How Your Shoulders Work - Two Joints, Not Just One!
The shoulder actually consists of two distinct joints, the shoulder joint and the shoulder girdle.
The Shoulder Joint
The arm bone (humerus) connected to socket of the shoulder blade makes up the shoulder joint. The shoulder joint allows for movement of the arm in many directions. All while keeping the shoulder blade locked in place. Your shoulder joint can move your arm forwards, backwards, sideways. As well as rotating your arm in the socket.
There are many different muscles that attached to the humerus and allow for these movements. The pectoral major, latissimus, and deltoid create forwards, backwards, and sideways movements of the arm. The rotator cuff set of muscles creates rotational movements. Contrary to popular belief there is no “rotator cuff muscle.” The rotator cuff actually refers to a set of 4 different muscles: supraspinatus, infraspinatus, teres major, and subscapularis.
The Shoulder Girdle
The shoulder girdle is made up of the shoulder blade and clavicle (collarbone) and their relation to the ribcage. The shoulder girdle allow for movement of the shoulder around the ribcage without having to move the arm. When you roll your shoulders without lifting your arms you are moving your shoulder girdle joints.
There are a lot of different muscles that move the shoulder girdle. These include trapezius, rhomboids, levator scapula, serratus anterior, and pectoralis minor. Interestingly, the shoulder girdle bones are basically free floating on top of the rib cage. The clavicle is attached to the sternum by ligaments in the way we think of most joints working. With the bones close together and separated by cartilage. There is a ligament that attaches the shoulder blade to the ribs. However, it is long and allows for a lot of movement. Making it unlike other ligaments in the body. This ligament's basic function is to keep the shoulder girdle from shifting too far in any direction.
