Hip Geometry Research Articles

Increased Plasma Osteoprotegerin Concentrations Are Associated with Indices of Bone Strength of the Hip

Osteoprotegerin (OPG) is an important regulator of bone turnover through its effects on osteoclastogenesis, yet findings from previous studies of circulating OPG and commonly measured bone indices in humans have been conflicting. We conducted a cross-sectional study to evaluate the association between plasma OPG and femoral neck (FN) bone density (BMD) and geometry in a large cohort of women and men. Participants included 1379 postmenopausal women and 1165 men, aged 50-89 yr (mean, 64 yr), in the Framingham Offspring Study. Dual x-ray absorptiometry was used to evaluate FN BMD and geometry (bone width, section modulus, and cross-sectional area at the narrow neck region). Plasma OPG concentrations were measured by ELISA. Sex-specific analysis of covariance was used to calculate means and assess linear trend in BMD and geometry values across OPG quartiles, adjusted for confounders. OPG concentrations were greater in women than men, increased with age, and were greater in smokers and those with diabetes and heart disease. Multivariable-adjusted mean FN BMD in women increased from the lowest to the highest OPG quartile (trend, P < 0.01). However, no linear trend between FN BMD and OPG was observed in men (trend, P = 0.34). Section modulus and bone width increased with OPG in men (trend, P < 0.01), whereas no association between hip geometry indices and OPG was observed in women. Higher OPG concentration may indicate greater skeletal strength in women and men, possibly through reducing bone loss in women and increasing periosteal apposition in men.

Lean mass and not fat mass is associated with male proximal femur strength.

Obesity is suspected to confer protection against fracture, but evidence is mixed. We examined proximal femur geometry and body composition measures in a diverse group of 1171 men (30-79 yr of age). Analyses showed that nonbone lean mass, but not fat mass, is independently associated with measures of proximal femur density, axial and bending strength, and resistance to buckling. Obesity is often said to confer protection against fracture, but the mechanisms driving such an association remain poorly understood. We hypothesized that the effect of increased body mass on bone structure would be accounted for by total and/or appendicular nonbone lean mass, and that once these trends were removed, fat mass would show no protective influence. To test this hypothesis, we examined body composition and geometric indices of proximal femur strength in an ethnically diverse (black, Hispanic, and white) sample of randomly selected men, 30-79 yr of age. Data were obtained from N = 1171 community-dwelling subjects enrolled in the cross-sectional Boston Area Community Health/Bone study. Body composition was obtained by DXA. Hip geometry parameters at the narrow neck, intertrochanter, and shaft were obtained using Hip Structural Analysis of DXA images. These measures included BMD, bone material in cross-sections (cross-sectional area), bending strength (section modulus), and propensity to buckle under compression (average buckling ratio). Analyses controlled for age, race/ethnicity, height, and physical activity. In exploratory analyses, lean mass, fat mass, and BMI were each positively associated with hip strength. However, controlling for lean mass was sufficient to remove the positive, and induce a negative, association for fat mass or BMI. Associations between lean mass and hip strength were strongest and resistant to control for other measures. Lean mass alone was sufficient to account for a substantial proportion of racial/ethnic difference in hip strength measures, whereas fat mass exhibited no comparable explanatory power. The positive association between relative weight and proximal femur strength is accounted for by lean mass, suggesting that, in men, the protective effect of BMI in preventing fracture is mediated not by adipose tissue but by the influence of increased muscle mass accompanying elevated BMI.

Subject-specific hip geometry affects predicted hip joint contact forces during gait

