Most people take their shoulders for granted until the day they start hurting.
Your shoulder is really an amazing piece of engineering – and perhaps best appreciated when taken to the limits of its abilities such as during a baseball pitch.
Your shoulder is probably the most complex joint in your body – and it certainly is the one which allows the most movement. Let’s compare your shoulder to a joint in your finger and your hip joint. Your finger joint can only move in one direction. It can be straight, fully bent, or somewhere in between. There is no movement from side to side, and there is no rotation… so it’s pretty much comparable to a hinge on a door. It doesn’t do much, but it is very stable.
Your hip is a little more complex. It can swing forward and backwards, move side to side and do some twisting and circular movements. This is a huge step up from your finger joint, and is made possible by the ball and socket arrangement of your bones. It is very much like a ball and hitch that you see on many vehicle trailers. The ball is secured deep within the hitch and allows movement in several directions. Because of the increased capacity for motion, the hip also requires many more muscle groups to stabilize it than the finger does.
Finally we come to the shoulder joint. Unlike the hip joint, the ball is very large compared to the socket, and the socket is flat and shallow. It is comparable to a golf ball on a tee. This allows more freedom of motion than any other joint in the body, but at the sacrifice of stability. You can move your shoulder in a full circle in several different planes and directions, plus it can rotate in place. In order to make this possible, there is a complex arrangement of muscles and ligaments which hold everything together. Unlike the hip, where the socket is anchored solidly to the core of your skeletal system, your shoulder socket is on your shoulder blade, which itself is essentially just floating around on top of your ribs. The only bony connection between your shoulder and the rest of your body is at the collarbone! This creates a great dependence on ligaments and muscles to hold everything together and comes with some consequences.
The good news is your shoulder is extremely versatile and can do some pretty amazing things. That bad news is that it is relatively unstable, and can be easily injured. Okay, you have probably endured enough anatomy for now – thank you for humoring me! In the next several posts I will discuss some specific shoulder problems and some possible solutions. Be sure to check it out!