Bone marrow levels of 25 hydroxy vitamin D are not depressed in cases of hip fracture compared with controls

There is little information on tissue as distinct from plasma levels of vitamin D metabolites in cases of hip fracture compared with controls. Femoral neck fractures in the elderly are associated with increased cortical remodelling and endosteal resorption, leading to regional increases in porosity and reduced cortical thickness. Vitamin D metabolites play a central role in the maintenance of normal serum calcium levels and may, through interactions with parathyroid hormone, exert an important influence on bone structure. To investigate whether hip fracture might be associated with tissue vitamin D deficiency, we have measured by radioimmunoassay the levels of 25 hydroxy vitamin D (25 (OH)D) in bone marrow samples extracted from the proximal femurs of 16 female subjects who had suffered fracture (mean age = 82.1 years, standard error (se) 1.9) and nine sex matched post mortem controls (mean age = 83.8 years, se 2.5). Twenty five (OH)D concentrations were significantly greater in the fracture cases (median = 3.7, IQR = 2.5–3.9 ng/g) than in the control group (median = 1.5, IQR = 0.9–2.3 ng/g; P = 0.0007, non‐parametric Wilcoxon/Kruskal–Wallis test). It was suggested in the 1970s that bone loss and hip fracture risk in the UK were driven by vitamin D deficiency. Our results suggest that the alterations in femoral neck bone microstructure and remodelling in hip fracture cannot be assigned to the single cause of relative deficiency of vitamin D. Vitamin D deficiency or insufficiency may nevertheless increase remodelling and loss of bone tissue and contribute causally to a minority of hip fractures. Copyright © 2013 John Wiley & Sons, Ltd.     

股骨近端三维有限元模型评价髋部骨折患者骨密度

目的：探究骨密度与老年髋部骨折股骨近端三维有限元模型密度的关系。方法：选取8 例老年髋部骨折,其中4 例股骨颈骨 折,4 例股骨转子间骨折;左侧肢体3 例,右侧肢体5 例。分别测定腰椎骨密度和双侧髋关节CT 资料,运用Mimics软件和abaqus 软件对健侧股骨近端进行重建和计算出该模型的密度。结果：股骨转子间骨折组腰椎骨密度为(-4.05± 0.24) g/cm2,三维有限元模 型密度为[(1.15± 0.02)× 106],均低于股骨颈骨折组的(-3.15± 0.54) g/cm2,[(1.34± 0.06)× 106],两组比较差异均有统计学意义（均 P<0.05）。腰椎的骨密度与三维有限元模型密度成线性正相关（r=0.881,P=0.004）。结论：骨密度与老年髋部骨折股骨近端三维有限 元模型密度成线性正相关的关系,可为进一步用有限元分析法探讨老年髋部骨折部位与骨密度的关系提供理论依据。     

Potential role of vitamin D receptor gene polymorphism in determining bone phenotype in young male athletes.

The genetic difference among individuals partly explains variance in adaptive response to exercise through gene-environment interaction. The aim of this cross-sectional study was to evaluate the role of the vitamin D receptor (VDR) gene polymorphism, which locates at the translation initiation site, in the adaptations of bone to long-term impact loading. The VDR genotypes, as detected by endonuclease Fok I, and bone phenotypes of the lumbar spine and femoral neck were examined in 44 highly trained young male athletes and 44 age-matched nonathletic controls. As a whole, the athletes had a significantly higher bone mineral content resulting from a combination of increased volume and density at both sites than the controls. When the athletes were compared with the controls within each VDR genotype, however, the increased spinal volume was found only in the athletes with the FF but not in those with the Ff genotype("F" for the absence of the endonuclease Fok I restriction site and "f" for its presence). Differences in bone mineral content in the lumbar spine and femoral neck between the controls and the athletes were greater in subjects with FF than those with Ff. Our results suggest a gene-environment interaction in that the bone phenotypes in individuals with FF adapt to impact loading by producing stronger bone structure than those with the Ff do.     

