A rare post-traumatic pseudocyst within a humeral shaft non-union: A two-stage surgical management strategy

Abstract

Background: Humeral shaft non-union is a challenging complication, particularly when accompanied by atypical pathology. The presence of an intraosseous pseudocyst within a non-union site is extremely rare and may mimic infection or neoplastic disease, necessitating careful diagnostic evaluation. Case Presentation: A 65-year-old female presented with persistent pain, swelling, and abnormal mobility 18 months after a mid-shaft humeral fracture treated with open reduction and internal fixation. Radiographs and CT imaging revealed an atrophic non-union with a large lytic cystic lesion. Initial surgery through a posterior approach demonstrated a cystic cavity containing 30 mL of serous fluid. The lesion was excised, and the implant was removed. Histopathology confirmed a pseudocyst lacking epithelial lining, and cultures were negative. After exclusion of infection and neoplastic pathology, definitive fixation was performed in a second stage using a posterolateral distal humerus locking compression plate with an onlay fibular graft. Postoperative recovery was uneventful, and functional improvement was achieved. Conclusion: Post-traumatic pseudocyst formation at a humeral non-union site is a rare but important differential diagnosis. A staged surgical approach with diagnostic clearance followed by rigid fixation and biological augmentation can successfully restore stability and function. This case emphasizes the need for high suspicion and thorough workup when lytic lesions are encountered in persistent non-union.