The volumetric bone density and cortical thickness in adult patients affected by osteogenesis imperfecta

Bone microarchitecture and strength assessment in adults with osteogenesis imperfecta using HR-pQCT: normative comparison and challenges

Data on bone microarchitecture in osteogenesis imperfecta (OI) are scarce. The aim of this cross-sectional study was to assess bone microarchitecture and strength in a large cohort of adults with OI using high-resolution peripheral quantitative computed tomography (HR-pQCT) and to evaluate challenges of using HR-pQCT in this cohort. Second-generation HR-pQCT scans were obtained at the distal radius and tibia in 118 men and women with Sillence OI type I, III, or IV using an extremity-length-dependent scan protocol. In total, 102 radius and 105 tibia scans of sufficient quality could be obtained, of which 11 radius scans (11%) and 14 tibia scans (13%) had a deviated axial scan angle as compared with axial angle data of 13 young women. In the scans without a deviated axial angle and compared with normative HR-pQCT data, Z-scores at the radius for trabecular bone mineral density (BMD), number, and separation were -1.6 ± 1.3, -2.5 ± 1.4, and -2.7 (IQR: 2.7), respectively. They were -1.4 ± 1.5 and -1.1 ± 1.2 for stiffness and failure load and between ±1 for trabecular thickness and cortical bone parameters. Z-scores were significantly lower for total and trabecular BMD, stiffness, failure load, and cortical area and thickness at the tibia. Additionally, local microarchitectural inhomogeneities were observed, most pronounced being trabecular void volumes. In the scans with a deviated axial angle, the proportion of Z-scores <-4 or >4 was significantly higher for trabecular BMD and separation (radius) or most total and trabecular bone parameters (tibia). To conclude, especially trabecular bone microarchitecture and bone strength were impaired in adults with OI. HR-pQCT may be used without challenges in most adults with OI, but approximately 12% of the scans may have a deviated axial angle in OI due to bone deformities or scan positioning limitations. Furthermore, standard HR-pQCT parameters may not always be reliable due to microarchitectural inhomogeneities nor fully reflect all inhomogeneities.

Characterizing Bone Phenotypes Related to Skeletal Fragility Using Advanced Medical Imaging

PURPOSE OF REVIEW

Summarize the recent literature that investigates how advanced medical imaging has contributed to our understanding of skeletal phenotypes and fracture risk across the lifespan.

RECENT FINDINGS

Characterization of bone phenotypes on the macro-scale using advanced imaging has shown that while wide bones are generally stronger than narrow bones, they may be more susceptible to age-related declines in bone strength. On the micro-scale, HR-pQCT has been used to identify bone microarchitecture phenotypes that improve stratification of fracture risk based on phenotype-specific risk factors. Adolescence is a key phase for bone development, with distinct sex-specific growth patterns and significant within-sex bone property variability. However, longitudinal studies are needed to evaluate how early skeletal growth impacts adult bone phenotypes and fracture risk. Metabolic and rare bone diseases amplify fracture risk, but the interplay between bone phenotypes and disease remains unclear. Although bone phenotyping is a promising approach to improve fracture risk assessment, the clinical availability of advanced imaging is still limited. Consequently, alternative strategies for assessing and managing fracture risk include vertebral fracture assessment from clinically available medical imaging modalities/techniques or from fracture risk assessment tools based on clinical risk factors. Bone fragility is not solely determined by its density but by a combination of bone geometry, distribution of bone mass, microarchitecture, and the intrinsic material properties of bone tissue. As such, different individuals can exhibit distinct bone phenotypes, which may predispose them to be more vulnerable or resilient to certain perturbations that influence bone strength.

Radiofrequency Echographic Multispectrometry (REMS): A New Option in the Assessment Bone Status in Adults with Osteogenesis Imperfecta