Hip loading affects bone remodeling and implant fixation. In this study, we have analyzed the effect of subject-specific modeling of hip geometry on muscle activation patterns and hip contact forces during gait, using musculoskeletal modeling, inverse dynamic analysis and static optimization. We first used sensitivity analysis to analyze the effect of isolated changes in femoral neck-length (NL) and neck-shaft angle (NSA) on calculated muscle activations and hip contact force during the stance phase of gait. A deformable generic musculoskeletal model was adjusted incrementally to adopt a physiological range of NL and NSA. In a second similar analysis, we adjusted hip geometry to the measurements from digitized radiographs of 20 subjects with primary hip osteoarthrosis. Finally, we studied the effect of hip abductor weakness on muscle activation patterns and hip contact force. This analysis showed that differences in NL (41–74 mm) and NSA (113–140°) affect the muscle activation of the hip abductors during stance phase and hence hip contact force by up to three times body weight. In conclusion, the results from both the sensitivity and subject-specific analysis showed that at the moment of peak contact force, altered NSA has only a minor effect on the loading configuration of the hip. Increased NL, however, results in an increase of the three hip contact-force components and a reduced vertical loading. The results of these analyses are essential to understand modified hip joint loading, and for planning hip surgery for patients with osteoarthrosis.

Reconstructed hip joint architecture with a standard hip arthroplasty with a unique declined offset

Possible advantages of the architectural restoration of the hip joint after total hip arthroplasty (THA) are numerous. The relationship between the femoral offset (FO) and the abductor moment arm and the polyethylene wear, loosening, instability, persistent limp due to gluteus medius insufficiency, even dislocation, leg length discrepancy have been reported (1-4). Architectural and mechanical hip restoration has to be technically easy, reproducible and transmissible. Controversies continue: standard implants or implants with specific offset, variety of series or modular device. We study the influence of using a standard stem series with a progressive unique offset on the hip geometry.

Age-related trends in hip geometry in Sri Lankan women: a cross-sectional study

Indices of hip geometry are known to be predictive of hip fractures while sex and ethnic differences in hip geometry have been previously demonstrated. Age-related trends in hip geometry among Asians, however, have not been studied sufficiently. A total of 280 healthy, perimenopausal women, aged between 32 and 97 years, were selected from the Community Study Area of the Faculty of Medicine, Galle, Sri Lanka. Hip DXA images were analyzed further to calculate the hip axis length, neck-shaft angle, and femoral neck width at the narrowest point of the femoral neck. Standard formulae were used to calculate cross-sectional area, cross-sectional moment of inertia, and section modulus in the femoral neck region. Mean (SD) age, weight, height, femoral neck bone mineral density (BMD), hip axis length, neck-shaft angle, neck width, cross-sectional area, and cross-sectional moment of inertia of the study sample were 56.8 (13.0) years, 47.8 (10.1) kg, 1.48 (0.06) m, 0.704 (0.147) g/cm(2), 90.6 (5.6) mm, 123.2 (5.7) degrees, 2.99 (0.24) cm, 2.00 (0.42) cm(2), and 1.62 (0.47) cm(4), respectively. Height and weight of subjects had positive correlations with most of the indices of hip geometry. Femoral neck BMD, cross-sectional area and section modulus showed a rapid reduction during the postmenopausal period. With advancing age, there was a marginal but statistically nonsignificant expansion of the neck width, increase in the hip axis length, and narrowing of the neck-shaft angle. In conclusion, this study demonstrated a gradual loss of BMD in postmenopausal age, accompanied by thinning of the cortical shell and deterioration of the resistance to bending in the femoral neck of this group of healthy women. The clinical relevance of the marginal changes seen in other indices such as neck-shaft angle, hip axis length, and neck width is not known.

Association between contact hip stress and RSA-measured wear rates in total hip arthroplasties of 31 patients

