Explaining the Shoulder
The shoulder is one of the most complicated joints in the body. It is one of the few ball and socket joints, yet it has the largest range of motion of any joint in the body.
The shoulder consists of many complicated mechanisms that all must work in tandem in order to function properly.
Since there are so many micro functions within the shoulder, there are multiple ways it can become injured. This is why shoulder injuries are some of the most common injuries treated in an orthopaedic setting. The best way to understand a shoulder injury is to understand the functionality of the joint. Let’s take a deeper dive into the shoulder joint to help you gain a better understanding of the source of your shoulder pain.
The Shoulder Joint
The shoulder joint itself is made up of three bones: the humerus (upper arm), the clavicle (the collar bone), and the scapula (the shoulder blade). The acromion, located at the end of the scapula, forms the top or the “roof” of the shoulder joint. But, there are actually four OTHER joints in the shoulder, each contributing to the functioning of the joint in their own way. When just one of these working joints is compromised, the functionality of the shoulder can be hindered.
The Other Joints
Glenohumeral Joint— where the ball of the humerus fits in a socket in the scapula, called the Glenoid.
Acromioclavicular (AC) Joint— where the clavicle joins the Acromion.
Sternoclavicular (SC) Joint— where the arms and shoulders are connected to and supported by the main skeleton. This joint is actually attached at the top of the sternum on the front of the chest.
Scapulothoracic Joint— allows the shoulder blade to glide across the rib cage. This joint is incredibly unique, as it is dependent on the network of muscles that move the joint. If one of these muscles is not functioning properly, the entire joint’s function is affected. These muscles keep the socket properly aligned during shoulder movements.
In all synovial joints, articular cartilage forms around the ball. This cartilage is slippery and allows the joints to glide with minimal resistance. There are many ligaments binding the shoulder joints together, connecting the bones to bones.
Joint Capsule— a water tight sack that surrounds a joint. The joint capsule is formed by a group of ligaments connecting the humerus to the glenoid and acts as the main stability source within the shoulder. When your shoulder dislocates, it’s at the expense of the joint capsule.
Glenoid Labrum—the socket of this ball-and-socket joint is shallow, making the glenoid labrum incredibly important. The glenoid labrum is almost flat at the end of the clavicle but has a raised rim around it, deepening the socket with the connective tissue and holding the ball in place.
Biceps tendon—the two tendons that connect the biceps to bone at the shoulder joint. The attachments are called the “long head” and the “short head” of the bicep muscles. Together, these two tendons are referred to as the “proximal bicep” tendons. Relating to shoulder to pain, the culprit is usually the long head, which courses through a groove in the arm bone, then through the rotator cuff, and attaches to the bone near the labrum.