Bone geometry, volumetric density, microarchitecture, and estimated bone strength assessed by HR-pQCT in adult patients with hypophosphatemic rickets

X-Linked Hypophosphatemia Management in Adults: An International Working Group Clinical Practice Guideline

PURPOSE

An international working group (IWG) consisting of experts in X-linked hypophosphatemia (XLH) developed global guidelines providing a comprehensive, evidence-based approach to XLH diagnosis, management, and monitoring.

METHODS

The IWG, consisting of 43 members as well as methodologists and a patient partner, conducted 2 systematic reviews (SRs) and narrative reviews to address key areas. The SRs addressed the impact of burosumab compared to conventional therapy (phosphate and active vitamin D) or no therapy on patient-important outcomes in adults. They also evaluated conventional therapy compared to no therapy. GRADE methodology was applied to evaluate the certainty of evidence. Non-GRADED recommendations were made in the presence of insufficient evidence to conduct SRs. These guidelines have been reviewed and endorsed by several medical and patient societies and organizations.

RESULTS

The diagnosis of XLH is based on integrating clinical evaluation, laboratory findings confirming renal phosphate wasting (following exclusion of conditions mimicking XLH), and skeletal imaging. Fibroblast growth factor 23 measurement and DNA analysis are of value in the diagnosis, if available. Pathogenic or likely pathogenic variants in the PHEX gene are confirmatory but not necessary for the diagnosis. Management requires a multidisciplinary team knowledgeable and experienced in XLH. Effective medical therapy with burosumab can improve fracture and pseudofracture healing.

MAIN CONCLUSION

In adults with XLH and fractures or pseudofractures, burosumab is recommended over no therapy (strong recommendation, GRADEd). Additionally, burosumab is suggested as the preferred treatment compared to conventional therapy (conditional recommendation, GRADEd) in the absence of fractures or pseudofractures. If burosumab is not available, symptomatic adults should be treated with conventional therapy (Non-GRADEd recommendation).

Evaluation of bone density and microarchitecture in adult patients with X-linked hypophosphatemic rickets: A pilot longitudinal study

X-linked Hypophosphatemia (XLH) is the most common type of inherited rickets. Although the clinical features are well characterized, bone structure, mineralization, and biomechanical properties are poorly known. Our aim was to analyze bone properties in the appendicular and axial skeleton of adults with XLH. In this observational case-control study, each affected patient (N = 14; 9 females; age 50 ± 15 years) was matched by sex, age and body mass index to a minimum of two healthy controls (N = 34). Dual-energy X-ray Absorptiometry (DXA) analyses revealed that areal bone mineral density (aBMD) was higher in XLH patients at the lumbar spine (Z score mean difference = +2.47 SD, P value = 1.4 × 10-3). Trabecular Bone Score was also higher at the lumbar spine (P value = 1.0 × 10-4). High Resolution peripheral Quantitative Computed Tomography (HRpQCT) demonstrated that bone cross-sectional area was larger at the distal radius (P value = 6 × 10-3). Total and trabecular volumetric BMD were lower at both sites. Trabecular bone volume fraction was also lower with fewer trabecular numbers at both sites. However, bone strength evaluated by micro-finite element analyzes revealed unaffected bone stiffness and maximum failure load. Evaluation of bone mineralization with aBMD by DXA at the distal radius correlated with vBMD by HRpQCT measurements at both sites. PTH levels were inversely correlated with trabecular vBMD and BV/TV at the tibia. We then followed a subset of nine patients (median follow-up of 4 years) and reassessed HRpQCT. At the tibia, we observed a greater decrease than expected from an age and sex standardized normal population in total and cortical vBMD as well as a trabecularization of the cortical compartment. In conclusion, in adult patients with XLH, bone mineral density is high at the axial skeleton but low at the appendicular skeleton. With time, microarchitectural alterations worsen. We propose that noninvasive evaluation methods of bone mineralization such as DXA including the radius should be part of the management of XLH patients. Larger studies are needed to evaluate the clinical significance of BMD changes in XLH patients under conventional or targeted therapies.

X-linked hypophosphataemia

X-linked hypophosphataemia is a genetic disease caused by defects in the phosphate regulating endopeptidase homolog X-linked (PHEX) gene and is characterised by X-linked dominant inheritance. The main consequence of PHEX deficiency is increased production of the phosphaturic hormone fibroblast growth factor 23 (FGF23) in osteoblasts and osteocytes. Chronic exposure to circulating FGF23 is responsible for renal phosphate wasting and decreased synthesis of calcitriol, which decreases intestinal phosphate absorption. These mechanisms result in lifelong hypophosphataemia, impaired growth plate and bone matrix mineralisation, and diverse manifestations in affected children and adults, including some debilitating morbidities and possibly increased mortality. Important progress has been made in disease knowledge and management over the past decade; in particular, targeting FGF23 is a therapeutic approach that has substantially improved outcomes. However, patients affected by this complex disease need lifelong care and innovative treatment strategies, such as gene repair of PHEX, are necessary to further limit the disease burden.

The sacroiliac joint: An original and highly sensitive tool to highlight altered bone phenotype in murine models of skeletal disorders

Bone disorders may affect the skeleton in different ways, some bones being very impaired and others less severely. In translational studies using murine models of human skeletal diseases, the bone phenotype is mainly evaluated at the distal femur or proximal tibia. The sacroiliac joint (SIJ), which connects the spine to the pelvis, is involved in the balanced transfer of mechanical energy from the lumbar spine to the lower extremities. Because of its role in biomechanical stress, the SIJ is a region of particular interest in various bone diseases. Here we aimed to characterize the SIJ in several murine models to develop a highly reliable tool for studying skeletal disorders. We performed a 12-month in vivo micro-computed tomography (micro-CT) follow-up to characterize the SIJ in wild-type (WT) C57BL/J6 mice and compared the bone microarchitecture of the SIJ and the distal femur at 3 months by micro-CT and histology. To test the sensitivity of our methodology, the SIJ and distal femur were evaluated at 3 and 6 months, in 2 murine models of skeletal disorder, X-linked hypophosphatemia (Hyp mice) and HLA-B27 transgenic mice and compared to WT mice. A multimodal analysis was performed, using a combination of microCT and histological analysis. With the Hyp model, the SIJ displayed more bone microarchitecture alterations than the distal femur. Hyp mice showed a significant reduction in trabecular bone at both the distal femur and sacral slope as compared with WT mice, with a significant positive correlation between trabecular bone parameters of the distal femur and sacral side of the SIJ. Furthermore, trabecular bone parameters (Bone Volume/Total Volume (BV/TV), trabecular thickness (Tb.Th), trabecular separation (Tb.Sp), trabecular number (Tb.N), trabecular pattern factor (Tb.Pf)) were significantly increased compared to femoral parameters at the SIJ. The sacral articular cortical bone, which is indicative of osteoarticular lesions, was altered in Hyp mice. Interestingly, in accordance to previous studies, HLA-B27 transgenic mice did not show any osteoarticular lesions as compared with WT mice. Cortical bone parameters (thickness, porosity), as well as scoring performed with double blinding, did not show difference between the 2 genotypes. The characterization and evaluation of the SIJ surface appears very sensitive to emphasize alterations of bone and joint. The SIJ may represent a valuable tool to investigate both bone and local osteoarticular alterations in murine models of skeletal disorders and might be a relevant site for assessing the response to treatment of chronic bone diseases.

