Effect of simulated changes in pelvic tilt on hip joint forces.

Musculoskeletal modeling is commonly used to simulate and compare various movements between individuals. For conditions such as femoroacetabular impingement syndrome (FAIS), individuals tend to walk with more anterior pelvic tilt than those without FAIS. However, it is unknown whether accounting for pelvic tilt in musculoskeletal modeling would lead to a change in muscle forces and in turn, joint forces. Gait data of six individuals were collected and processed using Vicon and Visual3D. Each participant's pelvic tilt was adjusted by ± 10° at all time points during gait. Three analyses were performed per individual: no adjustment in tilt, one posterior (positive) tilt, and one anterior (negative) tilt. The resulting data were imported into OpenSim to determine muscle forces and the resulting femur-on-acetabulum (hip joint) forces in the pelvic and femoral reference frames. Data for each participant were normalized for gait cycle and body weight in MATLAB, and statistical parametric mapping was used to determine if the differences in joint and muscle forces were significant across different pelvic orientations. Shifting from posterior to anterior pelvic tilt reduced resultant forces. In the pelvic reference frame, anteriorly-directed joint forces decreased, while medially-directed forces increased. In the femoral reference frame, anteriorly- and medially-directed joint forces increased, while superiorly-directed forces decreased. Anterior gluteus medius and iliacus muscle forces decreased, while quadratus femoris, piriformis, and gemellus muscle forces increased. Given these results, future studies using musculoskeletal modeling should account for pelvic tilt in musculoskeletal models to obtain more realistic comparisons between healthy and pathological conditions.