Neglected proximal humerus fracture nonunion: A narrative review.

Neglected proximal humerus fracture nonunion remains an uncommon but functionally devastating complication, arising from delayed presentation, missed diagnosis, or inadequate primary fixation. When nonunion occurs in this setting, it rarely reflects a single causative factor but instead represents a compounded pathological process involving mechanical instability, biological compromise, and progressive soft tissue contracture - each amplified by the duration of neglect. Contemporary understanding recognises that while most proximal humerus nonunions are mechanically driven, neglected cases are further complicated by humeral head ischemia, metaphyseal bone loss with distorted anatomy, and rotator cuff deficiency, rendering their management among the most technically demanding challenges in shoulder surgery. This narrative review provides a comprehensive and contemporary overview of the evaluation and management of neglected proximal humerus fracture nonunion. Epidemiology, pathoanatomy, and risk factors are discussed, highlighting the critical interplay between mechanical and biological determinants of failure. Classification systems including Checcia's morphological grouping and Valencia's distinction based on humeral head integrity are evaluated in the context of their practical surgical relevance. A structured diagnostic work-up incorporating plain radiography, CT, and MRI is outlined, with emphasis on the four determinants that govern surgical decision-making: patient age and functional demand, humeral head viability, bone stock, and rotator cuff integrity. Evidence-based surgical strategies are critically appraised, encompassing revision ORIF with structural bone grafting for biologically favourable younger patients, and reverse shoulder arthroplasty as the emerging gold standard for elderly patients with head nonviability or rotator cuff insufficiency. The paradigm shift from hemiarthroplasty to reverse shoulder arthroplasty is emphasised, alongside principles of prevention through anatomical primary fixation.