The Human Disharmony Loop: The Central and Villainous Roles of the Scapula and the Pectoralis Minor in Chronic Pain

Many patients suffer from chronic pain of the shoulder, neck, upper back, and/or arm. They may be diagnosed with fibromyalgia, complex regional pain syndrome, myofascial pain, thoracic outlet, subacromial pain, cervical radiculopathy, cervicogenic headaches, post-mastectomy pain, occupational shoulder disorder. These remain mysterious and challenging. The pectoralis minor (PM) is the only muscle of the scapula innervated by the lower trunk, potentially a sequela of the evolution from quadrupeds to bipeds. The Human Disharmony Loop (HDL) is a clinical model where this neurologic asymmetry renders the scapula prone to protraction, which pathologizes the full upper limb girdle and generates headaches and neck stiffness, upper back tightness, shoulder weakness, and hand numbness/tingling. We hypothesize some of the above diagnoses are manifestations of the HDL. 318 patients with the above who met HDL diagnostic criteria underwent PM tenotomy with brachial plexus neurolysis (PM + ICN). At 12 months, average pain decreased from 7.3/10 to 2.1/10, average shoulder abduction increased from 96 to 170 degrees, occipital headaches decreased from 77% to 2%. In summary, humans may be plagued by chronic pain because our scapula tends to protract, its ancestral quadrupedal state. Certain intractable patients may benefit substantially from PM + ICN.