Effect of external marker sets on between-day reproducibility of knee kinematics and kinetics in stair climbing and level walking.

The purpose of this study was to compare the between-day repeatability of the knee kinematics and kinetics in stair climbing and level walking among three marker sets: the Helen-Hays marker set with some markers on well-defined bony landmarks and some on not well-defined locations on soft tissues, the modified Helen-Hays marker set with a static calibration trial, and the UNC-CH marker set with all marker on well defined bony landmarks and a static calibration trial. Three-dimensional coordinates of markers in stair climbing and level walking were collected for six subjects on three days. Three-dimensional knee joint angles and resultant forces and moments were calculated. A between-day coefficient of multiple correlation was used to represent between-day repeatability of the knee joint angles, and resultant forces and moments during the stance phases of the stair climbing and level walking. Marker set had significant effect on the knee joint angles and resultant forces and moments (p < 0.02), except the knee axial force. The modified Helen-Hays marker set with a static calibration significantly improved the between-day repeatability for most of the knee angles and resultant forces and moments. The UNC-CH marker set with all markers on well-defined bony landmarks and a static calibration trial further improved the between-day repeatability of most the knee angles and resultant forces and moments.