This study aimed to estimate the utility of the Radiofrequency Echographic Multispectrometry (REMS) approach in the assessment of bone mineral density (BMD) in subjects with osteogenesis imperfecta (OI). In 41 subjects (40.5 ± 18.7 years) with OI and in 36 healthy controls, we measured BMD at the lumbar spine (LS-BMD), femoral neck (FN-BMD) and total hip (TH-BMD), employing a dual-energy X-ray absorptiometry tool. Additionally, REMS scans were also performed at the lumbar and femoral sites. The presence and number of reported fractures were assessed in the study population. Patients characterized by a history of fragility fractures represented 84.5% of the study population. OI subjects showed significantly reduced BMD values both at the level of the lumbar spine and the femoral subregions (p < 0.01) compared to healthy controls when performed using both the DXA and the REMS method. Dividing OI patients on the basis of the Sillence classification, no differences were found between the LS-BMD values carried out using the DXA technique between the OI type I group and OI Type III and IV groups. On the contrary, the OI Type III and IV groups presented significantly lower values of both Trabecular Bone Score (TBS) and LS-BMD through REMS with respect to OI type I patients (p < 0.05). Based on the data of this study, it is possible to conclude that even the new REMS assessment, which does not use ionizing radiation, represents an excellent method for studying the bone status in subjects affected by OI.

Bone Mass, Density, Geometry, and Stress-Strain Index in Adults With Osteogenesis Imperfecta Type I and Their Associations With Physical Activity and Muscle Function Parameters

Osteogenesis imperfecta (OI) is a clinically and genetically heterogeneous heritable connective tissue disorder mainly characterized by bone fragility and increased fracture risk. This study investigated bone parameters in adults with OI type I and their relationship with physical activity and muscle function parameters in comparison with controls. A total of 27 (15 women, 12 men) adults with OI type I and 27 healthy age- and sex-matched controls, with mean age 45 years (range 18-72 years), were included. Peripheral quantitative computed tomography was performed at the lower leg and forearm to assess muscle density, muscle and fat cross-sectional area (CSA) (66% site), and trabecular (4% site) and cortical bone parameters (66% site) at radius and tibia. Physical activity (step count and moderate-to-vigorous physical activity [MVPA]) was assessed by accelerometry, muscle function parameters by Leonardo mechanography (single two-legged jump - peak power), and hand grip dynamometry (maximal hand grip strength). Overall, the OI type I group had significantly lower muscle CSA at the lower leg and forearm, lower trabecular and cortical bone mineral content, lower polar stress-strain index (SSIp), and smaller cortices but higher cortical bone mineral density and lower step count and MVPA in comparison with controls. Maximal hand grip strength was positively associated with SSIp at radius (p = 0.012) in the control group but not in the OI type I group (p = 0.338) (difference in associations: p = 0.012). No other significantly different associations between bone and muscle function parameters or physical activity (step count or MVPA) were found in the OI type I versus control group. We conclude that adults with OI type I have smaller bones, lower trabecular bone mass, lower estimates of bone strength, and higher cortical density in comparison with controls and that there are some indications of a disturbed biomechanical muscle-bone relationship in adults with OI type I. © 2022 American Society for Bone and Mineral Research (ASBMR).

Comparison of Bone Microarchitecture Between Adult Osteogenesis Imperfecta and Early-Onset Osteoporosis

Diagnosis and management of adult individuals with low bone mass and increased bone fragility before the age of 50 can be challenging. A number of these patients are diagnosed with mild osteogenesis imperfecta (OI) through detection of COL1A1 or COL1A2 mutations; however, a clinical differentiation from early-onset osteoporosis (EOOP) may be difficult. The purpose of this study was to determine the bone microstructural differences between mild OI and EOOP patients. 29 patients showed mutations in COL1A1 or COL1A2 and were classified as OI. Skeletal assessment included dual-energy X-ray absorptiometry (DXA), high-resolution peripheral quantitative computed tomography (HR-pQCT), and bone turnover serum analyses. Bone microstructure of 21/29 OI patients was assessed and compared to 23 age- and sex-matched patients clinically classified EOOP but without mutations in the known disease genes as well as to 20 healthy controls. In the OI patients, we did not observe an age-dependent decrease in DXA Z-scores. HR-pQCT revealed a significant reduction in volumetric BMD and microstructural parameters in the distal radius and tibia in both the OI and EOOP cohorts compared to the healthy controls. When comparing the bone microstructure of OI patients with the EOOP cohort, significant differences were found in terms of bone geometry in the radius, while no significant changes were detected in all other HR-pQCT parameters at the radius and tibia. Taken together, adult mild OI patients demonstrate a predominantly high bone turnover trabecular bone loss syndrome that shows minor microstructural differences compared to EOOP without mutation detection.