Background The main concern in the long run of total hip replacements is aseptic loosening of the prosthesis. Optimization of the biomechanics of the hip joint is necessary for optimization of long-term success. A widely implementable tool to predict biomechanical consequences of preoperatively planned reconstructions still has to be developed. A potentially useful model to this purpose has been developed previously. The aim of this study is to quantify the association between the estimated hip joint contact force by this biomechanical model and RSA-measured wear rates in a clinical setting. Methods Thirty-one patients with a total hip replacement were measured with RSA, the gold standard for clinical wear measurements. The reference examination was done within 1 week of the operation and the follow-up examinations were done at 1, 2 and 5 years. Conventional pelvic X-rays were taken on the same day. The contact stress distribution in the hip joint was determined by the computer program HIPSTRESS. The procedure for the determination of the hip joint contact stress distribution is based on the mathematical model of the resultant hip force in the one-legged stance and the mathematical model of the contact stress distribution. The model for the force requires as input data, several geometrical parameters of the hip and the body weight, while the model for stress requires as input data, the magnitude and direction of the resultant hip force. The stress distribution is presented by the peak stress−the maximal value of stress on the weight-bearing area ( p max) and also by the peak stress calculated with respect to the body weight ( p max/ W B) which gives the effect of hip geometry. Visualization of the relations between predicted values by the model and the wear at different points in the follow-up was done using scatterplots. Correlations were expressed as Pearson r values. Results The predicted p max and wear were clearly correlated in the first year post-operatively ( r=0.58, p=0.002), while this correlation is weaker after 2 years ( r=0.19, p=0.337) and 5 years ( r=0.24, p=0.235). The wear values at 1, 2 and 5 years post-operatively correlate with each other in the way that is expected considering the wear velocity curve of the whole group. The correlation between the predicted p max values of two observers who were blinded for each other's results was very good ( r=0.93, p<0.001). Conclusion We conclude that the biomechanical model used in this paper provides a scientific foundation for the development of a new way of constructing preoperative biomechanical plans for total hip replacements.

Disproportional geometry of the proximal femur in patients with Turner syndrome: a cross‐sectional study

Patients with Turner syndrome (TS) have altered growth and increased risk of osteoporosis due to oestrogen deficiency and possibly a host of other factors. Thus, TS patients have a 4.9-fold increased risk of femoral neck fractures. Most patients are treated with oestrogen during puberty and adolescence to facilitate pubertal development and prevent secondary osteoporosis. The geometry of the hip is a predictor for hip fractures independent of bone mineral density (BMD). The purpose of the present study was to investigate the variation of the geometry of the hip in patients with TS in comparison with healthy controls. The study population comprised 58 patients with TS (aged 22-67 years) and 60 age-matched healthy women (aged 21-65 years). Hip axis length (HAL), neck width (NW), neck shaft angle (NSA), and femoral head-radius (HR) on dual-energy X-ray absorptiometry (DXA) screen images. These parameters related to age of oestrogen supplementation, menarche, and duration of oestrogen exposure. Height was 146.6 +/- 6.9 cm and 167.1 +/- 6.2 cm (P < 0.1) and weight 57.4 +/- 13.9 kg and 62.3 +/- 8.3 kg (P < 0.001) in patients and controls, respectively. After adjustment for differences in height, HAL was not significantly different (9.4 +/- 0.5 vs. 9.5 +/- 0.5 cm; NS) in TS compared with controls while NW was significantly increased (3.5 +/- 0.4 cm vs. 3.3 +/- 0.2 cm, P < 0.001), NSA was similar (129 +/- 4 degrees vs. 130 +/- 4 degrees , NS), and HR was significantly decreased (4.1 +/- 0.4 vs. 4.5 +/- 0.3 cm, P < 0.001). The duration of oestrogen exposure was significantly shorter among TS, but did not correlate significantly with the geometrical parameters in either TS or controls. Our data demonstrates that hip geometry is disproportionate in TS compared with normal controls. The altered hip geometry, however, cannot explain the increased risk of hip fracture in TS.

Bivariate Linkage Study of Proximal Hip Geometry and Body Size Indices: The Framingham Study

Femoral geometry and body size are both characterized by substantial heritability. The purpose of this study was to discern whether hip geometry and body size (height and body mass index, BMI) share quantitative trait loci (QTL). Dual-energy X-ray absorptiometric scans of the proximal femur from 1,473 members in 323 pedigrees (ages 31-96 years) from the Framingham Osteoporosis Study were studied. We measured femoral neck length, neck-shaft angle, subperiosteal width (outer diameter), cross-sectional bone area, and section modulus, at the narrowest section of the femoral neck (NN), intertrochanteric (IT), and femoral shaft (S) regions. In variance component analyses, genetic correlations (rho ( G )) between hip geometry traits and height ranged 0.30-0.59 and between hip geometry and BMI ranged 0.11-0.47. In a genomewide linkage scan with 636 markers, we obtained nominally suggestive linkages (bivariate LOD scores > or =1.9) for geometric traits and either height or BMI at several chromosomes (4, 6, 9, 15, and 21). Two loci, on chr. 2 (80 cM, BMI/shaft section modulus) and chr. X (height/shaft outer diameter), yielded bivariate LOD scores > or =3.0; although these loci were linked in univariate analyses with a geometric trait, neither was linked with either height or BMI. In conclusion, substantial genetic correlations were found between the femoral geometric traits, height and BMI. Linkage signals from bivariate linkage analyses of bone geometric indices and body size were similar to those obtained in univariate linkage analyses of femoral geometric traits, suggesting that most of the detected QTL primarily influence geometry of the hip.

