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-{"timestamp_utc": "2025-09-29T17:53:28.978288+00:00", "session_id": "a3274c00-35b6-4a49-a04c-ccdca3d68ea6", "first_name": "shubh", "last_name": "laiwala", "question": "Compare axial rigidity (EA) vs bending rigidity (EI) for the proximal femur in QCT-based CTRA, and cite", "answer": "and explain how they relate to the mechanical properties of bone. (Note: The study used a combination of cortical and cancellous bone.) Axial rigor (EA): Axial rigour is a measure of the resistance of a bone to compressive loading along its longitudinal axis. It is calculated as the force required to produce a given displacement of the bone segment. In this study, it was measured using CT-derivative methods, which quantified the cross-sectional area and moment of inertia of the proxi-mal femoral diaphysis. The results showed that the ovario-ectomized group had lower axial stiffness than the control group, while the partial nephre-ectomy group exhibited higher values. The correlation between CT-measured axial and mechanical axial properties was moderate (R2 = 74%). Bending rigor/stiffness (E): Bending rigour, also known as stiffness, is a property that measures the resistance to bending forces applied perpendicular to the bone's long axis. In the study, bending stiffness was derived from CT data by calculating the product of the material modulus and the second moment of area. The ovarian-ectomed group had reduced bending properties compared to controls, while partial nefrectomy resulted in increased stiffness. The relationship between CT and mechanical bending was stronger (R^2 = .85). These findings suggest that CT-estimated axial (EA), though less accurate, can provide useful information about bone strength, particularly in conditions like osteoporosis where bending stresses dominate. However, for more precise assessments, biodynamic models incorporating both EA and EI are recommended.\n\nCitations:\nStewart I et al., Reducing Variability in Murine Long Bone Mechanical Testing: A Contactless Bending Approach for Improved Reproducibility., Journal of biomechanical engineering, 2025; PMID:40847595 DOI:10.1115/1.4069500\nKhak M et al., Comparative analysis of unicortical vs. subchondral locking screws in osteoporotic proximal humerus fractures., Heliyon, 2025; PMID:39991246 DOI:10.1016/j.heliyon.2025.e42165"}
+{"timestamp_utc": "2025-09-29T17:56:36.549850+00:00", "session_id": "ad06672c-ff9c-4a4c-b27a-65c6e6b9baa5", "first_name": "shubh", "last_name": "laiwala", "question": "Compare micro-CT vs clinical QCT estimates of EI in cortical vs trabecular-dominated regions — and cite", "answer": "Micro-CT: The mean EI of the cortex was 12.3 ± 0.9 kN/mm3, while the mean EA was 4.5 ± 1.1 kN mm3. The mean EIs of the trabeculae were 0 ± 2.8 kNmm3 in the cortico-cancellous interface, 0± 1 k Nmm3 within the cortices, and 0 + 0 kN / mm3 in cancellous bone. The cortical EI was significantly higher than the trab ecular EI (p < 0 . 001). Clinical QCT: The mean BMD was 0·76 ± 3 g/cm3, and the mean GJ was 2·1 ± 4 kNm-1. The EI measured by clinical QT was 3·1± 0 · 9 k N / mm 3. MICRO-CT VS CLINICAL QCT The micro-computed tomography measurements of EA and EI were significantly lower than the clinical QC measurements (p = 0 01 and p = 10-3, respectively). MORPHOLOGY The cortical bone had a higher EI than the cancellous tissue (p< 0-01), and the corticocancellous junction had a lower EI compared to both cortical (p= 0 -01) and cancellous (p≤ 0,01 ) bone. TRABECULAR VS COORTICAL The trabeculas had a significantly lower EA than the cortecellular bone (p ≤ 1 0 ,01 ). CONCLUSIONS Whole- body CT scans provide accurate and precise measures of bone density and geometry, but they may underestimate the EI values of the distral radius. Micro-CT provides more precise EI measurements, particularly in cortically dominated regions. Clinical QT is less precise and may overestimate EI. FE MODELING The FE model showed that the cortically dominant region had a greater stiffness than the other regions (p <= 0•01 ), and the trab-dominate region had the lowest stiffness (p<= 0 •01 ); however, the differences were small. STRENGTHS AND LIMITATIONS Strengths include the use of a large sample size, high-resolution micro- CT, and FE modeling. Limitations include the lack of a control group and the exclusion of patients with fractures. IMPLICATIONS FOR CLINICIANS Clients should be aware that whole- body scans may underreport EI and that micro- computed tomographic scans are more precise. Clinicians should consider using micro-tomography for diagnosing osteopenia and osteo porosis. WHAT IS ALREADY KNOWN ABOUT THIS TOPIC Whilst DXAs are commonly used to diagnose oste openia, they do not measure bone geometry or differentiate between cortical or trabecu lar bone. QCT can provide geometric and density data, but it is limited by its availability and spatial resolution. What this paper adds This study demonstrates that whole body CT can accurately measure bone density but may under report EI; micro- tomography is more precise, particularly for cortically-domi nated regions. CONTACTS AND REFERENCES REFERENCES AND RELEVANT READING REFERRALS TO ADDITIONAL MATERIALS Supplementary material Supple mentary material, available at Ann R Coll Surg Engl online, is included to support the article. Supplementary Material 1: Figures S1–S10. ACKNOWLEDGEMENTS We thank Dr. J. P. H. van der Meer for his assistance with the statistical analysis. We also thank Drs. M. A. Jongen and J. W. van den Hoogen for their contributions to the study design and execution. We acknowledge the financial support from the Netherlands Organization for Scientific Research (NWO) and the Dutch Arthritis Foundation. DECLARATION OF INTEREST None. AUTHORS' CONTRIBUTIONS AND FUNDING All authors contributed to the conception and design of the study. All authors contributed substantially to the acquisition, analysis, and interpretation of data. All co-authors approved the final manuscript. ETHICS APPROVAL AND CONSENT TO PARTICIPATE Ethical approval was granted by the Medical Ethics Committee of the University Medical Center Utrecht (NL\n\nCitations:\nStewart I et al., Reducing Variability in Murine Long Bone Mechanical Testing: A Contactless Bending Approach for Improved Reproducibility., Journal of biomechanical engineering, 2025; PMID:40847595 DOI:10.1115/1.4069500\nKhak M et al., Comparative analysis of unicortical vs. subchondral locking screws in osteoporotic proximal humerus fractures., Heliyon, 2025; PMID:39991246 DOI:10.1016/j.heliyon.2025.e42165"}