The shoulder joint (glenohumeral joint) is made up of 3 bones: the humerus (the arm bone), the scapula (the shoulder blade) and the clavicle (collar bone). It is a shallow ball on socket joint that allows for motion in all planes.
There are 3 major ligaments of the shoulder joint (glenohumeral). When ligaments are frequently sprained, they become loose and lead to hypermobility.
This holds the shoulder blade to the collar bone. This is the most commonly sprained ligament of the shoulder.
This holds the shoulder blade to the collar bone.
This runs from one part of the shoulder blade to another.
The glenohumeral joint is a very shallow socket permitting the shoulder to have such great mobility. The bone ends are lined with articular cartilage to help protect the bone ends. In addition the shoulder so has a labrum which deepens the socket of the shoulder giving it added stability.
The labral can become torn causing stability issues within the shoulder. It can also lead to clicking, popping or catching of the shoulder which is often accompanied with pain and instability..
The muscles of the shoulder not only provide the motion to the shoulder, but also help provide much of the stability.
The rotator cuff is an integral part of the shoulder. Not only does it help provide the rotary motions of the shoulder, but it helps a great deal with shoulder stability and shoulder alignment (it helps keep the shoulder positioned in the center of the shoulder socket). The rotator cuff is made up of 4 muscles:
- Supraspinatus: This muscle runs on the top of the shoulder. It is small and naturally has a poor blood supply. Due to this as well as its location within the shoulder it is the most commonly injured muscle of the rotator cuff. Injuries include tendonitis, bursitis, impingement and tearing. This muscles helps with stability and is highly active with diagonal patterns.
- Infraspinatus: This muscle is located on the back side of the shoulder. It is one of two rotator cuff muscles that help to externally rotate the shoulder (rotate outward). When throwing, this muscle works to decelerate the arm.
- Teres Minor: This muscle is located on the back side of the shoulder. It is the other rotator cuff muscle that helps to externally rotate the shoulder (rotate outward). When throwing, this muscle too helps to decelerate the arm.
- Subscapularis: This is the largest of all the rotator cuff muscles. It is located on the front side of the shoulder blade and works to internal rotate the arm (rotating inward towards the stomach). Due to its size and strength it is very rare injured.
Other Shoulder Stabilizers
There are other muscles that play a key role in not only moving the shoulder, but stabilizing it.
The bicep muscles runs from the forearm and attached to the top of the shoulder joint. This helps you to raise your shoulder, plus it helps to stabilize the front side of the shoulder. Because of where it is attached it is often involved with rotator cuff tears.
Triceps run from the back of the elbow to the back side of the shoulder. The help extend the arm (pull it backwards) as well as stabilized the shoulder from the back side.
Chest and Back muscles
The large chest and back muscles play a major role in supporting the shoulder on the front and back sides. Stretching and strengthening these muscles
There are 3 muscles that make up the deltoid:
This is located on the front side of the shoulder and raises the arm to the front.
This located in the middle of the shoulder and raises the arm to the side.
This is located on the back of the shoulder and is responsible for pulling the arm backwards or behind you.
Bursa are fluid filled sacs that lie between two surfaces to help prevent friction, but if they become irritated and swollen they can become painful (bursitis).
The Brachial Plexus is a major branch of nerves that exits the neck and travels down the shoulder and arm to the hand. These nerves can become irritated at any level causing pain/numbness/tingling, etc. Even though these originate at the neck, symptoms can sometimes appear in the arm and hand.