Understanding Your Shoulder Complex

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What is the Shoulder Complex?

The shoulder complex consists of the clavicle (collarbone), scapula (shoulder blade) and the humerus (upper arm bone). These bones form 4 joints that work together to move your arm.
Think of the shoulder complex like a tent. A tent needs poles, pegs and guide ropes for the tent to be able to do its job. The poles and ropes together support and stabilize the tent, just like the muscles and ligaments work together to support and stabilize the shoulder complex.

The shoulder (glenohumeral) joint is a ball and socket joint between the head of humerus and the scapula. A potential problem with the shoulder joint is that it has a small and very flat socket, so the bones offer very little structural support. You can compare the flat socket of the shoulder joint to a golf ball sitting on a golf tee, with the head of humerus being the golf ball, and the socket of the scapula being the golf tee.


The shoulder joint is therefore designed more for movement rather than to take the weight of your body. This finely controlled movement relies on the delicate balance of the shoulder’s capsule, ligaments and muscles.

shoulder complex

Stability of the Shoulder Complex

The shoulder joint receives stability and control from muscles surrounding the joint. These muscles (there are 4 of them) are called the rotator cuff muscles. When evenly balanced they control the slide, glide and roll of the humeral head in its socket to allow painless movement of the arm.

Rotator Cuff

The socket must be positioned correctly in order to maintain smooth coordinated shoulder movement. Therefore it is also important that the muscles that control the scapula are able to control the movement of the socket.

The muscles that control the scapula are mainly attached to the spine and the scapula. They act to control the movement of the scapula around the back of the rib cage. There is more than one joint that comes into play during movement of the shoulder. The humerus moves upwards, the scapula rotates upwards and the clavicle rotates backward for the task to be completed. Timed coordinated movement at all joints must occur, otherwise
problems such as wear/tear can occur. When this occurs, pain may arise.

Rotator Cuff

Combined Movement of the Shoulder Complex: moving the arm out to the side

Depending on the level of your injury, you may or may not have all of your muscles around the shoulder working. In addition to muscle support around the shoulder joint, there is also capsular and ligament control. Ligaments are like rubber bands, which tighten up when stretched and therefore help to control (and restrict unwanted) shoulder joint movement.
The capsule surrounds the shoulder joint and is larger and stronger than ligaments, but has a similar function to them. These may be subjected to wear and tear and overstretching if the shoulder muscles are not able to function properly.
Stretches and positioning of your arm will assist with maintaining flexibility of your entire shoulder complex. Your Physiotherapist will be able to assist you to optimize your shoulder function with a long-term strength and conditioning program.

Understanding Your Shoulder Complex

See more: Tips & Instructions

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