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Abstract
Background Ranking the athletes according to their knee valgus angle contributes to the development of screening tools for the risk of knee injury. However, studies used different thigh marker clusters to calculate knee valgus angle in marker-based motion analysis system. There is a methodological concern on the thigh marker cluster design which relates to the reliability of measurement.
Objective To quantify the differences between six different thigh marker clusters in terms of the calculated knee valgus angles and the ranking of athletes according to the maximal knee valgus angle and knee valgus angle at initial contact.
Design A methodological study.
Setting A marker-based motion analysis system (Oqus, Qualisys, Gothenburg, Sweden) with 480 Hz frame rate was used. Six different marker clusters was put on the thigh of subjects. Subjects performed sidestep cutting and vertical drop jumping motions while being filmed with a skin marker-based motion capture system. The knee valgus angles from six different thigh marker clusters were calculated based on the dynamic trials.
Participants 19 elite female handball players and 22 elite female football players (n=41).
Main outcome measurements The calculated knee valgus angles and the resulting ranking of athletes from six different thigh marker clusters.
Results There was a discrepancy in knee valgus angles between the six marker sets up to 13.9° of peak valgus angle. The rank correlation coefficient varied from 0.505 to 0.974.
Conclusions The present study demonstrated that the choice of thigh marker clusters in analyses of drop jumps and sidestep cutting affected the magnitude of knee valgus angle, as well as the ranking of athletes. A standardized thigh marker cluster setup would facilitate the reliability of measurement, especially for a study on risk factor⇓⇓ .
Thigh skin marker cluster.
The mean (SD) of the outcome variables on different thigh marker clusters.