The Human Disharmony Loop: A Case Series Proposing the Unique Role of the Pectoralis Minor in a Unifying Syndrome of Chronic Pain, Neuropathy, and Weakness

<b>Background/Objectives</b>: Many patients evaluated by shoulder specialists suffer from intractable pain, neuropathy, and weakness. The pectoralis minor (PM) remains the only scapula muscle to receive lower trunk (C8-T1) input. We propose a novel syndrome: the Human Disharmony Loop. This model portrays how this unique PM innervation causes scapular dyskinesia, which deranges the anatomy of the upper limb girdle and produces a refractory symptom complex of pain, neuropathy, and weakness. We hypothesize that certain patients with historically intractable symptoms of the upper limb girdle may benefit from PM tenotomy. <b>Methods</b>: Ten patients of diverse etiologies presented with a similar constellation of complaints. The patients included a female athlete, a female with macromastia, a male bodybuilder, and patients with post-radiation breast cancer, post-operative shoulder arthroplasty, interscalene block injury, cervical spine disease, persistent impingement after rotator cuff repair, direct traction injury, and occupational disorder. All patients exhibited coracoid tenderness, scapula protraction with internal rotation and anterior tilt, and pain involving the neck, shoulder, and upper back. The patients demonstrated varying degrees of arm neuropathy, subacromial impingement, and occipital headaches. The patients failed all prior treatments by multiple subspecialists, including surgery. Each patient underwent isolated open PM tenotomy. <b>Results</b>: In all ten patients, PM tenotomy substantially reduced shoulder, upper back, and neck pain, cleared concomitant neuropathy, restored full motion, and eradicated occipital headaches. The response to surgery was rapid, dramatic, and durable. <b>Conclusions</b>: The unique asymmetric neurologic innervation to the sole ventral stabilizer of the scapula, the pectoralis minor, predisposes the human shoulder to neurologic and musculoskeletal imbalance. This produces the Human Disharmony Loop: a clinical syndrome spanning from the neck to the fingertips, with chronic pain, neuropathy, and weakness. These challenging patients may benefit dramatically from isolated PM tenotomy.