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Virtual Mechanical Testing Based on Low-Dose Computed Tomography Scans for Tibial Fracture

A Pilot Study of Prediction of Time to Union and Comparison with Subjective Outcomes Scoring

Dailey, Hannah L. PhD1; Schwarzenberg, Peter MS1; Daly, Charles J. BSc2; Boran, Sinéad A.M. MB(BCh), BAO(BCh), FRCSI3; Maher, Michael M. MD, FRCSI3; Harty, James A. MB(BCh), BAO, MSc, FRCSI3

doi: 10.2106/JBJS.18.01139
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Background: Quantitative outcomes assessment remains a persistent challenge in orthopaedic trauma. Although patient-reported outcome measures (PROMs) and radiographic assessments such as Radiographic Union Scale for Tibial Fractures (RUST) scores are frequently used, very little evidence has been presented to support their validity for measuring structural bone formation or biomechanical integrity.

Methods: In this pilot study, a sequential cohort of patients with a tibial shaft fracture were prospectively recruited for observation following standard reamed intramedullary nailing in a level-I trauma center. Follow-up at 6, 12, 18, and 24 weeks included radiographs and completion of PROMs (EuroQol 5-Dimension [EQ-5D] and pain scores). Low-dose computed tomography (CT) scans were also performed at 12 weeks. Scans were reconstructed in 3 dimensions (3D) and subjected to virtual mechanical testing via the finite element method to assess torsional rigidity in the fractured limb relative to that in the intact bone.

Results: Patients reported progressive longitudinal improvement in mobility, self-care, activity, and health over time, but the PROMs were not correlated with structural bone healing. RUST scoring showed moderate intrarater agreement (intraclass coefficient [ICC] = 0.727), but the scores at 12 weeks were not correlated with the time to union (R2 = 0.104, p = 0.193) and were only moderately correlated with callus structural integrity (R2 = 0.347, p = 0.010). In contrast, patient-specific virtual torsional rigidity (VTR) was significantly correlated with the time to union (R2 = 0.383, p = 0.005) and clearly differentiated 1 case of delayed union (VTR = 10%, union at 36 weeks) from the cases in the normally healing cohort (VTR > 60%; median union time, 19 weeks) on the basis of CT data alone.

Conclusions: PROMs provide insight into the natural history of the patient experience after tibial fracture but have limited utility as a measure of structural bone healing. RUST scoring, although reproducible, may not reliably predict time to union. In contrast, virtual mechanical testing with low-dose CT scans provides a quantitative and objective structural callus assessment that reliably predicts time to union and may enable early diagnosis of compromised healing.

Level of Evidence: Therapeutic Level IV. Please see Instructions for Authors for a complete description of levels of evidence.

1Department of Mechanical Engineering & Mechanics, Lehigh University, Bethlehem, Pennsylvania

2OrthoXel, DAC, Cork, Ireland

3Departments of Radiology (M.M.M.) and Orthopaedic Surgery (S.A.M.B. and J.A.H.), Cork University Hospital, University College Cork, Wilton, Cork, Ireland

E-mail address for H.L. Dailey: hannah.dailey@lehigh.edu

Investigation performed at Lehigh University, Bethlehem, Pennsylvania, and Cork University Hospital, University College Cork, Cork, Ireland

Disclosure: Funding to support study management was provided by a grant from OrthoXel, DAC. On the Disclosure of Potential Conflicts of Interest forms, which are provided with the online version of the article, one or more of the authors checked “yes” to indicate that the author had a relevant financial relationship in the biomedical arena outside the submitted work and “yes” to indicate that the author had a patent and/or copyright, planned, pending, or issued, broadly relevant to this work (http://links.lww.com/JBJS/F229).

Copyright © 2019 by The Journal of Bone and Joint Surgery, Incorporated
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