Femoral Neck Strength Research Articles

The susceptibility of the femoral neck to fracture: An assessment incorporating the effects of age-remodeling and stress reduction

Age-related bone remodeling may cause fragility of the femoral neck, thereby increasing fracture risk in elderly populations. We investigated the effects of age-remodeling and stress-reduction on the femoral neck region using the Finite Strip Method (FSM). We verified the possibility that the femoral neck is likely to undergo fracture through two mechanisms: yielding and local buckling. We hypothesized that the femoral necks of young subjects are more prone to fracture by yielding, whereas those of elderly subjects are more susceptible to fracture initiated by local buckling. The slices from the CT-scans of 15 subjects corresponding to the lowest area moment of inertia were segregated into cortex and trabeculae. Geometric and material properties for each strip were obtained from the CT-scans. The FSM, proposed here as an approximation to the better-known Finite Element Method (FEM), was implemented on a model comprising both cortex and trabeculae. Finite strip (FS) analyses were performed on models that incorporated the effects of age-related bone remodeling, as well as a reduction in physiological stress on the bone (as a result of weight loss). Comparisons were made with similar FS analyses performed on only the cortical shell, in order to ascertain the contributions of the trabeculae to femoral neck strength. We observed that the femoral necks of simulated young subjects manifested a marked predisposition to undergo yielding, whereas the femoral neck models of simulated elderly subjects were more prone to buckling before yielding. The trabecular degradation and cortical thinning involved in aging render the femoral neck more susceptible to failure by buckling.

Erratum to: Ethnic differences in composite indices of femoral neck strength

The scale factors provided by Hologic, Inc. to compute femoral neck axis length (FNAL) from the midline endpoint coordinates were off by a factor of 2; thus absolute values reported in Tables 1–4 of the paper for FNAL, bending strength index (BSI), and impact strength index (ISI) were scaled incorrectly. Corrected absolute values for FNAL and ISI are 0.5 times the reported FNAL and ISI values, and corrected absolute values for BSI are 2 times the reported BSI values. Thus, the FNAL rows in Tables 1 and 3 should be as shown below. The BSI and ISI cells in Tables 2 and 4 also need to be scaled by 2 and 0.5 respectively. For example, BSI in Caucasians (reference) in Table 2 (model 3) is 0.98; in US-born Chinese (reference) in Table 4 (model 3) is 1.14; and in US-born Japanese (reference) in Table 4 (model 3) is 1.24. Similarly, for example, ISI in Caucasians (reference) in Table 2 (model 3) is 0.18; in US-born Chinese (reference) in Table 4 (model 3) is 0.20; and in US-born Japanese (reference) in Table 4 (model 3) is 0.23. Note that effect sizes (and confidence intervals) for BSI and ISI in tables 2 and 4 are also similarly scaled.

Diabetes and Femoral Neck Strength: Findings from The Hip Strength Across the Menopausal Transition Study

Diabetes and Femoral Neck Strength: Findings from The Hip Strength Across the Menopausal Transition Study

Diabetes and Femoral Neck Strength: Findings from The Hip Strength Across the Menopausal Transition Study

Diabetes mellitus is associated with increased hip fracture risk, despite being associated with higher bone mineral density in the femoral neck. The objective of the study was to test the hypothesis that composite indices of femoral neck strength, which integrate dual-energy x-ray absorptiometry derived femoral neck size, femoral neck areal bone mineral density, and body size and are inversely associated with hip fracture risk, would be lower in diabetics than in nondiabetics and be inversely related to insulin resistance, the primary pathology in type 2 diabetes. This was a cross-sectional analysis. The study consisted of a multisite, multiethnic, community-dwelling sample of 1887 women in pre- or early perimenopause. Composite indices for femoral neck strength in different failure modes (axial compression, bending, and impact) were measured. Adjusted for age, race/ethnicity, menopausal stage, body mass index, smoking, physical activity, calcium and vitamin D supplementation, and study site, diabetic women had higher femoral neck areal bone mineral density [+0.25 sd, 95% confidence interval (CI) (+0.06, +0.44) sd] but lower composite strength indices [-0.20 sd, 95% CI (-0.38, -0.03) sd for compression, -0.19 sd, 95% CI (-0.38, -0.003) sd for bending, -0.19 sd, 95% CI (-0.37, -0.02) sd for impact] than nondiabetic women. There were graded inverse relationships between homeostasis model-assessed insulin resistance and all three strength indices, adjusted for the same covariates. Despite having higher bone density, diabetic women have lower indices of femoral neck strength relative to load, consistent with their documented higher fracture risk. Insulin resistance appears to play an important role in bone strength reduction in diabetes.

