The sternoclavicular joints can become axially compressed by poor posture resulting in an increased thoracic kyphosis and anteriorly place shoulder joints. This anterior position results in a shortening of the pectoralis major muscle and a chronic stretching of the posterior musculature as well. The shoulder as they move anteriorly also cause an internal rotation of the humorous which in turn causes a shortening of the clavicular head of the pectoralis major muscle. This shortening over time allows for the pectoralis major muscle to undergo a further shortening and more anterior stress is applied to the postural kyphosis. You might want to review Dr. V. Janda's work on the clinical implications of this muscular imbalance. The postural aberration causes the skull and cervical spine to translate anteriorly resulting in the scalene muscles to reverse their function which further accentuates the translatory glide in the sagittal plane. Another consequence of this scenario is activation or compromise of the back force transmission system (BFTS), see N. Bogduk's text or the Proceedings of the First Interdisciplinary Congress on Low Back Pain and its Relationship to the Sacro-iliac joint. The back force transmission system, when compromised can and will result in compensatory low back pain, but if you are not knowledgeable about this system, and you should be because that is how we all lift, then you will be a doctor of symptoms and not cause. Chiropractors are supposed to treat the cause and not the symptoms -- right? How many symptoms do you treat?
The postural scenario described above also shortens the distance from the sternum to the public ramus and this causes remote contracture or hypertonicity of the rectus abdominus muscle, which on a time continuum will further accentuate the thoracic deformity and the patient will have a positive self-perpetuating reflex loop that will keep them in this state of dysfunction forever. The interesting thing about the rectus situation is that is also causes contraction of the external oblique and transversus abdominus muscles, which coincidentally are major contributors to the back force transmission system -- another direct connection to the cause of the patient's low back pain. The external oblique muscles are the prime movers (rotation) of the lumbar spine and it is their contraction that causes multifidus to become active as an antagonist during trunk motions. It must be remembered that multifidus is not a rotator of the lumbar spine, see Bogduk, Clinical Anatomy of the Lumbar Spine.
Remember that all of the above could be initiated by the S-C joint dysfunction or that S-C joint dysfunction could be the result of any portion of the above failing to participate in its normal biomechanical state. The BFTS continues from the fascia of the trapezius, latissimus dorsi, the thoraco-lumbar fascia and conjoined area of the external oblique and transversus abdominus to form the lateral raphe. The systems continue interior as the fascial coverings of the gluteus maximus, hamstrings, and the gastro-soleus group to insert into the calcaneus. This means that it is very possible that the illusion of a flat foot is the result of some dysfunction as remote as the S-C joint. Does the patient need an orthotic or do you treat the cause? I really wonder.
Keith Innes, DC
Scarborough, Ontario