The Thoracic Spine and Shoulder Mechanics
Shoulder pain is one of the most common complaints of those contending with joint pain or musculoskeletal issues. Reaching over head or behind your back may become difficult, putting your seatbelt on or reaching into the backseat becomes painful. A number of things could be affecting these movements, however the focus of this post will be primarily on the upper back (thoracic spine) and its influence on shoulder motion. These two regions interact to a great degree, and altering the mechanics at one, will almost always affect the other.
The thoracic spine consists of twelve vertebrae and is the region between your neck and lower back. The shoulder blade (scapula) sits on top of a section of these vertebrae and contains the socket aspect of your shoulder joint. If your thoracic spine assumes a particular position, let’s say a flatter and less rounded position, the socket now changes orientation as well. The position of the socket has a huge influence on how your shoulder moves. Now, you might ask how or why the thoracic spine would attain a flat shape to begin with, a fair question. The classic cue of “shoulders back and down” or “stand up straight” often results in this thoracic position. Reason being that compression of the scapula against the thorax results in a flatter representation. The scapula literally pushes the ribs and vertebrae forward, flattening them in the process. Under this circumstance, the scapula has become glued to the thoracic spine and rib cage, the socket is pointing more sideways than forward, and the head of the humerus (ball of the ball-and-socket joint) follows suit.
If you need to reach to the side, no problem, the joint is capable of that in this position. If you need to reach somewhat more forward, or behind you, that becomes a problem if the thoracic shape and scapula orientation cannot change. The outward facing ball and socket are limited in their ability to turn inward, a direction required more so in those problematic directions.
Thoracic kyphosis, a normal curvature of the spine, is often accused of being the problem with shoulder issues. The explanation being the kyphosis is too prominent and limiting shoulder motion, and while this may not be entirely inaccurate it misses some of the nuance. Kyphosis is not equally distributed across the thoracic spine in most cases, so blanketing folks with the cue to squeeze their shoulders back and down might be oversimplifying. We want the thoracic spinal vertebrae to each move independent of one another. We want those vertebrae to movement independent of the scapula, which can move independent of the humerus (the upper arm). Those options must be available for less restricted, and more capable movement. There are times when glueing segments together can be useful, like when lifting something heavy, but that is a different circumstance.
The shape of the thoracic spine has a huge influence on the movement of the shoulder. Certain shapes allow for particular motions, and altering the shape as needed is what we might consider adaptability. The greater your ability to adapt, the more capable you are. There is a tremendous degree of subtlety in how we move, blanket statements and cues rarely acknowledge the nuances. Performing exercises and movements that create separation between body regions and allows them to move relative to one another, facilitates fluid movement options. This is where health resides.
Austin Ulrich, Physical Therapist