Ethnic differences in composite indices of femoral neck strength

Bone mineral density does not explain race/ethnicity differences in hip fracture risk. In this study, we demonstrated that race/ethnicity differences in composite hip strength indices were consistent with documented race/ethnicity differences in hip fracture risk, suggesting that unlike bone density, the composite indices may represent ethnicity-independent measures of bone strength. African-American and Asian women have lower risks of hip fracture than Caucasian women, but such racial/ethnic variation in hip fracture risk cannot be explained by bone mineral density (BMD). The composite indices of femoral neck strength integrate femoral neck and body size with BMD and predict hip fracture risk in Caucasian women. We hypothesize that unlike race/ethnic differences in BMD, race/ethnic differences in the composite strength indices would be consistent with race/ethnic differences in hip fracture risk. We studied a community-based sample of Caucasian (n = 968), African-American (n = 512), Chinese (n = 221), and Japanese (n = 239) women, premenopausal or in early perimenopause, from the Study of Women's Health Across the Nation. Unadjusted indices were similar in Caucasian and African-American women but higher in Asian women. After adjusting for age, body mass index, and menopause status, all three minority groups had higher composite strength indices than Caucasian women. Foreign-born Japanese women had higher unadjusted and adjusted composite strength indices than US-born Japanese women, but such differences by nativity were not observed in Chinese women. We concluded that composite strength indices have the potential to explain racial/ethnic differences in hip fracture risk, suggesting that composite strength indices may represent ethnicity-independent measures of bone strength. This contention needs to be verified by further research on the fracture predictive ability of composite strength indices in multi-ethnic longitudinal cohorts.

In utero and lactational exposure to Aroclor 1254 affects bone geometry, mineral density and biomechanical properties of rat offspring

Exposure to polychlorinated biphenyls (PCBs) induce a broad spectrum of toxic effects in various organs including bone. The most susceptible age-groups to the toxic effects of PCBs are foetuses and infants. The aim of the present study was to quantitatively evaluate changes in bone geometry, mineral density and biomechanical properties following perinatal exposure to the PCB mixture, Aroclor 1254 (A1254), and to examine the persistence of observed bone alterations by following the offspring over time. Sprague–Dawley rat offspring were exposed to A1254 from gestational day 1 to post-natal day (PND) 23. Femur and tibia were collected on PNDs 35, 77 and 350 and were analyzed by peripheral quantitative computed tomography and biomechanical testing. At PND35, exposure to A1254 induced short, thin femur and tibia, with reduced mechanical strength of femoral neck. No treatment-related bone changes were detected in offspring at PND77 or PND350. In conclusion, the present investigation suggests that perinatal exposure to A1254 leads to shorter, thinner and weaker bones in juvenile rats at PND35, with these effects being absent at later time-points as exposure is discontinued. The results indicate that the observed bone effects are mainly driven by the dioxin-like congeners, although it cannot exclude the contribution of the non dioxin-like congeners to the exposure outcome.

