The Anatomy of the Shoulder

We ask a lot of our shoulder joints. We need it to lift, carry or swing or throw whatever we choose. And we need it to be incredibly strong to support our body weight in an exercise like a push-up or swimming. But that flexibility has to come at a cost somewhere and the compromise is that the shoulder is, comparatively, far less stable. This is less stable than in comparison to the other ball-and-socket style joint that we have in our body – the hip joint. The other part of our shoulder is the acromioclavicular (AC) joint located at the top of the shoulder. This is the connection point between the collar bone (clavicle) and acromion of the scapula. We’re going to explore the shoulder in a little more detail and explain why this is the case.

As alluded to, the shoulder (or glenohumeral joint) is comprised of a ball and socket style arrangement. The ball is formed by the head of the humerus, our upper arm bone, and the socket is formed by the glenoid fossa of the scapula bone. That’s right – the shoulder blade that we can feel on the upper part of our backs extends all the way out to the widest part of our upper body and forms a shallow socket for the humerus to rest in. The reason this joint is far less stable than the hip joint is the nature of this shallow glenoid fossa. The similar structure in the hip has a far deeper socket.

There is benefit in this in the shoulder is that it allows for a large range of movement. Try this to visualise it better – you can take your arm up above your head, you can extend the arm out in front of you, plus you should be able to take your arm behind your back.

Because we have less bony support in the shoulder, our body is designed to gain more stability through other means. Namely, ligaments and muscles. The ligaments are thick, stable structures that hold the ball in the socket snuggly. The muscles contract to allow for movement of the arm in all directions. As you can see from the picture below, there are ligaments all around the shoulder that help to offer stability in a whole host of different positions the arm may find itself in. Likewise, we have a number of muscles that cross the shoulder joint and therefore impact on it.

The bicep, tricep, pectoralis, latissimus dorsi, rotator cuff, trapezius muscles all cross the shoulder joint in different positions and allow the shoulder to move in a variety of ways. They also act in a way to add stability for the shoulder, to reinforce the role of the ligaments.

If you’ve got pain in your shoulder, or if you feel something could be improved or optimised within the shoulder, please reach out to one of our Instinct Health physios today and let’s get your shoulder moving more freely, more easily and with greater strength!

Don’t forget to check out our Pilates and massage services while you’re here!

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The Anatomy of the Shoulder