Bone Geometry, Quality, and Bone Markers in Children with Type 1 Diabetes Mellitus

Adults with Type 1 diabetes mellitus show a high risk of bone fracture, probably as a consequence of a decreased bone mass and microarchitectural bone alterations. The aim of the study was to investigate the potential negative effects of type 1 diabetes on bone geometry, quality, and bone markers in a group of children and adolescents. 96 children, mean age 10.5 ± 3.1 years, agreed to participate to the study. Bone geometry was evaluated on digitalized X-rays at the level of the 2nd metacarpal bone. The following parameters were investigated and expressed as SDS: outer diameter (D), inner diameter (d), cortical area (CA), and medullary area (MA). Bone strength was evaluated as Bending Breaking Resistance Index (BBRI) from the geometric data. Bone turnover markers (PINP, CTX-I, and BAP), sclerostin, Dkk-1, PTH, and 25OH-Vitamin D were also assessed. A group of healthy 40 subjects of normal body weight and height served as controls for the bone markers. D (- 0.99 ± 0.98), d (- 0.41 ± 0.88), CA (- 0.85 ± 0.78), and MA (- 0.46 ± 0.78) were all significantly smaller than in controls (p < 0.01). BBRI was significantly lower (- 2.61 ± 2.18; p < 0.0001). PTH, PINP, and BAP were higher in the diabetic children. Multiple regression analysis showed that CA and D were influenced by insulin/Kg/day and by BMI, while d was influenced by PINP only. Type 1 diabetic children show smaller and weaker bones. The increased bone turnover could play a key role since it might amplify the deficit in bone strength associated with the inadequate osteoblastic activity caused by the disease itself.

Skeletal phenotypes in adult patients with osteogenesis imperfecta-correlations with COL1A1/COL1A2 genotype and collagen structure

Osteogenesis imperfecta (OI) is characterized by a high fracture rate and great heterogeneity. This cross-sectional study presents skeletal investigations and protein analyses in 85 adult OI patients. We find significant differences in bone mass, architecture, and fracture rate that correlate well with the underlying biochemical and molecular abnormalities.

INTRODUCTION

OI is a hereditary disease characterized by compromised connective tissue predominantly caused by mutations in collagen type 1 (COL-1) encoding genes. Widespread symptoms reflect the ubiquity of COL-1 throughout the body. The purpose of this study was to improve our understanding of clinical manifestations by investigating anthropometry and skeletal phenotypes (DXA, HRpQCT) in an adult OI population and compare the findings to underlying COL-1 genotype and structure.

METHODS

The study comprised 85 OI patients aged 45 (19-78) years, Sillence type I (n = 58), III (n = 12), and IV (n = 15). All patients underwent DXA, HRpQCT, spine X-ray, biochemical testing, and anthropometry. COL1A1 and COL1A2 were sequenced and 68 OI causing mutations identified (46 in COL1A1, 22 in COL1A2). Analysis of COL-1 structure (quantitative/qualitative defect) by SDS-PAGE was performed in a subset (n = 67).

RESULTS

A qualitative collagen defect predisposed to a more severe phenotype with reduced aBMD, more fractures, and affected anthropometry compared to patients with a quantitative COL-1 defect (p < 0.05). HRpQCT revealed significant differences between patients with OI type I and IV. Patients with type I had lower vBMD (p < 0.005), thinner cortexes (p < 0.001), and reduced trabecular number (p < 0.005) compared to patients with type IV indicating that HRpQCT may distinguish type I from type IV better than DXA.

CONCLUSION

The defective collagen in patients with OI has pronounced effects on the skeleton. The classical OI types based on the clinical classification show profound differences in bone mass and architecture and the differences correlate well with the underlying biochemical and molecular collagen abnormalities.

Dental panoramic indices and fractal dimension measurements in osteogenesis imperfecta children under pamidronate treatment

OBJECTIVES

To verify radiomorphometric indices and fractal dimension (FD) in dental panoramic radiographs (DPRs) of children with different types of osteogenesis imperfecta (OI) and also to verify the effect of pamidronate (PAM) treatment in such panoramic analyses.

METHODS

In this retrospective study, 197 DPRs of 62 children with OI Types I, III and IV who were in treatment with a comparable dosage of intravenous PAM were selected. The mandibular cortical width (MCW), mandibular cortical index, visual estimation of the cortical width and FD of three standardized trabecular and cortical mandibular regions of interest were obtained from the radiographs. Factorial analysis of variance and Fisher test were used to compare FD and MCW measurements in children with different types of OI for different PAM cycles.

