Analysis of Standing Balance on Sloped Surfaces in Individuals with Lumbar Disc Herniation

The change of balance control mechanism caused by lumbar disc herniation (LDH) has not been well understood. The aim of the study was to investigate the effects of LDH on the dynamical coordinations of center of pressure (COP) during standing on sloped surfaces. Eight LDH patients and 8 gender- and age-matched healthy subjects were recruited to participant in the experiment. Three surface conditions (declining, level and inclining) were set up. Limb load asymmetry (LLA) and individual leg COP (COP_{more-affected} and COP_{less-affected}) were calculated from the foot pressure distributions which recorded during quiet standing by a force plate. Cross recurrence quantification analysis (CRQA) was applied to assess the coordination of COP trajectories. Linear cross-correlation was applied to measure the correlation between CRQA parameters and COP area. LDH patients showed higher LLA and more deterministic structure of less-affected leg, especially on sloped surfaces, but there is not much difference in more-affected leg. CRQA parameters showed positive correlation with COP area on sloped surfaces. This study reveals that the LDH patients alter the postural control mechanism by magnifying the inter-limb asymmetry and reinforcing feedforward mechanism. The sloped surfaces magnified the changes of more deterministic and rigid patterns in less-affected side in the LDH. This study may provide a new strategy for clinical diagnosis and evaluation of LDH.