Effects of hip joint rotation on the trochanteric force and soft tissue thickness during sideways falls

We measured the trochanteric soft tissue thickness (TSTT) to determine the force magnitude delivered to the proximal femur (F_trochanteric), and examined how the TSTT and F_trochanteric were affected by hip rotation during sideways falls. Twenty individuals participated in pelvis release experiments. Trials were acquired with three hip rotations: 15° external, 0° (neutral), and 15° internal. During trials, kinetics and kinematics of the pelvis and lower extremities were recorded. Outcome variables included the effective stiffness of the pelvis (k), F_trochanteric, TSTT, and force magnitude attenuated by the TSTT (F_attenuation). The k and F_trochanteric were associated with hip rotation (F= 5.06, p= 0.011; F= 5.49, p= 0.008, respectively). Both outcome variables were 14 % and 15 % smaller in external compared to neutral and internal rotation, respectively (45.3 versus 52.8 kN/m; 5448 versus 6425 N). However, neither the TSTT nor the F_attenuation was associated with hip rotation (F= 2.92, p= 0.066; F= 2.30, p= 0.114, respectively). The F_trochanteric decreased with hip external rotation at impact. This was attributed to decreased pelvis stiffness rather than enhanced protective benefits (i.e., force attenuation) provided by the trochanteric soft tissue. These findings offer valuable insights into the distribution of hip impact forces and may contribute to a better understanding of hip impact biomechanics during falls.