The Human Disharmony Loop: The Anatomic Source Behind Subacromial Impingement and Pain

<b>Background:</b> Subacromial impingement or pain syndrome (SAPS) is the most common diagnosis for chronic shoulder pain. Current surgeries do not reduce long-term pain, suggesting they miss the root etiology. Previously, we described the Human Disharmony Loop (HDL), where the unique lower trunk innervation to the pectoralis minor (PM) causes scapular dyskinesis and deforms its connections, including tugging the acromion down and impinging the subacromial structures. We hypothesize that SAPS patients who meet HDL criteria would benefit significantly from PM tenotomy with infraclavicular brachial plexus neurolysis (PM + ICN) alone. <b>Methods:</b> SAPS patients who met HDL diagnostic criteria were treated with PM + ICN, with secondary distal neurolysis if needed. Outcomes included pain and shoulder abduction ROM. Six-month follow-up minimum was required. <b>Results</b>: <i>N</i> = 140 patients were included. Median age was 49. Prior surgeries included 27% subacromial decompression/acromioplasty, 21% rotator cuff repair, 16% biceps tenodesis, 4% SLAP repair, 2% labral repair, 7% distal clavicle resection, 10% reverse total shoulder arthroplasty (rTSA), 1% rib resection with scalenectomy, 16% cervical spine fusion, 28% distal neurolysis. Median pain decreased from 8 to 2 and median shoulder ROM increased from 90 to 180 degrees. Positive impingement signs on exam decreased from 100% to 11%. (<i>p</i> < 0.01) <b>Conclusions</b>: In a large series of SAPS patients, evaluation and treatment for the HDL significantly reduced pain and restored motion. These findings suggest that in many patients SAPS may be a subset of the HDL: the ventral PM disturbing the scapula constitutes the anatomic basis and optimal surgical target behind SAPS.