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

Background/Objectives: 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, unifying musculoskeletal and neurologic 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. Methods: Ten patients of diverse etiologies presented with a similar constellation of complaints. Patients included: female athlete, female with macromastia, male bodybuilder, post-radiation breast cancer, postoperative 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. Patients demonstrated varying degrees of arm neuropathy, subacromial impingement, occipital headaches. Patients failed all prior treatments by multiple subspecialists including surgery. Each patient underwent isolated open PM tenotomy. Results: PM tenotomy completely resolved presenting signs and symptoms in all patients. This included elimination of shoulder, upper back, and neck pain, clearance of concomitant neuropathy, resolution of rotator cuff impingement, restoration of full motion, and eradication of headaches. Response to surgery was rapid, dramatic, and durable. Conclusions: 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 the neck to the fingertips of chronic pain, neuropathy, and weakness. These challenging patients may benefit dramatically from isolated PM tenotomy.