Objective: This study aimed to determine the reliability levels of the radiographic union scale for tibial fractures (RUST) and the modified version of the system, mRUST, for femoral shaft fractures in pediatric and adult patients and to evaluate the value of the scores for total and each cortex in the decision making on fracture union. Methods: A total of 15 orthopedic surgeons scored the radiographs of 24 pediatric and 24 adult patients with femoral shaft fractures that were obtained at 0, 4, 8, 12, and 16 postoperative weeks treated with elastic stable intramedullary nail in pediatric patients and locked intramedullary nail in adult patients using the RUST and mRUST scores. Intra-class correlation coefficient (ICC) was used in the evaluation of reliability of the RUST and mRUST scores. The Fleiss kappa (k) coefficient was used in the agreement between evaluators regarding union decision (united or non-united). The thresholds for RUST and mRUST for radiographic union decision were determined. Receiver operating curves were created to evaluate the contribution of total and individual cortical scores in the decision of united or non-united. Results: Intra- and inter-rater reliabilities of mRUST (ICC: 0.92 and 0.86, respectively) were slightly higher than those of RUST (ICC: 0.81 and 0.77, respectively) with perfect intra- and inter-rater reliabilities for RUST (ICC: 0.92 and 0.90, respectively) and mRUST (ICC: 0.88 and 0.83, respectively) in pediatric patients and substantial intra- and inter-rater reliabilities in adult patients (ICC: 0.80 and 0.76, respectively, for mRUST, and 0.76 and 0.71, respectively, for RUST). At each time point, the mean mRUST and RUST scores were higher for pediatric fractures (p<0.001). The Fleiss k coefficient for union decision was perfect for pediatric fractures (0.88) and substantial for adult fractures (0.79). The total mRUST score had a higher predictive value of union than the total RUST score (area under the curve: 0.984 vs. 0.922 in adult fractures and 0.990 vs. 0.943 in pediatric fractures). A RUST score of ≥10 and mRUST score of ≥12 were excellent predictors of fracture union. Conclusion: Fracture union of simple two-part pediatric and adult femoral shaft fractures treated with intramedullary fixation can be reliably assessed using the RUST and mRUST scores. The diagnostic value of the mRUST score is more evident in adult fractures. Level of Evidence: Level II, Diagnostic Study Cite this article as: Mısır A, Yıldız Kİ, Kızkapan TB, Uzun E, Özçamdallı M, Oğuzkaya S. Reliability of RUST and modified RUST scores for evaluation of union in pediatric and adult femoral shaft fractures. Acta Orthop Traumatol Turc 2021; 55(2): 127-33.

Objectives: This study aims to evaluate the reliability of the radiographic union scale in tibial (RUST) fractures and modified RUST (mRUST) fractures in pediatric forearm fractures treated with elastic stable intramedullary nail (ESIN) and to investigate the effect of the experience of surgeon, thresholds for union, and delayed union decisions. Patients and methods: In this retrospective study, radiographic images of 20 patients (10 males, 10 females; mean age 8.64.3; range, 4 to 11 years) with forearm fractures treated using ESIN between January 2013 and December 2018 were scored by 20 observers based on the RUST and mRUST scores. The observers scored the radiographs at immediate postoperative period, and at 4-, 8-, and 12-week follow-up. Intraand interobserver agreement for each cortex, RUST, and mRUST were evaluated using intraclass correlation coefficient (ICC). The Fleiss' kappa (k) coefficient was used in the agreement between evaluators regarding union decision. Receiver operating curves were created to determine the thresholds for radiographic union and delayed union. Results: Intraand interobserver reliability of the mRUST score (ICC: 0.84 and 0.79) were slightly higher than that of the RUST score (ICC: 0.80 and 0.72). Pediatric orthopedic and trauma surgeons had slightly higher agreement than the residents and general orthopedists for the total mRUST and RUST scores of the eight-week radiographs. Mean RUST and mRUST scores at the union for all fractures were 10.2 +/- 3.4 and 13.0 +/- 2.1, respectively. Kappa value for union was moderate (0.74). The total mRUST score had a higher predictive value for union than the total RUST score (area under the curve: 0.986 vs. 0.889). A mRUST score of >= 12 and RUST score of >= 9 were considered as the predictors of union. In addition, a mRUST score of <= 7 and RUST score of <9 were considered as the predictors of delayed union. Conclusion: A moderate agreement for both RUST and mRUST scores was found. However, the agreement for mRUST was found to be slightly higher. Healing and union of forearm fractures treated with ESIN can be reliably assessed using RUST and mRUST.