JUMP LANDING MECHANICS OF ADOLESCENT ATHLETES DURING AGES OF PEAK ACL INJURY RISK: IDENTIFYING SEX DIFFERENCES WITH A PORTABLE MOTION SENSOR
Authors: Willis Brad W. , Sherman Seth , Gulbrandsen Trevor , Miller Scott M. , Siesener Nathan , Guess Trent M. , Blecha Kyle , Huo Zhiyu , Skubic Marjorie , Gray Aaron D. 
Published: March 2019

Background:

Anterior cruciate ligament (ACL) injury rates in adolescent female athletes are 3x greater than males, with peak incidence at 16 and 17 years of age for girls and boys, respectively. As increased knee valgus during a jump landing task has been linked to ACL injury risk, portable motion capture devices offer capabilities of widespread screening to enable targeted prevention programs. Studies examining sex differences in dynamic landing strategies using portable motion capture devices are limited, as many investigations utilize marker-based equipment prohibitive to space, cost and time. Our multidisciplinary team has previously validated a portable markerless motion sensor to determine the knee-ankle-separation-ratio (KASR) at initial contact (IC) and peak flexion (PF) of the drop vertical jump (DVJ). The KASR compares the horizontal distance between knee and ankle joint centers. The purpose of this study is to determine if a portable motion sensor will detect sex differences in KASR at IC and PF during the DVJ when comparing adolescent athletes at ages of peak ACL injury risk. We hypothesize that a portable motion sensor will detect sex differences in the KASR at IC and PF during the DVJ in adolescent athletes during ages of peak ACL injury risk.

Methods:

A total of 42 healthy adolescent athletes participated. Groups included 16 year-old females (n=26, mean height=65.5±2.9 inches, mean weight=135.9±22.1 pounds) and 17 year-old males (n=16, mean height=70.9±2.9 inches, mean weight=159.2±18.6 pounds). Instructions and demonstration of the DVJ were provided prior to recording, utilizing a 31 cm high jump platform. Participants completed the DVJ by dropping to the ground, followed by an immediate maximal vertical jump as if going for a basketball rebound (Figure 1). Three DVJ were completed, measured by a single portable markerless motion sensor with customized software calculating KASR at IC and PF. The camera was positioned one meter high and three meters in the front of the participant. A three-trial average was utilized for analyses. A KASR of 1.0 signifies the knees being directly over the ankles during landing, with < 1 and > 1 representing dynamic knee valgus and varus, respectively. Sex differences between KASR at IC and PF were analyzed using an independent samples t-test with significance at p<0.05.

Results:

Adolescent female athletes demonstrated lower KASR values at IC (female=0.98±0.12, male=1.07±0.11, p=0.02) and PF (female=1.01±0.15, male=1.15±0.21, p=0.03) during the DVJ as compared to males.

Conclusions/Significance:

A portable motion sensor found sex differences in landing mechanics among adolescent athletes during peak ages of ACL injury risk, offering potential for widespread screening and targeted ACL injury prevention programs. The identification of potential ACL injury risk factors, using portable motion sensor technology to inform individually directed prevention programs, may offer declines in health care cost and long-term disability of youth athletes.

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