人工髋关节置换术治疗高龄患者股骨粗隆间骨折的临床疗效研究

目的:探究人工髋关节置换术治疗高龄患者股骨粗隆间骨折的临床疗效。方法:选择40例高龄股骨粗隆间骨折患者并将其随机分为两组,观察组给予人工髋关节置换术治疗,对照组经股骨近端髓内钉内固定术治疗。观察比较两组L2-4椎体骨密度、疼痛程度、髋关节功能恢复情况及Harris评分。结果:治疗后,两组L2-4椎体骨密度均显著高于治疗前(P0.05),且观察组显著高于对照组(P0.05);观察组疼痛比例较治疗前明显降低(P0.05),且显著低于对照组(P0.05);观察组髋关节恢复优良率为95.0%,显著高于对照组(70.0%,P0.05);两组Harris评分均显著高于治疗前(P0.05),且观察组显著高于对照组(P0.05)。结论:采用人工髋关节置换术治疗高龄股骨粗隆间骨折的疗效明显优于经股骨近端髓内钉内固定术治疗,其可有效促进髋关节功能恢复,减轻患者疼痛。     

The Lichfield bone study: the skeletal response to exercise in healthy young men

The skeletal response to short-term exercise training remains poorly described. We thus studied the lower limb skeletal response of 723 Caucasian male army recruits to a 12-wk training regime. Femoral bone volume was assessed using magnetic resonance imaging, bone ultrastructure by quantitative ultrasound (QUS), and bone mineral density (BMD) using dual-energy X-ray absorptiometry (DXA) of the hip. Left hip BMD increased with training (mean ± SD: 0.85 ± 3.24, 2.93 ± 4.85, and 1.89 ± 2.85% for femoral neck, Ward's area, and total hip, respectively; all P < 0.001). Left calcaneal broadband ultrasound attenuation rose 3.57 ± 0.5% (P < 0.001), and left and right femoral cortical volume by 1.09 ± 4.05 and 0.71 ± 4.05%, respectively (P = 0.0001 and 0.003), largely through the rise in periosteal volume (0.78 ± 3.14 and 0.59 ± 2.58% for right and left, respectively, P < 0.001) with endosteal volumes unchanged. Before training, DXA and QUS measures were independent of limb dominance. However, the dominant femur had higher periosteal (25,991.49 vs. 2,5572 mm(3), P < 0.001), endosteal (6,063.33 vs. 5,983.12 mm(3), P = 0.001), and cortical volumes (19,928 vs. 19,589.56 mm(3), P = 0.001). Changes in DXA, QUS, and magnetic resonance imaging measures were independent of limb dominance. We show, for the first time, that short-term exercise training in young men is associated not only with a rise in human femoral BMD, but also in femoral bone volume, the latter largely through a periosteal response.     

Trabecular bone modeling and subcapital femoral fracture

Fragility fractures, including neck of femur fractures, result from reductions in the amount, quality and architecture of bone. The aim of this study was to compare the cancellous bone structure, and static indices of bone turnover, in female patients who had sustained fragility fracture at the femoral neck, with age-matched females without fragility fracture. Bone samples were taken from the intertrochanteric region of the proximal femur of female patients undergoing hip arthroplasty surgery for a subcapital fragility fracture of the femoral neck (#NOF) or from age-matched female control individuals at routine autopsy. The histomorphometric data, which were normally distributed, indicated no difference between the mean values for any of the structural parameters in control and fracture samples. In particular, the BV/TV values were not different and did not change significantly with age in these cohorts of individuals aged >65 years. The static indices of bone turnover, eroded surface (ES/BS) and osteoid surface (OS/BS), were positively correlated with age in the >65-year-old control group (p<0.05 and p<0.03, respectively). The median values for these indices were not different between the fracture and control groups. However, both the median and the range of OS/BS values were increased for >65-year-old controls compared with a group of younger females aged <65 years, suggesting an increase in bone formation in older females in the proximal femur after 65 years of age. When the data were further interrogated, a reduction in the percentage osteoid surface to eroded surface quotient (OS/ES) was found for the fracture group compared with the age-matched control group. These data indicate that perturbations in bone formation and/or resorption surface are potentially important in producing bone in the proximal femur with increased propensity to fracture. These data also support the concept that trabecular bone modeling may be a factor influencing bone strength in addition to bone mass.     

