Predicting experimentally-derived failure load at the distal radius using finite element modelling based on peripheral quantitative computed tomography cross-sections (pQCT-FE): A validation study

Lower bone strength in young patients with Fontan circulation compared to controls

OBJECTIVES

Previous reports indicate bone deficits in patients with Fontan circulation. However, the consequences of these deficits on bone strength and when these changes occur are unclear.

AIM

To compare the tibial bone strength-strain index between young patients (6-19 years) with Fontan circulation and age- and sex-matched controls, and to determine strength-strain-index in subgroups of children (6-12 years) and adolescents (13-19 years) versus controls.

METHOD

The tibia was examined with peripheral quantitative CT. Based on the assessed data, bone strength-strain index was calculated in the lateral and anterior-posterior directions.

RESULTS

Twenty patients with Fontan and twenty controls (mean age 13.0 ± 4.4 years; 50% females) were examined. Patients had a lower strength-strain index in the lateral direction compared to controls (808.4 ± 416.8mm3 versus 1162.5 ± 552.1mm3, p = 0.043). Subgroup analyses showed no differences regarding strength-strain index in children (6-12 years) with Fontan circulation compared to controls. However, the adolescents (13-19 years) with Fontan circulation had lower strength-strain indexes in both the lateral and anterior-posterior directions compared to controls (1041.4 ± 299.8mm3 versus 1596.4 ± 239.6mm3, p < 0.001, and 771.7 ± 192.4mm3 versus 1084.9 ± 215.0mm3, p = 0.004). When adjusted for height, there were differences between patients (6-19 years) and controls in strength-strain indexes in both the lateral and anterior-posterior directions. In subgroup analyses, the results remained robust.

CONCLUSION

Young patients (6-19 years) with Fontan circulation have a lower strength-strain index in the tibia compared to controls. Subgroup analyses show that this deficit is mainly driven by the differences in adolescents (13-19 years), which might suggest that bone strength decreases with age.

Quantifying Bone Strength Deficits in Young Adults Born Extremely Preterm or Extremely Low Birth Weight

The long-term bone health of young adults born extremely preterm (EP; <28 weeks' gestation) or extremely low birth weight (ELBW; <1000 g birth weight) in the post-surfactant era (since the early 1990s) is unclear. This study investigated their bone structure and estimated bone strength using peripheral quantitative computed tomography (pQCT)-based finite element modeling (pQCT-FEM). Results using this technique have been associated with bone fragility in several clinical settings. Participants comprised 161 EP/ELBW survivors (46.0% male) and 122 contemporaneous term-born (44.3% male), normal birth weight controls born in Victoria, Australia, during 1991-1992. At age 25 years, participants underwent pQCT at 4% and 66% of tibia and radius length, which was analyzed using pQCT-FEM. Groups were compared using linear regression and adjusted for height and weight. An interaction term between group and sex was added to assess group differences between sexes. Parameters measured included compressive stiffness (kcomp ), torsional stiffness (ktorsion ), and bending stiffness (kbend ). EP/ELBW survivors were shorter than the controls, but their weights were similar. Several unadjusted tibial pQCT-FEM parameters were lower in the EP/ELBW group. Height- and weight-adjusted ktorsion at 66% tibia remained lower in EP/ELBW (mean difference [95% confidence interval] -180 [-352, -8] Nm/deg). The evidence for group differences in ktorsion and kbend at 66% tibia was stronger among males than females (pinteractions  <0.05). There was little evidence for group differences in adjusted radial models. Lower height- and weight-adjusted pQCT-FEM measures in EP/ELBW compared with controls suggest a clinically relevant increase in predicted long-term fracture risk in EP/ELBW survivors, particularly males. Future pQCT-FEM studies should utilize the tibial pQCT images because of the greater variability in the radius possibly related to lower measurement precision. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

HR-pQCT parameters of the distal radius correlate with the bending strength of the radial diaphysis

High resolution, peripheral quantitative computed tomography (HR-pQCT) scanners can now characterize an individual's trabecular architecture, cortical structure, and volumetric bone mineral density at a nominal resolution of 61 μm. While predictions of failure load of the distal radius and tibial diaphysis in compression by finite element analysis (FEA) of HR-pQCT scans have been validated against mechanical tests of cadaveric bones in compression, namely for images with nominal resolutions of 82 μm and 165 μm, the HR-pQCT parameters that best predict bending strength of cortical bone remain unknown. Therefore, we scanned cadaveric forearms from 31 elderly donors (Female: 72.8 ± 8.8 years and Male: 72.1 ± 6.3 years), and then loaded the radial diaphysis to failure in three-point bending after denuding each bone (38 in total). The cortical parameters had stronger correlations with ultimate moment than the trabecular parameters such that cortical area and estimated failure load of the distal radius had the highest Spearman correlation coefficients (r = 0.89 and r = 0.81, respectively, p < 0.0001). Despite being a known determinant of bone strength, cortical porosity of the distal radius did not correlate with ultimate moment (p = 0.8537). In multivariate linear regressions with section modulus (SM) of the radial diaphysis as one of two predictors of bending strength, cortical area and cortical thickness were each significant contributors to the prediction of ultimate moment. Their contribution was one-half and one-third, respectively, of the contribution from SM. None of the HR-pQCT parameters were strongly correlated with post-yield displacement, an indicator of bone brittleness. In support of HR-pQCT imaging of the distal radius to identify individuals with osteoporosis, the present study found that parameters of the cortex and failure load predictions by linear FEA are strongly related to the bending strength of cortical bone.