Biomechanical robustness of a new proximal epiphyseal hip replacement to patient variability and surgical uncertainties: A FE study

The biomechanical behaviour of current hip epiphyseal replacements is notably sensitive to the typical variability of conditions following a standard surgery. The aim of the present study was to assess the biomechanical robustness to the variability of post-operative conditions of an innovative proximal epiphyseal replacement (PER) hip device featuring a short, curved and cemented stem. The risk of femoral neck fractures, prosthesis fractures and aseptic loosening were assessed through a validated finite element procedure following a systematic approach. Risk changes due to anatomical variations were assessed mimicking extreme conditions in terms of femoral size and level of osteoporosis. Failure risks associated with surgical uncertainties were assessed mimicking extreme conditions in terms of uncertainties on the prosthesis position/alignment, cement–bone interdigitation depth, and friction between the prosthesis and the hosting cavity. The femoral neck strength increased after implantation from 9% to 49% and was most sensitive to changes of the anatomo-physiological variables. The risk of stem fractures was low in all studied configurations. The risk of stem loosening was low and most sensitive to surgical uncertainties. In conclusion, the new device can be considered an effective alternative to current epiphyseal replacements. Care is recommended in a proper seating of the prosthesis in the femur.

Expected frequency of biomechanically adverse values of proximal femur geometric variables for fracture risk in the East Slovak female population (epidemiological study)

The geometric configuration of the proximal femur predicts the risk for fracture by fall independently of bone mineral density (BMD). The objective of the study was to determine the expected frequency of biomechanically adverse and extremely adverse values of proximal femur geometric variables alpha angle, theta angle, and HAL, increasing the risk of a femoral neck fracture by fall, in the East Slovak female population. DXA (dual energy X-ray absorbtiometry) measurements of the left proximal femur were obtained and analysed from sample 3151 East Slovak women aged 20-89 years, [Formula: see text] = 58.9 years, SD = 11.1, with risk factors for the development of osteoporosis, with osteopenia and osteoporosis using bone densitometer (Prodigy - Primo, GE, USA). Measured variables: 1. geometric variables: alpha angle, theta angle, HAL (hip axis length) and 2. biomechanical variable: FNS (femoral neck strength). 1. Goodness-of-Fit Test χ(2)-test (Chi-Squared Test). 2. Logistic regression. Biomechanically adverse value of angle α>6.869° can be expected in 10% of the East Slovak female population; extremely adverse value of angle α>12.3° in 1%; biomechanically adverse value of angle θ>129.405° in 20%; extremely adverse value of angle θ>132.290° in 10%; biomechanically adverse length of HAL>109.930 mm in 20%; extremely adverse length of HAL>113.015 mm in 10%. The study brings the first data determining the mean values and 95% C.I. for proximal femur geometric variable values in the East female Slovak population. Biomechanically adverse values of proximal femur geometric variables are values higher than the upper limit of 95% C. I. and these findings enable now physicians to identify the individuals at risk and at high risk of hip fracture by fall.

A new hip epiphyseal prosthesis: Design revision driven by a validated numerical procedure

An innovative epiphyseal device has been recently proposed claiming an effective bone–prosthesis load transfer and a nearly physiological bone stresses distribution. However preliminary experimental tests showed a 23% weakening of the femoral neck after implantation. Aim of this study was to revise the prosthesis geometry with the goal of enhancing the femoral neck strength after implantation, while maintaining unchanged the initial conceptual design. To this aim, the risk of femoral neck fractures, prosthesis fractures, aseptic loosening and excessive bone resorption were addressed through a validated finite element procedure following a systematic approach. The initial prosthesis geometry was revised to reduce each investigated failure risk below the threshold of acceptance (100%). The new geometry was re-assessed to verify the effectiveness of the revision. The first design was predicted to locally induce high bone strains and cement stresses, which translated in a risk of bone and cement failure exceeding the threshold of acceptance (>100%). The revised design preserved a good stability of the device, contemporary reducing the risk for bone (45%) and cement (60%) failure. If results will be confirmed by statistical and clinical experimentations, current clinical indications for hip epiphyseal devices might be extended.

