Silvia Cabral

Biomechanical strategies implemented to compensate for mild leg length discrepancy during gait

Although mild leg length discrepancy is related to lower limb injuries, there is no consensus regarding its effects on the biomechanics of the lower limbs during gait. Biomechanical data of 19 healthy participants were collected while they walked under different conditions as described: (1) control condition-wearing flat thick sandals; (2) short limb condition-wearing a flat thick sandal on the left and a flat thin sandal on the right foot; (3) long limb condition: wearing flat thin sandal on the left and flat thick sandal on the right foot. The thick and thin sandals had 1.45cm of mean thickness difference. The right lower limb data were analyzed for all conditions. Ankle, knee, hip and pelvis kinematics and internal moments were measured with a motion capture system and six force platforms. Principal component analysis was used to compare differences between conditions. The scores of the principal components were compared between conditions using one-way repeated measures ANOVA. Twelve gait variables were different between conditions: rearfoot dorsiflexion and inversion (p<0.001); ankle dorsiflexion and inversion moments (p<0.001); knee flexion angle and moment (p<0.001); knee adduction moment (p<0.001); hip flexion angle and moment (p<0.001); hip adduction angle (p=0.001) and moment (p=0.022); and pelvic ipsilateral drop (p<0.001). Mild leg length discrepancy caused compensatory changes during gait, apparently to equalize the functional length of the lower limbs. However, these strategies did not fully succeed, since both short and long limb conditions affected pelvic motion in the frontal plane. These results suggest that mild leg length discrepancy should not be overlooked in clinical settings.

A Global Gait Asymmetry Index.

High levels of gait asymmetry are associated with many pathologies. Our long-term goal is to improve gait symmetry through real-time biofeedback of a symmetry index. Symmetry is often reported as a single metric or a collective signature of multiple discrete measures. While this is useful for assessment, incorporating multiple feedback metrics presents too much information for most subjects to use as visual feedback for gait retraining. The aim of this article was to develop a global gait asymmetry (GGA) score that could be used as a biofeedback metric for gait retraining and to test the effectiveness of the GGA for classifying artificially-induced asymmetry. Eighteen participants (11 males; age 26.9 y [SD = 7.7]; height 1.8 m [SD = 0.1]; body mass 72.7 kg [SD = 8.9]) walked on a treadmill in 3 symmetry conditions, induced by wearing custom-made sandals: a symmetric condition (identical sandals) and 2 asymmetric conditions (different sandals). The GGA score was calculated, based on several joint angles, and compared between conditions. Significant differences were found among all conditions (P < .001), meaning that the GGA score is sensitive to different levels of asymmetry, and may be useful for rehabilitation and assessment.

Synergistic interaction between ankle and knee during hopping revealed through induced acceleration analysis

The forces produced by the muscles can deliver energy to a target segment they are not attached to, by transferring this energy throughout the other segments in the chain. This is a synergistic way of functioning, which allows muscles to accelerate or decelerate segments in order to reach the target one. The purpose of this study was to characterize the contribution of each lower extremity joint to the vertical acceleration of the bodys center of mass during a hopping exercise. To accomplish this, an induced acceleration analysis was performed using a model with eight segments. The results indicate that the strategies produced during a hopping exercise rely on the synergy between the knee and ankle joints, with most of the vertical acceleration being produced by the knee extensors, while the ankle plantar flexors act as stabilizers of the foot. This synergy between the ankle and the knee is perhaps a mechanism that allows the transfer of power from the knee muscles to the ground, and we believe that in this particular task the net action of the foot and ankle moments is to produce a stable foot with little overall acceleration.

Inter-session agreement and reliability of the Global Gait Asymmetry index in healthy adults

There has been a growing effort in restoring gait symmetry in clinical conditions associated with pronounced gait asymmetry. A prerequisite to achieve this is that the chosen approach can accurately assess symmetry and detect/impose changes that exceed the natural day to day variability. Global symmetry indices are superior to local and discrete indices because they capture the patients overall gait symmetry. However, their repeatability is unknown. This study assessed the inter-session agreement and reliability of the Global Gait Asymmetry index. Twenty-three healthy individuals participated in two 3D gait analyses, performed approximately one week apart. The 95% limits of agreement, standard error of measurement, smallest detectable change, and intraclass correlation coefficient were analysed. The obtained values showed this index has poor agreement and reliability between sessions. Therefore, it cannot be used to assess the patients progress overtime nor to compare symmetry levels among groups.

Joint moments’ contributions to vertically accelerate the center of mass during stair ambulation in the elderly: An induced acceleration approach

Falls are a serious problem faced by the elderly. Older adults report mostly to fall while performing locomotor activities, especially the ones requiring stair negotiation. During these tasks, older adults, when compared with young adults, seem to redistribute their lower limb joint moments. This may indicate that older adults use a different strategy to accelerate the body upward during these tasks. The purposes of this study were to quantify the contributions of each lower limb joint moment to vertically accelerate the center of mass during stair ascent and descent, in a sample of community-dwelling older adults, and to verify if those contributions were correlated with age and functional fitness level. A joint moment induced acceleration analysis was performed in 29 older adults while ascending and descending stairs at their preferred speed. Agreeing with previous studies, during both tasks, the ankle plantarflexor and the knee extensor joint moments were the main contributors to support the body. Although having a smaller contribution to vertically accelerate the body, during stair descent, the hip joint moment contribution was related with the balance score. Further, older adults, when compared with the results reported previously for young adults, seem to use more their knee extensor moment than the ankle plantarflexor moment to support the body when the COM downward velocity is increasing. By contributing for a better understanding of stair negotiation in community dwelling older adults, this study may help to support the design of interventions aiming at fall prevention and/or mobility enhancement within this population.

P 153 - Variability of gait parameters in children: The importance of normative data establishment

The aim of this study was to initiate the development of a database with the normative gait fundamental biomechanical parameters of a healthy pediatric population for the Laboratório de Biomecânica e Morfologia Funcional. Twenty-seven children cleared for neurological and musculoskeletal impairments, aged between seven and nine years old joined this study. From those twenty-seven, eleven completed a test-retest study with a median interval of seven days. Anthropometric, time-distance and peak values for the lower limb kinematic parameters were computed. The Interclass Correlation Coefficient (ICC) and the Standard Error of Measurement (SEM) were calculated for the kinematic parameters. Eight variables revealed SEM values between 2° and 5°, while all others were below 2°. Higher SEM was found for the variables Cadence (3.64 steps/min), Mean Value of Pelvic Tilt (2.48°), Maximum Hip Angle (2.56°), Minimum Hip angle (4.94°), Knee Angle at Initial Contact (2.40°), and Ankle ROM (2.79°). The MDC was below 6º in most of the variables.