Femoral neck strain prediction during level walking using a combined musculoskeletal and finite element model approach

Abstract

Recently, coupled musculoskeletal-finite element modelling approaches have emerged as a way to investigate femoral neck loading during various daily activities. Combining personalised gait data with finite element models will not only allow us to study changes in motion/movement, but also their effects on critical internal structures, such as the femur. However, previous studies have been hampered by the small sample size and the lack of fully personalised data in order to construct the coupled model. Therefore, the aim of this study was to build a pipeline for a fully personalised multiscale (body-organ level) model to investigate the strain levels at the femoral neck during a normal gait cycle. Five postmenopausal women were included in this study. The CT and MRI scans of the lower limb, and gait data were collected for all participants. Muscle forces derived from the body level musculoskeletal models were used as boundary constraints on the finite element femur models. Principal strains were estimated at the femoral neck region during a full gait cycle. Considerable variation was found in the predicted peak strain among individuals with mean peak first principal strain of 0.24% ± 0.11% and mean third principal strain of -0.29% ± 0.24%. For four individuals, two overall peaks of the maximum strains were found to occur when both feet were in contact with the floor, while one individual had one peak at the toe-off phase. Both the joint contact forces and the muscular forces were found to substantially influence the loading at the femoral neck. A higher correlation was found between the predicted peak strains and the gluteus medius (R2 ranged between 0.95 and 0.99) than the hip joint contact forces (R2 ranged between 0.63 and 0.96). Therefore, the current findings suggest that personal variations are substantial, and hence it is important to consider multiple subjects before deriving general conclusions for a target population.

Fig 1. Schematic drawing illustrating the measured morphological parameters of the femur.

Definition of each parameter is described in Table 2. (a) and (b): posterior view, (c): superior view of a femur.

Fig 2. Mesh convergence study.

Four different element sizes (2, 2.5, 3, 3.5, 4 mm) were tested. The mesh was converged at the 3 mm element size (highlighted above as ×). This element size was used for all five subjects in the final finite element analysis. DOF = degrees of freedom.

Fig 3. Multiscale modelling workflow.

Diagram illustrates the various steps of the multiscale modelling workflow followed in this study: musculoskeletal modelling (top left), CT based finite element modelling (top right), and body-organ coupling (bottom) by applying the muscle and joint forces to the finite element model.

Fig 4. First and third principal strains predicted by the finite element models of the five cases.

The peak strain values were predicted at each of the 100 intervals across one gait cycle.

Fig 5. Hip and knee joint contact forces and muscles forces.

A selection of the major muscles attached to the proximal femur as calculated by the musculoskeletal models along a full gait cycle for the five cases normalised by the body weight (BW).

Fig 6. Correlation analysis.

Correlation analyses performed for the peak first principal strain in the femoral neck and the gluteus medius muscle (left), and hip joint contact forces (right) acting on the femur during a full gait cycle normalised by the body weight (BW).

Fig 7. The overall First and third principal strain distribution within the femoral neck.

Strains are shown at 15%, 30%, 50%, and 75% of the gait cycle for all the cases. The locations of the peak strains are indicated by the red circle.

Fig 8. Peak first principal strain as predicted in the femoral neck at the 15%, 30%, and 50% of the gait cycle for all the cases.

Heel strike and toe off, at which the two peaks of the principal strain are predicted, are indicated in grey shaded area. The location of the peak first principal strain region is indicated by the red circle. Region of interest at which the peak strains were estimated is indicated on the bottom right of the figure.