The effects of a two-year randomized, controlled trial of whey protein supplementation on bone structure, IGF-1, and urinary calcium excretion in older postmenopausal women

The effects of dietary protein on bone structure and metabolism have been controversial, with evidence for and against beneficial effects. Because no long-term randomized, controlled studies have been performed, a two-year study of protein supplementation in 219 healthy ambulant women aged 70 to 80 years was undertaken. Participants were randomized to either a high-protein drink containing 30 g of whey protein (n = 109) or a placebo drink identical in energy content, appearance, and taste containing 2.1 g of protein (n = 110). Both drinks provided 600 mg of calcium. Dual-energy X-ray absorptiometric (DXA) hip areal bone mineral density (aBMD), 24-hour urinary calcium excretion, and serum insulin-like growth factor 1 (IGF-1) were measured at baseline and at 1 and 2 years. Quantitative computed tomographic (QCT) hip volumetric bone mineral density (vBMD) and a femoral neck engineering strength analysis were undertaken at baseline and at 2 years. Baseline average protein intake was 1.1 g/kg of body weight per day. There was a significant decrease in hip DXA aBMD and QCT vBMD over 2 years with no between-group differences. Femoral neck strength was unchanged in either group over time. The 24-hour urinary calcium excretion increased significantly from baseline in both groups at 1 year but returned to baseline in the placebo group at 2 years, at which time the protein group had a marginally higher value. Compared with the placebo group, the protein group had significantly higher serum IGF-1 level at 1 and 2 years (7.3% to 8.0%, p < .05). Our study showed that in protein-replete healthy ambulant women, 30 g of extra protein increased IGF-1 but did not have beneficial or deleterious effects on bone mass or strength. The effect of protein supplementation in populations with low dietary protein intake requires urgent attention.

Teriparatide [rhPTH (1-34)], But Not Strontium Ranelate, Demonstrated Bone Anabolic Efficacy in Mature, Osteopenic, Ovariectomized Rats

We compared teriparatide (TPTD) and strontium ranelate (SR) efficacy on bone formation activity in a mature rat model of estrogen-deficiency bone loss. Rats were ovariectomized (OVX) at age 6 months and permitted to lose bone for 2 months to establish osteopenia before initiation of treatment with TPTD (5 or 15 μg/kg · d sc) or SR (150 or 450 mg/kg · d oral gavage). After 3 wk, RT-PCR analyses of bone formation genes in the distal femur metaphysis showed significant elevation of collagen 1α2, osteocalcin, bone sialoprotein, alkaline phosphatase, and Runx2 gene expression at both TPTD doses, relative to OVX controls. SR had no significant effect on expression of these genes. TPTD treatment for 12 wk dose dependently increased lumbar vertebral (LV) and femoral midshaft bone mineral content (BMC) and bone mineral density over pretreatment and age-matched OVX controls. SR 150 increased BMC, and SR 450 increased BMC and bone mineral density of femoral midshaft and LV over OVX controls. There were significant dose-dependent TPTD increases of LV and femoral neck strength, and TPTD 15 also increased midshaft strength compared with pretreatment and age-matched OVX controls. SR did not enhance bone strength relative to pretreatment or age-matched OVX controls. Histomorphometry of the proximal tibial metaphysis showed dose-dependent effects of TPTD on trabecular area, number, width, and osteoblast surface, bone mineralizing surface, and bone formation rate relative to pretreatment and age-matched OVX controls, whereas SR had no effect on these parameters. These findings confirmed the bone anabolic efficacy of teriparatide, but not SR in mature, osteopenic, OVX rats.

Independent and Combined Effects of Calcium-Vitamin D3 and Exercise on Bone Structure and Strength in Older Men: An 18-Month Factorial Design Randomized Controlled Trial

Exercise and calcium-vitamin D are independently recognized as important strategies to prevent osteoporosis, but their combined effects on bone strength and its determinants remain uncertain. To assess whether calcium-vitamin D(3) fortified milk could enhance the effects of exercise on bone strength, structure, and mineral density in middle-aged and older men. An 18-month factorial design randomized controlled trial in which 180 men aged 50-79 years were randomized to the following: exercise + fortified milk; exercise; fortified milk; or controls. Exercise consisted of progressive resistance training with weight-bearing impact activities performed 3 d/week. Men assigned to fortified milk consumed 400 ml/d of 1% fat milk containing 1000 mg/d calcium and 800 IU/d vitamin D(3). Changes in bone mineral density (BMD), bone structure, and strength at the lumbar spine (LS), proximal femur, mid-femur, and mid-tibia measured by dual energy x-ray absorptiometry and/or quantitative computed tomography. There were no exercise-by-fortified milk interactions at any skeletal site. Main effect analysis showed that exercise led to a 2.1% (95% confidence interval, 0.5-3.6) net gain in femoral neck section modulus, which was associated with an approximately 1.9% gain in areal BMD and cross-sectional area. Exercise also improved LS trabecular BMD [net gain 2.2% (95% confidence interval, 0.2-4.1)], but had no effect on mid-femur or mid-tibia BMD, structure, or strength. There were no main effects of the fortified milk at any skeletal site. A community-based multi-component exercise program successfully improved LS and femoral neck BMD and strength in healthy older men, but providing additional calcium-vitamin D(3) to these replete men did not enhance the osteogenic response.

