Frontal-plane relationship between hip centers and ground reaction forces during static standing and gait:...

This study aimed to reveal the frontal plane relationship between the ground reaction force (GRF), hip center (HC), and Mikulicz line under various standing conditions and during gait.

A dual-design approach, combining a static experiment and gait-database analysis, was used. First, a static experiment was conducted with 10 healthy adults standing on force plates under five conditions: stance widths of 0, 5, 10, and 20 cm, and single-leg stance. Second, gait data from a public database (n = 162, age ≤50 years) were analyzed to calculate comparable parameters during the single stance phase. The GRF-HC distance and the angle between the GRF and the line through the center of pressure and HC (GRF-Mikulicz angle) were evaluated using analysis of variance.

Both the GRF-HC distance and the GRF-Mikulicz angle significantly differed among the bipedal standing conditions, with smallest values at 20 cm (1.3 cm, 0.3°) and largest at 0 cm (7.3 cm, 4.8°). Values at 0 cm did not significantly differ from single-leg standing (8.8 cm, 5.8°), and both fell within the ranges observed during the single stance phase of gait (6.5-9.2 cm, 4.8°-6.7°).

A 20 cm-stance width best aligns the GRF with Mikulicz line in static standing. Single-leg and closed-leg standing replicate GRF direction during gait. These findings may inform preoperative planning of total knee arthroplasty but require validation in larger and patient-based cohorts, given the small sample size and restriction to healthy subjects. This exploratory study should be interpreted with caution regarding direct clinical application.