JOT - 2026-06-22 - Journal Article
Reliability of modified Radiographic Union Scale for Tibial Fractures (mRUST) Scores in Ballistic Lower Extremity Trauma.
Sun P, Eurich J, Zhang D, Schimizzi G, Christiano A, Erdman MK
Topics
Key Takeaway
Inter-rater reliability of mRUST in ballistic femoral and tibial shaft fractures is only moderate (ICC 0.64 and 0.61, respectively), and a 3-month mRUST score <8 predicts nonunion with 100% sensitivity for femur but only 71% sensitivity for tibia.
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Summary
This study evaluated mRUST inter- and intra-rater reliability across three fellowship-trained trauma surgeons and its predictive value for nonunion at 9 months in ballistic AO/OTA 32 and 42 fractures treated with IMN at a single Level I center. Inter-rater ICC was 0.64 for femur and 0.61 for tibia; intra-rater ICC was 0.87 and 0.81, respectively—lower than published values for blunt trauma. A 3-month mRUST <8 predicted femoral nonunion with sensitivity 1.00/specificity 0.83, but tibial nonunion with only sensitivity 0.71/specificity 0.94.
Key Limitation
The nonunion prediction analysis is severely underpowered with only 28 femoral and 25 tibial cases having both a 3-month mRUST and determinable 9-month union status, making the sensitivity and specificity estimates unstable.
Original Abstract
OBJECTIVES
To investigate the reliability of the modified Radiographic Union Scale for Tibial Fractures (mRUST) scores in ballistic lower extremity trauma and to assess the ability of 3-month post-op mRUST in predicting union status at 9-months.
METHODS
Design: Retrospective review.
SETTING
Single Level 1 Trauma Center.
PATIENT SELECTION CRITERIA
Patients that sustained a ballistic femoral (AO/OTA 32) or tibial shaft fracture (AO/OTA 42) aged 18 or over and were treated with intramedullary nailing between 2019 and 2023.
OUTCOME MEASURES AND COMPARISONS
Inter- and intra-rater reliability of mRUST score measurements between three fellowship trained orthopaedic trauma surgeons was assessed. The sensitivity and specificity of predicting nonunion at 9-months postoperatively from mRUST 3-months postoperatively was assessed. Inclusion criteria for nonunion analysis required patients to have a 3-month mRUST score as well as a determinable union status.
RESULTS
107 ballistic femoral shaft fractures (203 radiograph sets; 100 male; mean age 31 [18-56]) and 62 ballistic tibial shaft fractures (153 radiograph sets; 51 male; mean age 33 [18-61]) were used to calculate reliability metrics. Inter-rater reliability (Intraclass Correlation Coefficient, ICC) of mRUST in ballistic femoral shaft fractures was 0.64 (95% CI[0.34,0.80]). Intra-rater reliability of mRUST in ballistic femoral shaft fractures was 0.87 (95% CI[0.85,0.89]). Inter-rater reliability of mRUST in ballistic tibial shaft fractures was 0.61 (95% CI[0.43,0.73]) and intra-rater reliability of mRUST in ballistic tibial shaft fractures was 0.81 (95% CI[0.77, 0.84]). In 28 ballistic femoral shaft fractures (24 male; mean age 31 [18-46]), an mRUST-3MO < 8 predicted nonunion in ballistic femoral shaft fractures with a sensitivity of 1.00 and specificity of 0.83. In 25 ballistic tibial shaft fractures (17 males; mean age 34 [18-61]), an mRUST-3MO < 8 predicted nonunion with a sensitivity of 0.71 and specificity of 0.94.
CONCLUSIONS
This study suggests that the modified Radiographic Union Scale for Tibial Fractures (mRUST) scores possess a lower inter and intra rater reliability in ballistic fractures compared to blunt fractures. They may predict union at 9-months well in ballistic femoral fractures, but only moderately in ballistic tibia fractures.
LEVEL OF EVIDENCE
Diagnostic Level III.