RESULTS

Children with all types of OI have thinner and more porous mandibular cortices at the beginning of treatment. There were significant differences between MCW and FD of the cortical bone, regarding different types of OI and number of PAM cycles (p = 0.037 and p = 0.044, respectively). FD measurements of the trabecular bone were not statistically different among OI types nor were PAM cycles (p > 0.05).

CONCLUSIONS

Children with OI presented cortical bone alterations after PAM treatment. Both MCW and the FD of the cortical bone were higher in children with OI after PAM treatment. It is argued that cortical bone should be considered for analyzing patients with OI, as well as to monitor the progress of PAM treatment.

Bone structure assessed by HR-pQCT, TBS and DXL in adult patients with different types of osteogenesis imperfecta

Bone microarchitecture by high-resolution peripheral quantitative computed tomography (HR-pQCT) was assessed in adult patients with mild, moderate, and severe osteogenesis imperfecta (OI). The trabecular bone score (TBS), bone mineral density (BMD) by dual-energy X-ray absorptiometry (DXA), and dual X-ray and laser (DXL) at the calcaneus were likewise assessed in patients with OI. Trabecular microstructure and BMD in particular were severely altered in patients with OI.

INTRODUCTION

OI is characterized by high fracture risk but not necessarily by low BMD. The main purpose of this study was to assess bone microarchitecture and BMD at different skeletal sites in different types of OI.

METHODS

HR-pQCT was performed in 30 patients with OI (mild OI-I, n = 18 (41.8 [34.7, 55.7] years) and moderate to severe OI-III-IV, n = 12 (47.6 [35.3, 58.4] years)) and 30 healthy age-matched controls. TBS, BMD by DXA at the lumbar spine and hip, as well as BMD by DXL at the calcaneus were likewise assessed in patients with OI only.

RESULTS

At the radius, significantly lower trabecular parameters including BV/TV (p = 0.01 and p < 0.0001, respectively) and trabecular number (p < 0.0001 and p < 0.0001, respectively) as well as an increased inhomogeneity of the trabecular network (p < 0.0001 and p < 0.0001, respectively) were observed in OI-I and OI-III-IV in comparison to the control group. Similar results for trabecular parameters were found at the tibia. Microstructural parameters were worse in OI-III-IV than in OI-I. No significant differences were found in cortical thickness and cortical porosity between the three subgroups at the radius. The cortical thickness of the tibia was thinner in OI-I (p < 0.001), but not OI-III-IV, when compared to controls.

CONCLUSIONS

Trabecular BMD and trabecular bone microstructure in particular are severely altered in patients with clinical OI-I and OI-III-IV. Low TBS and DXL and their significant associations to HR-pQCT parameters of trabecular bone support this conclusion.

Bone mass and mineralization in osteogenesis imperfecta

The main clinical features of osteogenesis imperfecta (OI) are low bone mass and high bone fragility. While the decrease in bone mass is generally regarded as an indicator of disease severity, bone fragility appears as the hallmark of the disorder. Bone has a multiscale hierarchical structural organization and is optimized to resist to fractures. In OI, modifications at the molecular level affect the total mechanical integrity of the bone. A specific characteristic in OI is that the bone matrix is abnormally high mineralized independently of the underlying mutation or clinical severity. The increased matrix mineralization affects bone material quality, leading to increased stiffness and brittleness and making bone prone to fractures. The purpose of this review is to give further insights on bone matrix mineralization in OI and to discuss advantages and pitfalls of invasive and noninvasive imaging techniques.

Osteogenesis imperfecta: clinical diagnosis, nomenclature and severity assessment

Recently, the genetic heterogeneity in osteogenesis imperfecta (OI), proposed in 1979 by Sillence et al., has been confirmed with molecular genetic studies. At present, 17 genetic causes of OI and closely related disorders have been identified and it is expected that more will follow. Unlike most reviews that have been published in the last decade on the genetic causes and biochemical processes leading to OI, this review focuses on the clinical classification of OI and elaborates on the newly proposed OI classification from 2010, which returned to a descriptive and numerical grouping of five OI syndromic groups. The new OI nomenclature and the pre-and postnatal severity assessment introduced in this review, emphasize the importance of phenotyping in order to diagnose, classify, and assess severity of OI. This will provide patients and their families with insight into the probable course of the disorder and it will allow physicians to evaluate the effect of therapy. A careful clinical description in combination with knowledge of the specific molecular genetic cause is the starting point for development and assessment of therapy in patients with heritable disorders including OI. © 2014 The Authors. American Journal of Medical Genetics Published by Wiley Periodicals, Inc. This is an open access article under the terms of the Creative Commons Attribution–NonCommercial–NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

