Pelvic muscle and acetabular contact forces during gait.

Locations, magnitudes, and directions of pelvic muscle and acetabular contact forces are important to model the effects of abnormal conditions (e.g., deformity, surgery) of the hip accurately. Such data have not been reported previously. We computed the three-dimensional locations of all pelvic muscle and acetabular contact forces during level gait. The approach first required computation of the intersegmental joint resultant forces and moments using limb displacement history, foot-floor forces, and estimated limb inertial properties from one subject. The intersegmental resultant moments were then distributed to the muscles using a 47-element muscle model and a non-linear optimization scheme. Muscle forces were vectorally subtracted from the intersegmental resultants to compute the acetabular contact forces. While the peak joint force magnitudes are similar to those reported previously for the femur, the directions of pelvic contact forces and muscle forces varied considerably over the gait cycle. These variations in contact force directions and three-dimensional forces could be as important as the contact force magnitudes in performing experimental or theoretical studies of loads and stresses in the periacetabular region.