Trabecular bone tissue strains in the healthy and osteoporotic human femur.

Quantitative information about bone tissue-level loading is essential for understanding bone mechanical behavior. We made microfinite element models of a healthy and osteoporotic human femur and found that tissue-level strains in the osteoporotic femoral head were 70% higher on average and less uniformly distributed than those in the healthy one. INTRODUCTION: Bone tissue stresses and strains in healthy load-adapted trabecular architectures should be distributed rather evenly, because no bone tissue is expected to be overloaded or unused. In this study, we evaluate this paradigm with the use of microfinite element (microFE) analyses to calculate tissue-level stresses and strains for the human femur. Our objectives were to quantify the strain distribution in the healthy femur, to investigate to what extent this distribution is affected by osteoporosis, to determine if osteoporotic bone is simply bone adapted to lower load levels, and to determine the "safety factor" for trabecular bone. MATERIALS AND METHODS: microFE models of a healthy and osteoporotic proximal femur were made from microcomputed tomography images. The models consisted of over 96 and 71 million elements for the healthy and osteoporotic femur, respectively, and represented their internal and external morphology in detail. Stresses and strains were calculated for each element and their distributions were calculated for a volume of interest (VOI) of trabecular bone in the femoral head. RESULTS: The average tissue-level principal strain magnitude in the healthy VOI was 304 +/- 185 microstrains and that in the osteoporotic VOI was 520 +/- 355 microstrains. Calculated safety factors were 8.6 for the healthy and 4.9 for the osteoporotic femurs. After reducing the force applied to the osteoporotic model to 59%, the average strain compared with that of the healthy femur, but the SD was larger (208 microstrains). CONCLUSIONS: Strain magnitudes in the osteoporotic bone were much higher and less uniformly distributed than those in the healthy one. After simulated joint-load reduction, strain magnitudes in the osteoporotic femur were very similar to those in the healthy one, but their distribution is still wider and thus less favorable.     

Stress distributions within the proximal femur during gait and falls: Implications for osteoporotic fracture

The rates of fracture at sites with different relative amounts of cortical and trabecular bone (hip, spine, distal radius) have been used to make inferences about the pathomechanics of bone loss and the existence of type I and type II osteoporosis. However, fracture risk is directly related to the ratio of tissue stress to tissue strength, which in turn is dependent not only on tissue composition but also tissue geometry and the direction and magnitude of loading. These three elements determine how the load is distributed within the tissue. As a result, assumptions on the relative structural importance of cortical and trabecular bone, and how these tissues are affected by bone loss, can be inaccurate if based on regional tissue composition and bone density alone. To investigate the structural significance of cortical and trabecular bone in the proximal femur, and how it is affected by bone loss, we determined the stress distributions in a normal and osteoporotic femur resulting from loadings representing: (1) gait; and (2) a fall to the side with impact onto the greater trochanter. A three-dimensional finite element model was generated based on a representative femur selected from a large database of femoral geometries. Stresses were analyzed throughout the femoral neck and intertrochanteric regions. We found that the percentage of total load supported by cortical and trabecular bone was approximately constant for all load cases but differed depending on location. Cortical bone carried 30% of the load at the subcapital region, 50% at the mid-neck, 96% at the base of the neck and 80% at the intertrochanteric region. These values differ from the widely held assumption that cortical bone carries 75% of the load in the femoral neck and 50% of the load at the intertrochanteric region. During gait, the principal stresses were concentrated within the primary compressive system of trabeculae and in the cortical bone of the intertrochanteric region. In contrast, during a fall, the trabecular stresses were concentrated within the primary tensile system of trabeculae with a peak magnitude 4.3 times that present during gait. While the distribution of stress for the osteoporotic femur was similar to the normal, the magnitude of peak stress was increased by between 33% and 45%. These data call into question several assumptions which serve as the basis for theories on the pathomechanics of osteoporosis. In addition, we expect that the insight provided by this analysis will result in the improved development and interpretation of non-invasive techniques for the quantification of in vivo hip fracture risk.     

Trabecular microfractures. Nature and distribution in the proximal femur

The nature and distribution of healing trabecular microfractures (TMF) of femoral heads were studied in 50 autopsy specimens, 30 patients with osteoarthritis (OA) of the hip and 45 patients with subcapital fractures of the femoral neck (SFFN). Macerated coronal slices were examined with a dissecting microscope, and the TMFs were identified where there was callus formation, either nodular or smooth. The number of TMFs did not differ significantly in the SFFN and age-matched control groups. The number of TMFs in the OA group was lower than in SFFN and age-matched control groups. The numbers of nodular TMFs in the control and SFFN groups did not differ significantly but were fewer in the OA group. Smooth TMFs were present in similar numbers in OA, control, and SFFN groups. The ratio of the nodular to smooth TMFs regressed with age. The greater proportion of nodular TMFs in older patients was indicative of an early stage of woven bone callus formation. In all three groups (excluding controls younger than 50 years of age), TMFs tended to appear some distance from the midpoint of the trabeculae. The number of TMFs in trabeculae parallel and perpendicular to the direction of principal stress was similar in all three groups.     