Shift in Calcium From Peripheral Bone to Axial Bone After Tumor Resection in Patients With Tumor-Induced Osteomalacia

CONTEXT

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome caused by excessive production of fibroblast growth factor 23 (FGF23) by a tumor. After successful tumor resection, patients can recover from hypophosphatemia quicky. However, data on the changes in bone mineral density (BMD) and microstructure in the short term after surgery remained unclear.

OBJECTIVE

This work aimed to investigate the postoperative changes in BMD and microstructure both in peripheral and axial bone in TIO patients.

METHODS

We evaluated BMD and microarchitecture in 22 TIO patients using high-resolution peripheral quantitative computed tomography (HR-pQCT) and dual-energy x-ray absorptiometry (DXA) before and 3 months after surgery in this retrospective study.

RESULTS

In this study, a total of 22 TIO patients who had recovered serum phosphate levels postoperatively were enrolled. After surgery, areal BMD (aBMD) increased by 21.6% in the femoral neck, by 18.9% in the total hip, and by 29.5% in the lumbar spine. Moreover, TBS increased by 14.1% (all P < .001). In contrast, trabecular or cortical volumetric BMD (vBMD), and microstructure of trabecular bone (trabecular number, separation and bone volume ratio) and cortical bone (cortical thickness and porosity) at the distal radius or tibia were further deteriorated. Correlation analyses found that changes in femoral neck and total hip aBMD were both conversely associated with changes in trabecular vBMD and bone volume ratio, while positively correlated with change in trabecular separation at the distal radius.

CONCLUSION

Although aBMD and microstructure in the axial bone were improved, vBMD and microstructure in the peripheral bone were further impaired shortly after surgery. Correlation of improvement of aBMD in the total hip and femoral neck with deterioration of vBMD and microstructure at the distal radius indicated a shift in calcium from the peripheral bone to the axial bone in the short term after tumor resection in TIO patients.

Evaluation of the trabecular bone score in 35 children and adults with X-linked hypophosphatemic rickets

INTRODUCTION

 The aim of this study is to evaluate and compare the trabecular bone scores (TBSs) of 11 children and 24 adults with X-linked hypophosphatemic rickets (XLH) and non-XLH subjects from a tertiary center.

MATERIALS AND METHODS

 The areal bone mineral density at the lumbar spine (LS-aBMD) and LS-aBMD Z score were analyzed by dual-energy X-ray absorptiometry. The bone mineral apparent density (BMAD) and LS-aBMD Z score adjusted for height Z score (LS-aBMD-HAZ) were calculated. The TBS was determined using TBS iNsight software based on DXA images from the Hologic QDR 4500 device.

RESULTS

The XLH patients exhibited a higher mean LS-aBMD Z score, BMAD, and TBS than the non-XLH subjects (p < 0.01). LS-aBMD-HAZ and BMAD were greater in the XLH children than those in their corresponding non-XLH subjects (p < 0.01 and p = 0.02), and the XLH children trended toward a greater TBS (p = 0.06). The XLH adults had a higher LS-aBMD Z score, BMAD, and TBS than the non-XLH subjects (p < 0.01). When stratified by metabolic status according to the serum values of bone formation markers, compensated adult patients had a higher LS-aBMD Z score, BMAD, and TBS than non-XLH subjects (p < 0.01). Noncompensated patients had higher LS-aBMD Z scores and BMAD results than non-XLH subjects. However, TBS values did not differ statistically significantly between those groups (p = 0.45).

CONCLUSION

The higher LS-aBMD Z score, BMAD, and TBS result in the XLH patients compared to non-XLH subjects indicates an increased amount of trabecular bone within the lumbar spine, regardless of extraskeletal calcifications.

Comparison of bone microstructure and strength in the distal radius and tibia between the different types of primary hypertrophic osteoarthropathy: an HR-pQCT study

Primary hypertrophic osteoarthropathy (PHO) is a hereditary bone disease that is grouped into PHO autosomal recessive 1 (PHOAR1) and PHO autosomal recessive 2 (PHOAR2) due to different causative genes. Data comparing bone microstructure between the two subtypes are scarce. This is the first study to find that PHOAR1 patients had inferior bone microstructure compared with PHOAR2 patients.

PURPOSE

The primary goal of this study was to assess bone microarchitecture and strength in PHOAR1 and PHOAR2 patients and to compare them with age- and sex-matched healthy controls (HCs). The secondary goal was to assess the differences between PHOAR1 and PHOAR2 patients.

METHODS

Twenty-seven male Chinese PHO patients (PHOAR1 = 7; PHOAR2 = 20) were recruited from Peking Union Medical College Hospital. The areal bone mineral density (aBMD) was assessed by dual-energy X-ray absorptiometry (DXA). Peripheral bone microarchitecture at the distal radius and tibia were evaluated by high-resolution peripheral quantitative computed tomography (HR-pQCT). Biochemical markers of PGE2, bone turnover, and Dickkopf-1 (DKK1) were investigated.

RESULTS

Compared with HCs, PHOAR1 and PHOAR2 patients had distinctively larger bone geometry, substantially lower vBMD at the radius and tibia, and compromised cortical microstructure at the radius. For trabecular bone, PHOAR1 and PHOAR2 patients showed different changes at the tibia. PHOAR1 patients had significant deficits in the trabecular compartment, resulting in lower estimated bone strength. Conversely, PHOAR2 patients showed a higher trabecular number, narrower trabecular separation, and lower trabecular network inhomogeneity than HCs, translating into preserved or slightly high estimated bone strength.

CONCLUSION

PHOAR1 patients had inferior bone microstructure and strength compared with PHOAR2 patients and HCs. Additionally, this study was the first to find differences in the bone microstructure between PHOAR1 and PHOAR2 patients.

Bone characteristics of autosomal dominant hypophosphatemic rickets patients

OBJECTIVE

Autosomal dominant hypophosphatemic rickets (ADHR) is a rare disease caused by activating mutations in fibroblast growth factor 23 (FGF23) gene. With FGF23 activation, ADHR is a good model to explore the effects of FGF23 on skeletal development and mineralization. However, the bone microarchitecture of ADHR patients is poorly investigated. This study aims to illustrate the bone properties of ADHR patients and clarify the effect of FGF23 on load bearing and non-load bearing bone.

METHODS

Bone microarchitectures of 11 ADHR subjects and sex- and age-matched healthy controls were analyzed by HR-pQCT. The effect of FGF23 mutations on load bearing and non-load bearing bone was explored by comparison of bone microarchitecture in distal radius and distal tibia. The BMD, bone microarchitecture and bone strength were compared between 7 ADHR patients and 7 age- and sex-matched XLH patients.

RESULTS

Among 11 subjects with FGF23 mutations, 10 patients presented with obvious symptoms, five of which had received 1-3 years of iron supplement, neutral phosphate, and calcitriol treatments. The symptomatic patients presented with low bone density and fractures in X rays, with decreased Z score of aBMD (L1-L4: -1.3 ± 1.4, femoral neck: -2.1 ± 1.8, total hip: -1.85 ± 1.6). Compared with controls, HR-pQCT analysis of 5 untreated ADHR patients showed increased total area (+61.6 %, p = 0.03) and cortical perimeter (+17.2 %, p = 0.03) in distal radius. No significant differences were found in other parameters in distal radius. In distal tibia, the patients presented obvious defects in cancellous bone, with decreased trabecular vBMD (-62.9 %, p = 0.003), trabecular BV/TV (-48.7 %, p = 0.003) and trabecular number (-42.2 %, p = 0.001). The trabecular separation (+113.3 %, p = 0.007) and trabecular network inhomogeneity (+226.7 %, p = 0.001) were accordingly increased. In addition to another 5 treated patients, the bone microarchitecture changes revealed similar pattern, but the increase of total area and cortical perimeter in distal radius was no longer statistically significant. The non-symptomatic ADHR patient demonstrated slightly decreased total vBMD, trabecular vBMD and trabecular BV/TV in distal tibia. The changing pattern of bone geometry and microarchitecture of ADHR patients were similar to XLH patients but showed less deficit and stronger bone strength.

