Incidence, risk factors, and consequences of radiographic pin migration after pinning of pediatric supracondylar humeral fractures

Current literature on pin migration is inconsistent and its significance is not understood. We aimed to investigate the incidence, magnitude, predictors, and consequences of radiographic pin migration after pediatric supracondylar humeral fractures (SCHF). We retrospectively reviewed pediatric patients treated with reduction and pinning of SCHF at our institution. Baseline and clinical data were collected. Pin migration was assessed by measuring the change in distance between pin tip and humeral cortex on sequential radiographs. Factors associated with pin migration and loss of reduction (LOR) were assessed. Six hundred forty-eight patients and 1506 pins were included; 21%, 5%, and 1% of patients had pin migration ≥5mm, ≥10mm, and ≥20mm respectively. Mean migration in symptomatic patients was 20mm compared to a migration of 5mm in all patients with non-negligible migration (P<0.001). Pin migration>10mm was strongly associated with LOR [odds ratio (OR)=6.91; confidence interval (CI), 2.70–17.68]. Factors associated with increased migration included increased days to pin removal (β=0.022; CI, 0.002–0.043), migration outwards versus inwards (=1.02; CI, 0.21–1.80), and BMI>95th percentile (OR=1.63; [1.06–2.50]). Factors not associated with migration included cross-pinning, number of pins, and fracture grade. In summary, we identified a 5% incidence of radiographic pin migration≥10mm and determined the factors associated with it. Pin migration became radiographically significant at >10mm where it was strongly associated with LOR. Our findings contribute to the understanding of pin migration and suggest that interventions targeting pin migration may decrease the risk of LOR.