An experimental design comparing kinematic changes in the lumbar spine axis in subjects with and without low back pain (LBP) while standing on one leg with and without visual feedback.
The purpose of this study was to evaluate the lumbar stability index, which includes relative holding time (RHT) and relative standstill time (RST), in subjects with and without LBP.
Summary of Background Data.
Even though a number of studies have evaluated postural adjustments based on kinematic changes in subjects with LBP, lumbar spine stability has not been examined for abnormal postural responses with visual feedback.
All participants were asked to maintain the stork test position (standing on one leg with the contra lateral hip flexed 90°) for 25 seconds. The outcome measures included RHT and RST for the axes of the core spine and lumbar spine. Independent t tests were used to compare the differences between groups. Two-way repeated measure analysis of variance was used to compare the differences for both axes. The age variable was used as a covariate to control confounding effects for the data analyses.
The RHT was longer for the lumbar spine axis in subjects without LBP than those with LBP, especially without visual feedback. There was also significant interaction in RST between subjects with and without LBP (F = 7.18, P = 0.01). For the core axis of the trunk, significant differences existed based on the main effect of side (F = 9.07, P = 0.004), trunk rotation (F = 24.30, P = 0.001), and both of these interactions (F = 8.93, P = 0.004). However, there was a lack of significant interaction with age for the lumbar and core spine axes (F = 0.06, P = 0.81).
Although the control group included slightly younger volunteers compared with the LBP group, the stability index of the core spine significantly decreased in RHT and RST, especially when visual feedback was blocked for subjects with LBP. The interaction between visual feedback and trunk rotation indicated that core spine stability is critical in coordinating balance control. A trunk muscle imbalance may contribute to unbalanced postural activity, which could prompt a decreased, uncoordinated bracing effect in subjects with LBP. As a result, core spine training could be used in the prevention of postural instability in such subjects.