CONCLUSION

ADHR patients presented increased total area and cortical perimeter in distal radius, and obvious defect in cancellous bone in distal tibia. FGF23 have impairment effect on trabecular bone especially in weight bearing site.

Bone microstructure evaluated by TBS and HR-pQCT in Chinese adults with X-linked hypophosphatemia

X-linked hypophosphatemia (XLH) is the most common form of heritable hypophosphatemic rickets. Although generalized mineralization defects have been observed, elevated areal bone mineral density (aBMD) in the lumbar spine measured by dual-energy X-ray absorptiometry (DXA) has also been found in XLH. In contrast, high-resolution peripheral quantitative computed tomography (HR-pQCT) revealed lower volumetric BMD (vBMD) and damaged bone microstructure in the peripheral bone in XLH. Trabecular bone score (TBS), which can assess the trabecular microstructure in the lumbar spine, has not been explored in XLH. This study aimed to explore TBS and its correlations with biochemical indices and HR-pQCT parameters in adult XLH patients. A total of 66 patients with XLH (26 men and 40 women) aged 29.6 ± 9.6 years and 66 age- and sex-matched healthy controls were included. Z score of lumbar spine aBMD was relatively high [2.0 (0.6, 3.7)], with normal TBS (1.475 ± 0.129) in the XLH patients. HR-pQCT revealed larger total and trabecular area in the peripheral bone in the XLH group compared with the control group. In addition, lower trabecular and cortical vBMD, lower trabecular number with greater separation, and lower bone strength at both the radius and tibia were found in the XLH group compared with the control group. Smaller cortical area, lower thickness and higher porosity in the XLH group compared with controls were only found at the radius. TBS was not associated with any biochemical indices, while better HR-pQCT parameters correlated with higher serum phosphate and lower ALP levels. TBS was positively related with aBMD but not HR-pQCT parameters. In conclusion, adult patients with XLH had high bone mass and normal TBS in the lumbar spine but compromised microarchitecture and bone strength in the peripheral bone. This finding indicated a site-specific effect of the disease on the skeleton in the XLH patients.

Bone Geometry, Density, Microstructure, and Biomechanical Properties in the Distal Tibia in Patients With Primary Hypertrophic Osteoarthropathy Assessed by Second-Generation High-Resolution Peripheral Quantitative Computed Tomography

Periosteosis refers to pathological woven bone formation beneath the cortical bone of the long bones. It is an imaging hallmark of primary hypertrophic osteoarthropathy (PHO) and also considered as one of the major diagnostic criteria of PHO patients. Up to date, detailed information on bone quality changes in long bones of PHO patients is still missing. This study aimed to evaluate bone microarchitecture and bone strength in PHO patients by using high-resolution peripheral quantitative computed tomography (HR-pQCT). The study comprised 20 male PHO patients with the average age of 27.0 years and 20 age- and sex-matched healthy controls. The areal bone mineral density (aBMD) was assessed at the lumbar spine (L₁ -L₄ ) and hip (total hip and femoral neck) by dual-energy X-ray absorptiometry (DXA). Bone geometry, volumetric bone mineral density (vBMD), and microstructure parameters at the distal tibia were evaluated by using HR-pQCT. Bone strength was evaluated by finite element analysis (FEA) based on HR-pQCT screening at distal tibia. Urinary prostaglandin E₂ (PGE₂ ), serum phosphatase (ALP), beta-C-telopeptides of type I collagen (β-CTX), soluble receptor activator of nuclear factor-κB ligand (sRANKL), osteoprotegerin (OPG), and neuronal calcitonin gene-related peptide (CGRP) were investigated. As compared with healthy controls, PHO patients had larger bone cross-sectional areas; lower total, trabecular, and cortical vBMD; compromised bone microstructures with more porous cortices, thinned trabeculae, reduced trabecular connectivity, and relatively more significant resorption of rod-like trabeculae at distal tibia. The apparent Young's modulus was significantly lower in PHO patients. The concentration of PGE₂ , biomarkers of bone resorption (β-CTX and sRANKL/OPG ratio), and the neuropeptide CGRP were higher in PHO patients versus healthy controls. PGE₂ level correlated negatively with vBMD and estimated bone strength and positively with bone geometry at distal tibia. The present HR-pQCT study is the first one illustrating the microarchitecture and bone strength features in long bones. © 2021 American Society for Bone and Mineral Research (ASBMR).

Bone Impairment in a Large Cohort of Chinese Patients With Tumor-Induced Osteomalacia Assessed by HR-pQCT and TBS

Tumor-induced osteomalacia (TIO) is a rare paraneoplastic syndrome caused by excessive production of fibroblast growth factor 23 (FGF23) by a tumor. Previous studies have revealed generalized mineralization defects and low areal bone mineral density (aBMD) in TIO. However, data on the bone microarchitecture in TIO are limited. In this study, we evaluated the microarchitecture in the peripheral (distal radius and tibia) and axial (lumbar spine) skeleton using high-resolution peripheral quantitative computed tomography (HR-pQCT) and trabecular bone score (TBS) and investigated related factors in a large cohort of Chinese patients with TIO. A total of 186 patients with TIO who had undergone dual-energy X-ray absorptiometry (DXA) or HR-pQCT scans were enrolled. Compared with age-, sex-, and body mass index (BMI)-matched healthy controls, TIO patients (n = 113) had lower volumetric BMD, damaged microstructure, and reduced bone strength in the peripheral skeleton, especially at the tibia. The average TBS obtained from 173 patients was 1.15 ± 0.16. The proportion of patients with abnormal TBS (<1.35) was higher than that with low L₁ to L₄ aBMD Z-score (Z ≤ -2) (43.9% versus 89.6%, p < 0.001). Higher intact fibroblast growth factor 23 (iFGF23), intact parathyroid hormone (iPTH), alkaline phosphatase, and β-isomerized C-terminal telopeptide of type I collagen (β-CTx) levels, more severe mobility impairment, and a history of fracture were associated with poorer HR-pQCT parameters but not with lower TBS. However, greater height loss and longer disease duration were correlated with worse HR-pQCT parameters and TBS. Moreover, TBS was correlated with both trabecular and cortical HR-pQCT parameters in TIO. In conclusion, we revealed impaired bone microarchitecture in the axial and peripheral skeleton in a large cohort of Chinese TIO patients. HR-pQCT parameters and TBS showed promising advantages over aBMD for assessing bone impairment in patients with TIO. A longer follow-up period is needed to observe changes in bone microarchitecture after tumor resection. © 2021 American Society for Bone and Mineral Research (ASBMR).

