Editor's note: This part one of a three-part series.
Shoulder anatomy and posture
Shoulder pain and injuries account for approximately 25 percent of all doctor visits. The shoulder girdle is complex with multiple joints and muscles working together to allow us to move our shoulder through many planes of motion. The shoulder consists of the humerus, scapula, clavicle bones. (see illustration). The are four joints that contribute to the mobility of the shoulder: scapulothoracic, glenohumeral, acromioclavicular and sternoclavicular. If you refer to the illustration you will see that the joints are basically named by the two bones that come together to form the joint. The glenohumeral joint (where the long bone of the arm meets the body) is what most people commonly refer to as the shoulder joint. However it is a combination of movement at all four joints that allows us to actually move our arm through such a wide range of motion. Loss of movement in any of the four joints will result in compensatory movements in the other joints and muscles.
Besides the four joints that work together to allow us to move at the shoulder we also need good mobility in our upper back or thoracic spine to reach full shoulder range of motion. Normal shoulder range of motion is being able to reach our arm up over our head to 180 degrees and out to the side up to 180 degrees.
The shoulder joint is a “ball and socket” joint. However, it does not have a deep socket. The lack of deep socket is what allows for our the great mobility we have at the shoulder. Think of the socket as a golf ball on a tee. (See illustration 2) Our freedom of movement at the shoulder comes with the cost of lack of stability. The shoulder is supported and held onto our body with soft tissues such as the joint capsule, ligaments, and muscles. The joint capsule, ligaments and muscles all provide stabilization to the shoulder joint.
Lifting our arms overhead requires multiple muscles to work together in a synchronized fashion. This includes muscle in our upper back to stabilize and position the shoulder blade (scapula) and the muscles of our arm including the deltoids and the often discussed rotator cuff muscles. We will discuss the muscles in detail in Part 2.
Posture plays a major role in the health of our shoulders.
Let’s have you experience this for yourself! Sit slouched at the edge of a chair. Lift your arms as high as you can without moving out of the slouched position. Now sit up tall and lift your arms overhead. Was there a difference? I bet that you were able to lift your arm higher when you were sitting up tall versus a slouched position. Slouching results in the scapula (shoulder blade) being rotated up and forward. This affects the position of the glenohumeral joint and the humerus (long bone of the upper arm) is more prone to rub underneath acromion process of the shoulder blade. So as you experienced you can see the importance of practicing good posture to keep your shoulders healthy!
The shoulder girdle is complex with 4 bones, multiple joints and muscles all contributing to allow us the seemingly easy task of lifting our arms overhead. Posture is key to overall good shoulder health.
See you back here for Part 2 for a discussion about the key muscles for shoulder health.