Effects of age and sex on the strength and cortical thickness of the femoral neck

A group of 48 men (22 aged 65–75years, 26 aged 80–90years) and 59 women (32 aged 65–75years, 27 aged 80–90years) were enrolled in the Age, Gene/Environment Susceptibility-Reykjavik study and imaged with in vivo volumetric Quantitative Computed Tomography (QCT) to investigate the effects of age and sex on femoral neck structure and strength. Femoral neck cross-sectional moment of inertia for bending directions near those of standing and walking (IAP), bending strength (My), and axial compressive strength (Fy) were computed at the location of minimum cross-sectional area (minCSA). Local cortical thickness was computed in the inferior femoral neck based on density profiles extending through the cortex of the minCSA femoral neck section. Multivariate models accounting for height, weight, and age group (younger or older) showed that men had a 46% higher My and a 23% higher Fy than women, while women had a 13% thicker inferior cortex than men. Cortical thickness in the inferoposterior region of the femoral neck was significantly related to bending and axial strength after adjusting for overall volumetric bone mineral density. Both minCSA and IAP were higher in the older, gender-pooled age group, but Fy and My did not differ between the two age groups. The results suggest that age-related expansion of the femoral neck primarily occurs in the superior and inferior directions and helps maintain homeostasis of femoral neck stiffness and strength. The higher bending strength of the male femoral neck may partly explain why elderly men have a lower risk of hip fracture than elderly women.

Increased training loads do not magnify cancellous bone gains with rodent jump resistance exercise

This study sought to elucidate the effects of a low- and high-load jump resistance exercise (RE) training protocol on cancellous bone of the proximal tibia metaphysis (PTM) and femoral neck (FN). Sprague-Dawley rats (male, 6 mo old) were randomly assigned to high-load RE (HRE; n = 16), low-load RE (LRE; n = 15), or sedentary cage control (CC; n = 11) groups. Animals in the HRE and LRE groups performed 15 sessions of jump RE during 5 wk of training. PTM cancellous volumetric bone mineral density (vBMD), assessed by in vivo peripheral quantitative computed tomography scans, significantly increased in both exercise groups (+9%; P < 0.001), resulting in part from 130% (HRE; P = 0.003) and 213% (LRE; P < 0.0001) greater bone formation (measured by standard histomorphometry) vs. CC. Additionally, mineralizing surface (%MS/BS) and mineral apposition rate were higher (50-90%) in HRE and LRE animals compared with controls. PTM bone microarchitecture was enhanced with LRE, resulting in greater trabecular thickness (P = 0.03) and bone volume fraction (BV/TV; P = 0.04) vs. CC. Resorption surface was reduced by nearly 50% in both exercise paradigms. Increased PTM bone mass in the LRE group translated into a 161% greater elastic modulus (P = 0.04) vs. CC. LRE and HRE increased FN vBMD (10%; P < 0.0001) and bone mineral content (∼ 20%; P < 0.0001) and resulted in significantly greater FN strength vs. CC. For the vast majority of variables, there was no difference in the cancellous bone response between the two exercise groups, although LRE resulted in significantly greater body mass accrual and bone formation response. These results suggest that jumping at minimal resistance provides a similar anabolic stimulus to cancellous bone as jumping at loads exceeding body mass.

