The effects of age and sex on biomechanical asymmetries of the lower limbs during a walk, run and side-cut task
Date
2020-05-04T16:08:25Z
Authors
DeAdder, Nick
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Abstract
INTRODUCTION: The anterior cruciate ligament (ACL) is an important contributor to knee joint stability during athletic maneuvers such as a side-cut. ACL rupture is associated with short- and long-term consequences that place a heavy burden on the health care system. 70-80% of all ACL injuries are non-contact in nature and are 2-8X more prevalent in females. The concept of limb lateralization may explain differences in dynamic control between the lower limbs and may be evidence for the unconscious preference toward greater loading of one limb versus the other, thus resulting in asymmetry of lower limbs. The purpose of this study was threefold: i) to identify if asymmetry existed beyond a clinically accepted 10% threshold for peak hip and knee joint flexion and abduction moments as well as peak hip and knee flexion angles and flexion angles at initial contact (IC) in an athletic population across age and sex, as well as during walk, run, and side-cut tasks, ii) identify the proportion of each population that experienced greater than 10% (>10%) asymmetry for each of the biomechanical variables of interest, and iii) to identify if differences in asymmetry exist across age and sex to further understand if asymmetry may function as an etiological risk factor for ACL injury. METHODS: Bilateral data was collected for 122 healthy high-performance cutting sport athletes. Four populations were identified based on age and sex (pre-pubescent males/females; post-pubescent males/females). Mean peak hip and knee internal joint flexion and abduction moments and mean peak hip and knee flexion angles and flexion angles at initial contact were calculated for stance phase of over-ground walking, running and side-cut tasks. Right and left limbs were reclassified as greater or lesser to prevent obscuring absolute asymmetry. Calculated asymmetry measures were subject to a 2x2 ANOVA to detect statistically significant differences among groups. The proportions of participants experiencing >10% asymmetry were calculated for each population and differences between populations was tested using a Chi-Square Test. Confidence intervals for the proportion of subjects with >10% asymmetry between limbs were estimated based on the binomial distribution. RESULTS: The percentage of asymmetry for peak extension and peak abduction moments as well as flexion angles at instant of contact during all tasks were greater than expected for all populations. At least 27% of the total population had >10% asymmetry across all variables and across all tasks. Age effects were noted for peak hip flexion and hip flexion angles at initial contact for all tasks, peak knee flexion angle (pKFA) and knee flexion angle at initial contact (KFA_IC) during the cut task, and peak knee extension moment (pKEM) during the walking task. In all cases, pre-pubescent athletes displayed greater asymmetry than post-pubescent athletes. Main effects of sex were noted for KFA_IC during the walk task and pKEM during the running task. In both cases, males displayed a greater asymmetry than females. No interaction effects were found. Differences in proportions of participants experiencing >10% asymmetry were found for pKFA during the walk and cutting tasks. Differences in the proportion of athletes exhibiting >10% asymmetry were found for pKFA during walk and cut tasks. CONCLUSION: Findings of this study may have important implications on gait evaluations, particularly in clinical and research settings where asymmetry is used as an outcome. The high proportion of the healthy population exhibiting >10% asymmetry suggests additional research is required to determine acceptable levels of lower limb kinematic and kinetic asymmetry in a healthy population as well as for return to play criteria. High variance for each variable among groups may have been a limiting factor for identifying age and sex effects.
Description
Anterior cruciate ligament (ACL) injury is one of the most common and traumatic sports-related injuries to the knee joint. ACL injury continues to receive widespread attention throughout medical and sporting communities due to the severity and the potential effects associated with the injury. Though many envision these injuries to be the result of a devastating blow to the knee or body during sport, it is less commonly known to the general public that approximately 70-80% of ACL injuries occur in the absence of contact and are usually the result of a combination of several factors when performing high-risk sporting maneuvers such as sudden deceleration, abrupt cutting to change direction and jump landing. These maneuvers are thought to elicit increased mechanical load on the ACL and can force the lower-limb into a high risk injury position called the ‘position of no return,’ which is categorized by internal rotation at the hip, along with hip adduction as well as knee valgus, external tibial rotation and subtalar pronation.8 The most concerning aspect of noncontact ACL injuries is the one-off nature of the injury, where the athlete sustains the injury during a maneuver they have performed safely countless times over their career.
This study was designed to address four main areas that were identified through careful review of the existing literature on noncontact ACL injuries. The four areas that will be discussed in the following sections include: i) age of participating athletes at risk of injury, ii) biomechanics of the lower limb, iii) asymmetries of lower limb biomechanics as defined by a clinically accepted return-to-play threshold and iv) asymmetry as a potential risk factor for, and a potential explanation of the one-off nature of ACL injury.
This study was the first to use a clinically relevant definition of asymmetry to investigate lower limb biomechanics for a healthy athletic population during gait. In addition, this was the first study to use that same clinically relevant definition to investigate lower limb biomechanics for an athletic population during sport-specific athletic tasks such as running, and side-cutting. Finally, this study will assess asymmetry of the lower limbs for walk, run and side-cut tasks across age and sex.
Keywords
biomechanics, asymmetry, symmetry, ACL, anterior cruciate ligament, knee, valgus, flexion