The subjective postural vertical in standing: reliability and normative data for healthy subjects

Impaired verticality perception can cause falls, or even the inability to stand, due to lateropulsion or retropulsion. The internal estimate of verticality can be assessed through the subjective visual, haptic, or postural vertical (SPV). The SPV reflects impaired upright body orientation, but has primarily been assessed in sitting position. The internal representations of body orientation might be different between sitting and standing, mainly because of differences in somatosensory input for the estimation of SPV. To test the SPV during standing, we set up a paradigm using a device that allows movement in three dimensions (the Spacecurl). This study focused on the test-retest and interrater reliabilities of SPV measurements (n = 25) and provides normative values for the age range 20-79 years (n = 60; 10 healthy subjects per decade). The test-retest and interrater reliabilities for SPV measurements in standing subjects were good. The normality values ranged from -1.7° to 2.3° in the sagittal plane, and from -1.6° to 1.2° in the frontal plane. Minor alterations occurred with aging: SPV shifted backward with increasing age, and the variability of verticality estimates increased. Assessment of SPV in standing can be done with reliable results. SPV should next be used to test patients with an impaired sense of verticality, to determine its diagnostic value in comparison to established tools.