A quantitative computed tomography-based finite element analysis of iatrogenic fracture during shoulder dislocation reduction: biomechanical mechanism and efficacy of prophylactic K-wire fixation.

BACKGROUND: Iatrogenic fracture during closed reduction of anterior shoulder dislocation with greater tuberosity fracture is a serious complication. This study aimed to quantify its biomechanical risk and evaluate prophylactic Kirschner wire (K-wire) fixation. METHODS: We retrospectively analyzed 126 patients (age ≥ 50 years). A patient-specific finite element model of the proximal humerus was created from quantitative computed tomography (QCT) data. Parametric models with different greater tuberosity defect sizes (0-40%) were loaded under pure axial traction (300N) or combined (axial 300 N + lateral) loading. A model with two parallel K-wires (2.5 mm) was also analyzed. FINDINGS: The clinical incidence of iatrogenic fracture was 0.79%. Finite element analysis showed: (1) Greater tuberosity defects drastically reduced structural load capacity; a 10% defect lowered failure load to <10% of intact. (2) Combined loading reduced failure load by 60-70% versus pure traction. (3) The predicted fracture site was consistently the medial surgical neck. (4) Under combined loading, K-wires gave minimal protection (<5% load increase). INTERPRETATION: Greater tuberosity defects critically weaken the proximal humerus by disrupting the lateral tension band. Lateral reduction stress is the primary biomechanical cause of iatrogenic fracture, against which temporary K-wire fixation offers limited protection. For elderly patients, closed reduction should emphasize gentle axial traction while minimizing lateral lever forces.