Potential influences on optimizing long-term musculoskeletal health in children and adolescents with X-linked hypophosphatemia (XLH)

In recent years, much progress has been made in understanding the mechanisms of bone growth and development over a lifespan, including the crosstalk between muscle and bone, to achieve optimal structure and function. While there have been significant advances in understanding how to help improve and maintain bone health in normal individuals, there is limited knowledge on whether these mechanisms apply or are compromised in pathological states. X-linked hypophosphatemia (XLH) (ORPHA:89936) is a rare, heritable, renal phosphate-wasting disorder. The resultant chronic hypophosphatemia leads to progressive deterioration in musculoskeletal function, including impaired growth, rickets, and limb deformities in children, as well as lifelong osteomalacia with reduced bone quality and impaired muscle structure and function. The clinical manifestations of the disease vary both in presentation and severity in affected individuals, and many of the consequences of childhood defects persist into adulthood, causing significant morbidity that impacts physical function and quality of life. Intervention to restore phosphate levels early in life during the critical stages of skeletal development in children with XLH could optimize growth and may prevent or reduce bone deformities in childhood. A healthier bone structure, together with improved muscle function, can lead to physical activity enhancing musculoskeletal health throughout life. In adults, continued management may help to maintain the positive effects acquired from childhood treatment, thereby slowing or halting disease progression. In this review, we summarize the opinions from members of a working group with expertise in pediatrics, epidemiology, and bone, joint and muscle biology, on potential outcomes for people with XLH, who have been optimally treated from an early age and continue treatment throughout life.

Bone Volumetric Density, Microarchitecture, and Estimated Bone Strength in Tumor-Induced Rickets/Osteomalacia Versus X-linked Hypophosphatemia in Chinese Adolescents

Tumor-induced rickets/osteomalacia (TIR/O) severely impairs bone microarchitecture and bone strength. However, no study has described the microarchitectural quality of bone in adolescent patients with TIR/O. TIR/O affects bone quality more severely than the inherited causes of hypophosphatemia, the most common form of which is X-linked hypophosphatemia (XLH). Nevertheless, differences of the microarchitectural quality of the bone between TIR/O and XLH have never been clarified. Therefore, in this study, we used high-resolution peripheral quantitative computed tomography to assess bone microarchitecture in five Chinese adolescent TIR/O patients, and these were compared with 15 age- and gender-matched XLH patients as well as 15 age- and gender-matched healthy controls. Compared with the healthy controls, the TIR/O patients presented with significantly lower volumetric bone mineral densities (vBMDs), severely affected bone microarchitecture, and profoundly weaker bone strength. The distal tibia was more severely affected than the distal radius. Compared with the XLH patients, the TIR/O patients showed deteriorated bone quality notably at the distal tibia and in the cancellous compartment, reflected by 45.9% lower trabecular vBMD (p = 0.029), 40.2% lower trabecular fraction (p = 0.020), 40.6% weaker stiffness (p = 0.058), and 42.7% weaker failure load (p = 0.039) at the distal tibia. The correlation analysis showed that a higher level of serum FGF23 and a lower level of serum phosphate were associated with a poorer bone microarchitecture and a weaker estimated bone strength in the hypophosphatemic patients of our study. In conclusion, our study demonstrated significantly lower vBMDs, severely impaired bone microarchitecture, and profoundly weaker bone strength in Chinese adolescent patients with TIR/O, notably at the distal tibia, compared with the same parameters in age- and sex-matched healthy controls and XLH patients, which was possibly caused by excessive FGF23 production and secretion, chronically severe hypophosphatemia, and weak mechanical stimulus at the lower extremities. These findings further our understanding of the impact of different kinds of hypophosphatemic rickets/osteomalacia on bone quality.

Conductive Hearing Loss in the Hyp Mouse Model of X-Linked Hypophosphatemia Is Accompanied by Hypomineralization of the Auditory Ossicles

X-linked hypophosphatemia (XLH) is a hereditary musculoskeletal disorder caused by loss-of-function mutations in the PHEX gene. In XLH, increased circulating fibroblast growth factor 23 (FGF23) levels cause renal phosphate wasting and low concentrations of 1,25-dihydroxyvitamin D, leading to an early clinical manifestation of rickets. Importantly, hearing loss is commonly observed in XLH patients. We present here data from two XLH patients with marked conductive hearing loss. To decipher the underlying pathophysiology of hearing loss in XLH, we utilized the Hyp mouse model of XLH and measured auditory brain stem responses (ABRs) and distortion product otoacoustic emissions (DPOAEs) to functionally assess hearing. As evidenced by the increased ABR/DPOAE threshold shifts in the mid-frequency range, these measurements indicated a predominantly conductive hearing loss in Hyp mice compared to wild-type (WT) mice. Therefore, we carried out an in-depth histomorphometric and scanning electron microscopic analysis of the auditory ossicles. Quantitative backscattered electron imaging (qBEI) indicated a severe hypomineralization of the ossicles in Hyp mice, evidenced by lower calcium content (CaMean) and higher void volume (ie, porosity) compared to WT mice. Histologically, voids correlated with unmineralized bone (ie, osteoid), and the osteoid volume per bone volume (OV/BV) was markedly higher in Hyp mice than WT mice. The density of osteocyte lacunae was lower in Hyp mice than in WT mice, whereas osteocyte lacunae were enlarged. Taken together, our findings highlight the importance of ossicular mineralization for hearing conduction and point toward the potential benefit of improving mineralization to prevent hearing loss in XLH. © 2021 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Adult rheumatologic features, treatment and complications of X-linked hypophosphatemia

X-linked hypophosphatemia (XLH) is a rare genetic phosphate disorder caused mainly by PHEX mutations. Unlike for children, knowledge of the disease's manifestations in adults is limited. Musculoskeletal symptoms are the main feature of the disease in young adults associated with a heavy burden on patients' life. They include fractures and pseudofractures, pain, joint stiffness, osteoarthritis, enthesopathies, and muscle weakness, eventually leading to impaired quality of life. Conventional treatment with phosphate supplements and vitamin D analogs is indicated in symptomatic patients. Appropriate rehabilitation is also a key to the management of the disease to improve physical function and decrease pain, stiffness, and fatigue. Regarding the incidence and consequences of musculoskeletal features in XLH, all patients should be assessed by a bone disease specialist and, if necessary, managed by a multidisciplinary team.

Microarchitectural parameters and bone mineral density in patients with tumour-induced osteomalacia by HR-pQCT and DXA

INTRODUCTION

Tumour-induced osteomalacia (TIO) is a rare paraneoplastic condition characterised by decreased tubular phosphate reabsorption. The purpose of this study is to evaluate bone mineral density (BMD) and microarchitecture in six TIO patients, compared with 18 healthy controls.

METHODS

Volumetric BMD and microarchitecture were evaluated by high-resolution peripheral quantitative computed tomography (HR-pQCT), and areal BMD by dual-energy X-ray absorptiometry (DXA). Differences between groups were significant for p < .05.

RESULTS

All TIO subjects were healthy until the development of diffuse bone pain and multiple skeletal fractures and deformities. At baseline, sPi and TmPi/GFR were low and patients were on vitamin D and phosphate replacement at the study. Compared with controls, TIO patients had lower aBMD at lumbar spine and hip, and lower vBMD at trabecular, cortical and entire bone, at distal radius (R) and distal tibia (T): trabecular vBMD (R = 118.3 × 177.1; T = 72.3 × 161.3 gHA/cm³ ); cortical vBMD (R = 782.3 × 866.5; T = 789.1 × 900.9 gHA/cm³ ); total region vBMD (R = 234.5 × 317; T = 167.1 × 295.8 gHA/cm³ ). Bone microarchitecture was very heterogeneous among patients and significantly different from controls: lower cortical thickness (R = 0.59 × 0.80; T = 0.90 × 1.31 mm), bone volume-to-total volume ratio (R = 0.09 × 0.14; T = 0.06 × 0.13) and Tb.N (R = 1.46 × 2.10; T = 0.93 × 1.96 mm^-1 ) and also higher Tb.Sp (R = 0.70 × 0.41; T = 1.28 × 0.45 mm) and Tb.1/N.SD (R = 0.42 × 0.18; T = 0.87 × 0.20 mm).

