Common Injuries and Treatments
Most people visualize the shoulder as a "ball and socket" joint similar to the hip. In truth, there are 4 joints that make up the shoulder joint complex and only the scapulohumeral joint looses resembles a "ball and socket" joint.
The 4 joints are:
- The joint where the upper arm bone (humerus) attaches to the shoulder blade (scapula) - called the scapulohumeral joint - is a very loose "ball and socket" joint. The round upper end of the humerus (the "ball") attaches to a flat surface on the scapula called the acetabulum (the "socket"). This loose attachment is stabilized by a strong group of ligaments (attach bone to bone) called the capsule. And the "socket" is deepened by a band of fibrous tissue called the labrum. This soft tissue stability allows for a large range of motion, but also predisposes this joint to lots of injuries.
- The bony part on the top of the shoulder is the joint where the collarbone (clavicle) attaches to the shoulder blade (scapula). It's called the acromioclavicular joint and is part of the bony connection that anchors the shoulder to the body. This joint is stabilized by a very strong ligament (attaches bone to bone) and has only a very small amount of movement.
- The joint where the collarbone (clavicle) attaches to the breast bone (sternum) is called the sternoclavicular joint. It also is important in anchoring the shoulder to the body and is stabilized by a strong ligament (attaches bone to bone) allowing very little movement.
- The joint between the shoulder blade (scapula) and the back of the rib cage (thorax) is called the scapulothoracic joint. Most of the key muscles that stabilize and move the shoulder are anchored on the shoulder blade. Fluid movement of the scauplothoracic joint is key for proper shoulder mechanics.
The shoulder moves in 3 main planes of movement allowing a lot of motion. It can move forward and back, in and out, as well as rotate in and out. The arm has a large range of movement so you can reach behind your back to tuck in a shirt and reach fully overhead to change a light bulb. With all of this movement, there is a great need for appropriate muscle strength to control and drive this motion.