Assessment of hip fracture risk related to the structure

Bone strength is determined not only by BMD, but also by many other bone quality relating factors such as bone structure etc.. Hip fractures are the most serious fragile fractures, considering that controlling their risk factors will successfully prevent these fractures. Recently Hip structure (strength) analyses have become available during standard DXA measurements. Bending strength and stability of the bone can be determined by their obtained parameters such as section modulus, cross sectional area and buckling ratio. These parameters shift towards fragile by aging, especially remarkably reduce after 70 years. It has been reported that both anti-resorptive agents and anabolic PTH increase bone strength in different manner. Further progressed 3 dimensional femoral neck strength analysis using CT scanning are now under development.

The Co-effect of Cordyceps sinensis and Strontium on Osteoporosis in Ovariectomized Osteopenic Rats

The co-effect of Cordyceps sinensi (CS; caterpillar fungus) and strontium on ovariectomized osteopenic rats was studied in this paper. After the rats were treated orally with CS, strontium (SR), and CS rich in strontium (CSS), respectively, the urine calcium, plasma calcium, plasma phosphorus, bone mineral content, mechanical testing, and the mass of uterus, thymus, and body were examined. Both CSS and SR have a positive effect on mechanical strength and mineral content of ovariectomized osteopenic rats. However, femoral neck strength in the CSS-treated group was higher than those in the SR-treated groups. CSS and SR significantly decreased urinary calcium excretion and plasma total calcium and inorganic phosphate concentrations. On the contrary, CS and CSS significantly increased weights of atrophic uteri and weights of body and also decreased the thymus mass in animals, whereas SR did not exhibit any such effects. Our experiments have demonstrated that CSS possess a preferable effect against the decrease of bone strength and bone mineral mass caused by osteoporosis. It was caused by the co-effect of CS and strontium. The mechanism of it includes decreases bone resorption, increases bone formation, increases in body weight, and enhances 17β-estradiol-producing as well as enhancing the immune functions in animals. The data provide an important proof of concept that CSS might be a new potential therapy for the management of postmenopausal osteoporosis in humans.

Zinc supplementation can protect from enhanced risk of femoral neck fracture in male rats chronically exposed to cadmium

The aim of this study was to evaluate whether zinc (Zn) supplementation can protect from an enhanced risk of femoral neck fracture due to chronic exposure to cadmium (Cd). For this purpose, biomechanical properties of the neck and bone mineral density (BMD) at the proximal femur of rats receiving Cd (5 or 50 mg/l) or/and Zn (30 or 60 mg/l) in drinking water for 6 and 12 months were evaluated. The exposure to 5 and 50 mg Cd/l decreased the proximal femur BMD and affected biomechanical properties of the femoral neck. In the rats treated with 5 mg Cd/l, weakening of the femoral neck strength was observed after 12 months, whereas at higher exposure – already after 6 months. The supplementation with 30 and 60 mg Zn/l, enhancing its daily intake by 68% and 138%, respectively, compared to the standard diet, had beneficial influence on the femoral neck biomechanical properties during the exposure to Cd, but it had no impact on the proximal femur BMD. Zn administration during the 12-month exposure to 5 mg Cd/l totally prevented the weakening of the neck. Zn supplementation during the 6-month treatment with 50 mg Cd/l entirely prevented the Cd-induced decrease in the neck fracture strength; however, at the longer exposure to Cd the protective effect of Zn was only partial. The beneficial Zn influence was independent on its dose. The results allow the conclusion that an increase in the daily intake of Zn during moderate and relatively high exposures to Cd can reduce femoral neck susceptibility to fracture. Based on the findings, it seems that enhanced Zn consumption in subjects chronically exposed to Cd may, at least partly, protect from the enhanced risk of femoral neck fracture.

