The effect of hip muscle contraction on stress response of the lower extremities during the normal walking

Abstract

There is a growing concern to determine the essential characteristics of mechanical coupling between muscles and bone tissue during the normal walking cycle undertaken as a common daily activity. The physiological and biomechanical aspects of the musculoskeletal model propose that muscle contraction induce mechanical stimuli to muscle attachment sites, thereby creating skeletal movement. However, the main question remains regarding how the muscle contraction affects the femoral bone structure and its stress responses. This study aimed to determine the influence of muscle contraction on stress distribution and deformation characteristics of the lower limb. Analytical and numerical approaches were used to provide adequate data and evidence for achieving the goal of the study. For the analytical method, two main studies were defined including a skeletal model (without considering muscle contraction, 3D-No Mus) and a musculoskeletal model (with the effects of muscle contraction, 3D-All Mus). For the numerical method, a skeletal study on hip muscles (i.e. 3D-H Mus) and one on knee muscles (i.e. 3D-K Mus) were added to ensure the results were not achieved randomly. Computed tomography (CT) and magnetic resonance imaging (MRI) was used to obtain an authentic CAD model of the lower extremities of a healthy male. A unique CAD model, including seven major hip and knee joint components and 19 muscle groups were developed for the quasi-static finite element (FE) analysis. Hip contact force (HCF) was predicted using two-dimensional (2D) and three-dimensional (3D) equilibrium static equations for the single support stance and pre-swing phase of the gait cycle. The estimated HCF in the single support stance was 11% higher than the pre-swing phase of the gait and no considerable variation was identified between 2D and 3D studies. On the other hand, the effect of muscle contraction on the HCF of the musculoskeletal model was approximately two times higher than the estimated HCF for the skeletal model. An analytical approach was used to predict normal and shear stress for three susceptible regions of the femur including femoral head, head-neck and mid-plane diaphysis. The results demonstrated that the muscle contraction increased both normal and shear stresses on the femoral head of the 3D-All Mus model by 230% compared to the skeletal model without any muscles (3D-No Mus) in the single support stance. Furthermore, the muscle contraction in the 3D-All Mus increased the shear stress on the femoral neck region in the single support stance and pre-swing phase of the gait cycle on average 228% and 218%, respectively, compared to the shear stress in the skeletal model (3D-No Mus). In the single support stance, muscle contraction in a human musculoskeletal (3D-All Mus) model increased the normal and shear stress on the femoral diaphysis on average 229% and 236%, respectively, compared with the skeletal model (3D-No Mus). Muscle contraction significantly enhanced the stress response of muscle attachment sites as well as the overall stress of the femur using FE analysis. This study indicated that muscle contraction increased normal stress at the single support and swing stance of the gait cycle by 190% and 143%, respectively. However, the observed results for shear stress presented a lower increase. The effect of muscle contraction on the stress response of the meniscus was also examined. It was observed that the effect of knee muscle contraction increased the maximum principal stress on the meniscus by 800% compared with the study where muscles were excluded during the gait cycle. Additionally, the obtained stress distribution on the femur and menisci demonstrated that the effect of muscles significantly eliminated the risk of stress concentration occurrence. Furthermore, in the pre-swing phase of the gait cycle, the normal stress predicted by the analytical method was 30% greater than the normal stress estimated by FE analysis. However, for normal stress in the single support stance, the results of FE analysis had a high correspondence with the analytical approach and improved the existing assumption about the effect of muscle contraction on the stress behaviour of the femur. In conclusion, the outcome of this thesis presents a new paradigm where muscle contractions on the musculoskeletal model significantly increased stress characteristics on the femur and other lower extremities during normal walking.