The thoracic spine is the only system in the body that directly impacts four other systems. These systems from top to bottom include the cervical spine, thoracic cage (ribs), scapula/clavicle and lumbar spine. In addition, it shares many muscles with the shoulder and cervical segments. Very few individuals display the required thoracic mobility needed to optimize the functioning of these four systems. Thoracic mobility problems can thus be a possible root of many problems from neck and shoulder to low back pain. The problem lies in the fact that the human body is very good at compensating, sacrificing movement quality in order to gain movement quantity. So when thoracic mobility is lost, these other segments must undergo additional biomechanically disadvantageous movement.
To show the importance of thoracic spine extension, shoulder pain will be used as an example. Due to the interdependent relationship of the glenohumeral joint, the scapula, and the thoracic spine, all three of these systems should be examined for problems causing the associated pain. Relevant to this post, the orientation of the thoracic spine determines scapular positioning, creating the platform for normal glenohumeral movement. If a certain degree of thoracic kyphosis is present, the curvature of the ribs interferes with the scapular upward rotation and depression necessary to complete shoulder flexion. To illustrate this, simply crouch over, slumping your shoulders forward (by the way, what you just did is called a “crunch”, but that topic will have to wait for a future post) and raise your arms forward as high as you can without extending your low back. Now, stick your chest out and stand as upright as possible and perform the same movement. Proper scapular positioning allows prerequisite stability for the optimal degrees of posterior tilt and upward rotation as the arm goes into either flexion or abduction. Further down the chain, this allows the humerus to remain centered in the glenoid as the motion occurs preventing excessive impingement.
When the scapula is not moving or is not positioned properly, shoulder pain can develop, as accessory movements including excessive anterior and superior glide must occur to complete movements. In addition, when addressing range of motion limitations in the glenohumeral joint, thoracic mobility must again be taken into account. There are instances where either shoulder internal or external rotation deficits are indeed due to a problem confined to the joint, but more often than not the problem lies elsewhere. An upright posture and some thoracic extension is required for both patterns, so if this is restored range of motion will automatically improve without ever touching the glenohumeral joint.
The shoulder pain example primarily looked at limitations in extension, but now let’s briefly look at what happens when rotation is limited. Thoracic spine rotation is a combo of extension on one side and flexion of the other. That means if thoracic extension is limited, rotation will be limited as well. Rotation should primarily occur throughout the thoracic rather than the lumbar spine. This is due to the anatomical differences in the two regions. The apophyseal joints which connect the vertebrae are orientated in the frontal plane throughout the thoracic spine, making them better suited to rotation, whereas their transition to a sagittal plane orientation in the lumbar spine makes them better suited for flexion and extension. When looking at rotational sports, one can see the importance of adequate thoracic rotation. If rotation is limited, it will occur somewhere else -- most likely in the lumbar spine. This creates a predisposition towards low back pain as the lumbar spine is being asked to do extra work to make up for the mobility deficit in the thoracic spine.
That concludes Part 1; in Part 2, I will explain how to assess thoracic mobility and sort out what the root cause of the limitation is.
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