BACKGROUND: Intramedullary nailing is widely acknowledged as the preferred treatment for tibial shaft fractures. However, delayed union remains common in non-isthmal patterns. We aimed to assess the factors and imaging parameters associated with nonunion or delayed union following intramedullary nailing in these patients. METHODS: This retrospective study included patients with non-isthmal tibial shaft fractures who underwent intramedullary nailing from 2015 to 2020. The fracture site diameter to the isthmus canal diameter ratio (FI ratio) was measured on pre- and postoperative AP radiographs. Delayed union was defined as no union at 6 months, with union by 12 months. The variables were tested with univariate analyses and multivariable logistic regression; ROC analysis determined a cut-off. RESULTS: A total of 66 patients were included, and delayed union occurred in 34 (51.5%). Forty-seven patients sustained infra-isthmal fractures, while 19 patients experienced supra-isthmal fractures. The postoperative FI ratio was higher in the delayed-union group (median 1.67 vs 1.36; p=0.001) and was the only independent predictor on multivariable analysis (p=0.007). A postoperative FI ratio ≥1.43 predicted delayed union with sensitivity 0.79 and specificity 0.66 (AUC 0.74); delayed union was more frequent when FI ≥1.43 than <1.43 (27/39 69.2% vs 7/27 25.9%, OR=6.43). Intraoperative blood loss was associated with univariate testing (p=0.013) but not after adjustment; nail-canal ratio, fracture length, and screw-fracture distance were not significant. CONCLUSION: The postoperative FI ratio is a feasible indicator of delayed union in patients who received intramedullary nailing for supra-isthmal or infra-isthmal tibial shaft fractures. A postoperative FI ratio ≥ 1.43 indicates a significantly higher risk of delayed union. In such cases, it may be recommended that patients undergo prolonged protected weight-bearing and shortened follow-up intervals.
Kuo et al. (2026) studied this question.