Hip structural geometry in old and old-old age: Similarities and differences between men and women

Introduction Changes in hip structure and geometry during aging contribute to decreased bone strength. Little is known, however, about these characteristics at advanced age, when fragility fractures are common. We examined hip structural geometry in men and women of old age (72–84 years) and old-old age (85–96 years) to determine (1) gender differences; (2) whether or not these differences are consistent with the increased occurrence of hip fracture in elderly women, compared to men; and (3) whether or not gender-specific changes are consistent with the increased occurrence of fragility fractures after age 80 in both men and women. Methods We used Hip Structure Analysis (HSA) software to analyze bone densitometry scans from 916 community-dwelling men and women aged 72–96 years. We examined gender differences in hip geometry by age group (72–74, 75–79, 80–84, and ≥ 85 years) and between gender-specific age groups using multivariable linear regression. Results At the femoral narrow neck, there was no gender difference at age 72–74 in bone mineral density (BMD), cortical thickness (CT), and buckling ratio (BR). In contrast, at age 85 or older women had 13% less BMD and CT than men and 8% higher BR. At the intertrochanteric region, women ≥ 85 years had 25–31% less BMD, cross-sectional bone area (CSA), and CT than men of comparable age, and 38% higher BR. These gender differences were approximately 10–20% greater than those between men and women in their 70s. In gender-specific comparisons, women showed increasing change in structural geometry with increasing age. At both narrow neck and trochanteric regions, women ≥ 85 years had nearly 35% higher BR, 15% less BMD and CT, and 10% less CSA than women aged 72–74 years. At the narrow neck, they also had 6% greater outer diameter than the youngest women and 8% lower section modulus (Z), an index of bending strength. In contrast, men showed significant age differences only at the narrow neck region, and only at 85 years or older, including 22% higher BR, 10% less BMD and CT, and 5% greater outer diameter, compared to men in their early 70s. Unlike women, men showed no age-associated decline in section modulus. Conclusions Gender differences in hip geometry consistent with increased fragility and fracture risk in elderly women, compared to men, continue into old-old age. Both men and women 85 or older show the most unfavorable features, suggesting a structural basis for the increased occurrence of hip fracture in both sexes at advanced age.

Physical activity and femoral neck bone strength during childhood: The Iowa Bone Development Study

Structural adaptations of bone to changing mechanical loads have recently been documented during adolescence. However, little is known about how bone adapts structurally during the earlier years. Using a longitudinal observational design spanning 6 years of growth (age range 4 to 12 years), we investigated associations between everyday physical activity and hip geometry in a cohort of healthy Midwestern children ( n = 468). Femoral neck (FN) cross sectional area (CSA, cm 2) and FN section modulus (Z, cm 3) were used to describe hip geometry. CSA and Z, indices of axial and bending strength, were assessed using dual-energy X-ray absorptiometry (DXA) scans and the hip structure analysis (HSA) program. Moderate and vigorous physical activity (MVPA) was assessed using accelerometry-based activity monitors and calculated as the number of minutes ≥ 3000 accelerometry movement counts. Data were analyzed using multilevel (random- and fixed-effects) regression models with adjustment for age (year), height (cm), and weight (kg) or lean mass (kg). For boys and girls, MVPA was a positive independent predictor of CSA and Z ( p < 0.05). On average, children who participated in 40 min of MVPA per day would be expected to have 3% to 5% greater CSA and Z than peers participating in 10 min of MVPA per day. Ten-minute increases in daily MVPA had similar effects on CSA in girls and Z in boys as did each additional 1 kg of body weight. When lean mass was substituted for weight, MVPA continued to be a positive independent predictor of CSA and Z for boys, but not girls. This study demonstrates that everyday amounts of physical activity in children are associated with indices of FN bone strength during childhood. Differences in lean mass mediate associations between physical activity and hip geometry in girls, but only somewhat in boys. These results suggest that physical activity is an important contributor to bone strength prior to adolescence and that increasing levels of physical activity during childhood are likely to enhance optimal bone strength.

