Recommendations for High-resolution Peripheral Quantitative Computed Tomography Assessment of Bone Density, Microarchitecture, and Strength in Pediatric Populations

Assessing bone mineral density and cortical geometry using high-resolution peripheral quantitative computed tomography in pediatric survivors of high-risk neuroblastoma with severe growth failure

INTRODUCTION

Survival of children with high-risk neuroblastoma (HR-NBL) has increased with multimodal therapy. cis-Retinoic acid (cis-RA), cornerstone of HR-NBL therapy, can cause osteoporosis and premature physeal closure. This study utilized high-resolution peripheral quantitative computed tomography (HR-pQCT), for 3D measures of volumetric bone mineral density (BMD) and microarchitecture, to assess impact of HR-NBL therapy on skeletal structure.

METHODS

We prospectively enrolled 20 HR-NBL survivors and 20 age-, sex-, and race-matched healthy reference participants. We assessed leg lean mass adjusted for leg length by DXA and strength using a Biodex dynamometer. Tibia bone microarchitecture was assessed via HR-pQCT scans at 4 % of tibia length and a cortical site at 30 %. We compared tibia length (cm), cortical and trabecular vBMD (mg HA/cm3), geometric and structural parameters between groups. Linear regression models assessed group differences in bone microarchitecture adjusted for leg lean mass.

RESULTS

Compared to reference participants, tibia length was significantly shorter in HR-NBL survivors (31.6 cm [27.7,39.5] vs. 36.1 cm [30.4,40], p < 0.005), consistent with significantly lower height Z-score in the HR-NBL cohort (p < 0.001). HR-NBL survivors demonstrated lower cortical area (178.3mm2 [121.9273.5] vs. 214.6mm2 [159.4326.9], p < 0.05) and cortical perimeter (60.0 mm [51.9,82.5] vs. 68.8 mm [57.7,90.8], p < 0.01). After adjusting for tibia length, these differences were no longer significant. Total, cortical, and trabecular volumetric BMD, were not significantly different between groups. Cortical geometry and peak torque deficits were associated with muscle deficits when adjusted for leg lean mass (p < 0.001).

CONCLUSION

Bone density was not severely impacted in HR-NBL survivors. Muscle deficits persisted years after treatment and underscored cortical geometry deficits.

Ambulatory children with spastic cerebral palsy have smaller bone area and deficits in trabecular microarchitecture

Cerebral palsy (CP) is a non-progressive neurological syndrome resulting in abnormal muscle tone, movement, and posture. It is unclear whether ambulatory children with CP have deficits in bone quantity or quality. Furthermore, the relationship between abnormal muscle tone, altered function, and bone health remains largely unexplored. This observational study investigated bone mineral density (BMD) and microarchitecture in ambulatory children with spastic CP and associations of BMD with function, muscle spasticity, and gait. Children with spasticity in both lower limbs (n = 12) aged 3-8 years were recruited. Areal BMD was measured with dual energy x-ray absorptiometry (DXA) at the proximal femur and lateral distal femur and compared to normative data. High resolution peripheral quantitative computed tomography (HR-pQCT) was performed at the metaphyseal tibia and radius in a subset of participants (n = 5) and compared to healthy children (n = 7). Gait pathology and cardiopulmonary function were investigated with the Gait Deviation Index, Edinburgh Visual Gait Score, and energy expenditure index. DXA areal BMD (aBMD) Z-scores at the lateral distal femur were within a normal range. However, the CP group's median aBMD Z-score at the proximal femur was -1.8 (IQR: -2.2, -1.2, p = .03) indicating potential skeletal fragility. Strong correlations were found between gait pathology and DXA-based bone outcomes (correlation coefficient 0.62 [p = .04] to 0.73 [p = .01]) as well as energy expenditure index and DXA-based bone outcomes (correlation coefficient -0.63 [p = .03] to -0.98 [p ≤ .001]). At the metaphyseal tibia, children with spastic CP had significant deficits in HR-pQCT-measured bone geometry and trabecular microarchitecture: 35% lower total area, 42% lower trabecular area, and 48% lower trabecular number than controls. HR-pQCT parameters were similar between groups at the metaphyseal radius. These differences in tibial metaphysis size and trabecular microarchitecture are similar to those observed in disuse and thus could be a result of abnormal biomechanics or low levels of physical activity.

