Changes in sensory organization test scores with age.

Introduction

Falling by elderly people is a significant public health problem. Thirty to forty per cent of community-dwelling elderly people fall each year [1, 2] and falling is associated with high rates of morbidity and mortality [3-6]. Of elderly people who fall, approximately two-thirds have balance problems [2] and approximately half of these have vestibular disorders [5]. Thus falling may indicate one or more serious health conditions, among which may be vestibular impairments.

Adequate diagnosis and treatment of problems that cause falling require accurate information on balance in the elderly population but few data have been available. On a simple mechanical apparatus, Overstall et al. showed age-associated differences in the angle of sway during quiet stance [5]. More sophisticated tests of dynamic postural control in a population sample aged 7-81 years indicated a significant association of age with the magnitude of postural sway and the number of falls in response to sensory disturbances [7, 8]. Recent studies with behavioural tests and stabilometry have shown age-associated changes in static balance and in vertical spatial orientation skills that are related to vestibular function [9, 10]. Possibly as a consequence of decreased proprioceptive function in older people [10], differences in the kinematics of movement have been found between young adults and older adults under 80 years of age [11] and between young and middle-aged adults [12]. Differences in sway velocity between young and elderly adults have also been reported [13]. There has been a recent review of the relevant literature [14].

Few studies have addressed dynamic balance in subjects over 80 years of age as indicated by their performance on the standard diagnostic tests for vestibular and balance disorders. In the past 20 years several standardized, computerized balance tests have become commercially available. These `posturography' tests are now considered part of the complete test battery to assess vestibular function, since vestibulo-spinal pathways contribute to postural control [15, 16].

To maintain balance when the feet are stabilized, people use stereotyped synergies or movement patterns known as strategies [17, 18]. Normal subjects typically use combinations of two strategies: (1) the `ankle strategy', with most active anteroposterior sway about the ankles and little active hip flexion--extension; and (2) the `hip strategy', with most anteroposterior sway about the hip [17, 18]. Somatosensory or vestibular impairments cause changes in the use of these strategies under some circumstances [18].

Many elderly people complain of the symptoms of vestibular disorders [5, 19, 20], but little normative data are available on this population, especially at the upper end of the age range. We evaluated dynamic postural control in well elderly people using a standard posturography battery. This battery, the EquiTest (NeuroCom) has two subtests, Motor Coordination and Sensory Organization Test (SOT), each of which generates several measures. Recent evidence suggests that the SOT is more useful for detecting abnormalities than either the motor coordination subtest or the scores on centre of gravity alignment [21]. Therefore, this report is limited to SOT …