Tracking ability in subjects symptomatic of cumulative trauma disorder: does it relate to disability?

Symptoms of upper extremity cumulative trauma disorders (CTDs) often include weakness, discomfort, pain, numbness and stiffness, which are generally assessed clinically by using static tests or isolated movements. Little is known about the dynamic, functional ability of the upper extremity in CTD, yet, more than impairment, performance variables may relate to disability. The objectives of this study were to determine whether a manual tracking task was sensitive to the presence of symptoms associated with CTD and whether tracking performance related to disability. Forty-five volunteers who had frequently experienced one or more symptoms consistent with upper extremity CTD for at least 1 year and 22 control subjects performed the manual tracking task. Using a hand-held stylus over a digitizing tablet, subjects tracked a target that moved pseudo-randomly and was displayed on a computer screen. The root mean square error of the linear difference between target and stylus positions provided a measure of overall performance accuracy. Quadrant specific performance was also calculated to determine whether the location of the target (hence hand and wrist position) influenced performance. Additionally, the symptomatic group completed the Disability of the Arm, Shoulder and Hand (DASH) questionnaire reflecting physical disability level. Performance accuracy was poorer in symptomatic subjects than controls (p<0.001) and was influenced by target location (p<0.0001). The overall performance was associated with physical disability (r = 0.54). The findings suggest that tracking performance is sensitive to the presence of CTD symptoms and related to disability level. Further validation is required to determine whether the performance measure is sensitive to disease progression or intervention-induced changes.