CONCLUSION

In this original study of TIO patients, DXA and HR-pQCT evaluation identified lower areal and volumetric BMD and severely impaired microarchitecture at cortical and trabecular bones, which probably contribute to bone fragility and fractures.

Contribution of imaging to the diagnosis and follow up of X-linked hypophosphatemia

X-linked hypophosphatemia (XLH) is the most common form of inheritable rickets. The disease is caused principally by PHEX mutations leading to increased concentrations of circulating intact FGF23, hence renal phosphate wasting, hypophosphatemia, and decreased circulating levels of 1,25(OH)₂ vitamin D. The chronic hypophosphatemia leads to rickets and osteomalacia through a combination of mechanisms, including a lack of endochondral ossification and impaired mineralization. Imaging has a major role in determining the diagnosis of rickets and its cause, detecting complications as early as possible, and helping in treatment monitoring.

Traditional and Non-traditional Risk Factors for Osteoporosis in CKD

Osteoporosis is a state of bone fragility with reduced skeletal resistance to trauma, and consequently increased risk of fracture. A wide range of conditions, including traditional risk factors, lifestyle choices, diseases and their treatments may contribute to bone fragility. It is therefore not surprising that the multi-morbid patient with chronic kidney disease (CKD) is at a particularly high risk. CKD is associated with reduced bone quantity, as well as impaired bone quality. Bone fragility in CKD is a composite of primary osteoporosis, accumulation of traditional and uremia-related risk factors, assaults brought on by systemic disease, and detrimental effects of drugs. Some risk factors are modifiable and represent potential targets for intervention. This review provides an overview of the heterogeneity of bone fragility in CKD.

Impact of Early Conventional Treatment on Adult Bone and Joints in a Murine Model of X-Linked Hypophosphatemia

X-linked hypophosphatemia (XLH) is the most common form of genetic rickets. Mainly diagnosed during childhood because of growth retardation and deformities of the lower limbs, the disease affects adults with early enthesopathies and joint structural damage that significantly alter patient quality of life. The conventional treatment, based on phosphorus supplementation and active vitamin D analogs, is commonly administered from early childhood to the end of growth; unfortunately, it does not allow complete recovery from skeletal damage. Despite adequate treatment during childhood, bone and joint complications occur in adults and become a dominant feature in the natural history of the disease. Our previous data showed that the Hyp mouse is a relevant model of XLH for studying early enthesophytes and joint structural damage. Here, we studied the effect of conventional treatment on the development of bone and joint alterations in this mouse model during growth and young adulthood. Mice were supplemented with oral phosphorus and calcitriol injections, following two timelines: (i) from weaning to 3 months of age and (ii) from 2 to 3 months to evaluate the effects of treatment on the development of early enthesophytes and joint alterations, and on changes in bone and joint deformities already present, respectively. We showed that early conventional treatment improved bone microarchitecture, and partially prevented bone and joint complications, but with no noticeable improvement in enthesophytes. In contrast, later administration had limited efficacy in ameliorating bone and joint alterations. Despite the improvement in bone microarchitecture, the conventional treatment, early or late, had no effect on osteoid accumulation. Our data underline the usefulness of the Hyp murine model for preclinical studies on skeletal and extraskeletal lesions. Although the early conventional treatment is important for the improvement of bone microarchitecture, the persistence of osteomalacia implies seeking new therapeutic strategies, in particular anti-FGF23 approach, in order to optimize the treatment of XLH.

Clinical Characteristics and Bone Features of Autosomal Recessive Hypophosphatemic Rickets Type 1 in Three Chinese Families: Report of Five Chinese Cases and Review of the Literature

Autosomal recessive hypophosphatemic rickets type 1 (ARHR1) was reported to be caused by homozygous mutation of dentin matrix protein 1 (DMP1). To date, very few cases have been reported. Here, we summarized clinical, laboratory and imaging findings of ARHR1 patients in our hospital. Literature review was performed to analyze genotype-phenotype correlation. Five Chinese patients from three unrelated pedigrees presented with lower extremity deformity and short stature. Hypophosphatemia, elevated alkaline phosphatase, high intact fibroblast growth factor 23 and sclerostin were found. X-ray uncovered coexistence of osteomalacia and osteosclerosis. Although areal bone mineral density (aBMD) of axial bone measured by dual-energy X-ray absorptiometry was relatively high in all patients, volumetric BMD (vBMD) and microstructure of one adult patient's peripheral bone detected by HR-pQCT were damaged. Mutation analyses of DMP1 revealed three homozygous mutations including two novel mutations, c.54 + 1G > C and c.94C > A (p.E32X), and a reported mutation c.184-1G > A. Genotype-phenotype correlation analysis including 30 cases (25 from literature review and 5 from our study) revealed that patients harboring mutations affecting C-terminal fragment of DMP1 presented with shorter stature (Z score of height = - 3.4 ± 1.6 vs - 1.0 ± 1.6, p = 0.001) and lower serum phosphate level (0.70 ± 0.15 vs 0.84 ± 0.16, p = 0.03) than those harboring mutations only affecting N-terminal fragment. In summary, we reported five Chinese ARHR1 patients and identified two novel DMP1 mutations. High aBMD and local osteosclerosis in axial bone with low vBMD and damaged microstructure in peripheral bone were featured. Genotype-phenotype correlation analysis confirmed the important role of C-terminal fragment of DMP1.

Mineralized tissues in hypophosphatemic rickets

Hypophosphatemic rickets is caused by renal phosphate wasting that is most commonly due to X-linked dominant mutations in PHEX. PHEX mutations cause hypophosphatemia indirectly, through the increased expression of fibroblast growth factor 23 (FGF23) by osteocytes. FGF23 decreases renal phosphate reabsorption and thereby increases phosphate excretion. The lack of phosphate leads to a mineralization defect at the level of growth plates (rickets), bone tissue (osteomalacia), and teeth, where the defect facilitates the formation of abscesses. The bone tissue immediately adjacent to osteocytes often remains unmineralized ("periosteocytic lesions"), highlighting the osteocyte defect in this disorder. Common clinical features of XLH include deformities of the lower extremities, short stature, enthesopathies, dental abscesses, as well as skull abnormalities such as craniosynostosis and Chiari I malformation. For the past four decades, XLH has been treated by oral phosphate supplementation and calcitriol, which improves rickets and osteomalacia and the dental manifestations, but often does not resolve all aspects of the mineralization defects. A newer treatment approach using inactivating FGF23 antibodies leads to more stable control of serum inorganic phosphorus levels and seems to heal rickets more reliably. However, the long-term benefits of FGF23 antibody treatment remain to be elucidated.

