1,721,173 research outputs found
Muskuloskeletale belastungen im schafshinterlauf: mechanische rahmenbedingungen der heilung
No full textAlthough the sheep is a standard model for the analysis of biological healing processes after surgical intervention at the knee and shank, the in vivo tibio-femoral joint contact forces and the resulting musculoskeletal loading conditions have yet to be studied in detail.The three-dimensional kinematics of three Merino-mix sheep right hind limbs were recorded using reflective markers that were attached to Schanz’ screws, firmly anchored in the bone. This motion data was used together with the simultaneously measured external loading (ground reaction forces) to calculate the muscle and joint contact forces, as well as the internal loads within the bones. Whilst the motion mainly occurred in the sagittal plane, significant out of plane motion was observed, especially at the hip and knee joint (ab/adduction hip: 13°, knee: 10°; internal/external rotation hip: 12°, knee: 14°). The axial component of the tibio-femoral contact force was 2.1 times body weight (BW). The medio-lateral and anterior-posterior shear forces amounted to only 0.7 times BW. The loading in the diaphysis of the tibia under physiological musculoskeletal conditions was mainly axial compression (0.89 BW) together with only small shear forces (0.15 BW). The results of the musculoskeletal analyses presented here add to the understanding of the mechanical loading conditions in sheep. This expanded knowledge aids in the interpretatio
Mechanical conditions in the internal stabilization of proximal tibial defects
No full textObjectivesThe goal was to design a method which would permit an assessment of the suitability of a newly developed implant under physiological-like loading conditions. Information obtained from such an analysis is expected to delineate more clearly the indications for a new device prior to clinical utilization.DesignIn vitro mechanical stiffness testing and finite element analysis.MethodsFrom in vitro testing of proximal tibiae with defects, the stiffness of an internal stabilization system was determined. Using a finite element model, the loading of both the implant and bone was analyzed including all muscle forces. The variation in implant loading and interfragmentary strain for different defect locations was also investigated.ResultsConventional stiffness testing demonstrated the comparability of the experimental findings with the finite element predictions. Under physiological-like loading the implant experienced high bending and von Mises stresses if defects in the region of the shaft were stabilized. A short working length increased implant loading up to the yield strength of the material.ConclusionsThe finite element analysis illustrated the appropriateness of this new device for proximal defects of the tibia, but the implant should be used hesitantly in fractures or defects extending into the diaphyseal region of the bone.RelevanceThis new analytical approach helped to identify clinical indications for the implant in which its mechanical attributes would prove advantageous
Interaction of mechanics and biology in knee joint restoration and regeneration: from cells to limbs--multi-scale approaches for clinical applications. Berlin, 28-30 June 2006
No full textTHA loading arising from increased femoral anteversion and offset may lead to critical cement stresses
No full textAseptic loosening of artificial hip joints is believed to be influenced by the design and orientation of the implant. It is hypothesised that variations in implant anteversion and offset lead to changes in the loading of the proximal femur, causing critical conditions to both the bone and cement. The goal of this study was therefore to analyse the role of these parameters on loading, bone strains and cement stresses in total hip arthroplasty (THA). A validated musculo-skeletal model was used for the analysis of muscle and joint contact forces during walking and stair climbing. Two different anteversion angles (4[deg] vs. 24[deg]) and prostheses offsets (standard vs. long) were analysed. The loads for each case were applied to a cemented THA finite element model. Generally, stair climbing caused higher bone strains and cement stresses (max. +25%) than walking. Variations in anteversion and offset caused changes in the loading environment, bone strain distribution and cement stresses. Compared to the standard THA configuration, cement stresses were raised by increasing anteversion (max. +52%), offset (max. +5%) and their combination (max. +67%). Femoral anteversion, offset and their combination may therefore lead to an increased risk of implant loosening. Analyses of implant survival should consider this as a limiting factor in THA longevity. In clinical practice, implant orientation, especially in regard to pre- and post-operative anteversion, should be considered to be more critical
A survey of formal methods for determining functional joint axes
No full textAxes of rotation e.g. at the knee, are often generated from clinical gait analysis data to be used in the assessment of kinematic abnormalities, the diagnosis of disease, or the ongoing monitoring of a patient's condition. They are additionally used in musculoskeletal models to aid in the description of joint and segment kinematics for patient specific analyses. Currently available methods to describe joint axes from segment marker positions share the problem that when one segment is transformed into the coordinate system of another, artefacts associated with motion of the markers relative to the bone can become magnified. In an attempt to address this problem, a symmetrical axis of rotation approach (SARA) is presented here to determine a unique axis of rotation that can consider the movement of two dynamic body segments simultaneously, and then compared its performance in a survey against a number of previously proposed techniques. Using a generated virtual joint, with superimposed marker error conditions to represent skin movement artefacts, fitting methods (geometric axis fit, cylinder axis fit, algebraic axis fit) and transformation techniques (axis transformation technique, mean helical axis, Schwartz approach) were classified and compared with the SARA. Nearly all approaches were able to estimate the axis of rotation to within an RMS error of 0.1 cm at large ranges of motion (90°). Although the geometric axis fit produced the least RMS error of approximately 1.2 cm at lower ranges of motion (5°) with a stationary axis, the SARA and Axis Transformation Technique outperformed all other approaches under the most demanding marker artefact conditions for all ranges of motion. The cylinder and algebraic axis fit approaches were unable to compute competitive AoR estimates. Whilst these initial results using the SARA are promising and are fast enough to be determined “on-line”, the technique must now be proven in a clinical environment