Moment coefficients of skewness in the femoral neck cortical bone distribution of BAR 1002’00

The cortical bone distributions in the femoral necks of apes and humans differ as a result of different loading environments caused by the realignment of the hip abductor apparatus. Femoral neck cortical bone in extant humans is very thin superiorly and thicker inferiorly, while the cortical bone in apes tends to be more uniformly thick. The unique internal anatomy of extant humans allows inferences to be made about primary locomotor function from incomplete femora. Here the differences in cortical bone distributions are quantified using moment coefficient of skewness. Skewness coefficients at two locations along the neck of the 6 million years old African femoral specimen BAR 1002’00 were compared to samples of 9 extant adult humans and 10 adult chimpanzees. The skewness coefficients of cortical bone in the femoral neck of BAR 1002’00 are more similar to those of chimpanzees than to humans, although the contrast is less pronounced in the region closer to the neck-shaft junction than more proximally toward the femoral head; this pattern indicates that in at least one respect this specimen attributed to Orrorin tugenensis manifests structural features suggesting influences of a hip abductor apparatus that had not yet evolved to the same extent as in extant humans.     

In-Vivo Assessment of Femoral Bone Strength Using Finite Element Analysis (FEA) Based on Routine MDCT Imaging: A Preliminary Study on Patients with Vertebral Fractures

PurposeTo experimentally validate a non-linear finite element analysis (FEA) modeling approach assessing in-vitro fracture risk at the proximal femur and to transfer the method to standard in-vivo multi-detector computed tomography (MDCT) data of the hip aiming to predict additional hip fracture risk in subjects with and without osteoporosis associated vertebral fractures using bone mineral density (BMD) measurements as gold standard.MethodsOne fresh-frozen human femur specimen was mechanically tested and fractured simulating stance and clinically relevant fall loading configurations to the hip. After experimental in-vitro validation, the FEA simulation protocol was transferred to standard contrast-enhanced in-vivo MDCT images to calculate individual hip fracture risk each for 4 subjects with and without a history of osteoporotic vertebral fractures matched by age and gender. In addition, FEA based risk factor calculations were compared to manual femoral BMD measurements of all subjects.ResultsIn-vitro simulations showed good correlation with the experimentally measured strains both in stance (R² = 0.963) and fall configuration (R² = 0.976). The simulated maximum stress overestimated the experimental failure load (4743 N) by 14.7% (5440 N) while the simulated maximum strain overestimated by 4.7% (4968 N). The simulated failed elements coincided precisely with the experimentally determined fracture locations. BMD measurements in subjects with a history of osteoporotic vertebral fractures did not differ significantly from subjects without fragility fractures (femoral head: p = 0.989; femoral neck: p = 0.366), but showed higher FEA based risk factors for additional incident hip fractures (p = 0.028).ConclusionFEA simulations were successfully validated by elastic and destructive in-vitro experiments. In the subsequent in-vivo analyses, MDCT based FEA based risk factor differences for additional hip fractures were not mirrored by according BMD measurements. Our data suggests, that MDCT derived FEA models may assess bone strength more accurately than BMD measurements alone, providing a valuable in-vivo fracture risk assessment tool.     

Alpine skiing is associated with higher femoral neck bone mineral density

Objective:

To evaluate the influence of elite-level alpine skiing on athletes’ skeleton.

Methods:

Thirteen professional alpine skiers (9 males and 4 females with mean age of 22.6 years) and their age- and height matched control subjects were measured with dual energy X-ray absorptiometry (total body, lumbar spine, proximal femur, forearm) and quantitative ultrasound (hand).

Results:

After adjusting for sex, age, weight and height, between-group differences were 15% (p=0.012) for the lumbar spine, 14% (p=0.022) for the femoral neck, 10% (p=0.051) for the total hip, and 11% (p=0.001) for the total body favoring the alpine skiers. However, after controlling for total body lean mass (~muscle mass), the group-differences lost their statistical significance, the borderline 10% difference (p=0.051) in femoral neck BMD excluded.

Conclusion:

Factors contributing to the alpine skiers’ higher BMD may not only include the greater muscle mass (~stronger muscles) of these athletes but also a large number of impacts and possibly other high-frequency features in external loading generated by the high-speed skiing performance.     

