Is postural sway in a one-leg static balance task a determinant for frontal-plane knee joint loads and excursions in a vertical drop-jump?

Masteroppgave - Norges idrettshøgskole, 2011Background: Team handball and soccer world have a high incidence of anterior cruciate ligament (ACL) injuries. This injury has severe consequences such as long term rehabilitation, sport disability and osteoarthritis. The mechanism of injury is still debated, and some, but not all risk factors are known. Preventive training programs have shown to reduce the incidence of ACL injury; many of these programs include balance training, yet it is not known whether poor balance is a risk factor for ACL injury. A comprehensive knowledge of the risk to sustain an ACL injury would increase the ability to identify players at risk and to improve existing preventive training regimes. Frontal plane knee joint kinetics and kinematics of a vertical drop-jump (VDJ) have in a previous study been used to identify athletes at risk. Purpose: This study is part of an extensive cohort study that aims to identify risk factors of ACL injuries in female team handball and soccer players. The objective of this study is to explore the possible association between postural sway (PS), of one-leg static stance and knee joint kinetic and kinematics of a VDJ by 3D motion analysis? Study design: Cross sectional study. Methods: Out of 184 female team handball players and 187 female soccer players from the top divisions in Norway that attended the VDJ and one-leg static balance test, 151 team handball results and 156 soccer results were valid and analyzed. The one-leg static balance was recorded as mediolateral and anterioposterior velocity (m/sec), total distance (mm) and 95% ellipse area (mm2) of PS, while the frontal plane knee joint kinetics and kinematics was measured as frontal plane projection angle (°), valgus angle (°) and valgus moment (Nm/kg). Results: There were only four statistically significant associations of PS measures and knee joint kinetics and kinematics out of 48 possible. The significant associations were between frontal plane projection angle and mediolateral sway, total distance and 95% ellipse area, and between valgus angle and 95% confidence area. The R2 coefficients for the statistically significant associations were small. Conclusion: The results of this study did not reveal any consistent association between PS in one-leg static balance and FPPA, valgus angle and valgus moments in VDJ. Considering the limitations in this study, a possible association between postural sway and knee joint kinetic and kinematics should not be dismissed