Evaluation of the First Metacarpal Bone Head and Distal Radius Bone Architecture Using Fractal Analysis of Adolescent Hand-Wrist Radiographs

The purpose of this study was to investigate changes in bone trabecular structure during adolescence using the fractal analysis (FA) method on hand-wrist radiographs (HWRs) and to evaluate the relationship of these changes with pubertal growth stages. HWRs of healthy individuals aged 8-18 years were included (N = 600). Pubertal stages were determined by the Fishman method and divided into 10 groups (early puberty [EP], pre-peak [PRPK], peak [PK], post-peak [PTPK], late puberty [LP]). FA was performed using FIJI (ImageJ) software and the BoneJ plugin on circular regions of interest (ROIs) selected from the first metacarpal bone head and distal radius. Image processing steps were applied according to the White and Rudolph method. Differences between groups were statistically evaluated. Fractal dimension (FD) values of the distal radius (RAFAM) and metacarpal bone head (MAFAM) showed significant differences according to pubertal growth stages (p < 0.05). The highest FD value was observed in the LP group, and the lowest FD value was observed in the EP group (except MAFAM in females). FD generally increased from EP to LP in the whole population, but a significant decrease was observed in all groups during the PK period. This decrease was more pronounced in RAFAM of males. These findings suggest a potential decrease of bone mechanical properties in the PK, which is found the be more suitable for orthodontic treatment in the literature. FA on HWRs is a useful and sensitive tool for quantitatively assessing pubertal changes in trabecular bone microarchitecture. The findings demonstrate a significant decrease in FD in both bone regions during the pubertal growth spurt, particularly at the peak period. This may indicate a temporary reduction in bone mechanical strength during this critical stage and could contribute to increased distal radius fracture incidence. Clinically, the relationship between FD and pubertal stages suggests this method could serve as a valuable biomarker in orthodontic treatment planning, allowing for optimized timing of interventions. Furthermore, it may aid in pediatric fracture risk assessment, potentially leading to preventative strategies for high-risk individuals.

Distinguishing risk of curve progression in adolescent idiopathic scoliosis with bone microarchitecture phenotyping: a 6-year longitudinal study

Low bone mineral density and impaired bone quality have been shown to be important prognostic factors for curve progression in adolescent idiopathic scoliosis (AIS). There is no evidence-based integrative interpretation method to analyze high-resolution peripheral quantitative computed tomography (HR-pQCT) data in AIS. This study aimed to (1) utilize unsupervised machine learning to cluster bone microarchitecture phenotypes on HR-pQCT parameters in girls with AIS, (2) assess the phenotypes' risk of curve progression and progression to surgical threshold at skeletal maturity (primary cohort), and (3) investigate risk of curve progression in a separate cohort of girls with mild AIS whose curve severity did not reach bracing threshold at recruitment (secondary cohort). Patients were followed up prospectively for 6.22 ± 0.33 years in the primary cohort (n = 101). Three bone microarchitecture phenotypes were clustered by fuzzy C-means at time of peripubertal peak height velocity (PHV). Phenotype 1 had normal bone characteristics. Phenotype 2 was characterized by low bone volume and high cortical bone density, and phenotype 3 had low cortical and trabecular bone density and impaired trabecular microarchitecture. The difference in bone quality among the phenotypes was significant at peripubertal PHV and continued to skeletal maturity. Phenotype 3 had significantly increased risk of curve progression to surgical threshold at skeletal maturity (odd ratio [OR] = 4.88; 95% CI, 1.03-28.63). In the secondary cohort (n = 106), both phenotype 2 (adjusted OR = 5.39; 95% CI, 1.47-22.76) and phenotype 3 (adjusted OR = 3.67; 95% CI, 1.05-14.29) had increased risk of curve progression ≥6° with mean follow-up of 3.03 ± 0.16 years. In conclusion, 3 distinct bone microarchitecture phenotypes could be clustered by unsupervised machine learning on HR-pQCT-generated bone parameters at peripubertal PHV in AIS. The bone quality reflected by these phenotypes was found to have significant differentiating risk of curve progression and progression to surgical threshold at skeletal maturity in AIS.

Bone mass accrual in children

PURPOSE OF REVIEW

Bone accrual during childhood and adolescence is critical for the attainment of peak bone mass and is a major contributing factor towards osteoporosis in later life. Bone mass accrual is influenced by nonmodifiable factors, such as genetics, sex, race, ethnicity, and puberty, as well as modifiable factors, such as physical activity and diet. Recent progress in bone imaging has allowed clinicians and researchers to better measure the morphology, density, and strength of the growing skeleton, thereby encompassing key characteristics of peak bone strength. In this review, the patterning of bone accrual and contributors to these changes will be described, as well as new techniques assessing bone mass and strength in pediatric research and clinical settings.

RECENT FINDINGS

This review discusses factors influencing peak bone mass attainment and techniques used to assess the human skeleton.

SUMMARY

The rate of bone accrual and the magnitude of peak bone mass attainment occurs in specific patterns varying by sex, race, ethnicity, longitudinal growth, and body composition. Physical activity, diet, and nutritional status impact these processes. There is a need for longitudinal studies utilizing novel imaging modalities to unveil factors involved in the attainment and maintenance of peak bone strength.