Side-to-side differences in bone strength in master jumpers and sprinters

Introduction: This study evaluated side-to-side difference in tibial bone structure, calf muscle cross-sectional area (CSA) and hopping force in master athletes as a result of training for sports with different magnitudes of inter-leg loading difference. Methods: Tibial bone parameters (at 4%, 14%, 38% and 66% tibial length proximal to distal end), muscle CSA (at 66% tibial length) and hopping forces of both legs of 51 master athletes (conditioned jumpers, conditioned triple jumpers, unconditioned jumpers, hurdlers and sprinters) were examined using pQCT. In epiphyseal 4% slice bone CSA (Ar.tot), total BMC (vBMC.tot), trabecular BMC (vBMC.tb) cortical BMC (vBMC.ct), and trabecular BMD (vBMD.tb) were measured. In diaphyseal slices, Ar.tot, vBMC.ct, cortical density (vBMD.ct), cross-sectional moment of inertia (CSMI) and calf muscle CSA (MuscA) were examined. Results: In conditioned jumpers, side-to-side differences in favour of take-off leg were found in 4% slice in vBMC.tb (+4.1%) (P<0.05). A side-to-side difference was found in 66% slice vBMC.ct and CSMI (both P<0.05), with conditioned jumper (+2.8% and 6.6%) and triple jumper (+2.7% and 7.2%) values higher than other groups. Conclusion: The results suggest that regular training in high-impact sports with uneven lower limb loading results in side-to-side differences in skeletal adaptation independent of age and gender, suggesting that high-impact exercise is effective in maintaining bone strength throughout human lifespan.     

Use of a statistical model of the whole femur in a large scale,multi-model study of femoral neck fracture risk

Interpatient variability is often overlooked in orthopaedic computational studies due to the substantial challenges involved in sourcing and generating large numbers of bone models. A statistical model of the whole femur incorporating both geometric and material property variation was developed as a potential solution to this problem. The statistical model was constructed using principal component analysis, applied to 21 individual computer tomography scans. To test the ability of the statistical model to generate realistic, unique, finite element (FE) femur models it was used as a source of 1000 femurs to drive a study on femoral neck fracture risk. The study simulated the impact of an oblique fall to the side, a scenario known to account for a large proportion of hip fractures in the elderly and have a lower fracture load than alternative loading approaches. FE model generation, application of subject specific loading and boundary conditions, FE processing and post processing of the solutions were completed automatically. The generated models were within the bounds of the training data used to create the statistical model with a high mesh quality, able to be used directly by the FE solver without remeshing. The results indicated that 28 of the 1000 femurs were at highest risk of fracture. Closer analysis revealed the percentage of cortical bone in the proximal femur to be a crucial differentiator between the failed and non-failed groups. The likely fracture location was indicated to be intertrochantic. Comparison to previous computational, clinical and experimental work revealed support for these findings.     

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.     

Design considerations for ceramic resurfaced femoral head: effect of interface characteristics on failure mechanisms

Ceramic hip resurfacing may offer improved wear resistance compared to metallic components. The study is aimed at investigating the effects of stiffer ceramic components on the stress/strain-related failure mechanisms in the resurfaced femur, using three-dimensional finite element models of intact and resurfaced femurs with varying stem–bone interface conditions. Tensile stresses in the cement varied between 1 and 5 MPa. Postoperatively, 20–85% strain shielding was observed inside the resurfaced head. The variability in stem–bone interface condition strongly influenced the stresses and strains generated within the resurfaced femoral head. For full stem–bone contact, high tensile (151–158 MPa) stresses were generated at the cup–stem junction, indicating risk of fracture. Moreover, there was risk of femoral neck fracture due to elevated bone strains (0.60–0.80% strain) in the proximal femoral neck region. Stresses in the ceramic component are reduced if a frictionless gap condition exists at the stem–bone interface. High stresses, coupled with increased strain shielding in the ceramic resurfaced femur, appear to be major concerns regarding its use as an alternative material.     

动力加压髋螺钉对股骨上段生物力学特征性的影响

目的：探讨股骨上端骨折,以动力加压髋螺钉进行骨固定治疗,骨折愈合后,取出动力加压髋螺钉以后的股骨上段与完整的股骨上段的生物力学特性相比较,为临床内固定取出术后功能锻炼的强度提供量化依据。方法：收集8具新鲜尸体股骨标本进行实验应力分析,分别测定完整股骨上段和动力加压髋螺钉取出后股骨上段的力学特性改变。结果：动力加压髋螺钉取出术后股骨上段的力学特性与完整股骨上段的力学特性相比有显著的差异（P＜0．01）。结论：股骨上端骨折如果以动力加压髋螺钉为治疗手段,在骨折愈合取出内固定后,功能锻炼只能控制在慢速步行水平,不能进行奔跑、跳跃等活动,以防止再骨折等并发症的发生。     

A 42-year-old patient presenting with femoral head migration after hemiarthroplasty performed 22 years earlier: a case report

Introduction

Treatment of femoral neck fractures in young adults may require total hip arthroplasty or hip hemiarthroplasty using a bipolar cup. The latter can, however, result in migration of the femoral head and poor long-term results.