Re: The adult hip joint in Saudi Arabia

Re: The adult hip joint in Saudi Arabia

Vitamin K2 supplementation improves hip bone geometry and bone strength indices in postmenopausal women.

SummaryVitamin K mediates the synthesis of proteins regulating bone metabolism. We have tested whether high vitamin K2 intake promotes bone mineral density and bone strength. Results showed that K2 improved BMC and femoral neck width, but not DXA-BMD. Hence high vitamin K2 intake may contribute to preventing postmenopausal bone loss.IntroductionVitamin K is involved in the synthesis of several proteins in bone. The importance of K vitamins for optimal bone health has been suggested by population-based studies, but intervention studies with DXA-BMD as a clinical endpoint have shown contradicting results. Unlike BMC, DXA-BMD does not take into account the geometry (size, thickness) of bone, which has an independent contribution to bone strength and fracture risk. Here we have tested whether BMC and femoral neck width are affected by high vitamin K intake.MethodsA randomized clinical intervention study among 325 postmenopausal women receiving either placebo or 45 mg/day of vitamin K2 (MK-4, menatetrenone) during three years. BMC and hip geometry were assessed by DXA. Bone strength indices were calculated from DXA-BMD, femoral neck width (FNW) and hip axis length (HAL).ResultsK2 did not affect the DXA-BMD, but BMC and the FNW had increased relative to placebo. In the K2-treated group hip bone strength remained unchanged during the 3-year intervention period, whereas in the placebo group bone strength decreased significantly.ConclusionsVitamin K2 helps maintaining bone strength at the site of the femoral neck in postmenopausal women by improving BMC and FNW, whereas it has little effect on DXA-BMD.

Bone mineral density and hip structural analysis in type 1 diabetic men

The risk of non-vertebral fractures is increased in men with type 1 diabetes (DM1) but studies have shown only moderately decreased or normal bone mineral density (BMD) in these patients. No previous studies have evaluated hip strength and geometry indices in DM1 patients. This study was therefore designed to characterize associations between BMD, dual X-ray absorptiometry (DXA)-based hip strength indices, metabolic control, and DM1chronic complications. The study was performed on 36 males aged 43.6 +/- 5.1 years with long-lasting DM1 and 36 healthy males matched for age, weight, and height. BMD in lumbar spine, total hip, upper and lower part of the femoral neck, hip axis length, cross-sectional area and moment of inertia (CSMI), and glycated hemoglobin (HbA1c) were measured. DM1 men had decreased spine BMD (P < 0.05) and normal total hip BMD in comparison with controls. Hip geometry and strength indices were comparable in both groups. However, M1 men had decreased CSMI and upper femur BMD but these differences did not reach statistical significance (P = 0.06). BMD changes and hip strength parameters did not correlate with HbA1c. Middle-aged DM1 men have decreased lumbar spine BMD, normal hip BMD and normal hip strength indices. These changes are not influenced by metabolic control and presence of chronic microvascular complications.

Femoral neck structure in hip fracture

Hip fracture occurs relating to fall and decreased mechanical integrity of the femoral neck. Mechanical strength of the femoral neck is determined by both bone mineral density and other factors such as bone quality and hip geometry. Histomorphometrical studies show that cortical thinning, regional hyper-mineralization, decreased osteocyte lacunae and microdamage accumulation occur in aged or fractured subjects, suggesting that bone quality contributes mechanical integrity of femoral neck. Recent dual energy X-ray absorptiometry (DXA) studies revealed that hip axis length, longer in femoral neck fracture patients may contribute to the risk of femoral neck fracture.

