Impairment of static upright posture in subjects with undifferentiated arthritis in sacroiliac joint in conjunction with elevation of streptococcal serology

Abstract

Background and objectives: Our latest work has demonstrated a strong correlation between the anti-streptolysin O (ASO) titer and the sacroiliac (SI) joint scintigraphy in subjects with undifferentiated arthritis [Journal of Rheumatology 34 (2007), 1746-1752]. Of a significant percentage in those subjects with sacroiliac disorder reported suffering from postural abnormality. The purpose of this study was to determine whether there was an abnormality of upright postural sway in those subjects.

Methods: All subjects who have been examined for ASO titer levels and SI joint scintigraphy were divided into two groups according to the reference level of ASO titer in our central laboratory, and were subjected to ten sway tests to assess static postural sway when they were standing upright. The comparisons of the sway parameters were analyzed by using two sample t-test for continuous variables and repeated-measures analysis of variance (ANOVA) for the degree effect and interaction effect (sloped degree x group) in varying stressful conditions (eyes open vs closed, plantar flexion or dorsiflexion of feet).

Results: In a total of 84 subjects, mean age was 23 years (range 18.0-36.4). Compared with the low ASO (ASO titer <or=116 IU/mL) group, the two sample t-test showed that high ASO (ASO titer >116 IU/mL) group had 2.76-, 4.46- and 4.59-fold in sway area, 1.32-, 1.50- and 1.61-fold in sway velocity, and 2.02-, 1.97- and 1.70-fold in sway intensity, over the study period at 0 degrees, 10 degrees, and 20 degrees in conditions of eyes open and plantar flexion. The values of sway velocity/intensity obtained with eyes open and plantarflexion/dorsiflexion had lower intensity values when compared with those obtained in closed eyes and plantar flexion/dorsiflexion in high ASO group, but not the same as in low ASO group. Repeated-measures ANOVA showed that the sloped degree only affected the sway area in condition of eyes closed and dorsiflexion (P = 0.016), and affected the velocity/intensity in all conditions tested (all P < 0.0001). In consideration of interaction effect, the sloped degree showed significant difference in sway area in conditions of eyes open and plantar flexion/dorsiflexion (P = 0.03 and P = 0.0113), in sway velocity in most conditions tested (P < 0.05), and in sway intensity in condition of eyes open and dorsiflexion only (P = 0.0004).

Conclusion: Subjects with high level of streptococcal serology demonstrated increased sway on all postural control measures as compared to those with low serology. Proprioceptive deficits in the SI joint might contribute to the postural impairment measured in this study.