Case presentation

We report a case of femoral head migration after hemiarthroplasty performed for femoral neck fracture that had occurred 22 years earlier, when the patient (a Japanese man) was 20 years old. He experienced peri-prosthetic fracture of the femur, subsequent migration of the prosthesis, and a massive bone defect of the pelvic side acetabular roof. After bone union of the femoral shaft fracture, the patient was referred to our hospital for reconstruction of the acetabular roof. Intra-operatively, we placed two alloimplants of bone from around the transplanted femoral head into the weight-bearing region of the acetabular roof using an impaction bone graft method. We then implanted an acetabular roof reinforcement plate and a cemented polyethylene cup in the position of the original acetabular cup. Eighteen months post-operatively, X-rays showed union of the transplanted bone.

Conclusions

Treatment of femoral neck fractures in young adults is usually accomplished by osteosynthesis, but it may be complicated by femoral head avascular necrosis or by infection or osteomyelitis. In such cases, once an infection has subsided, either hip hemiarthroplasty using a bipolar cup or total hip arthroplasty may be required. However, if the acetabular side articular cartilage is damaged, a bipolar cup should not be used. Total hip arthroplasty should be performed to prevent migration of the implant.     

Strain energy in the femoral neck during exercise

Physical activity is recommended to mitigate the incidence of hip osteoporotic fractures by improving femoral neck strength. However, results from clinical studies are highly variable and unclear about the effects of physical activity on femoral neck strength. We ranked physical activities recommended for promoting bone health based on calculations of strain energy in the femoral neck. According to adaptive bone-remodeling theory, bone formation occurs when the strain energy (S) exceeds its homeostatic value by 75%. The potential effectiveness of activity type was assessed by normalizing strain energy by the applied external load. Tensile strain provided an indication of bone fracture. External force and joint motion data for 15 low- and high-load weight-bearing and resistance-based activities were used. High-load activities included weight-bearing activities generating a ground force above 1 body-weight and maximal resistance exercises about the hip and the knee. Calculations of femoral loads were based on musculoskeletal and finite-element models. Eight of the fifteen activities were likely to trigger bone formation, with isokinetic hip extension (ΔS=722%), one-legged long jump (ΔS=572%), and isokinetic knee flexion (ΔS=418%) inducing the highest strain energy increase. Knee flexion induced approximately ten times the normalized strain energy induced by hip adduction. Strain and strain energy were strongly correlated with the hip-joint reaction force (R²=0.90–0.99; p<0.05) for all activities, though the peak load location was activity-dependent. None of the exercises was likely to cause fracture. Femoral neck mechanics is activity-dependent and maximum isokinetic hip-extension and knee-flexion exercises are possible alternative solutions to impact activities for improving femoral neck strength.     

During sideways falls proximal femur fractures initiate in the superolateral cortex: Evidence from high-speed video of simulated fractures

Results of recent imaging studies and theoretical models suggest that the superior femoral neck is a location of local weakness due to an age-related thinning of the cortex, and thus the site of hip fracture initiation. The purpose of this study was to experimentally determine the spatial and temporal characteristics of the macroscopic failure process during a simulated hip fracture that would occur as a result of a sideways fall. Twelve fresh frozen human cadaveric femora were used in this study. The femora were fractured in an apparatus designed to simulate a fall on the greater trochanter. Image sequences of the surface events related to the fractures were captured using two high-speed video cameras at 9111 Hz. The videos were analyzed with respect to time and load to determine the location and sequence of these events occurring in the proximal femur. The mean failure load was 4032 N (SD 370 N). The first surface events were identified in the superior femoral neck in eleven of the twelve specimens. Nine of these specimens fractured in a clear two-step process that initiated with a failure in the superior femoral neck, followed by a failure in the inferior femoral neck. This cadaveric model of hip fracture empirically confirms hypotheses that suggested that hip fractures initiate with a failure in the superior femoral neck where stresses are primarily compressive during a sideways fall impact, followed by a failure in the inferior neck where stresses are primarily tensile. Our results confirm the superolateral neck of the femur as an important region of interest for future hip fracture screening, prevention and treatment research.     

Bone related health status in adolescent cyclists

Purpose

To describe bone status and analyse bone mass in adolescent cyclists.

