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Bone quality in children is generally measured with dual-energy X-ray absorptiometry (DXA). Digital X-ray radiogrammetry (DXR) uses BoneXpert to measure cortical bone quality on hand radiographs. This prospective study compared DXR and DXA results in children with high probability of secondary low bone quality, defined as DXA of the lumbar spine (DXA LS ) Z -score ≤ − 2.0. One hundred one children underwent both DXA and DXR assessment. DXA LS Z -scores were also adjusted for bone age. DXR Z -scores were compared with both DXA LS Z -scores, using Pearson correlations, Bland-Altman analysis, and sensitivity-specificity analysis. Mean bone age, DXR, and both DXA Z -scores were significantly impaired. Pearson correlation coefficients were significant between DXR Z -scores and both DXA LS Z -scores 0.507–0.564 ( p < 0.001). Bland-Altman analysis showed a mean difference of 0.05–0.48 between DXR and both DXA Z -scores and showed more than 90% similarity for both DXA LS Z -scores ≤ − 2.0. DXR had a sensitivity of 67–71% and specificity of 77–83% compared to both DXA LS Z -scores. Conclusion : DXR correlates well with as well DXA LS as bone age-adjusted DXA LS Z -scores and shows good agreement with as well DXA LS as bone age-adjusted DXA LS Z -scores ≤ − 2.0. DXR shows best results when compared with DXA LS Z -scores. What is Known: • Digital X-ray radiogrammetry (DXR) may correlate well with dual-energy X-ray absorptiometry (DXA) in pediatric, adolescent, and adult patients. • DXR is a feasible method for assessment of bone quality in children. What is New: • This is the first prospective study in children with suspected secondary low bone quality that illustrates correlation between DXR and bone age-adjusted DXA Z-scores and that shows good agreement between DXR and DXA as bone age-adjusted DXA Z-scores ≤ −2.0. • Our results suggest DXR to be a good alternative for DXA for determining low bone quality.

Background During long-term follow-up of children treated with the ketogenic diet therapy (KDT) have an increased incidence of bone fractures. However, the exact contribution of KDT to a decreased bone mineral density (BMD) remains unclear. Objective This study aimed to evaluate (changes in) BMD in children treated with KDT and to evaluate whether intravenous bisphosphonate therapy may be effective. Design In this retrospective, observational cohort study, all children treated with KDT from 2010 until 2018 at the Radboudumc Amalia Children's hospital were included. Patients who were on KDT for more than 6 months and who had at least two dualenergy X-ray (DXA)-scans were eligible for inclusion for longitudinal analysis. Z-scores of DXA-scans were compared over the course of time.Results In 34 out of 68 patients, one or more lumbar DXA-scans were performed, with a mean lumbar Z-score of À1.32 AE 1.74. Of these 68 patients, 8.8% got a fracture during KDT, and also 8.8% got kidney stones. In 20 patients, more than one DXA-scan was performed. A statistically not significant decrease in BMD (0.22 Z-score/year) was found. However, there was an increase in BMD in the five patients treated with intravenous bisphosphonate therapy. This was statistically significant in comparison to the nonbisphosphonate treated group (p ¼ 0.034). Conclusion Children on KDT have low normal BMD which may decrease further during KDT. For this reason monitoring of BMD is crucial, as is monitoring of kidney stones and hypercalciuria. Intravenous bisphosphonate therapy may have a positive effect, when other therapies have failed.

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