Shoulders That Sing!: Week 3

Which of the four shoulder joints contributes the most to our arm movement?

Which of the shoulder joints allows for the movement of our arm in all planes of motion (extension, flexion, adduction, abduction, internal rotation, external rotation, circumduction)?

Which structure does the four muscled rotator cuff work to control and stabilize?

If your answer was the glenohumeral joint to all of these, you are correct!

  1. The ball and socket joint of our shoulder (aka our glenohumeral joint- GH joint), is greatly challenged in stability and the rotator cuff is a wonderful series of 4 muscles and tendons specifically designed to help our GH joint maintain stability

The glenohumeral joint, is also sometimes called the ball and socket joint (because that is its shape!). Similar to the hip, the ball and socket joint shape of the shoulder allows for all of the available physiologic motions (see list above).

Unlike the hip, which derives stability in part from the depth of congruency between the femur and pelvis, the ball of the humerus is barely seated in the depression (acromium) of the shoulder blade. Most biomechanics research suggests that at a given time, only 25% of the area of the ball of the humerus is in contact with the shallow depression of the acromium.