聚醚醚酮髋股骨头假体置换术后股骨近段的力学分析

[目的]探讨复合材料住全髋股骨头假体中的应用前景，旨在寻找能与股骨紧密结合、增加股骨近端应力传递的新型假体，期望进一步提高全髋关节置换术的远期疗效。[方法]5对人体新鲜尸体股骨平均分成左右2组，1组行钴铬钼合金（CoCrMo）股骨头假体置换术，另1组行碳纤维增强聚醚醚酮（CF／PEEK）假体置换术。在假体和近端股骨表面粘贴应变片，模拟单肢站立施加载荷。首先记录正常股骨产生的应变分布，然后行2种假体的股骨头置换术，再记录2组标本所产生的应变分布。[结果]股骨应变在假体植入后，从近端到远端逐渐增加，变化形式与完整股骨的应变形式相似，并且在假体远端最大。2种假体植入后，股骨内外侧表面的应变皆减少；但CF／PEEK假体组产生的应变形式和大小比CoCrMo合金假体组更接近正常股骨。[结论]CF／PEEK复合材料股骨头假体能提供术后即刻稳定性和良好的近端载荷传递，因此能进一步减少应力遮挡、骨吸收、骨萎缩，最终避免假体松动失败。     

A method for assessment of the shape of the proximal femur and its relationship to osteoporotic hip fracture

The shape of the proximal femur has been demonstrated to be important in the occurrence of fractures of the femoral neck. Unfortunately, multiple geometric measurements frequently used to describe this shape are highly correlated. A new method, active shape modeling (ASM) has been developed to quantify the morphology of the femur. This describes the shape in terms of orthogonal modes of variation that, consequently, are all independent. To test this method, digitized standard pelvic radiographs were obtained from 26 women who had suffered a hip fracture and compared with images from 24 age-matched controls with no fracture. All subjects also had their bone mineral density (BMD) measured at five sites using dual-energy X-ray absorptiometry. An ASM was developed and principal components analysis used to identify the modes which best described the shape. Discriminant analysis was used to determine which variable, or combination of variables, was best able to discriminate between the groups. ASM alone correctly identified 74% of the individuals and placed them in the appropriate group. Only one of the BMD values (Wards triangle) achieved a higher value (82%). A combination of Wards triangle BMD and ASM improved the accuracy to 90%. Geometric variables used in this study were weaker, correctly classifying less than 60% of the study group. Logistic regression showed that after adjustment for age, body mass index, and BMD, the ASM data was still independently associated with hip fracture (odds ratio (OR)=1.83, 95% confidence interval 1.08 to 3.11). The odds ratio was calculated relative to a 10% increase in the probability of belonging to the fracture group. Though these initial results were obtained from a limited data set, this study shows that ASM may be a powerful method to help identify individuals at risk of a hip fracture in the future.     

体脂量是绝经后女性股骨近端骨强度的决定因素

正Lower body weight or body mass index(BMI)has been known to be higher risk of developing osteoporosis and low-energy fractures via mechanical loading and other factors in both men and women[1].Recently,there have been new insights into the relationships between body composition and bone health.However,most of the previous studies regarding the relative effect of body composition on bone mass yielded inconsistent     

Strain distribution in the proximal human femur. An in vitro comparison in the intact femur and after insertion of reference and experimental femoral stems

Six pairs of human cadaver femora were divided equally into two groups one of which received a non-cemented reference implant and the other a very short non-dependent experimental implant. Thirteen strain-gauge rosettes were attached to the external surface of each specimen and, during application of combined axial and torsional loads to the femoral head, the strains in both groups were measured. After the insertion of a non-cemented femoral component, the normal pattern of a progressive proximal-to-distal increase in strains was similar to that in the intact femur and the strain was maximum near the tip of the prosthesis. On the medial and lateral aspects of the proximal femur, the strains were greatly reduced after implantation of both types of implant. The pattern and magnitude of the strains, however, were closer to those in the intact femur after insertion of the experimental stem than in the reference stem. On the anterior and posterior aspects of the femur, implantation of both types of stem led to increased principal strains E1, E2 and E3. This was most pronounced for the experimental stem. Our findings suggest that the experimental stem, which has a more anatomical proximal fit without having a distal stem and cortex contact, can provide immediate postoperative stability. Pure proximal loading by the experimental stem in the metaphysis, reduction of excessive bending stiffness of the stem by tapering and the absence of contact between the stem and the distal cortex may reduce stress shielding, bone resorption and thigh pain.     

