Virtual structural analysis of tibial fracture healing from low-dose clinical CT scans

Abstract

Quantitative assessment of bone fracture healing remains a significant challenge in orthopaedic trauma research. Accordingly, we developed a new technique for assessing bone healing using virtual mechano-structural analysis of computed tomography (CT) scans. CT scans from 19 fractured human tibiae at 12 weeks after surgery were segmented and prepared for finite element analysis (FEA). Boundary conditions were applied to the models to simulate a torsion test that is commonly used to access the structural integrity of long bones in animal models of fracture healing. The output of each model was the virtual torsional rigidity (VTR) of the healing zone, normalized to the torsional rigidity of each patient's virtually reconstructed tibia. This provided a structural measure to track the percentage of healing each patient had undergone. Callus morphometric measurements were also collected from the CT scans. Results showed that at 12 weeks post-op, more than 75% of patients achieved a normalized VTR (torsional rigidity relative to uninjured bone) of 85% or above. The predicted intact torsional rigidities compared well with published cadaveric data. Across all patients, callus volume and density were weakly and nonsignificantly correlated with normalized VTR and time to clinical union. Conversely, normalized VTR was significantly correlated with time to union (R 2 = 0.383, p = 0.005). This suggests that fracture scoring methods based on the visual appearance of callus may not accurately predict mechanical integrity. The image-based structural analysis presented here may be a useful technique for assessment of bone healing in orthopaedic trauma research.

Virtual mechanical tests out‐perform morphometric measures for assessment of mechanical stability of fracture healing in vivo

“…For example, we recently developed CT-derived computational methods to calculate the virtual torsional rigidity (VTR) of human tibial fractures after 12 weeks of healing. 9 In a pilot study, we showed that this measure is strongly correlated with clinical healing outcomes, such as time to clinical union. 10 Furthermore, integrating image-based models in preclinical in vivo studies may reduce the required number of experimental animals, in accordance with three R principles, by allowing noninvasive follow-up assessments of structural healing kinetics.…”

“…[1][2][3][4][5][6][7][8] This technique is able to accurately capture both the complex geometries and localized material acquired by the CT scan to build representative animalspecific or patient-specific models. 9,10 FEA can then be used to simulate different loading scenarios and assess the structural biomechanics of the anatomy of interest.…”

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

“…The process has been documented in extensive detail elsewhere. 18 The strict workflow control produces data that is highly repeatable and any two individuals following the proscribed process would produce nearly identical summary measures. This study also suggests some potential difficulties with the widely used RUST score.…”

“…The complete workflow for generating the injured and intact models is summarized in Figure 1 and discussed in detail elsewhere. 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.…”

Virtual Mechanical Tests Out-Perform Morphometric Measures for Assessment of Fracture Healing In Vivo

“…[1][2][3][4][5][6][7][8] This technique is able to accurately capture both the complex geometries and localized material acquired by the CT scan to build representative animal-specific or patient-specific models. 9,10 FEA can then be used to simulate different loading scenarios and assess the structural biomechanics of the anatomy of interest.…”