ANALYSIS OF POSITION SENSE IN HUMAN SHOULDER

Abstract

Position sense was investigated under various conditions in 6 individuals by means of pointing type of test. The experiments measured the amount and pattern of errors in positioning the shoulder at 48 representative points in the frontal field of the shoulder in 91 subjects. The amount and pattern of error varied widely. The largest mean errors were usually found around reference points situated in the 2 and 4 o''clock sectors. The pattern of errors about given reference points were quite consistent when retested in the same individual. Daily variation of overall accuracy in individuals was much less than variations between individuals. The distribution of overall accuracy among the group showed a mean calculated to be 3.3 cm. In view of the method employed, the maximum accuracy is probably 1/2 of the observed accuracy, or 1.7 cm. Analysis of the data indicates that position sense discrimination must depend upon frequency analysis of the active proprioceptors rather than mere activity or inactivity of proprioceptors. It is suggested that the sequence of sensations elicited by a passive movement of a constant rate is first the awareness of a vague sensation of movement, followed by an awareness of the general direction of movement and finally replaced by an appreciation of the rather exact position of the limb as it is moved; all of these sensations being mediated by the same proprioceptors and normally following each other so quickly as to be indistinguishable at the conscious level.