Correlation between RUST assessments of fracture healing to structural and biomechanical properties

Abstract

Radiographic Union Score for Tibia (RUST) and modified RUST (mRUST) are radiographic tools for quantitatively evaluating fracture healing using a cortical scoring system. This tool has high intra-class correlation coefficients (ICCs); however, little evidence has evaluated the scores against the physical properties of bone healing. Closed, stabilized fractures were made in the femora of C3H/HeJ male mice (8-12 week-old) of two dietary groups: A control and a phosphate restricted diet group. Micro-computed tomography (µCT) and torsion testing were carried out at post-operative days (POD) 14, 21, 35, and 42 (n = 10-16) per group time-point. Anteroposterior and lateral radiographic views were constructed from the µCT scans and scored by five raters. The raters also indicated if the fracture were healed. ICCs were 0.71 (mRUST) and 0.63 (RUST). Both RUST scores were positively correlated with callus bone mineral density (BMD) (r = 0.85 and 0.80, p < 0.001) and bone volume fraction (BV/TV) (r = 0.86 and 0.80, p < 0.001). Both RUST scores positively correlated with callus strength (r = 0.35 and 0.26, p < 0.012) and rigidity (r = 0.50 and 0.39, p < 0.001). Radiographically healed calluses had a mRUST ≥13 and a RUST ≥10 and had excellent relationship to structural and biomechanical metrics. Effect of delayed healing due to phosphate dietary restrictions was found at later time points with all mechanical properties (p < 0.011), however no differences found in the RUST scores (p > 0.318). Clinical relevance of this study is both RUST scores showed high correlation to physical properties of healing and generally distinguished healed vs. non-healed fractures. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:945-953, 2018.

Virtual Mechanical Testing from Low-Dose CT Scans Predicts Tibial Fracture Time to Union and Outperforms Subjective Outcomes Scoring

“…This study also suggests some potential difficulties with the widely used RUST score. Our RUST scores intra-class correlation coefficient (ICC = 0.727) was comparable to the RUST repeatability recently reported by many other investigators, 9,10,22,23,28,29 but was not as good as the original reports. 8 Notably, none of these reports show that RUST scoring meets the strictest definition of ICC>0.9 for an assessment to be deemed "reasonable for clinical measurements", 30 even in studies using simple transverse osteotomies in animal models.…”

“…8 Notably, none of these reports show that RUST scoring meets the strictest definition of ICC>0.9 for an assessment to be deemed "reasonable for clinical measurements", 30 even in studies using simple transverse osteotomies in animal models. 22,23 Furthermore, our data indicates that RUST scores may not have prognostic validity for predicting longitudinal outcomes, an issue that was raised early in the history of the RUST scoring, 31 but has been neglected in favor of repeated examination of inter-and intra-rater reliability. Interpreted cautiously, our data supports the general conclusion that RUST is useful for differentiating between healed and unhealed fractures, but may be lacking in sensitivity and specificity as a surrogate measure of callus structural integrity, particularly in early healing (non-united RUST < 10).…”

“…18 A virtual torsion test was chosen as the summary measure of mechanical integrity in each model. Torsional stiffness relative to intact paired controls is often used as a summary indicator of healing in preclinical models, [19][20][21][22][23] because it is direction independent. 24…”

Smoking Alters Inflammation and Skeletal Stem and Progenitor Cell Activity During Fracture Healing in Different Murine Strains

“…( 31 ) The formation of calluses and the visibility of fracture lines on radiographs of femora were observed. Afterwards, the RUST score, ( 16 ) which has been proved to be a reliable and valid strategy to assess fracture healing in both clinical and animal studies, ( 32,33 ) was used to provide a way for quantification and statistical analysis. Our results showed that CS 129X1/SvJ mice exhibited less callus formation and visible fracture lines, while other groups showed robust healing.…”

A quantitative serum biomarker of circulating collagen X effectively correlates with endochondral fracture healing

“…Orthopedic surgeons rely on subjective physical examinations, clinical experience, and radiographic techniques to visually assess the development of mineralized tissue in order to diagnose healing progression. [5][6][7][8] Delayed healing and non-union are clinical diagnoses based on symptoms of pain, instability, and poor radiographic bone healing at a time point after which healing should be expected. Criteria that define delayed union and non-union in clinical settings are variable, and there remains no single consensus definition.…”