Biomechanical study of the leg length discrepancy effect on body postural stability

Leg length discrepancy (LLD) can cause balance disorder due to the asymmetry in both legs, thus could contribute to poor stability. The patients with LLD may face difficulty when performing physical activities on a daily basis and prone to having risk for falls. Although the effect of LLD on the kinematic and kinetic responses in static standing have been widely discussed but studies on LLD during dynamic walking still relatively very few. The dynamic walking parameters such as centre of pressure (COP) and centre of mass (COM) are commonly used to reflect the balance response. The use of these parameters in investigating the posture stability cannot be avoided, even should be extended. Hence, this study was carried out to investigate the effect of LLD on the dynamic stability during walking by utilising the COP–COM trajectories. Eighteen healthy participants were recruited from the university’s student population to perform the experiment as artificial LLD patients. The participants were assigned to walk for 10 m track distance by wearing a pair of sandals. To replicate the LLD, insole was inserted on the participant’s right sandal. Thickness of the insole was increased from 0.5 cm to 4.0 cm, with increment of 0.5 cm thick. The motion of markers was captured by Qualysis track manager motion analysis system (with five cameras) and the ground reaction force was measured by two Bertec force plates, with 1.0 to 2.0 ms-1 of walking speed. SPSS v23 was employed for statistical analyses by using one-way ANOVA with least significant difference (LSD) and Turkey’s post-hoc test. The postural stability of LLD patients was quantified in the present study by introducing a new approach in COP–COM distance. The results show that the subjects with LLD having greater distance of COP–COM trajectories than normal subjects which reflect to the instability during walking. The significant difference between normal and LLD subject on COP–COM distance was obtained starting at 3.0 cm (p<0.05) in both directions. However, majority of the dynamic walking parameters revealed that at the minimum LLD level of 2.0 cm (p<0.05) influenced the LLD’s patient stability especially in medial-lateral direction. The reaction force was found concentrated on the short leg rather than long leg, thus contribute to tendency for fall on this side. The method introduced in this study will provide a new insight on the assessment of postural stability during walking that could potentially be used for other type of diseases particularly orthopaedics disorder.