Bone Measures by Dual-Energy X-Ray Absorptiometry and Peripheral Quantitative Computed Tomography in Young Women With Type 1 Diabetes Mellitus

Understanding bone fragility in young adult females with type 1 diabetes mellitus (T1DM) is of great clinical importance since the high fracture risk in this population remains unexplained. This study aimed to investigate bone health in young adult T1DM females by comparing relevant variables determined by dual-energy X-ray absorptiometry (DXA), peripheral quantitative computed tomography (pQCT) at the tibia and pQCT-based finite element analysis (pQCT-FEA) between T1DM subjects (n = 21) and age-, height- and weight-matched controls (n = 63). Tibial trabecular density (lower by 7.1%; 228.8 ± 33.6 vs 246.4 ± 31.8 mg/cm³, p = 0.02) and cortical thickness (lower by 7.3%; 3.8 ± 0.5 vs 4.1 ± 0.5 cm, p = 0.03) by pQCT were significantly lower in T1DM subjects than in controls. Tibial shear stiffness by pQCT-FEA was also lower in T1DM subjects than in controls at both the 4% site (by 17.1%; 337.4 ± 75.5 vs 407.1 ± 75.4 kN/mm, p < 0.01) and 66% site (by 7.9%; 1113.0 ± 158.6 vs 1208.8 ± 161.8 kN/mm, p = 0.03). These differences remained statistically significant after adjustment for confounding factors. No difference between groups was observed in DXA-determined variables (all p ≥ 0.08), although there was a trend towards lower aBMD at the lumbar spine in T1DM subjects than in controls after adjustment for confounders (p = 0.053). These novel findings elicited using pQCT and pQCT-FEA suggest a clinically significant impact of T1DM on bone strength in young adult females with T1DM. Peripheral QCT and pQCT-FEA may provide more information than DXA alone on bone fragility in this population. Further longitudinal studies with a larger sample size are warranted to understand the evolution and causes of bone fragility in young T1DM females.

Loss of bone density and bone strength following premenopausal risk-reducing bilateral salpingo-oophorectomy: a prospective controlled study (WHAM Study)

Prophylactic oophorectomy is recommended for women at high risk for ovarian cancer, but the associated impact on bone health is of clinical concern. This prospective, controlled study demonstrated substantial loss of bone density and bone strength following surgical menopause. Postoperative hormone therapy alleviated, but not fully prevented, spinal bone loss.

INTRODUCTION

This prospective study investigated bone health in women following premenopausal oophorectomy.

METHODS

Dual-energy x-ray absorptiometry (DXA), peripheral quantitative computed tomography (pQCT), and pQCT-based finite element analysis (pQCT-FEA) were used to assess bone health between systemic hormone therapy (HT) users and non-users after premenopausal risk-reducing bilateral salpingo-oophorectomy (RRBSO) compared with premenopausal controls over 24-month follow-up.

RESULTS

Mean age was 42.4 ± 2.6 years (n = 30) for the surgery group and 40.2 ± 6.3 years for controls (n = 42), and baseline bone measures were similar between groups. Compromised bone variables were observed at 24 months after RRBSO, among which areal bone mineral density (aBMD) at the lumbar spine, tibial volumetric cortical density (Crt vBMD), and tibial bending stiffness (k_bend) had decreased by 4.7%, 1.0%, and 12.1%, respectively (all p < 0.01). In non-HT users, significant losses in lumbar spine (5.8%), total hip (5.2%), femoral neck (6.0%) aBMD, tibial Crt vBMD (2.3%), and k_bend (14.8%) were observed at 24 months (all p < 0.01). HT prevented losses in k_bend, tibial Crt vBMD, and aBMD, except for modest 2.3% loss at the lumbar spine (p = 0.01).

CONCLUSION

This prospective, controlled study of bone health following RRBSO or premenopausal oophorectomy demonstrated substantial loss of bone density and bone strength following RRBSO. HT prevented loss of bone density and bone stiffness, although there was still a modest decrease in lumbar spine aBMD in HT users. These findings may inform decision-making about RRBSO and clinical management following premenopausal oophorectomy.