Analysis of relative kinematic index with normalized standing time between subjects with and without recurrent low back pain.

PURPOSE: Although subjects with recurrent low back pain (LBP) demonstrate altered postural control, their postural steadiness during one leg standing is unknown. The purpose of this study was to investigate postural steadiness based on relative kinematic index of the lower limbs and trunk with normalized standing time in subjects with recurrent LBP during dominant and non-dominant leg standing.

METHODS: Sixty individuals participated in the study, including 29 subjects in the control group (18 male, 11 female) and 31 subjects with recurrent LBP (21 male, 10 female). The outcome measures included relative kinematic index of the body regions and normalized standing time during the one leg standing test. The relative kinematic index was the ratio between standstill time and successful standing time. The normalized standing time was defined as a ratio between the successful standing time and the requested standing time.

RESULTS: The control group demonstrated significantly longer normalized standing time on the dominant (t = -2.57, p = 0.013) and non-dominant (t = -2.78, p = 0.007) legs than the LBP group. The relative kinematic index of the core spine model significantly decreased for the dominant (t = -3.01, p = 0.004) and non-dominant (t = -3.06, p = 0.003) legs in the LBP group. In addition, the kinematic index indicated pelvis and non-dominant shank during dominant leg standing (R 2  = 0.97) in the LBP group. In the control group, the pelvis was significantly correlated with the core spine model during standing on the dominant (R 2  = 0.95) and non-dominant (R 2  = 0.97) legs.

CONCLUSIONS: The relative kinematic index of the pelvis was found to be most significant for longer standing durations in both groups. In the LBP group, the shank and foot were significantly higher in addition to the pelvis due to possible compensatory motion. The control group took advantage of pelvic control with the core spine to minimize lower limb movements. Clinicians need to consider the core spine for pelvic control to refine postural adaptations in subjects with recurrent LBP.