Gait Asymmetry in Hip Osteoarthritis Patients

Gait asymmetry
Gait is a basic daily physical activity and is known to be one of the most universal and complex of all human activities. It has to be accomplished by the complex and coordinated pattern of nerve signals sent to the muscles, which move the joints, limbs, and remainder of the body in an orderly, stable manner.
Gait symmetry has been defined as the perfect agreement of the external kinetics and kinematics of the left and right legs. More precisely, some people suggest that “gait symmetry” is when there is no statistical differences are noted on parameters measured bilaterally. Therefore, “gait asymmetry” can be defined that when both limbs behave distinctly.
Human gait seems to be naturally asymmetry. The asymmetrical behavior of the gait was observed not only in the spatiotemporal and kinematic parameters but also in the kinetic and electromyography (EMG) data during normal gait.
Spatial-temporal parameters
In the spatiotemporal parameters, velocity profiles, step length and stride length have frequently been reported. Previous studies have been found that step length and stride length were different between left and right leg. The stride time was also different between left and right leg. Combined the effect of the stride length and stride time, the velocity of stride was also different between left and right leg.
Kinematics
In the kinematics parameters, it has been found different profiles of angular changes in the sagittal plane during normal gait in both male and female. The values of relative asymmetry index (RAI) was greatest for the ankle, and much lower for the knee and hip.
Kinetics
Although spatio-temporal and kinematics parameters can provide an overall impression of gait, from another perspective, they might provide only insight into the effect of the movement but not the cause. It would be reasonable to concentrate on more informative biomechanical parameters which provide insight into both effect and cause of the action (e.g. force).
The previous study investigated the variability and symmetry of ground reaction force during walking; it has been found that substantial asymmetries in time domain variables in the medio-lateral component of ground reaction force (GRF). Additionally, the external knee adductor moment at the first peak was also found asymmetry in normal gait.
EMG
Using EMG data, the soleus and rectus femoris muscles have been reported asymmetries in amplitude profiles. Subsequently, the other research also found the gait asymmetry in medial hamstrings during push-off, soleus during the entire phase, and the medial gastrocnemius at push-off. 
Step length asymmetry in hip osteoarthritis (OA) patients
Even though there is asymmetry in the normal gait, there is marked differences have been noted between the affected and unaffected limbs in pathological gait, and this difference is larger than in normal gait. For individuals with hip OA, their capacity to walk is often compromised. The most common gait deviation in hip OA population is small step length in the affected limb, large step length in contralateral limb, and significant step length asymmetry. In the previous studies showed that individuals with hip OA had a smaller step length of the affected limb than controls in self-selected walking speed studies. An important contributing factor that beside the gait limitation that is mainly due to the abnormalities in the affected limb, might be the impaired functions of the ankle musculature lead to propulsion weakness and will rely more on the contralateral limb. It has been found that the step length in the affected limb compared to the contralateral limb in individual with hip OA was smaller. Additionally, the step length of the contralateral limb of the individuals with hip OA was greater than controls in overground studies. walking with larger steps while maintaining the same step frequency requires the center of mass (COM) velocity to increase in magnitude and to undergo a greater direction change in the step-to-step transition. This may influence the mechanical energy exchange during walking. Therefore, walking with larger step length in the contralateral limb and smaller step length in the affected limb in hip OA individuals, create the significant step length asymmetry, may decrease the mechanical energy exchange and increase the energy expenditure during walking. Increasing the energy cost of walking may exacerbate the reduction of the energy reserve for physical activity in this population.
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