1,721,033 research outputs found
Musculoskeletal loading database: loading conditions of the proximal femur
No full textKnowledge of musculoskeletal loading conditions in humans is mandatory for the design of endoprosthestic and osteosynthetic devices. Also, new treatment options such as tissue generation and transplantation require knowledge of the mechanical loads under which tissue formation and regeneration takes place. In this manuscript, a database on musculo-skeletal loading of the proximal femur is presented. The data are based on individual patient gait and radiological data. By means of inverse dynamics and optimization techniques, the internal loads acting at the joint and within the muscles have been determined. The calculated hip contact force has been validated by means of in vivo measurements in four patients. The database is freely available and gives an estimate on internal loads acting at the proximal femur for activities like walking and stair climbing
Bewertung der stabilität von frakturfixationssystemen: mechanische vorrichtung zur untersuchung der 3-D-steifigkeit in vitro.
No full textDifferent fixation systems are used for fracture and defect treatment. A prerequisite for complication free healing is sufficient mechanical stability of the osteosynthesis. In vitro investigations offer the possibility of both analysing and assessing the pre-clinical fixation stability. Due to the complex loading environment in vivo, stiffness analysis should include a complete determination of the stiffness under standardised conditions. Based on a mathematical procedure to calculate the 3-D stiffness, a mechanical testing device for the 3-D loading of fixation systems was designed and integrated in the existing test set-up. The set-up consisted of a material testing machine to produce the necessary loads and an optical measurement device to detect the resulting inter-fragmentary movements. To validate the testing device, the 3-D stiffness matrices of different Ilizarov fixator configurations were determined and compared. The good reproducibility of the test was reflected in the small intra-individual variability of the stiffness components. A distinct direction dependence of the fixator stiffness was observed. Increasing the number of rings led to a stiffness increase of up to 50%, especially in bending. The presented testing device allows a complete standardised determination of the stiffness of different fixation systems. It considers the direction dependence of the stiffness and creates a prerequisite for a more direct implant comparison
Cementless stem fixation and primary stability under physiological-like loads in vitro
No full textPrimary stability and in consequence osteointegration are commonly related to the stem anchorage but also to the complex musculoskeletal loading of the hip region. This study investigated the influence of metaphyseal and meta-diaphyseal anchorage on the primary stability of cementless stems under physiological-like loading in vitro. Metaphyseal and meta-diaphyseal anchoring stems (n=6 each) were implanted into composite femora. Musculoskeletal loads, validated by in vivo data (peak joint force 2348 N), were applied using a mechanical set-up. Interface movements were recorded by seven displacement transducers and primary stability was compared. Both stems exhibited similar movement patterns and principally moved distally with a retroversional twist. Although elastic movements were comparable, the metaphyseal stem exhibited higher plastic deformations than the meta-diaphyseal stem, particularly for the metaphyseal, medio-lateral and antero-posterior components. Under physiological-like loading, the metaphyseal stem allowed higher interface movements and tended to initially migrate faster than the meta-diaphyseal stem and then stabilized. Elastic movements were comparable and seemed to be less influenced by the anchoring concept than by the mechanical properties of the bone. The analyses emphasize the importance of metaphyseal bone in proximal anchorage and the necessity of an accurate canal preparation to prevent excessive initial migration
Response to: "Stair climbing is more critical than walking in pre-clinical assessment of primary stability in cementless THA in vitro" [J. Biomech. 2005;38: 1143-1154]
No full textOn the biomechanics of the hip: relevance of femoral anteversion for hip contact force and loading using a short-stemmed prostheses (in German)
No full textShort-stemmed hip implants were established in total hip arthroplasty in the last years. Also patients with secondary osteoarthritis of the hip with pathological anteversion of the femoral neck are treated increasingly using this method. Therefore an investigation was performed to analyze the resulting hip contact force and femoral loading in the proximal femur at the solid model of the “standardized femur”. Two different situations of femoral component anteversion were simulated. Increased hip contact forces and an increase of medial and lateral cortex loads result in the anteverted model. With present level of knowledge about the influence of the hip contact force the use of short-stemmed implants is not uncritically in patients with degenerative osteoarthritis of the hip combined with rotational disorders of the proximal femur. The selection of the tribological pairing is to be considered more strongly regarding the wear behavior
The influence of alignment on the musculo-skeletal loading conditions at the knee
No full textBackground and AimHigh tibial osteotomies attempt to recreate physiologically normal joint loading. Previous studies have discussed the influence of mal-alignment on the distribution of static loads to the medial and lateral compartments of the knee. The aim of this study was to determine the influence of mal-alignment on the tibio-femoral loading conditions during dynamic activities. Material and MethodsUsing a musculo-skeletal model of the lower limb, which had been previously validated with in vivo data, in this study we modified the alignment of the knee in four patients, from a normal position to the extremes of 8 degrees valgus and 10 degrees varus mal-alignment. The resulting tibio-femoral joint contact forces were examined while patients were walking and stair climbing. ResultsVarying the mal-alignment resulted in a highly individual response in joint loads. Deviations from the normal alignment produced an increase in loading, with valgus generating a more rapid increase in loading than a varus deformity of the same amount. Varus deformities of 10 degrees resulted in increases in peak contact force from an average of 3.3-times bodyweight (BW) up to a peak of 7.4 BW (+45% to +114%) while patients were walking, whilst increases of 15% up to 35% were determined for stair climbing. Increases of up to 140% were calculated at 8 degrees valgus during walking and up to 53% for stair climbing. ConclusionThis study demonstrated a clear dependence of the individual joint loads on axial knee alignment. Based on the sensitivity of joint loading to valgus mal-alignment, more than 3 degrees of over-correction of a varus deformity to valgus should be carefully reconsidered