Densitometric and geometric measurement of the proximal femur in elderly women with and without osteoporotic vertebral fractures by volumetric quantitative multi-slice CT

There is a lack of research on volumetric multi-slice CT (MSCT) application in hip densitometric assessment and geometric measures in elderly women with osteoporotic vertebral fractures. A total of 237 elderly women were divided into three groups based on BMD values of the lumbar spine (AP-SPINE) and/or the femoral neck (NECK) by dual energy X-ray absorptiometry (DXA): osteoporosis with (OP_FX, 53 cases) or without vertebral fracture (OP_NONFX, 94 cases), or normal BMD (CONTROL, 90 cases). Volumetric BMD of trabecular bone (TRAB), integral bone (INTGL) and cortical bone (CORT) with neck axis length (NAL) and minimum cross-section area (mCSA) measures of the left femoral neck were calculated, respectively, by using OsteoCAD software based on MSCT scans of the abdominal-pelvic region of all participants, then the index of femoral neck strength (FNSI) was estimated. The values of TRAB, CORT and INTGL of OP_FX were significantly lower than those of OP_NONFX, with the decrease in 6.8-21.8%, as well as being lower than those in CONTROL, whereas no significant differences in the values of AP-SPINE and NECK were found between OP_FX and OP_NONFX. No significant difference of the value of mCSA was found among these three groups. The NAL value of OP_NONFX was larger than that of CONTROL. FNSI of femoral neck in OP_FX (0.42±0.15g(2)/cm(4)) was significantly lower than OP_NONFX (0.50±0.14g(2)/cm(4)) (p<0.05). vQCT measurement seemed to be more effective than DXA in evaluating hip densitometric changes and discriminating osteoporotic elderly subjects with fractured vertebrae from the non-fractured in a group of Chinese women.

Performance of the resurfaced hip. Part 2: The influence of prosthesis stem design on remodelling and fracture of the femoral neck

Hip resurfacing is a popular treatment for osteoarthritis in young, active patients. Previous studies have shown that occasional failures--femoral neck fracture and implant loosening, possibly associated with bone adaptation--are affected by prosthesis sizing and positioning, in addition to patient and surgical factors. With the aim of improving tolerance to surgical variation, finite element modelling was used to indicate the effects of prosthesis metaphyseal stem design on bone remodelling and femoral neck fracture, with a range of implant orientations. The analysis suggested that the intact femoral neck strength in trauma could be maintained across a wider range of varus-valgus orientations for short-stemmed and stemless prostheses. Furthermore, the extent of periprosthetic bone remodelling was lower for the short-stemmed implant, with slightly reduced stress shielding and considerably reduced densification around the stem, potentially preventing further progressive proximal stress shielding. The study suggests that a short-stemmed resurfacing head offers improved tolerance to misalignment and remodelling stimulus over traditional designs. While femoral neck fracture and implant loosening are multifactorial, biomechanical factors are of clear importance to the clinical outcome, so this may reduce the risk for patients at the edge of the indications for hip resurfacing, or shorten the surgical learning curve.

Peripubertal estrogen levels and physical activity affect femur geometry in young adult women

The growing skeleton is particularly responsive to exercise around the time of puberty, suggesting a possible role for estrogen in mechanical adaptation in young women. We assessed femoral neck strength index at age 17 in young women with varying adolescent physical activity levels and E2 levels in the first 3 years after menarche. The results indicate that both E2 levels in the first year after menarche and adolescent physical activity are positively associated with bone strength in young adulthood, such that hormone levels may modify human osteogenic responses to exercise. It is well established that physical activity contributes to bone strength in young females, but less is known about how peripubertal estrogen affects skeletal responses to exercise. We used data from 84 participants in the Penn State Young Women's Health Study to test the prediction that young women who (1) had higher E2 levels during the first year after menarche or (2) were more physically active in adolescence will have greater bone strength at the end of adolescence. Subjects were divided into tertiles of physical activity and of E2 level in the first, second, and third postmenarchal years, and femoral strength was calculated from dual-energy X-ray absorptiometry scans of the proximal femur using hip structure analysis. At age 17, subjects with the highest E2 levels in year 1 after menarche had 5-14% greater strength in the narrow neck and intertrochanteric region, and the most active subjects had 10-11% greater strength in the femoral narrow neck vs. less active girls. This study suggests that both physical activity and peripubertal estrogen have important influences on young adult bone strength and that hormone levels may be mediators of human osteogenic responses to exercise.