Methods

Male road cyclists (n = 22) who had been training for a minimum of 2 years and a maximum of 7 years with a volume of 10 h/w, were compared to age-matched controls (n = 22) involved in recreational sports activities. Subjects were divided in 2 groups based on age: adolescents under 17 yrs (cyclists, n = 11; controls, n = 13) and over 17 yrs (cyclists, n = 11; controls, n = 9). Peak oxygen uptake (VO₂max) was measured on a cycloergometer. Whole body, lumbar spine, and hip bone mineral content (BMC), density (BMD) and bone area were assessed using dual x-ray absorptiometry (DXA). Volumetric BMD (vBMD) and bone mineral apparent density (BMAD) were also estimated.

Results

The BMC of cyclists was lower for the whole body, pelvis, femoral neck and legs; BMD for the pelvis, hip, legs and whole body and legs bone area was lower but higher in the hip area (all, P≤0.05) after adjusting by lean mass and height. The BMC of young cyclists was 10% lower in the leg and 8% higher in the hip area than young controls (P≤0.05). The BMC of cyclists over 17 yrs was 26.5%, 15.8% and 14.4% lower BMC at the pelvis, femoral neck and legs respectively while the BMD was 8.9% to 24.5% lower for the whole body, pelvis, total hip, trochanter, intertrochanter, femoral neck and legs and 17.1% lower the vBMD at the femoral neck (all P≤0.05). Grouped by age interaction was found in both pelvis and hip BMC and BMD and in femoral neck vBMD (all P≤0.05).

Conclusion

Cycling performed throughout adolescence may negatively affect bone health, then compromising the acquisition of peak bone mass.     

Analysis of the periprosthetic femoral bone reaction after uncemented total hip arthroplasty with computertomography assisted osteodensitometry in vivo: 6-year follow-up]

AIMS: We prospectively analyzed the cancellous and cortical periprosthetic femoral bone reaction after implantation of a cementless total hip arthroplasty with computertomography assisted osteodensitometry after a mean of 1 and 6 years. MATERIALS AND METHODS: Twenty-one patients (? age at implantation: 52 years) with osteoarthrits of the hip joint received 21 cementless hip prostheses with a three-dimensionally tapered design. All patients were analyzed clinically, with CT-osteodensitometry and plain radiography after a mean of 10 days, at 1 and 6 years postoperatively. Cancellous and cortical bone density was evaluated automatically using a special software tool. RESULTS: The proximal region of the stem showed progessive cortical (? -15% 1 year, -25% 6 years post-OP) and cancellous (? -26% 1 year, -49% 6 years post-OP) bone density loss. Cortical bone density loss was lower and non-progressive at the diaphysis (? -7% 1 year, -9% 6 years post-OP) and the distal region (? -6% 1 year, -4% 6 years post-OP) of the stem. All stems showed no signs of loosening on plain radiography and good clinical results according to the Harris hip score. CONCLUSION: Computertomography assisted osteodensitometry is the only method which allows discrimination between periprosthetic cortical and cancellous bone density changes in vivo. The analyzed uncemented stem fixates at the diaphysis and distal region. Due to the changed biomechanical loading after stem implantation, progressive proximal cancellous bone density loss was measured for the first time in vivo. Its role in the pathogenesis of implant loosening is still unknown and needs to be further elucidated.     

Emerging evidence that adaptive bone formation inhibition by non-steroidal anti-inflammatory drugs increases stress fracture risk

There is mounting evidence suggesting that the commonly used analgesics, non-steroidal anti-inflammatory drugs (NSAIDs), may inhibit new bone formation with physical training and increase risk of stress fractures in physically active populations. Stress fractures are thought to occur when bones are subjected to repetitive mechanical loading, which can lead to a cycle of tissue microdamage, repair, and continued mechanical loading until fracture. Adaptive bone formation, particularly on the periosteal surface of long bones, is a concurrent adaptive response of bone to heightened mechanical loading that can improve the fatigue resistance of the skeletal structure, and therefore may play a critical role in offsetting the risk of stress fracture. Reports from animal studies suggest that NSAID administration may suppress this important adaptive response to mechanical loading. These observations have implications for populations such as endurance athletes and military recruits who are at risk of stress fracture and whose use of NSAIDs is widespread. However, results from human trials evaluating exercise and bone adaptation with NSAID consumption have been less conclusive. In this review, we identify knowledge gaps that must be addressed to further support NSAID-related guidelines intended for at-risk populations and individuals.