Frontal-plane relationship between hip centers and ground reaction forces during static standing and gait: Implications for preoperative planning of total knee arthroplasty.

Abstract

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.