Biomechanical and metabolic performance of a new orthotic knee joint principle for stance phase safety

Fig. 2. Changes in inclination angle associated with peak joint reaction forces during stance with increasing NSA. UM is the reference undeformed model. ing a decrease in the peak mediolateral component with increasing NSA. A distinct trend to increased peak vertical joint reaction forces with increased NSA was found. As a result, the inclination angle of the resultant reaction force in the frontal plane decreased substantially with decreasing NSA, introducing a more vertical alignment of the reaction force at peak loading (Fig. 2). Although, the sagittal plane angle showed variations in the individual model, no clear relation with the changes in NSA could be established. When halving the abductor muscle force generating capacity, all components of the reaction forces decreased. However, the previously described relations of the joint reaction forces with NSA were unchanged. 6. Discussion The interaction between hip geometry, muscle moment generating capacity and hip loading can be analyzed using inverse dynamics based on personalized musculoskeletal modeling. Our results show an important interaction between NSA and mediolateral reaction forces, causing a more vertical inclination angle in the frontal plane during gait. This therefore will result in a more vertical loading of the implant when peak reaction forces are applied during gait. Although we did not analyze the interaction between NSA, NL and PW, our findings do suggest that a minimal NSA angle needs to be preserved in order to limit the mediolateral force component and limit the resulting bending stress in the femoral shaft. The calculation of individual hip loading by use of musculoskeletal modeling and inverse analysis may contribute to understanding the effect of hip joint loading on bone remodeling and implant load shearing.

Subject specific hip geometry after THP influences hip joint reaction forces during gait

Subject specific hip geometry after THP influences hip joint reaction forces during gait

Proximal hip geometry is linked to several chromosomal regions: Genome-wide linkage results from the Framingham Osteoporosis Study

Introduction Femoral geometry contributes to bone strength and predicts hip fracture risk. The purpose of this study was to evaluate heritability ( h 2) of geometric indices of the proximal hip and to perform whole-genome linkage analyses of these traits, adjusted for body size. Methods DXA scans of the proximal femur from 1473 members of 323 pedigrees (age range 31–96 years) from the population-based Framingham Osteoporosis Study were obtained. Using the hip structural analysis program, we measured femoral neck length (FNL, cm) and neck-shaft angle (NSA); subperiosteal width (WID, cm), cross-sectional area (CSA, cm 2); and section modulus (Z, cm 3) at the narrowest section of the neck (NN), intertrochanteric (IT) and femoral shaft (S) regions. Linkage analyses were performed for the above indices with a set of 636 markers using variance components maximum likelihood method. Results Substantial genetic influences were found for all geometric phenotypes, with h 2 values between 0.28 (NSA) and 0.70 (IT_WID). Adjustment for height and BMI did not alter h 2 of NSA and FNL but decreased h 2 of the cross-sectional indices. We obtained substantial linkage (multipoint LOD > 3.0) for S_Z at 2p21 and 21q11 and S_WID at Xq25–q26. Inclusion of height and BMI as covariates resulted in much lower LOD scores for S_Z, whereas linkage signals for S_Z at 4q25, S_CSA at 4q32 and S_CSA and S_Z at 15q21 increased after the adjustment. Linkage of FNL at 1q and 13q, NSA at 2q and NN_WID at 16q did not change after the adjustment. Conclusion Suggestive linkages of bone geometric indices were found at 1q, 2p, 4q, 13q, 15q and Xq. The identification of significant linkage regions after adjustment for BMI and height may point to QTLs influencing femoral bone geometry independent of body size.

Sex Hormone Status May Modulate Rate of Expansion of Proximal Femur Diameter in Older Women alongside Other Skeletal Regulators

