Background Compromised balance in ankylosing spondylitis (AS) is mostly related to poor posture. Other possibly implicated contributers to poor balance are joint pains and cord pathology. There are few studies in the literature about balance problems in AS patients, which used different assessment methodologies. The sensory organization test (SOT) was not previously used to assess the equilibrium state in AS. This test can provide information about the overall balance state and the ability of patients to maintain balance during different conditions. Its use in evaluating patients with AS may provide better insight on the balance state of AS patients who are at an increased risk of falls resulting from poor balance control.
Objectives To assess the postural profile in patients with AS using the SOT and to determine the correlation between equilibrium scores and clinical, functional, and electrophysiological findings.
Methods Twenty AS patients and fifteen healthy controls were included in the study. Bath Ankylosing Spondylitis Disease Activity index (BASDAI), Bath Ankylosing Spondylitis Functional index (BASFI) and Bath Ankylosing Spondylitis Metrology Index (BASMI) were evaluated in AS patients. The postural profile was evaluated in all patients and controls using the SOT. This test evaluates the ability to make effective use of visual, vestibular, and somatosensory inputs separately and to suppress sensory information that is inappropriate. The SOT protocol consists of six experimental conditions. The complete protocol consists of three trials for each of the six conditions, a total of 18 trials. Each trial lasts for 20 seconds. The tested patient was instructed to remain upright and as steady as possible during each trial. The measured parameters included the equilibrium scores and sensory ratios, center of gravity (COG) alignment, and the strategy used to regain balance. Electrophysiological studies (somatosensory evoked potentials and H/M ratio) for detection of central nervous system lesions were also carried out.
Results No significant differences were found between patients and controls as regards the equilibrium scores, sensory ratios, or strategy scores. All patients, except for two, had their composite equilibrium score well within the normal limits. Three patients were abnormally more reliant on the hip strategy to regain balance. The COG was excessively displaced anteriorly in AS patients with significant differences from controls. Electrophysiological abnormalities, consistent with posterior column involvement, were detected in six patients (30%), with additional pyramidal tract affection in one of them. There was no correlation between BASDAI, BASFI, BASMI or electrophysiological findings and the equilibrium scores.
Conclusions Most AS patients were unexpectedly posturally stable, as their equilibrium scores were maintained within normal values. Although, there was excessive forward displacement of the COG in AS patients, yet its negative effect on posture was compensated for by the downward shift of the COG which can explain the maintained stability of those patients. The equilibrium scores did not correlate with clinical, functional, or electrophysiological findings.
Disclosure of Interest None Declared