Comparison of different symmetry indices for the quantification of dynamic joint angles

Abstract

Background Symmetry is a sign of physiological and healthy movements, as pathologies are often described by increased asymmetries. Nevertheless, based on precisely measured data, even healthy individuals will show small asymmetries in their movements. However, so far there do not exist commonly accepted methods and reference values for gait symmetry in a healthy collective. Therefore, a comparison and presentation of reference values calculated by 3 different methods of symmetry indices for lower limb joint angles during walking, ascending, and descending stairs were shown. Methods Thirty-five healthy participants were analyzed during walking, ascending, and descending stairs with the help of the inertial measurement system MyoMotion. Using the normalized symmetry index (SInorm), the symmetry index (SI) as the integral of the symmetry function, and another normalized symmetry index (NSI), the symmetry of joint angles was evaluated. For statistical evaluation of differences, repeated measurement models and Bland–Altman-Plots were used. Results Apart from a bias between the symmetry indices, they were comparable in the predefined limits of 5%. For all parameters, significantly higher asymmetry was found for ankle dorsi/-plantarflexion, compared with the hip and knee flexion. Moreover, the interaction effect of the joint and movement factors was significant, with an increased asymmetry of the hip and knee during descending stairs greater than while ascending stairs or walking, but a reduced symmetry of the ankle during walking when compared to descending. The movement only showed significant effects when analyzing the SInorm. Conclusion Even for healthy individuals, small asymmetries of movements were found and presented as reference values using 3 different symmetry indices for dynamic lower limb joint angles during 3 different movements. For the quantification of symmetrical movements differences between the joints, movements, and especially their interaction, are necessary to be taken into account. Moreover, a bias between the methods should be noted. The potential for each presented symmetry index to identify pathological movements or track a rehabilitation process was shown but has to be proven in further research. Trial registration: DRKS00025878.

Spine and lower body symmetry during treadmill walking in healthy individuals—In-vivo 3-dimensional kinematic analysis

“…The angular data was split into individual strides, and a time normalized waveform (0–100%) of the average gait cycle was generated with 1% sample steps [ 12 , 15 , 16 ], with 0% corresponding to heel contact of the concerned leg. Strides were defined to start with the initial contact and end with the following initial contact of one foot [ 23 ]. The 3D angles of the upper thorax, lower thorax, upper lumbar, lower lumbar and pelvis segments, as well as the hip, knee, and ankle joints were calculated to evaluate spine, pelvis and lower body kinematic gait symmetry.…”

“…Statistical parametric mapping and the normalized symmetry index, presented by Gouwanda et al [ 21 ], were calculated for assessing gait symmetry of the spine and pelvis angular motions, as well as lower body joint angles. The normalized symmetry index (SI norm ) was calculated based on Eq 1 [ 19 – 21 , 23 ].…”

“…Consequently, better implementation and evaluation of restorative interventions requires appropriate assessment and characterization of normative gait symmetry in healthy individuals. Several studies have investigated on gait symmetry [ 17 – 23 ], as well as on spine and lower body kinematics during gait [ 6 , 8 , 9 , 24 – 27 ]. Despite such contributions, up to date, there is no generally accepted standard for assessing symmetry [ 23 ].…”

“…Several studies have investigated on gait symmetry [ 17 – 23 ], as well as on spine and lower body kinematics during gait [ 6 , 8 , 9 , 24 – 27 ]. Despite such contributions, up to date, there is no generally accepted standard for assessing symmetry [ 23 ]. Typically, the symmetry index, symmetry ratio, and statistical approaches are implemented to determine gait symmetry [ 21 ].…”

“…Therefore, the purpose of the present study was to analyze 3D spine, pelvis, and lower body gait symmetry kinematics during normal and fast treadmill walking in healthy individuals. This study applies statistical parametric mapping (SPM) [ 12 ], detecting significant differences between left and right-side movements, as well as the normalized symmetry index [ 21 , 23 ] approaches to determine spine, pelvis, and lower body asymmetries. We hypothesized that there are significant differences between the spine and pelvis angular movements associated with the left lower limb motions and spine and pelvis angular movements associated with the right lower limb motions, as well as between the left and right lower extremity joint angles during normal and fast treadmill walking in healthy individuals.…”