Decreased Compressional Sound Velocity Is an Indicator for Compromised Bone Stiffness in X-Linked Hypophosphatemic Rickets (XLH)

Objectives: To assess the diagnostic potential of bidirectional axial transmission (BDAT) ultrasound, and high-resolution peripheral quantitative computed tomography (HR-pQCT) in X-linked hypophosphatemia (XLH, OMIM #307800), a rare genetic disorder of phosphate metabolism caused by mutations in the PHEX gene. Methods: BDAT bone ultrasound was performed at the non-dominant distal radius (33% relative to distal head) and the central left tibia (50%) in eight XLH patients aged between 4.2 and 20.8 years and compared to twenty-nine healthy controls aged between 5.8 and 22.4 years. In eighteen controls, only radius measurements were performed. Four patients and four controls opted to participate in HR-pQCT scanning of the ultradistal radius and tibia. Results: Bone ultrasound was feasible in patients and controls as young as 4 years of age. The velocity of the first arriving signal (ν_FAS) in BDAT ultrasound was significantly lower in XLH patients compared to healthy controls: In the radius, mean ν_FAS of XLH patients and controls was 3599 ± 106 and 3866 ± 142 m/s, respectively (-6.9%; p < 0.001). In the tibia, it was 3578 ± 129 and 3762 ± 124 m/s, respectively (-4.9%; p = 0.006). HR-pQCT showed a higher trabecular thickness in the tibia of XLH patients (+16.7%; p = 0.021). Conclusions: Quantitative bone ultrasound revealed significant differences in cortical bone quality of young XLH patients as compared to controls. Regular monitoring of XLH patients by a radiation-free technology such as BDAT might provide valuable information on bone quality and contribute to the optimization of treatment. Further studies are needed to establish this affordable and time efficient method in the XLH patients.

The Osteocyte as the New Discovery of Therapeutic Options in Rare Bone Diseases

Osteocytes are the most abundant (~95%) cells in bone with the longest half-life (~25 years) in humans. In the past osteocytes have been regarded as vestigial cells in bone, since they are buried inside the tough bone matrix. However, during the last 30 years it has become clear that osteocytes are as important as bone forming osteoblasts and bone resorbing osteoclasts in maintaining bone homeostasis. The osteocyte cell body and dendritic processes reside in bone in a complex lacuno-canalicular system, which allows the direct networking of osteocytes to their neighboring osteocytes, osteoblasts, osteoclasts, bone marrow, blood vessels, and nerves. Mechanosensing of osteocytes translates the applied mechanical force on bone to cellular signaling and regulation of bone adaptation. The osteocyte lacuno-canalicular system is highly efficient in transferring external mechanical force on bone to the osteocyte cell body and dendritic processes via displacement of fluid in the lacuno-canalicular space. Osteocyte mechanotransduction regulates the formation and function of the osteoblasts and osteoclasts to maintain bone homeostasis. Osteocytes produce a variety of proteins and signaling molecules such as sclerostin, cathepsin K, Wnts, DKK1, DMP1, IGF1, and RANKL/OPG to regulate osteoblast and osteoclast activity. Various genetic abnormality-associated rare bone diseases are related to disrupted osteocyte functions, including sclerosteosis, van Buchem disease, hypophosphatemic rickets, and WNT1 and plastin3 mutation-related disorders. Meticulous studies during the last 15 years on disrupted osteocyte function in rare bone diseases guided for the development of various novel therapeutic agents to treat bone diseases. Studies on genetic, molecular, and cellular mechanisms of sclerosteosis and van Buchem disease revealed a role for sclerostin in bone homeostasis, which led to the development of the sclerostin antibody to treat osteoporosis and other bone degenerative diseases. The mechanism of many other rare bone diseases and the role of the osteocyte in the development of such conditions still needs to be investigated. In this review, we mainly discuss the knowledge obtained during the last 30 years on the role of the osteocyte in rare bone diseases. We speculate about future research directions to develop novel therapeutic drugs targeting osteocyte functions to treat both common and rare bone diseases.

The Importance of Biologically Active Vitamin D for Mineralization by Osteocytes After Parathyroidectomy for Renal Hyperparathyroidism

Hypomineralized matrix is a factor determining bone mineral density. Increased perilacunar hypomineralized bone area is caused by reduced mineralization by osteocytes. The importance of vitamin D in the mineralization by osteocytes was investigated in hemodialysis patients who underwent total parathyroidectomy (PTX) with immediate autotransplantation of diffuse hyperplastic parathyroid tissue. No previous reports on this subject exist. The study was conducted in 19 patients with renal hyperparathyroidism treated with PTX. In 15 patients, the serum calcium levels were maintained by subsequent administration of alfacalcidol (2.0 μg/day), i.v. calcium gluconate, and oral calcium carbonate for 4 weeks after PTX (group I). This was followed in a subset of 4 patients in group I by a reduced dose of 0.5 μg/day until 1 year following PTX; this was defined as group II. In the remaining 4 patients, who were not in group I, the serum calcium (Ca) levels were maintained without subsequent administration of alfacalcidol (group III). Transiliac bone biopsy specimens were obtained in all groups before and 3 or 4 weeks after PTX to evaluate the change of the hypomineralized bone area. In addition, patients from group II underwent a third bone biopsy 1 year following PTX. A significant decrease of perilacunar hypomineralized bone area was observed 3 or 4 weeks after PTX in all group I and II patients. The area was increased again in the group II patients 1 year following PTX. In group III patients, an increase of the hypomineralized bone area was observed 4 weeks after PTX. The maintenance of a proper dose of vitamin D is necessary for mineralization by osteocytes, which is important to increase bone mineral density after PTX for renal hyperparathyroidism. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

High FGF23 levels are associated with impaired trabecular bone microarchitecture in patients with osteoporosis

This cross-sectional study examined the associations between c-terminal FGF23 levels, laboratory markers of bone metabolism and bone microarchitecture in 82 patients with osteoporosis. Higher FGF23 levels were associated with impaired trabecular but not cortical bone microarchitecture, and this was confirmed after adjusting for confounding variables such as age or BMI.

INTRODUCTION

Fibroblast growth factor 23 (FGF23) is an endocrine hormone-regulating phosphate and vitamin D metabolism. While its mode of action is well understood in diseases such as hereditary forms of rickets or tumor-induced osteomalacia, the interpretation of FGF23 levels in patients with osteoporosis with regard to bone microarchitecture is less clear.

METHODS

C-terminal FGF23 levels and bone turnover markers were assessed in 82 patients with osteoporosis (i.e., DXA T-score ≤ - 2.5 at the lumbar spine or total hip). Bone microarchitecture was measured by high-resolution peripheral quantitative computed tomography (HR-pQCT) at the distal radius and tibia. Data were analyzed in a cross-sectional design using correlation and regression models.

RESULTS

We found a significant negative logarithmic correlation between FGF23 levels and trabecular but not cortical bone microarchitecture at both skeletal sites. Furthermore, using a multiple linear regression model, we confirmed FGF23 as a predictor for reduced trabecular parameters even when adjusting for confounding factors such as age, BMI, phosphate, bone-specific alkaline phosphatase, vitamin D3, and PTH.

CONCLUSIONS

Taken together, high FGF23 levels are associated with impaired trabecular bone microarchitecture in osteoporosis patients, and this association seems to occur after adjustment of confounding variables including phosphate and vitamin D. Future longitudinal studies are now needed to validate our findings and investigate FGF23 in relation to fracture risk.