Evaluation of teriparatide treatment in adults with osteogenesis imperfecta

BACKGROUND

Adults with osteogenesis imperfecta (OI) have a high risk of fracture. Currently, few treatment options are available, and bone anabolic therapies have not been tested in clinical trials for OI treatment.

METHODS

79 adults with OI were randomized to receive 20 μg recombinant human parathyroid hormone (teriparatide) or placebo for 18 months in a double-blind, placebo-controlled trial. The primary endpoint was the percent change in areal bone mineral density (aBMD) of the lumbar spine (LS), as determined by dual-energy X-ray absorptiometry. Secondary endpoints included percent change in bone remodeling markers and vertebral volumetric BMD (vBMD) by quantitative computed tomography, estimated vertebral strength by finite element analysis, and self-reported fractures.

RESULTS

Compared with the placebo group, the teriparatide group showed increased LS aBMD (6.1% ± 1.0% vs. 2.8% ± 1.0% change from baseline; P < 0.05) and total hip aBMD (2.6% ± 1.0% vs. -2.4% ± 1.0% change; P < 0.001). Vertebral vBMD and strength improved with teriparatide therapy (18% ± 6% and 15% ± 3% change, respectively), but declined with placebo (-5.0% ± 6% and -2.0% ± 3% change; P < 0.05 for both comparisons). Serum procollagen type 1 N-terminal propeptide (P1NP) and urine collagen N-telopeptide (NTx) levels increased with teriparatide therapy (135% ± 14% and 64% ± 10% change, respectively). Teriparatide-induced elevation of P1NP levels was less pronounced in severe forms of OI (type III/IV) compared with the milder form (type I). Type I OI patients exhibited robust BMD increases with teriparatide; however, there was no observed benefit for those with type III/IV OI. There was no difference in self-reported fractures between the 2 groups.

CONCLUSIONS

Adults with OI, particularly those with less severe disease (type I), displayed a teriparatide-induced anabolic response, as well as increased hip and spine aBMD, vertebral vBMD, and estimated vertebral strength. Trial registration. Clinicaltrials.gov NCT00131469. Funding. The Osteoporosis Imperfecta Foundation, Eli Lilly and Co., the National Center for Advancing Translational Science (NCATS) at the NIH (grant no. UL1RR024140), and the Baylor College of Medicine General Clinical Research Center (grant no. RR00188).

Teriparatide treatment in adult patients with osteogenesis imperfecta type I

Osteogenesis imperfecta (OI) is a hereditary disease characterized by low bone mass, increased bone fragility, short stature, and skeletal deformities. This study focuses on OI type I, the mildest form of the disease. Bisphosphonates represent the prevailing standard of care in patients with OI. Teriparatide (TPD) is a PTH analog with bone-anabolic actions which has been approved for osteoporosis treatment. Thirteen postmenopausal women with type I OI who had been on treatment with neridronate for at least 2 years and who incurred new vertebral fracture during treatment were treated with TPD for 18 months. Bone mineral density (BMD) increased significantly over 18 months up to 3.5 % at the lumbar spine (p = 0.001), while no significant changes were noted in hip BMD. Serum markers of bone formation and of bone resorption increased significantly during the treatment. The Wnt inhibitors serum dickkopf-1 (DKK1) and sclerostin were also measured. A nonsignificant increase was seen in serum sclerostin levels, while serum DKK1 rose gradually and significantly during TPD treatment. In patients affected by type I OI, TPD treatment is associated with a remarkable response in markers of bone formation. This suggests a normal osteoblastic response to TPD. However, the observed increases in BMD were somewhat lower than those in postmenopausal or senile osteoporosis treated with TPD for the same lag time. Our results open the possibility to develop TPD for the treatment of adult type I OI, but particularly for the lack of a control group, a properly designed controlled study is warranted.

