Gaele Ducher

The Impact of Recent Technological Advances on the Trueness and Precision of DXA to Assess Body Composition

The introduction of dual‐energy X‐ray absorptiometry (DXA) in the 1980s for the assessment of areal bone mineral density (BMD) greatly benefited the field of bone imaging and the ability to diagnose and monitor osteoporosis. The additional capability of DXA to differentiate between bone mineral, fat tissue, and lean tissue has contributed to its emergence as a popular tool to assess body composition. Throughout the past 2 decades, technological advancements such as the transition from the original pencil‐beam densitometers to the most recent narrow fan‐beam densitometers have allowed for faster scan times and better resolution. The majority of reports that have compared DXA‐derived body composition measurements to the gold standard method of body composition appraisal, the four‐compartment model, have observed significant differences with this criterion method; however, the extent to which the technological advancements of the DXA have impacted its ability to accurately assess body composition remains unclear. Thus, this paper reviews the evidence regarding the trueness and precision of DXA body composition measurements from the pencil‐beam to the narrow fan‐beam densitometers.

Peripheral quantitative computed tomography in children and adolescents: the 2007 ISCD Pediatric Official Positions.

Peripheral quantitative computed tomography (pQCT) has mainly been used as a research tool in children. To evaluate the clinical utility of pQCT and formulate recommendations for its use in children, the International Society of Clinical Densitometry (ISCD) convened a task force to review the literature and propose areas of consensus and future research. The types of pQCT technology available, the clinical application of pQCT for bone health assessment in children, the important elements to be included in a pQCT report, and quality control monitoring techniques were evaluated. The review revealed a lack of standardization of pQCT techniques, and a paucity of data regarding differences between pQCT manufacturers, models and software versions and their impact in pediatric assessment. Measurement sites varied across studies. Adequate reference data, a critical element for interpretation of pQCT results, were entirely lacking, although some comparative data on healthy children were available. The elements of the pQCT clinical report and quality control procedures are similar to those recommended for dual-energy X-ray absorptiometry. Future research is needed to establish evidence-based criteria for the selection of the measurement site, scan acquisition and analysis parameters, and outcome measures. Reference data that sufficiently characterize the normal range of variability in the population also need to be established.

Overweight children have a greater proportion of fat mass relative to muscle mass in the upper limbs than in the lower limbs: implications for bone strength at the distal forearm

BACKGROUND The influence of adiposity on upper-limb bone strength has rarely been studied in children, despite the high incidence of forearm fractures in this population. OBJECTIVE The objective was to compare the influence of muscle and fat tissues on bone strength between the upper and lower limbs in prepubertal children. DESIGN Bone mineral content, total bone cross-sectional area, cortical bone area (CoA), cortical thickness (CoTh) at the radius and tibia (4% and 66%, respectively), trabecular density (TrD), bone strength index (4% sites), cortical density (CoD), stress-strain index, and muscle and fat areas (66% sites) were measured by using peripheral quantitative computed tomography in 427 children (206 boys) aged 7-10 y. RESULTS Overweight children (n = 93) had greater values for bone variables (0.3-1.3 SD; P < 0.0001) than did their normal-weight peers, except for CoD 66% and CoTh 4%. The between-group differences were 21-87% greater at the tibia than at the radius. After adjustment for muscle cross-sectional area, TrD 4%, bone mineral content, CoA, and CoTh 66% at the tibia remained greater in overweight children, whereas at the distal radius total bone cross-sectional area and CoTh were smaller in overweight children (P < 0.05). Overweight children had a greater fat-muscle ratio than did normal-weight children, particularly in the forearm (92 +/- 28% compared with 57 +/- 17%). Fat-muscle ratio correlated negatively with all bone variables, except for TrD and CoD, after adjustment for body weight (r = -0.17 to -0.54; P < 0.0001). CONCLUSIONS Overweight children had stronger bones than did their normal-weight peers, largely because of greater muscle size. However, the overweight children had a high proportion of fat relative to muscle in the forearm, which is associated with reduced bone strength.