Tibio-femoral loading during human gait and stair-climbing
No full textSurgical intervention of the knee joint routinely endeavours to recreate a physiologically normal joint loading environment. The loading conditions resulting from osteotomies, fracture treatment, ligament replacements and arthroplasties of the knee are considered to have an impact on the long term clinical outcome; however knowledge regarding the in vivo loading conditions in the knee is limited. Using a previously validated musculo-skeletal model of the human lower limb, this study has focused on predicting the tibio-femoral joint contact forces that occur in the human knee during the common daily activities of walking and stair-climbing.The average resultant peak tibio-femoral contact force during walking was 3.1 times body weight (BW) across four THA patients. Inter-individual variations proved larger than the variation of forces for each patient repeating the same task. Forces through the knee were considerably larger during stair climbing than during walking: the average maximum resultant force during stair climbing was 5.4 BW although peaks of up to 6.2 BW were calculated for one particular patient. Average anterior-posterior peak shear components of 0.6 BW were determined during walking and 1.3 BW during stair climbing.These results confirm both the joint contact forces reported in the literature and the importance of muscular activity in creating high forces across the joint. The magnitudes of these forces, specifically in shear, have implications for all forms of surgical intervention of the knee. The data demonstrate that high contact and shear forces are generated during weight bearing combined with knee flexion angles greater than approximately 15 degrees. Clinically, the conditions that produce these larger contact forces in the knee should be avoided during post-operative rehabilitation
A comparison of techniques for fixation of the quadriceps muscle-tendon complex for in vitro biomechanical testing of the knee joint in sheep
No full textWhilst in vitro testing can contribute to a better understanding of the biomechanical interactions at the knee joint, the application of physiological-like muscle forces in vitro remains challenging. One main difficulty seems to be the adequate fixation of the muscle–tendon complex to the mechanical apparatus that provides the forces in vitro. The goal of this study was to compare the ability of different muscle–tendon fixation mechanisms, including a new technique developed to optimise the interface grip of the soft tissues, to reliably transmit physiological in vivo loads through the muscle–tendon complex to the attached bone. The fixations of three quadriceps components in 16 right knees of skeletally mature female merino sheep were loaded to failure using four different fixation techniques (aluminium clamp, freeze clamp, suture technique and a new extension hull technique). Each technique was tested 12 times: 4 times on each individual quadriceps component. A factorial analysis for repeated measurements was undertaken to examine differences between the different fixation techniques. The extension hull technique and the aluminium clamp performed similarly, exceeding the computationally determined physiological forces in all but one trial and achieved higher failure loads than the suture technique. Although the freeze clamp reached the highest mean load to failure, it also failed more often than the extension hull technique. This comparison of the fixation techniques suggests that the new extension hull technique is a suitable fixation method for applying physiological-like muscle loading in an in vitro set-up. It cannot only be handled in a very simple manner, but also possesses a compact, lightweight construction, providing the possibility for the application of more complex loading conditions that include, e.g. the action of multiple muscles of the knee flexor and extensor group concurrently
The direct lateral approach: impact on gait patterns, foot progression angle and pain in comparison with a minimally invasive anterolateral approach
No full textINTRODUCTION: Minimally invasive total hip arthroplasty has been successfully introduced in the past decade. Nevertheless, standard approaches such as the direct lateral approach are still commonly used in orthopaedic surgery due to easy handling, good intra-operative overview and low complication rates. However, a frequent occurrence of fatty atrophy within the anterior third of the gluteus medius muscle has been demonstrated when using the modified direct-lateral approach (mDL), which may be associated with a reduction in function, limitation of internal leg rotation, gait disorders and pain. The question addressed in this study is whether mDL-approach leads to unfavourable changes in foot progression angle (FPA), gait and to more postoperative pain compared with a minimally invasive anterolateral approach (ALMI). METHODS: Thirty patients with primary osteoarthritis of the hip were recruited for this study. All subjects received an uncemented THA (Alloclassic((R))-Zweymuller stem, Allofit((R)) Cup, FA Zimmer((R))), 15 through an ALMI-approach and 15 via the mDL-approach. Gait analyses were performed both preoperatively and 3 months after surgery to measure FPA, step length, stance duration, cadence and walking speed. Additionally, the Harris-Hip Score, pain according to the visual analogue scale and the Trendelenburg sign were evaluated. RESULTS: No influence of the surgical approach could be observed on the gait patterns or FPA. Furthermore, neither increased external rotation of the limb nor restriction of internal rotation during walking could be established. Pain and Harris-Hip Score did not differ significantly between the two groups. CONCLUSION: In comparison with an ALMI approach, the mDL approach did not lead to a change in FPA postoperatively. No detrimental effect could be found on the gait pattern or pain after surgery. Based on these measurements, the minimally invasive anterolateral approach did not appear to provide functional benefits in outcome over the mDL approach. Consequently, both surgical approaches seem to be equally applicable approaches with good to very good functional results
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