Bone geometry, density, and microarchitecture in the distal radius and tibia in adults with osteogenesis imperfecta type I assessed by high-resolution pQCT

Osteogenesis imperfecta (OI) is a hereditary disorder characterized by decreased biosynthesis or impaired morphology of type I collagen that leads to decreased bone mass and increased bone fragility. We hypothesized that patients with OI have altered bone microstructure and bone geometry. In this cross-sectional study we compared patients with type I OI to age- and gender-matched healthy controls. A total of 39 (13 men and 26 women) patients with OI, aged 53 (range, 21-77) years, and 39 controls, aged 53 (range, 21-77) years, were included in the study. Twenty-seven of the patients had been treated with bisphosphonates. High-resolution peripheral quantitative computed tomography (HR-pQCT) at the distal radius and distal tibia and dual-energy X-ray absorptiometry of total hip, femoral neck, trochanteric region, and the lumbar spine (L1-L4) were performed. The patients were shorter than the controls (159 ± 10 cm versus 170 ± 9 cm, p < 0.001), but had similar body weight. In OI, areal bone mineral density (aBMD) was 8% lower at the hip (p < 0.05) and 13% lower at the spine (p < 0.001) compared with controls. The trabecular volumetric bone mineral density (vBMD) was 28% lower in radius (p < 0.001) and 38% lower in tibia (p < 0.001) in OI compared with controls. At radius, total bone area was 5% lower in OI than in controls (p < 0.05). In the tibia, cortical bone area was 18% lower in OI (p < 0.001). In both radius and tibia the number of trabeculae was lower in patients compared to the controls (35% and 38%, respectively, p < 0.001 at both sites). Furthermore, trabecular spacing was 55% higher in OI in both tibia and radius (p < 0.001 at both sites) when compared with controls. We conclude that patients with type I OI have lower aBMD, vBMD, bone area, and trabecular number when compared with healthy age- and gender-matched controls.

Bone mass, bone markers and prevalence of fractures in adults with osteogenesis imperfecta

Still little is known about the manifestations of osteogenesis imperfecta (OI) in adults. We therefore initiated this study of bone mass, bone turnover and prevalence of fractures in a large cohort of adult patients. We found a surprising low prevalence (10%) of osteoporosis. These patients, however, expressed the most severe disease.

PURPOSE

To characterize bone mineral density, bone turnover, calcium metabolism and prevalence of fractures in a large cohort of adults with osteogenesis imperfecta.

METHODS

One hundred fifty-four patients with adult OI participated and 90 (age range 25-83) provided dual X-ray absorptiometry (DXA) measurements. According to Sillence classification criteria, 68 persons were classified as OI type I, 9 as type III, 11 type IV and 2 were unclassified. Fracture numbers were based on self-reporting. Biochemical markers of bone turnover were measured and bone mineral density (BMD) of the spine, femoral neck and total body were determined by DXA.

RESULTS

Only 10% of adults with OI exhibited osteoporotic T scores (T ≤ -2.5) but compared to patients with normal T scores this subgroup had a threefold higher fracture risk (22 vs. 69). s-PTH, s-Ca and 25[OH] vitamin D were all normal. Bone markers did not display major deviations from normal, but patients with OI type III displayed higher resorption marker levels than type I and IV. Multivariate regression analysis showed that only gender and total body BMD were significant determinants of fracture susceptibility, and the differences for total body BMC, BMD and Z scores were significant between the OI subtypes.

CONCLUSIONS

In adult OI, DXA measurements only identified few patients as osteoporotic. These patients, however, exhibited a much higher fracture propensity. Due to deformities, low body height and pre-existing fractures, DXA assessment is complicated in this disease, and further studies are needed to work out how to minimize the impact of these confounders.

High and low density in the same bone: a study on children and adolescents with mild osteogenesis imperfecta

