The effect of boundary constraints on finite element modelling of the human pelvis

The use of finite element analysis (FEA) to investigate the biomechanics of anatomical systems critically relies on the specification of physiologically representative boundary conditions. The biomechanics of the pelvis has been the specific focus of a number of FEA studies previously, but it is also a key aspect in other investigations of, for example, the hip joint or new design of hip prostheses. In those studies, the pelvis has been modelled in a number of ways with a variety of boundary conditions, ranging from a model of the whole pelvic girdle including soft tissue attachments to a model of an isolated hemi-pelvis. The current study constructed a series of FEA models of the same human pelvis to investigate the sensitivity of the predicted stress distributions to the type of boundary conditions applied, in particular to represent the sacro-iliac joint and pubic symphysis. Varying the method of modelling the sacro-iliac joint did not produce significant variations in the stress distribution, however changes to the modelling of the pubic symphysis were observed to have a greater effect on the results. Over-constraint of the symphysis prevented the bending of the pelvis about the greater sciatic notch, and underestimated high stresses within the ilium. However, permitting medio-lateral translation to mimic widening of the pelvis addressed this problem. These findings underline the importance of applying the appropriate boundary conditions to FEA models, and provide guidance on suitable methods of constraining the pelvis when, for example, scan data has not captured the full pelvic girdle. The results also suggest a valid method for performing hemi-pelvic modelling of cadaveric or archaeological remains which are either damaged or incomplete

Relationships between walking speed, T-score and age with gait parameters in older post-menopausal women with low bone mineral density

Background: The gait patterns of women with low bone mineral density (BMD) or osteoporosis have not been thoroughly explored, and when examined, often studied in relation to falls and kyphosis. Research question: The aim of this study was to investigate the relationships between gait parameters and comfortable, self-selected walking speed and BMD in older post-menopausal women with a broad range of T-scores (healthy to osteoporotic). Methods: 3D kinematic and kinetic data were collected from forty-five women mean (SD) age 67.3 (1.4) years during level walking at their preferred speed. Multiple regression analyses explored the explained variance attributable to speed, femoral neck T-score, and age. Results: The mean (SD) walking speed 1.40 (0.19) m·s−1explained the variance in most temporal-spatial, kinematic and joint powers (R2= 12–68%, P ≤ 0.01). T-score accounted for (R2= 23%, P ≤ 0.001) of the shared explained variance in stride width. It also increased the explanatory power for knee flexion (R2= 7%, P ≤ 0.05) and knee range of motion (R2= 12%, P ≤ 0.01). Power absorption by the knee flexors in terminal swing (K4) was the only power burst resulting in significant slope coefficients for all predictor variables (R2= 52 and 54%) (P ≤ 0.001) and (R2= 68%, P ≤ 0.05). Significance: Speed alone explained most of the variance in the gait parameters, while speed and T-score combined increased the explanatory power of the regression models for some of the knee joint variables. Our findings demonstrated that older post-menopausal women, with a broad range of T-scores, are able to walk at comfortably fast speeds, generating gait patterns similar to those of younger women. The results also suggest that strengthening the hip abductor, knee extensor and flexor muscle groups may benefit the gait patterns of older postmenopausal women with low BMD