Congenital hypophosphataemia in adults: determinants of bone turnover markers and amelioration of renal phosphate wasting following total parathyroidectomy

Congenital hypophosphataemia (CH) is a collection of disorders that cause defective bone mineralisation manifesting with rickets in childhood and osteomalacia in adulthood. Bone turnover markers (BTMs) are surrogate measures of metabolic bone disease severity. We explored the utility of BTMs in 27 adults with CH: 23 had X-linked hypophosphataemia (XLH), of whom 2 were hypoparathyroid post-total parathyroidectomy (PTx); 2 had autosomal dominant hypophosphataemic rickets (ADHR), and 2 had none of the known mutations. We measured the renal tubular maximum reabsorption rate of phosphate (TmP/GFR), C-terminal fibroblast growth factor 23 (FGF23), parathyroid hormone (PTH), ionised calcium, 1,25-dihydroxyvitamin D [1,25(OH)₂D], and a panel of BTMs: serum bone-specific alkaline phosphatase (bone ALP), osteocalcin (Oc), total procollagen type I amino-terminal propeptide (PINP), and carboxy-terminal telopeptide of type I collagen (CTX); and urine amino-terminal telopeptides of type I collagen (uNTX). After excluding 2 patients with XLH and PTx, the frequency of abnormal elevation in BTMs was: bone ALP (96%); CTX (72%); PINP (52%); uNTX (48%); Oc (28%). The strongest association with bone ALP was TmP/GFR. Those patients receiving phosphate supplements and alfacalcidol had significant elevation in CTX. The 2 patients with XLH and PTx had normalisation of TmP/GFR and near normalisation of BTMs post-operatively, despite marked elevation in both C-terminal and intact FGF23. In conclusion, BTMs in our CH patients indicated that most have abnormalities consistent with osteomalacia and many have mild secondary hyperparathyroidism; and the normalisation of TmP/GFR after total PTx in 2 cases of XLH remains unexplained, but possible causes are speculated.

The Lifelong Impact of X-Linked Hypophosphatemia: Results From a Burden of Disease Survey

CONTEXT

X-linked hypophosphatemia (XLH) is characterized by excess fibroblast growth factor 23 (FGF23), hypophosphatemia, skeletal abnormalities, and growth impairment. We aimed to understand the burden of disease of XLH across the lifespan.

METHODS

Responses were collected from adults with XLH and parents/caregivers of a child with XLH in an online survey, including multiple-choice and open-ended questions on demographics, disease manifestations, treatment history, assistive device use, and age-specific patient-reported outcomes (PROs).

RESULTS

Data were collected from 232 adults with XLH (mean age, 45.6 years; 76% female) and 90 parents/caregivers of a child with XLH (mean age, 9.1 years; 56% female). Mean age recalled for symptom onset was 3.2 years for adults and 1.3 years for children. When surveyed, nearly all children (99%) and 64% of adults were receiving oral phosphate, active vitamin D, or both. Prior participation in a trial investigating burosumab, a fully human monoclonal antibody against FGF23, was reported in 3% of children and 10% of adults; of these respondents, only one child reported current treatment with burosumab at the time of the survey. Both children and adults reported typical features of XLH, including abnormal gait (84% and 86%, respectively), bowing of the tibia/fibula (72% and 77%), and short stature (80% and 86%). Nearly all adults (97%) and children (80%) reported bone or joint pain/stiffness. Adults reported a history of fractures (n/N = 102/232; 44%), with a mean (SD) age at first fracture of 26 (16) years. Adults reported osteophytes (46%), enthesopathy (27%), and spinal stenosis (19%). Mean scores for PROs evaluating pain, stiffness, and physical function were worse than population norms. Analgesics were taken at least once a week by 67% of adults.

CONCLUSIONS

Despite the common use of oral phosphate and active vitamin D established in the 1980s, children with XLH demonstrate a substantial disease burden, including pain and impaired physical functioning that persists, as demonstrated by similar responses reported in adults with XLH.

Elevated Bone Remodeling Markers of CTX and P1NP in Addition to Sclerostin in Patients with X-linked Hypophosphatemia: A Cross-Sectional Controlled Study

Aspects of bone remodeling have only been scarcely studied in X-linked hypophosphatemia (XLH). In this cross-sectional controlled study, we assessed biochemical indices of bone remodeling and sclerostin in 27 adult patients (median age 47 [range 24-79] years, 19 women, 8 men) with XLH matched with 81 healthy control subjects (1:3) with respect to age-, sex-, and menopausal status. Markers of bone resorption (carboxyterminal cross-linked telopeptide of type 1 collagen, CTX) and formation (N-terminal propeptide of type 1 procollagen, P1NP) were higher in XLH patients compared to controls (median [IQR] 810 [500-1340] vs 485 [265-715] ng/l and 90 [57-136] vs 49 [39-65] ug/l, respectively, both p < 0.001) as well as sclerostin (0.81 [0.60-1.18] vs 0.54 [0.45-0.69] ng/ml, p < 0.001). Similar differences were found when comparing currently treated (with phosphate and alfacalcidol) (n = 11) and untreated (n = 16) XLH patients with their respective controls. We found no significant associations with treatment status and indices of bone remodeling or sclerostin although sclerostin tended to be increased in untreated versus treated (p = 0.06). In contrast to previous histomorphometric studies suggesting a low remodeling activity in XLH, these biochemical indices suggest high osteoblast and osteoclast activity. Further studies are needed to ascertain if the higher sclerostin level in XLH is related to osteocyte dysfunction or represents a secondary phenomenon.

X-ray densitometric indices of proximal phalanx, medial phalanx and ungular pelvic limb bones as criteria for age diagnosis of cattle in forensic veterinary expertise

Morphological parameters of biological material are extremely informative in diagnostic studies, in particular, to determine the species, sex, time of death, the term of burial. The most informative object for these tasks is the skeleton, because changes in the bones are stored for a long time, while soft tissue is subjected to rotting. Bone tissue is the most durable, but at the same time, it is very labile and reacts to all metabolic processes in the body. The object of the study was proximal phalanx, medial phalanx and ungular bone of the pelvic limb of cattle ranging in age from newborn to 12 years old. Radiography of the proximal phalanx, medial phalanx and ungular bones of the pelvic limb was performed on the Arman apparatus. The bones were subjected to X-ray in the lateromedial projection. The inner and outer sections of the tubular bone were determined. The mathematical modeling of the interaction of X-rays and the cortical layer of bones of fingers (proximal phalanx, medial phalanx and ungular) of cattle was carried out in this work. It is established that this process is described by Bouger's law. The physico-mathematical model of proximal phalanx, medial phalanx and ungular bones has been calculated, on the basis of which it was possible to calculate the X-ray densitometric indices of these bones of cattle. The age features of dynamics of X-ray densitometric indices of the proximal phalanx, medial phalanx and ungular bones were established and a method of determining the age of cattle according to this criterion was proposed. A mathematical model for the proximal phalanx, medial phalanx and ungular bones of the pelvic limbs of cattle that can be applied in X-ray densitometry uses: for the average third proximal phalanx – section of heterogeneous tubular structure modeled by a semicircle; for a medial phalanx bone – a section of a triangular shape; for the ungular bone – a heterogeneous structure, the plantar surface is inscribed in a rectangle. The process of interaction of X-rays with the bone structure of the examined pelvic limb bones can be described by Bouguer's law. The developed mathematical modeling of this interaction and the algorithm for its analysis is the basis for determining the age of cattle for X-ray densitometric indices of the proximal phalanx, medial phalanx and ungular bones of pelvic limbs. By X-ray densitometry of the proximal phalanx and medial phalanx bones of the pelvic limbs extremities one can diagnose the age of bovine animals from birth to 5 years, but according to ungular bones – from birth to 10 years. X-ray densitometry of medial phalanx and ungular bones of pelvic limbs can be used for diagnosing bovine cattle in a complex with other morphological, chemical and physical methods of investigation.

