Fracture-isthmus diameter ratio predicts delayed union in tibial nailing.

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 anteroposterior (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; receiver operating characteristic (ROC) analysis determined a cutoff.

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 (area under the curve [AUC] 0.74); delayed union was more frequent when FI ≥1.43 than <1.43 (27/39 [69.2%] vs 7/27 [25.9%], odds ratio [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.