Children and adolescents with osteogenesis imperfecta (OI) generally have low bone mineral density (BMD) at the lumbar spine and hip. However, the effects of the disease on diaphyseal bone have not been well characterized, even though long-bone fractures are common in such patients. In this study on 42 fully mobile children and adolescents with mild OI (age 6-19 years; 17 girls), lumbar spine, radius (metaphysis and diaphysis) and second metacarpal (diaphysis) were analyzed using dual-energy X-ray absorptiometry, peripheral quantitative computed tomography and radiogrammetry, respectively. Bone mineral content at the lumbar spine, radial metaphysis and radial diaphysis was between 25% and 31% lower than in age-matched healthy children and adolescents. At the lumbar spine and radial metaphysis, bone size (as estimated from projection area and cross-sectional area, respectively) was normal or only slightly below the results expected for healthy individuals, whereas bone size was very small at the diaphyseal sites of the radius and the second metacarpal. Total volumetric BMD is defined as the ratio between bone mineral content and bone volume. Therefore, these differences in bone size between skeletal locations led to markedly discrepant results for total volumetric BMD. Total volumetric BMD was low at the lumbar spine (23% below result expected for healthy subjects of the same age) and the radial metaphysis (-15%) but elevated at the radial diaphysis (+25%; all differences to controls significant at P < 0.001). Despite high volumetric BMD, estimated bending strength at the radial diaphysis was very low. These results demonstrate that volumetric BMD can be abnormally high and low within the same bone in the same individual and highlight the fact that volumetric BMD at diaphyseal sites does not provide a good estimate of bone strength when bone size is abnormal.

Intravenous bisphosphonate therapy increases radial width in adults with osteogenesis imperfecta

Neridronate therapy in adult patients with OI significantly increases the cross-sectional area of the proximal radius. This observation may provide an additional explanation for the antifracture efficacy of bisphosphonates.

INTRODUCTION

Bisphosphonate therapy decreases by 70-90% the fracture risk in patients with osteogenesis imperfecta (OI). This decrease is somewhat greater than that expected from the BMD changes, supporting the hypothesis that bisphosphonate therapy is associated with structural changes, not detectable by BMD measurements.

MATERIALS AND METHODS

To explore this hypothesis, pQCT measurements at the nondominant radius were obtained in a group of adult OI patients participating in a randomized clinical trial with neridronate.

RESULTS

The total volumetric BMD of the ultradistal radius rose significantly in patients treated with neridronate and calcium + vitamin D (neridronate group) compared with patients treated with calcium + vitamin D alone (control group). No significant differences were observed in trabecular BMD and in volumetric cortical density in either group. In the neridronate group, the cross-sectional area rose significantly versus both baseline values and the control group. These latter changes were associated with approximately 20% increases in bending breaking resistance index (BBRI).

CONCLUSION

Our observation, if extended to postmenopausal osteoporosis, may provide a new explanation for the fracture risk reduction observed in osteoporotic patients treated with bisphosphonates.

Regional differences in cortical bone mineral density in the weight-bearing long bone shaft--a pQCT study

This study used a multislice peripheral quantitative computed tomography (pQCT) to measure volumetric BMD (vBMD) and cortical thickness for investigating regional adaptation in lower tibial shaft in 72 healthy postmenopausal women aged 47-60. Tomographic slices were analysed on four distinct cortical regions: the anterior, posterior, medial and lateral cortical wall. One-way analysis of variance (ANOVA) test was used to compare the vBMD in the four regions. The results showed that the posterior cortex had the highest vBMD (1923 +/- 135.3 mg/cm(3)), significantly (P < 0.001) higher than the anterior cortex (1805 +/- 110.6 mg/cm(3)), medial cortex (1863 +/- 103.6 mg/cm(3)) and lateral cortex (1815 +/- 111.6 mg/cm(3)); whereas there was no significant difference (P > 0.05) between the medial and lateral cortices located near the neutral plane of bending. The anterior cortex had the greatest thickness (2.56 +/- 0.47 mm), significantly (P < 0.001) greater than that of the posterior cortex (2.11 +/- 0.27 mm), medial cortex (2.20 +/- 0.39 mm) and lateral cortex (2.03 +/- 0.29 mm). The vBMD of the posterior cortex was a significant 6.5% higher than that of the anterior cortex (P < 0.001); whereas the anterior cortical thickness was a significant 21.3% greater than that of the posterior cortex (P < 0.001). There was no linear relationship found between cortical vBMD and cortical thickness measured at the four cortical regions (r = 0.086, P > 0.05). In conclusion, the regional differences, with higher vBMD found in posterior cortex, might be a result of mechanical adaptation, which caused the posterior cortex to sustain higher compressive loading than the anterior tensile cortex during the landing phase in the gait cycles of individuals. Nevertheless, regional geometric adaptation in anterior cortical thickness might be adapted to accommodate for the reduced vBMD and to reduce the bending stress in this region.