Usefulness of serum D-dimer for preoperative diagnosis of infected nonunion after open reduction and internal fixation

Purpose: Infected nonunion after open reduction internal fixation (ORIF) is a serious complication. The aim of this study was to evaluate the usefulness of serum D-dimer for preoperative diagnosis of infected nonunion. Patients and methods: Patients undergoing debridement and external fixation for infected nonunion (n=32) and replacement of internal fixation due to aseptic failure (n=34) were enrolled and compared in this retrospective study. The optimum cutoff value of D-dimer for identification of infected nonunion was determined by calculating the Youden J statistic. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of four preoperative laboratory parameters-serum D-dimer level, white blood cell (WBC) count, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP)-for diagnosis of infected nonunion were compared. Results: Serum D-dimer level was significantly higher in patients with infected nonunion than in patients with aseptic nonunion: 2.62 mg/mL (range, 0.13-11.90 mg/mL) vs 0.35 mg/mL (range, 0.07-6.46 mg/mL; p<0.001). WBC count, CRP, and ESR demonstrated sensitivity of 12.5% (95% CI: 4.08-29.93), 40.6% (95% CI: 24.22-59.21), and 56.3% (95% CI: 37.88-73.16), respectively, and specificity of 94.1% (95% CI: 78.94-98.97), 88.2% (95% CI: 71.61-96.16), and 85.3% (95% CI: 68.17-94.46), respectively. Using the Youden index, 1.70 mg/mL was determined as the optimal threshold value for serum D-dimer for the diagnosis of infected nonunion. The sensitivity and specificity of serum D-dimer (>1.70 mg/mL) were 75.0% (95% CI: 56.25-87.87) and 91.2% (95% CI: 75.19-97.69). Conclusions: Serum D-dimer level may be useful for preoperative prediction of infected nonunion in patients after ORIF.