# Influence of Skin Marker Positioning and Their Combinations on Hip Joint Center Estimation Using the Functional Method

## TL;DR

This study examines how placing skin markers in different positions affects the accuracy of estimating hip joint center during gait analysis.

## Contribution

The study identifies optimal skin marker combinations for accurate hip joint center estimation using functional methods.

## Key findings

- Marker combinations on the pelvis and proximal muscles yield HJC estimates close to predictive methods.
- Combinations excluding pelvic markers result in less accurate HJC estimation.
- Calibration movement trials help evaluate the effectiveness of marker placements.

## Abstract

Accurate estimation of hip joint center (HJC) position is crucial during gait analysis. HJC is obtained with predictive or functional methods. But in the functional method, there is no consensus on where to place the skin markers and which combination to use. The objective of this study was to analyze how different combinations of skin markers affect the estimation of HJC position relative to predictive methods. Forty-one healthy volunteers were included in this study; thirteen markers were placed on the pelvis and hip of each subject’s lower limbs. Various marker combinations were used to determine the HJC position based on ten calibration movement trials, captured by a motion capture system. The estimated HJC position for each combination was evaluated by focusing on the range and standard deviation of the mean norm values of HJC and the mean X, Y, Z coordinates of HJC for each limb. The combinations that produced the best estimates incorporated the markers on the pelvis and on proximal and easily identifiable muscles, with results close to predictive methods. The combination that excluded the markers on the pelvis was not robust in estimating the HJC position.