Blood flow changes to the proximal femur during total hip arthroplasty.

OBJECTIVE: To determine the changes in perfusion to the proximal femur that occur during cemented and uncemented total hip arthroplasty (THA). DESIGN: Case series. SETTING: A single tertiary-care centre. PATIENTS: Twenty-two consecutive patients. Those who had undergone previous hip surgery or received systemic corticosteroid therapy were excluded. INTERVENTION: Cemented (11 procedures) or uncemented (12 procedures) THA. MAIN OUTCOME MEASURE: Changes in blood flow at the level of the proximal femur, measured with laser Doppler flowmetry at 4 different times during THA. RESULTS: In both the cemented and the uncemented procedure overall proximal femoral blood flow was reduced (p = 0.002, p = 0.008, respectively). A greater reduction in overall proximal femoral perfusion was seen in the cemented group compared with the uncemented group (p = 0.004). This greater reduction in perfusion was seen primarily in the proximal femoral diaphysis (p = 0.004). CONCLUSION: The extensive canal preparation involved with the cemented procedure or the introduction of bone cement under pressure into the femoral canal may contribute to the greater reduction in perfusion to the proximal femur.     

绝经后女性股骨近端骨密度与骨质疏松性骨折相关性研究

目的：研究绝经后女性股骨近端骨密度的变化规律与骨质疏松症、骨质疏松性骨折间的关系。方法采用法国Medlink公司Osteocore 3型双能X线骨密度仪,对本地区417例绝经后女性股骨颈、大转子、粗隆间、全髋进行骨密度测定。结果骨折组各年龄段、各部位的BMD均比非骨折组低（ P＜0．05）。随着年龄的增长,股骨近端骨量逐渐丢失,除了45～50组,其余各年龄段骨折组的患病率明显高于非骨折组（ P＜0．05）,骨密度值越低,骨折危险性越大。结论绝经后女性股骨近端骨密度与发生骨质疏松性骨折的风险呈明显负相关性,应该注意预防。     

The role of the calcar femorale in stress distribution in the proximal femur

Objective: To investigate the role of the calcar femorale in stress distribution in the proximal femur. Methods: Twenty‐five specimens of proximal femurs were fixed to simulate single‐limb stance. Strain gauges were applied to record the strain under different loads. Strain values of 27 selected sites in the proximal femur were recorded and analyzed at the level of 100 N, 200 N, 300 N, 400 N, 500 N, 600 N and 700 N, respectively before and after disruption of the calcar femorale. Results: When a normal load was being borne, strain values measured in the posterior and medial aspects of the proximal femur were greater than those measured in the anterior and lateral aspects, no matter whether the calcar femorale was disrupted or not. However after disruption of the calcar femorale, strain values in the posterior and medial aspects of the proximal femur increased significantly, whereas those of the anterior and lateral aspects decreased significantly. Conclusion: The calcar femorale redistributes stress in the proximal femur by decreasing the load in the posterior and medial aspects and increasing the load in the anterior and lateral aspects.     

漯河地区中老年骨质疏松性骨折与股骨近端骨密度相关性研究

目的 调查漯河地区中老年骨密度(BMD)的变化规律和骨折之间的关系。方法 采用法国Medlink公司的的双能X线骨密度仪对漯河地区649名中老年人进行健侧髋部股骨颈、大转子、粗隆间和全髋的骨密度值测量。结果 骨折组各年龄段、各部位的BMD均比非骨折组低（P<0.05）。随着年龄的增长股骨近端骨量逐渐丢失,除了45~组,其余区域各年龄段骨折组的患病率明显高于非骨折组(P<0.05),骨密度值越低,骨折危险性越大。结论 中老年人骨近端骨密度值与发生骨质疏松性骨折之间存在密切关系,不容忽视。     

Impact direction from a fall influences the failure load of the proximal femur as much as age-related bone loss

