Introduction: When describing the biomechanical status of the musculoskeletal system of the hip joint, we determine the mechanical parameters as are forces and stresses that have an influence on joint. To evaluate the latter there are used simple mathematical models, in which the human body is formed as a system of connected segments managed by muscles that attach them. An example of such models is the HIPSTRESS method. Purpose: To directly measure the position of muscle attachment points and calculate the cross-sectional areas of hip joint muscles, important for calculating the distribution of the resultant hip force and for determining contact hip stress in position of one-leg stance using the HIPSTRESS method. The purpose was also to directly determine the geometric parameters from magnetic resonance images and to estimate the error we make when the hip forces and stresses are calculated indirectly by re-scaling the reference values with respect to bone structures. Methods: Magnetic resonance imaging was used retrospectively to measure origins, insertions and cross-sectional areas of the hip joint muscles. The image data was taken for the purpose of examining the proximal femora of a 17-year-old boy, and data from the healthy side was used. The input data on positions of muscle attachment points were assessed directly from magnetic resonance images, and by re-scaling the data of the aknowledged HIPSTRESS model according to the shape of pelvis and proximal femora. The resultant hip force and distribution of contact stress were calculated using three different mathematical models within the HIPSTRESS method. Results: We established that the validated HIPSTRESS model overestimates the value of hip force by 16 % and peak hip stress by 20 %, while one-muscle model overestimates force by 9 % and peak hip stress by 1 % in comparison to HIPSTRESS model with magnetic resonance. The validated HIPSTRESS model and one-muscle model underestimate the inclination of the resultant hip force and the position of the stress pole. The validated HIPSTRESS model overestimated with body weight normalized biomechanical parameters for less than 20 % compared to the HIPSTRESS model with magnetic resonance. We also established a good data match between the resultant hip force and peak contact hip stress, which were calculated from both HIPSTRESS models, and a good match between the HIPSTRESS models and one-muscle model. We found that the added muscles in the HIPSTRESS model with magnetic resonance did not significantly contribute to the value of the hip joint load. Conclusion: All three models are comparable to each other in calculated resultant hip force, peak hip stress and hip joint load with added muscles. In clinical practice, we recommend the HIPSTRESS model with magnetic resonance to evaluate geometric and biomechanical data, since it provides more accurate measurement outcomes, but it is currently usable on small number of included subjects due to time-consuming.
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