Compression or tension? The stress distribution in the proximal femur (original) (raw)
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In vivo measurements show tensile axial strain in the proximal lateral aspect of the human femur
Journal of Orthopaedic Research, 1997
Two conflicting theories exist concerning the stress pattern for the proximal lateral aspect of the human femur. According to the classic theory of Pauwels, a bending moment on the femur leads to compression medially and to tension laterally. The alternative theory is that muscle forces contribute to a moment-free loading of the femur, with both the medial and lateral cortices subjected to compression. To examine these theories, we measured the strain at the external surface of the proximal lateral aspect of the femur of two female patients undergoing surgery for "snapping hip syndrome." During the surgical procedure, a strain-gauge rosette was bonded to the lateral aspect of the femur and the cortical strains were monitored while the patient performed a series of activities. In both patients, principle tensile strain increased significantly during onelegged stance, walking, and stair climbing as compared with that during two-legged stance. During each loading situation, the principal tensile strain was aligned within 22" to the longitudinal femoral axis. Dynamic strain measurements consistently revealed tensile axial strain at the lateral aspect of the femur during each activity. The present study supports the classic bending theory of Pauwels and demonstrates that the proximal lateral aspect of the femur is subjected to tension during the stance phase of gait.
Effect of Geometry Variation on the Mechanical Behavior of the Proximal Femur
Journal of Advances in Medicine and Medical Research, 2019
The mechanical behavior of a proximal femur under a normal body weight loading was examined. The geometry of the proximal femur was created in a finite element model using 29 reference points measured on the CT scan images of a patient. Four additional sets of measurements were calculated using ± (1) and ± (2) the standard deviation of the original set and the result of models was compared. The stress distribution and the locations of critical normal and shear stress, as well as the effect of the femur geometry which may be most susceptible to failure were examined. The findings of this study demonstrate an inferior distribution of stress in the plus-standard deviation models and indicate less ability to bear weight. The minus-standard deviation models appear to be better suited to bearing weight and indicate a more even distribution of the stresses generated within the proximal femur.
A minimal parametric model of the femur to describe axial elastic strain in response to loads
Medical Engineering & Physics, 1996
Evaluating the state of stress/strain for a given geometry and load in femurs can be done both experimentally, measuring strain at a limited number of locations, and theoretically with finite ekment models. Another approach is to describe the state of strain with a fm synthetic indices. For this purpose the reverse elastic problem (i.e. bone parameters are estimated given the strain d&ibution and loads) needs to be solved as opposed to the finite element direct problem.
Journal of Biomechanics, 2011
Proximal femur Femoral neck and head Linear elastic behavior In vitro bone fracture Brittle failure a b s t r a c t It has not been demonstrated whether the human proximal femur behaves linearly elastic when loaded to failure. In the present study we tested to failure 12 cadaveric femurs. Strain was measured (at 5000 Hz) on the bone surface with triaxial strain gages (up to 18 on each femur). High-speed videos (up to 18,000 frames/s) were taken during the destructive test. To assess the effect of tissue preservation, both fresh-frozen and formalin-fixed specimens were tested. Tests were carried out at two strain-rates covering the physiological range experienced during daily motor tasks. All specimens were broken in only two pieces, with a single fracture surface. The high-speed videos showed that failure occurred as a single abrupt event in less than 0.25 ms. In all specimens, fracture started on the lateral side of the neck (tensile stress). The fractured specimens did not show any sign of permanent deformation. The forcedisplacement curves were highly linear (R 2 40.98) up to 99% of the fracture force. When the last 1% of the force-displacement curve was included, linearity slightly decreased (minimum R 2 ¼ 0.96). Similarly, all force-strain curves were highly linear (R 2 4 0.98 up to 99% of the fracture force). The slope of the first part of the force-displacement curve (up to 70% fracture force) differed from the last part of the curve (from 70% to 100% of the fracture force) by less than 17%. Such a difference was comparable to the fluctuations observed between different parts of the curve. Therefore, it can be concluded that the proximal femur has a linear-elastic behavior up to fracture, for physiological strain-rates.
