athletes are most at risk of shoulder muscle injuries. Older adults and those in occupations that involve repetitive or overhead motion or heavy lifting are also at risk.
A study found that shoulder pain was most prevalent in those age 55 to 64, affecting about 50 percent in that age group. About 18 million Americans per year are affected by shoulder pain, according to a review. Rotator cuff tears are the most frequent cause.
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