Recent studies have shown that factors related to fall biomechanics may play as important a role in the etiology of hip fracture as age-related bone loss. Motivated by finite element analyses that showed failure of the proximal femur to be sensitive to loading direction, our objective with the current investigation was to determine experimentally if changes in impact direction affect the failure load of the elderly proximal femur. Thirty-three cadaveric femurs were assigned randomly to three groups of 11 and tested at one of three loading angles, 0°, 15°, or 30°, representing a fall on the hip rolled slightly forward, to the side, or rolled slightly backwards, respectively. Femurs were scanned using dualenergy X-ray absorptiometry (DXA) to assess bone mineral density (BMD) and tested to failure in a fall loading configuration at a displacement rate of 100 mm/second. Using an analysis of covariance to adjust for total hip BMD, we found that failure load decreased by 24% as the loading angle changed from 0° to 30°. This reduction in failure load is comparable to that associated with about 25 years of age-related bone loss after the age of 65. Therefore, the impact direction associated primarily with a fall is a critical determinant of hip fracture risk that is both independent of bone density and associated with fall biomechanics.     

Long proximal femoral nail in ipsilateral fractures proximal femur and shaft of femur

Background:

Ipsilateral fractures of the proximal femur and femoral shaft are extremely uncommon injuries which occur in young adults who sustain a high energy trauma. A variety of management modalities have been tried to treat this complex fracture pattern ranging from conservative approach to recently introduced reconstruction nails. All these approaches have their own difficulties. We studied the outcome of long proximal femoral nail (LPFN) in the management of concomitant ipsilateral fracture of the proximal femur and femoral shaft.

Materials and Methods:

We analysed the prospective data of 36 consecutive patients who had sustained a high energy trauma (30 closed fractures and 6 open shaft fractures) who had concomitant ipsilateral fractures of the femoral shaft associated with proximal femur fractures treated with LPFN between December 2005 and December 2011. The mean age was 39 years (range 28-64 years). Twenty nine males and seven females were enrolled for this study.

Results:

The patients were followed up at three, six, twelve, and eighteen months. The mean healing time for the neck fractures was 4.8 months and for the shaft fractures was 6.2 months. The greater trochanter was splintered and widened in two cases which eventually consolidated. Two patients had superficial infection, two patients had lateral migration of the screws with coxa vara which was due to severe osteoporosis detected during the followup. We had two cases of nonunion of shaft fracture and one case of nonunion of neck fracture. Two cases of avascular necrosis of femoral head were detected after 2 years of followup. No cases of implant failure were noted. Limb shortening of less than 2 cms was noted in four of our patients. The functional assessment system of Friedman and Wyman was used for evaluating the results. In our series 59.9% (n = 23) were rated as good, 30.6% (n = 11) as fair, and 5.5% (n = 2) as poor.

Conclusion:

Long PFN is a reliable option for concomitant ipsilateral diaphyseal and proximal femur fractures.     

A biomechanical study comparing proximal femur nail and proximal femur locking compression plate in fixation of reverse oblique proximal femur fractures

BackgroundThe reverse oblique trochanteric fractures are common fractures and its treatment poses a challenge. The purpose of this study was to compare the biomechanical parameters of the construct using proximal femoral nail (PFN) and proximal femoral locking compression plates (PFLCP) in these fractures using cadaveric specimens.Materials and MethodsTwenty freshly harvested cadaveric femoral specimens were randomly assigned to two groups after measuring bone mineral density, ten of which were implanted with PFN and the other ten with PFLCP. The constructs were made unstable to simulate reverse oblique trochanteric fracture (AO type 31A3.3) by removing a standard size posteromedial wedge. These constructs were tested in a computer controlled cyclic compressive loading with 200 kg at a frequency of 1 cycle/s (1 Hz) and test was observed for 50,000 cycles or until implant failure, whichever occurred earlier. Peak displacements were measured and analysis was done to determine axial stiffness and subsidence in axial loading.ResultsAll the specimens in PFN group completed 50,000 cycles and in PFLCP group, seven specimens completed 50,000 cycles. Average subsidence in PFN group was 1.24 ± 0.22 mm and in PFLCP group was 1.48 ± 0.38 mm. The average stiffness of PFN group (72.6 ± 6.8 N/mm) was significantly higher than of PFLCP group (62.4 ± 4.9 N/mm) (P = 0.04). The average number of cycles sustained by PFLCP was 46634 and for PFN group was 50,000 (P = 0.06).ConclusionThe PFN is biomechanically superior to PFLCP in terms of axial stiffness, subsidence and number of specimens failed for the fixation of reverse oblique trochanteric fractures of femur.     

Extraction of a supracondylar nail through the proximal femur during total hip arthroplasty

With the increasing popularity of supracondylar femoral intramedullary nails, removal of these devices may become necessary during total hip arthroplasty. The present article describes a technique for extracting these nails in a retrograde fashion through the proximal femur, thus sparing the patient a knee arthrotomy.