Little is known of associations between hip geometry and skeletal regulators. This is important because geometry is a determinant of both hip function and resistance to fracture. We aimed to determine the effects of sex hormone status and other candidate regulators on hip geometry and strength. A random sample of 351 women aged 67-79 had two to four hip dual-energy x-ray absorptiometry scans performed over 8 yr of follow-up. Hip structural analysis software was used to measure subperiosteal diameter (PD) and the distance from the center of mass to the lateral cortical margin (d-lat) on three 5-mm-thick cross-sectional regions: narrow neck, intertrochanter, and shaft. Section modulus (Z), bone mineral density (grams per centimeter squared), and an index of bone mineral content (cross-sectional area) were calculated as estimators of bone strength. Serum analytes measured at baseline included SHBG, estradiol, PTH, creatinine, albumin, vitamin D metabolites, and glutamate- and gamma-carboxyglutamate-osteocalcin (OC). A linear mixed model was used to model associations with predictor variables, including testing whether the predictors significantly modified the effect of aging. Aging was associated with increasing PD and d-lat, and higher baseline SHBG significantly modified this effect, in the case of PD, increasing the rates of change at the narrow neck region by 19% for SHBG level 2 sd higher than population mean (P = 0.026). Higher baseline creatinine was independently associated with faster increases in PD and d-lat with aging (P < 0.041). Z declined faster with aging if baseline PTH was higher, and higher albumin had a contrary effect. Z was positively associated with free estradiol and inversely associated with SHBG and glutamate-OC. These results show large effects of SHBG on the regulation of proximal femur expansion and bending resistance, probably acting as a surrogate for low bioavailable estrogen. Potentially important effects for fracture resistance in old age were also revealed for PTH, markers related to renal function and the nutritional markers albumin and undercarboxylated OC.

Age Trends in Femur Stresses From a Simulated Fall on the Hip Among Men and Women: Evidence of Homeostatic Adaptation Underlying the Decline in Hip BMD

Age trends in proximal femur stresses were evaluated by simulating a fall on the greater trochanter using femur geometry from hip DXA scans of 5334 white men and women in the NHANES III survey. Expansion of femur outer diameter seems to counter net bone loss so that stresses remain similar across age groups, but stresses are higher in older women than in older men. The age decline in hip BMD is caused by both bone loss and expansion of outer diameter that increases the region size over which mass is measured in a DXA scan. Because expansion has an opposing effect on structural strength, it may be a homeostatic adaptation to net bone loss to ensure that load stresses are kept within a narrow range. Age trends in femur stresses were evaluated with an engineering beam simulation of a fall on the greater trochanter. Hip geometry was extracted from hip DXA scans using the Hip Structure Analysis (HSA) software on 2613 non-Hispanic white men and 2721 women from the third National Health and Nutrition Examination Survey (NHANES III). Using body weight as load, stresses were computed on the inferior-medial and superior-lateral femur neck at its narrowest point and the medial and lateral shaft 2 cm distal to the midpoint of the lesser trochanter. Stresses and the underlying geometries in men and women >50 years oaf age were compared with those 20-49 years of age. Compared with men <50 years of age, stresses in older men were 6% lower on both surfaces of the shaft, 4% lower on the inferior-medial neck, and not different on the superior-lateral neck. In women >50 years of age, stresses on the proximal shaft and inferior-medial neck remained within 3% of young values but were 13% greater on the superior-lateral neck. Neck stresses in young women were lower on the superior-lateral than the inferior-medial neck, but lateral stress increased to the level on the medial surface in older women. Stresses were higher in women than in men, with a greater gender difference in those >50 years of age. We conclude that femur expansion has a homeostatic effect in men and women that opposes bone loss so that stresses change little with age. Because expansion preserves stresses with progressively less bone mass, the process may reduce structural stability in the femoral neck under fall conditions, especially in the elderly female.

Usefulness of hip BMD and geometry as diagnostic methods to predict hip fracture in women

and BMC (6, 9, and 15%, respectively). TB fat mass showed an increment of 6.7 kg (P < 0.001) mainly due to trunk fat mass (+70%). TB lean mass showed a decline of 5 kg (P < 0.05) mainly due to a diminution in peripheral lean mass: 3 kg in legs ( 16%, P < 0.0001) and 1.3 kg in arms ( 9%, P < 0.002). CONCLUSIONS: Through the decades we observed: 1—A slight (6%) diminution in DMO, with a higher diminution in area and BMC (9 and 15% respectively). 2—An increase in Total Fat Mass, predominantly in the trunk, that may have implications for the risk of cardiovascular and metabolic syndromes, and a diminution in TB lean mass, predominantly in the legs, probably related to decreased physical activity and hormonal changes. 3—Total and subregional BMD and BC reference values were obtained.