Comparative Discriminative Performance of Cast, Gap, and Three-Point Indices in Predicting Malunion in Elderly...

Background and Objectives: Distal radius fractures (DRFs) are among the most common upper-extremity injuries in the elderly, with malunion leading to long-term pain and disability. This study aimed to compare the discriminative performance of the Cast Index (CI), Gap Index (GI), and Three-Point Index (TPI) for predicting malunion during follow-up after closed reduction and casting in elderly patients with dorsally displaced DRFs. Materials and Methods: This study retrospectively analyzed 274 patients aged ≥65 years (mean 73.6 ± 6.5 years) with dorsally displaced Arbeitsgemeinschaft für Osteosynthesefragen/Orthopaedic Trauma Association (AO/OTA) 2R3A fractures treated conservatively between 2018 and 2023. Standard posteroanterior and lateral radiographs were evaluated immediately post-reduction, at 7-10 days, and at 4 weeks. Cast, Gap, and Three-Point Indices were measured independently by two observers, and the mean values were analyzed. Receiver operating characteristic (ROC) analysis was used to evaluate discriminative performance for the detection of malunion. Subgroup analyses were performed based on fracture stability according to La Fontaine criteria. Results: At the final follow-up, 136 fractures (49.6%) maintained acceptable alignment, while 138 fractures (50.4%) experienced malunion. There was no significant difference in radiographic parameters between groups immediately post-reduction or at 7-10 days. The Gap and Three-Point Indices were significantly higher in the malunion group at 7-10 days and at 4 weeks (p < 0.001), but the Cast Index showed no significant between-group difference. At 7-10 days, the Gap Index [Area Under the Curve (AUC) = 0.641; cut-off = 0.33] and the Three-Point Index (AUC = 0.640; cut-off = 1.51) demonstrated modest discriminative ability. In stable fractures, both indices were statistically significantly higher in the malunion group, whereas in unstable fractures, only the Three-Point Index was statistically significantly higher in the malunion group (p < 0.001). Conclusions: The Gap and Three-Point Indices showed greater discriminative ability than the Cast Index for malunion after conservative management of DRFs in elderly patients. Thresholds of GI ≥ 0.33 and TPI ≥ 1.51 at 7-10 days may serve as practical quantitative indicators to identify patients who may warrant closer follow-up and possible cast reassessment in conjunction with standard radiographic assessment and clinical judgment.