Physiologically based boundary conditions in finite element modelling
No full textFinite element analysis has been used extensively in the study of bone loading and implant performance, such as in the femur. The boundary conditions applied vary widely, generally producing excessive femoral deformation, and although it has been shown that the muscle forces influence femoral deflections and loading, little consideration has been given to the displacement constraints. It is hypothesised that careful application of physiologically-based constraints can produce physiological deformation, and therefore straining, of the femur. Joint contact forces and a complete set of muscle forces were calculated based on the geometry of the Standardized Femur using previously validated musculoskeletal models. Five boundary condition cases were applied to a finite element model of the Standardized Femur: A) diaphyseally-constrained with hip contact and abductor forces; B) case A plus vasti forces; C) case A with complete set of muscle forces; D) distally-constrained with all muscle forces; E) physiological constraints with all muscle forces. It was seen that only the physiological boundary conditions, case E, produced physiological deflections (<2.0mm) of the femoral head in both the coronal and sagittal planes, which resulted in minimal reaction forces at the constrained nodes. Strains in the mid-diaphysis varied by up to 600 micro-strain under walking loads and 1000 micro-strain under stair climbing loads. The mode of loading, as indicated by the strain profiles on the cortex also varied substantially under these boundary conditions, which has important consequences for studies that examine localised bone loading such as fracture or bone remodelling simulations
Mechanical conditions in the initial phase of bone healing
No full textBackgroundBone healing is sensitive to the initial mechanical conditions with tissue differentiation being determined within days of trauma. Whilst axial compression is regarded as stimulatory, the role of interfragmentary shear is controversial. The purpose of this study was to determine how the initial mechanical conditions produced by interfragmentary shear and torsion differ from those produced by axial compressive movements. MethodsThe finite element method was used to estimate the strain, pressure and fluid flow in the early callus tissue produced by the different modes of interfragmentary movement found in vivo. Additionally, tissue formation was predicted according to three principally different mechanobiological theories. FindingsLarge interfragmentary shear movements produced comparable strains and less fluid flow and pressure than moderate axial interfragmentary movements. Additionally, combined axial and shear movements did not result in overall increases in the strains and the strain magnitudes were similar to those produced by axial movements alone. Only when axial movements where applied did the non-distortional component of the pressure-deformation theory influence the initial tissue predictions. InterpretationThis study found that the mechanical stimuli generated by interfragmentary shear and torsion differed from those produced by axial interfragmentary movements. The initial tissue formation as predicted by the mechanobiological theories was dominated by the deformation stimulus
A survey of formal methods for determining the centre of rotation of ball joints
No full textThe determination of an accurate centre of rotation (CoR) from segment marker positions is of interest across a wide range of applications, but particularly for clinical gait analysis and for estimating the hip joint centre during surgical intervention of the knee, for limb alignment purposes. For the first time in this survey of formal methods, we classify, analyse and compare different methods (geometric, algebraic, bias compensated algebraic, and Pratt sphere fit methods, as well as the centre transformation technique, the Holzreiter approach, the helical pivot technique, the Schwartz transformation techniques, the minimal amplitude point method and the Stoddart approach) for the determination of spherical joint centres from marker position data. In addition, we propose a new method, the symmetrical CoR estimation or SCoRE, in which the coordinates of the joint centre must only remain constant relative to each segment, thus not requiring the assumption that one segment should remain at rest. For each method, 1000 CoR estimations were analysed with the application of isotropic, independent and identically distributed Gaussian noise (standard deviation 0.1 cm) to each of the marker positions, to all markers on the segment simultaneously and the two in combination. For the test conditions used here, most techniques were capable of determining the CoR to within 0.3 cm, as long as the spherical range of motion (RoM) of the joint was 45° or more. Under the most stringent conditions tested, however, the SCoRE was capable of best determining the CoR, to within approximately 1.2 mm with a RoM of 20°. The correct selection and application of these methodologies should help improve the accuracy of surgical navigation and clinical kinematic measurement
On the influence of mechanical conditions in osteochondral defect healing
No full textDespite the introduction of new surgical techniques, the treatment of cartilage defects remains challenging. Delay or complete failure of cartilage healing is associated with problems in biological regeneration. The influence of mechanical conditions on this process, however, remains unevaluated. Osteochondral defects were generated on the left femoral condyle in 18 Yucatan minipigs. After 4, 6 and 12 weeks the defect filling, trabecular orientation and bone density were compared to the intact contralateral side. The mechanical straining during this period was then analyzed using an adaptive finite element technique. Histologically, the osteochondral defects showed bone resorption at the base and bone formation from the circumference. At 12 weeks, the macroscopically healed specimens showed fibrous cartilage formation, a minimally organized trabecular structure and increased trabecular volume fraction compared to the controls (p<0.002). The amount of cancellous, cartilagineous, and fibrous tissue and the defect size as measured in histomorphometric analysis for the three time points (4, 6 and 12 weeks) was comparable in magnitude to that predicted by finite element analysis. The simulated osteochondral healing process was not fully capable of re-establishing a hyaline-like cartilage layer. The correlation between simulation and histology allows identification of mechanical factors that appear to have a larger impact on the healing of osteochondral defects than previously considered
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