Skeletal Benefits After Long‐Term Retirement in Former Elite Female Gymnasts

Bone strength benefits after long‐term retirement from elite gymnastics in terms of bone geometry and volumetric BMD were studied by comparing retired female gymnasts to moderately active age‐matched women. In a cross‐sectional study, 30 retired female gymnasts were compared with 30 age‐matched moderately active controls. Bone geometric and densitometric parameters were measured by pQCT at the distal epiphyses and shafts of the tibia, femur, radius, and humerus. Muscle cross‐sectional areas were assessed from the shaft scans. Independent t‐tests were conducted on bone and muscle variables to detect differences between the two groups. The gymnasts had retired for a mean of 6.1 ± 0.4 yr and were engaged in ≤2 h of exercise per week since retirement. At the radial and humeral shafts, cortical cross‐sectional area (CSA), total CSA, BMC, and strength strain index (SSIpol) were significantly greater (13–38%, p ≤ 0.01) in the retired gymnasts; likewise, BMC and total CSA were significantly greater at the distal radius (22–25%, p ≤ 0.0001). In the lower limbs, total CSA and BMC at the femur and tibia shaft were greater by 8–11%, and trabecular BMD and BMC were only greater at the tibia (7–8%). Muscle CSA at the forearm and upper arm was greater by 15–17.6% (p ≤ 0.001) but was not different at the upper and lower leg. Past gymnastics training is associated with greater bone mass and bone size in women 6 yr after retirement. Skeletal benefits were site specific, with greater geometric adaptations (greater bone size) in the upper compared with the lower limbs.

Effects of repetitive loading on the growth-induced changes in bone mass and cortical bone geometry: a 12-month study in pre/peri- and postmenarcheal tennis players.

Pre‐ and early puberty may be the most opportune time to strengthen the female skeleton, but there are few longitudinal data to support this claim. Competitive female premenarcheal (pre/peri, n = 13) and postmenarcheal (post, n = 32) tennis players aged 10 to 17 years were followed over 12 months. The osteogenic response to loading was studied by comparing the playing and nonplaying humeri for dual‐energy X‐ray absorptiometry (DXA) bone mineral content (BMC) and magnetic resonance imaging (MRI) total bone area (ToA), medullary area (MedA), cortical area (CoA), and muscle area (MCSA) at the humerus. Over 12 months, growth‐induced gains (nonplaying arm) in BMC, ToA, and CoA were greater in pre/peri (10% to 19%, p < .001) than in post (3% to 5%, p < .05 to .001) players. At baseline, BMC, ToA, CoA, and MCSA were 8% to 18% greater in the playing versus nonplaying arms in pre/peri and post players (all p < .001); MedA was smaller in the playing versus nonplaying arms in post only players (p < .05). When comparing the annual gains in the playing arm relative to changes in the nonplaying arm, the increases in ToA and CoA were greater in pre/peri than post players (all p < .05). The smaller the side‐to‐side differences in BMC and CoA at baseline, the larger the exercise benefits at 12 months (r = −0.39 to −0.48, p < .01). The exercise‐induced change in MCSA was predictive of the exercise benefits in BMC in pre/peri players only (p < .05). In conclusion, both pre/peri‐ and postmenarcheal tennis players showed significant exercise‐induced skeletal benefits within a year, with greater benefits in cortical bone geometry in pre/perimenarcheal girls.

Short-term and long-term site-specific effects of tennis playing on trabecular and cortical bone at the distal radius.

Mechanical loading during growth magnifies the normal increase in bone diameter occurring in long bone shafts, but the response to loading in long bone ends remains unclear. The aim of the study was to investigate the effects of tennis playing during growth at the distal radius, comparing the bone response at trabecular and cortical skeletal sites. The influence of training duration was examined by studying bone response in short-term (children) and long-term (young adults) perspectives. Bone area, bone mineral content (BMC), and bone mineral density (BMD) of the radius were measured by DXA in 28 young (11.6 ± 1.4 years old) and 47 adult tennis players (22.3 ± 2.7 years old), and 70 age-matched controls (12 children, 58 adults) at three sites: the ultradistal region (trabecular), the mid-distal region, and the third-distal region (cortical). At the ultradistal radius, young and adult tennis players displayed similar side-to-side differences, the asymmetry in BMC reaching 16.3% and 13.8%, respectively (P < 0.0001). At the mid- and third-distal radius, the asymmetry was much greater in adults than in children (P < 0.0001) for all the bone parameters (mid-distal radius, +6.6% versus +15.6%; third-distal radius, +6.9% versus +13.3%, for BMC). Epiphyseal bone enduring longitudinal growth showed a great capacity to respond to mechanical loading in children. Prolonging tennis playing into adulthood was associated with further increase in bone mineralization at diaphyseal skeletal sites. These findings illustrate the benefits of practicing impact-loading sports during growth and maintaining physical activity into adulthood to enhance bone mass accrual and prevent fractures later in life.

Fractal analysis of bone texture: a screening tool for stress fracture risk?

