Pain expression in patients with shoulder pathology: validity, properties and relationship to sickness impact

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Abstract
This study dealt with the validity and correlates of facial expressions of pain. Twenty-four patients seeking treatment for gleno-humeral joint pain and 12 controls underwent a standardized physiotherapy assessment protocol involving active and passive arm movements, and experimental pain induced by pressure. Subjects rated pain intensity on each trial using categorical, sensory and affective scales. Independent of testing, they completed a questionnaire measure of sickness impact. Facial behavior was measured by an abbreviated version of the Facial Action Coding System. Facial actions that related to pain indices included eyebrow lowering, narrowing and closing of the eyes, lip pulling, nose wrinkling and mouth opening. Facial actions during clinical tests showed consistent relationships with sensory and affective pain scales. Greater physical disability was associated with more intense pain actions on active, but not passive, tests. the results upport the validity and generality of facial measures of pain, show thay they yield graded sensitive information and suggest that they encode information about the psychosocial context of pain problems. Theoretical implications of these findings are discussed.