Young's Modulus and Load Complexity: Modeling Their Effects on Proximal Femur Strain
Anatomical Record-advances in Integrative Anatomy and Evolutionary Biology, 2018
Finite element analysis (FEA) is a powerful tool for evaluating questions of functional morphology, but the application of FEA to extant or extinct creatures is a non-trivial task. Three categories of input data are needed to appropriately implement FEA: geometry, material properties, and boundary conditions. Geometric data are relatively easily obtained from imaging techniques, but often material properties and boundary conditions must be estimated. Here we conduct sensitivity analyses of the effect of the choice of Young's Modulus for elements representing trabecular bone and muscle loading complexity on the proximal femur using a finite element mesh of a modern human femur. We found that finite element meshes that used a Young's Modulus between 500 and 1,500 MPa best matched experimental strains. Loading scenarios that approximated the insertion sites of hip musculature produced strain patterns in the region of the greater trochanter that were different from scenarios that grouped muscle forces to the superior greater trochanter, with changes in strain values of 40% or more for 20% of elements. The femoral head, neck, and proximal shaft were less affected (e.g. approximately 50% of elements changed by 10% or less) by changes in the location of application of muscle forces. From our sensitivity analysis, we recommend the use of a Young's Modulus for the trabecular elements of 1,000 MPa for the proximal femur (range 500-1,500 MPa) and that the muscular loading complexity be dependent on whether or not strains in the greater trochanter are the focus of the analytical question.
Evaluation of the combined bending and compression stress field in a human proximal femur
Revista mexicana de ingeniería biomédica, 2003
One of the topics that has attracted attention is the exact evaluation of the mechanical behavior of the human femur. Several studies have been done, in order to establish if the femur is under compression or bending. For this purpose, experimental stress analysis has been applied, common techniques such as reflection photoelasticity or strain gages have been used. In the first case, the complete
Injury, 1999
A loading model permitting the application of relevant loads to the diaphysis and constructed on the basis of current knowledge of the biomechanics of the femur will be presented. This model takes into account the force acting through the ilio-tibial tract in the frontal plane and the forces acting on the condyles in the sagittal plane. There is compression on the femoral head and on the condyles and tension on the greater trochanter. Experimental verification using human cadaveric femora instrumented with strain gauges has shown that the adequate loading condition is:-a line of force tangential to the femoral head a line of force tangential to the dorsal aspect of the distal junction of the diaphysis and metaphysis. Under these conditions, the calculated forces will accord well with values assessed in vivo. The model described here represents a simple procedure for experimental load application, producing realistic strain values. The proximal part of the bone is placed under tension on the dorsal aspect; the medial aspect is under compression. The strain pattern develops such that the tensile forces affect the anterior aspect distally and compression the dorsal aspect.
The State of Stresses in the Proximal Femoral Bone in Bipodal and Unipodal Support
2018
In this study, we are trying to determine the stresses state of the proximal femoral bone in the case of bipodal and unipodal support. Apply the section method by evaluating axial force N, shear force T and bending moment M i , and plotting the variation diagrams. By drawing the force and moment variation diagrams, the maximum loaded transversal secţion is highlighted, corresponding to the intertrochanteric area for both cases of support. For unipodal support, in the intertrochanterian area, the stresses produced by the axial force, shear force and bending moment are calculated, their variation diagrams are drawn and the maximum loaded fiber is identified.
Influence of Muscle Forces on Stresses in the Human Femur
2014
Bone growth and development is highly sensitive to the mechanical loading to which it is subjected. Due to its adaptive ability, abnormal loading can cause the bone to develop in an abnormal way. The mechanical loading both comes from external forces which depend on the physical activity and internal forces which come from the muscles that are attached to the bones. Motion disorders, such as cerebral palsy, often involve spastic muscle tone in the lower limbs which both causes altered internal loading and external loading in how it contributes to altered gait pattern. Several bone deformities are seen in patients with cerebral palsy in which two commonly occur at the femur neck. These are increased neck shaft angle (coxa valga) and increased femoral anteversion angle.Studies investigating femoral deformation in patients with cerebral palsy have been made in regards of using mechanobiological principles (the osteogenic index), to predict these previously mentioned deformities by usin...
Evaluación del campo de estrés combinado de flexión y compresión en un fémur proximal humano
Revista mexicana de ingeniería biomédica, 2003
One of the topics that has attracted attention is the exact evaluation of the mechanical behavior of the human femur. Several studies have been done, in order to establish if the femur is under compression or bending. For this purpose, experimental stress analysis has been applied, common techniques such as reflection photoelasticity or strain gages have been used. In the first case, the complete