Impact of Conventional Medical Therapy on Bone Mineral Density and Bone Turnover in Adult Patients with X-Linked Hypophosphatemia: A 6-Year Prospective Cohort Study

X-linked hypophosphatemia (XLH) is a rare, inheritable disorder manifesting as rickets in children and osteomalacia in adults. While conventional medical treatment with oral phosphate and alfacalcidol is recommended in childhood, it is undecided whether adults should continue therapy. The aim of this 6-year prospective study was to determine the impact of conventional medical treatment on areal bone mineral density (aBMD), bone turnover markers (BTMs) and measures of calcium homeostasis in 27 adult patients with XLH, 11 of whom received medical treatment. Lumbar spine and total hip aBMD, as assessed by DXA, and biochemical measures of calcium, phosphate, PTH, 1,25 dihydroxyvitamin D₂₊₃ (1,25(OH)₂D), fibroblast growth factor 23 (FGF23), P1NP and CTX were measured at baseline and at follow-up. The renal tubular reabsorption of PO₄ (TmPO₄/GFR) was calculated at both time points. Multilevel mixed-effects linear regression models were used for analyses. During the study period, spine and hip aBMD did not change significantly between treated and non-treated XLH patients. There was a trend towards a decrease in calcium, phosphate and TmPO₄/GFR in the treatment group (p = 0.057, p = 0.080 and p = 0.063, respectively), whereas PTH, FGF23, 1,25(OH)₂D and P1NP did not change significantly in either groups. However, CTX increased significantly in the treated compared to non-treated group (p = 0.044). Continuing conventional medical therapy in adulthood, although associated with increased bone resorption, does not promote or prevent loss of bone mass as evidenced from the stable aBMD of the hip and spine in XLH patients.

Evaluation of bone mineral density and microarchitectural parameters by DXA and HR-pQCT in 37 children and adults with X-linked hypophosphatemic rickets

In X-linked hypophosphatemic (XLH) rickets, dual-energy X-ray absorptiometry (DXA) measurements must be analyzed with caution. High-resolution peripheral quantitative computed tomography (HR-pQCT) analysis suggested that XLH primarily affects the cancellous compartment, with the tibia more affected than the radius. Effective treatment of XLH appears to positively affect bone mineralization, mainly in the bone cortex.

INTRODUCTION

The purpose of this study is to evaluate bone mineral density (BMD) and microarchitecture in 37 patients (13 children and 24 adults) with XLH confirmed by PHEX mutations from a tertiary center compared to healthy controls.

METHODS

Areal BMD (aBMD) was evaluated by DXA, whereas volumetric BMD (vBMD) and microarchitectural parameters were analyzed by HR-pQCT.

RESULTS

Adult XLH patients had higher lumbar aBMD (p < 0.01) than the controls. At the radius, the vBMD was similar between XLH patients and controls. At the tibia, XLH patients had lower total vBMD (p = 0.04), likely resulting from decreased trabecular vBMD (p < 0.01), and this difference was observed in the children and adult groups. Analysis based on metabolic status showed that the adult XLH patients with non-compensated disease had lower cortical vBMD at the tibia than the compensated XLH patients (p = 0.03). The microarchitectural differences at the radius and tibia included lower trabecular number (p < 0.01), greater trabecular separation (p < 0.01), and higher trabecular network inhomogeneity (p < 0.01) in XLH patients compared to their controls. At the radius, adults exhibited greater trabecular deficits than were seen in children.

CONCLUSIONS

In XLH patients, DXA measurements must be analyzed with caution due to the interference of anatomic and anthropometric factors. HR-pQCT analysis suggested that XLH primarily affects the cancellous compartment, with the tibia more affected than the radius. Effective treatment of XLH appears to positively affect bone mineralization, mainly in the bone cortex.

Orthopedic complications in diabetes

Diabetes is associated with a number of lower extremity orthopedic conditions and complications including fractures, Charcot neuroarthropathy, plantar ulcers, and infection. These complications are of significant clinical concern in terms of morbidity, mortality, and socioeconomic costs. A review of each condition is discussed, with particular emphasis on the clinical importance, diagnostic considerations, and orthopedic treatment recommendations. The goal of the article is to provide a clinical picture of the challenges that orthopedic surgeons confront, and highlight the need for specific clinical guidelines in diabetic patients.

Bone Geometry, Volumetric Density, Microarchitecture, and Estimated Bone Strength Assessed by HR-pQCT in Adult Patients With Type 1 Diabetes Mellitus

The primary goal of this cross-sectional in vivo study was to assess peripheral bone microarchitecture, bone strength, and bone remodeling in adult type 1 diabetes (T1D) patients with and without diabetic microvascular disease (MVD+ and MVD-, respectively) and to compare them with age-, gender-, and height-matched healthy control subjects (CoMVD+ and CoMVD-, respectively). The secondary goal was to assess differences in MVD- and MVD+ patients. Fifty-five patients with T1DM (MVD+ group: n = 29) were recruited from the Funen Diabetes Database. Dual-energy X-ray absorptiometry (DXA), high-resolution peripheral quantitative computed tomography (HR-pQCT) of the ultradistal radius and tibia, and biochemical markers of bone turnover were performed in all participants. There were no significant differences in HR-pQCT parameters between MVD- and CoMVD- subjects. In contrast, MVD+ patients had larger total and trabecular bone areas (p = 0.04 and p = 0.02, respectively), lower total, trabecular, and cortical volumetric bone mineral density (vBMD) (p < 0.01, p < 0.04, and p < 0.02, respectively), and thinner cortex (p = 0.03) at the radius, and lower total and trabecular vBMD (p = 0.01 and p = 0.02, respectively) at the tibia in comparison to CoMVD+. MVD+ patients also exhibited lower total and trabecular vBMD (radius p = 0.01, tibia p < 0.01), trabecular thickness (radius p = 0.01), estimated bone strength, and greater trabecular separation (radius p = 0.01, tibia p < 0.01) and network inhomogeneity (radius p = 0.01, tibia p < 0.01) in comparison to MVD- patients. These differences remained significant after adjustment for age, body mass index, gender, disease duration, and glycemic control (average glycated hemoglobin over the previous 3 years). Although biochemical markers of bone turnover were significantly lower in MVD+ and MVD- groups in comparison to controls, they were similar between the MVD+ and MVD- groups. The results of our study suggest that the presence of MVD was associated with deficits in cortical and trabecular bone vBMD and microarchitecture that could partly explain the excess skeletal fragility observed in these patients.

Osteoporosis therapy: a novel insight from natural homeostatic system in the skeleton

The skeleton normally responds to mechanical environment to maintain the resulting elastic deformation (strain) of bone, while increased bone strength by an osteoporosis drug results in decreased bone strain. Thus, it can be hypothesized that the effect of osteoporosis therapy is limited by natural homeostatic system in the skeleton. This logic is consistent with the fact that there exists a powerful effect that returns bone mass to its pre-treatment level after the withdrawal of treatment with osteoporosis agents. The present hypothesis provides a new significant insight into the mechanisms by which osteoporosis drugs improve bone fragility. Here we briefly discuss the effects of teriparatide, romosozumab, and odanacatib on bones in animals and humans.