Quantitative vibration threshold testing in carpal tunnel syndrome: analysis strategies for optimizing reliability

Tuning forks and electronic vibrometers have been used to quantify vibration sensation thresholds, which are thought to be affected early in carpal tunnel syndrome (CTS). The purpose of this study was to identify a reliable testing procedure for a newly designed, computer-controlled vibrometer (PCV50; Ztech, Salt Lake City, UT). Fifty-two patients (mean age 48+/-8 years) with electromyographically confirmed CTS were tested on one occasion. The computer-controlled vibrometer, with a fixed frequency of 50 Hz, used stepwise changes in amplitude to determine vibration sensation threshold. Each patient had three vibrometer measures (trials) taken on the pulp of the third digit of their right and left hands during the first test session and were retested by a single repetition 40 to 60 minutes later (retest). Intraclass correlation coefficients (ICCs) were used to examine several data analysis strategies. The strategy that generated the highest ICCs for both the right and left hands assumed that the first trial was a learning or practice attempt, and compared the average of the second and third trials with the score from the second session (ICC=0.86 and 0.89, respectively). The computer-controlled vibrometer offered an easily administered, quantitative, and comfortable means to assess median nerve function. Using this reliable testing procedure will allow for additional investigations to determine its usefulness in the early detection and accurate quantification of CTS-related impairment.