Background  The aim of this study was to identify specific bone characteristics of stress fracture (SF) cases in sportswomen. To date, no tool is able to distinguish individuals who are at risk, limiting preventive measures.

Effects of Repetitive Loading on Bone Mass and Geometry in Young Male Tennis Players: A Quantitative Study Using MRI†‡

Pre‐ and early puberty seem to be the most opportune times for exercise to improve bone strength in girls, but few studies have addressed this issue in boys. This study investigated the site‐, surface‐, and maturity‐specific exercise‐induced changes in bone mass and geometry in young boys. The osteogenic effects of loading were analyzed by comparing the playing and nonplaying humeri of 43 male pre‐, peri‐, and postpubertal competitive tennis players 10–19 yr of age. Total bone area, medullary area, and cortical area were determined at the mid (40–50%) and distal humerus (60–70%) of both arms using MRI. Humeral bone mass (BMC) was derived from a whole body DXA scan. In prepubertal boys, BMC was 17% greater in the playing compared with nonplaying arm (p < 0.001), which was accompanied by a 12–21% greater cortical area, because of greater periosteal expansion than medullary expansion at the midhumerus and periosteal expansion associated with medullary contraction at the distal humerus. Compared with prepuberty, the side‐to‐side differences in BMC (27%) and cortical area (20–33%) were greater in peripuberty (p < 0.01). No differences were found between peri‐ and postpuberty despite longer playing history in the postpubertal players. The osteogenic response to loading was greater in peri‐ compared with prepubertal boys, which is in contrast with our previous findings in girls and may be caused by differences in training history. This suggests that the window of opportunity to improve bone mass and size through exercise may be longer in boys than in girls.

Obstacles in the Optimization of Bone Health Outcomes in the Female Athlete Triad

Maintaining low body weight for the sake of performance and aesthetic purposes is a common feature among young girls and women who exercise on a regular basis, including elite, college and high-school athletes, members of fitness centres, and recreational exercisers. High energy expenditure without adequate compensation in energy intake leads to an energy deficiency, which may ultimately affect reproductive function and bone health. The combination of low energy availability, menstrual disturbances and low bone mineral density is referred to as the ‘female athlete triad’. Not all athletes seek medical assistance in response to the absence of menstruation for 3 or more months as some believe that long-term amenorrhoea is not harmful. Indeed, many women may not seek medical attention until they sustain a stress fracture.This review investigates current issues, controversies and strategies in the clinical management of bone health concerns related to the female athlete triad. Current recommendations focus on either increasing energy intake or decreasing energy expenditure, as this approach remains the most efficient strategy to prevent further bone health complications. However, convincing the athlete to increase energy availability can be extremely challenging.Oral contraceptive therapy seems to be a common strategy chosen by many physicians to address bone health issues in young women with amenorrhoea, although there is little evidence that this strategy improves bone mineral density in this population. Assessment of bone health itself is difficult due to the limitations of dual-energy X-ray absorptiometry (DXA) to estimate bone strength. Understanding how bone strength is affected by low energy availability, weight gain and resumption of menses requires further investigations using 3-dimensional bone imaging techniques in order to improve the clinical management of the female athlete triad.

Cortical and Trabecular Bone at the Forearm Show Different Adaptation Patterns in Response to Tennis Playing

Bone responds to impact-loading activity by increasing its size and/or density. The aim of this study was to compare the magnitude and modality of the bone response between cortical and trabecular bone in the forearms of tennis players. Bone area, bone mineral content (BMC), and bone mineral density (BMD) of the ulna and radius were measured by dual-energy X-ray absorptiometry (DXA) in 57 players (24.5 +/- 5.7 yr old), at three sites: the ultradistal region (50% trabecular bone), the mid-distal regions, and third-distal (mainly cortical bone). At the ultradistal radius, the side-to-side difference in BMD was larger than in bone area (8.4 +/- 5.2% and 4.9 +/- 4.0%, respectively, p < 0.01). In the cortical sites, the asymmetry was lower (p < 0.01) in BMD than in bone area (mid-distal radius: 4.0 +/- 4.3% vs 11.7 +/- 6.8%; third-distal radius: 5.0 +/- 4.8% vs 8.4 +/- 6.2%). The asymmetry in bone area explained 33% of the variance of the asymmetry in BMC at the ultradistal radius, 66% at the mid-distal radius, and 53% at the third-distal radius. The ulna displayed similar results. Cortical and trabecular bone seem to respond differently to mechanical loading. The first one mainly increases its size, whereas the second one preferentially increases its density.