POSITION OF THE WRIST ASSOCIATED WITH THE LOWEST CARPAL-TUNNEL PRESSURE - IMPLICATIONS FOR SPLINT DESIGN

Increased carpal-tunnel pressure has been implicated in the pathophysi ology of carpal tunnel syndrome, but it is not known whether splints t hat immobilize the wrist in a functional position of extension minimiz e carpal tunnel pressure. To determine the position of the wrist that results in the lowest carpal-tunnel pressure, twenty control subjects and four patients who had carpal tunnel syndrome were evaluated with u se of a new dynamic method that continuously measures carpal tunnel pr essure throughout the range of motion of the wrist, The pressure was m easured by means of a pressure transducer connected to a flexible cath eter that had been inserted into the carpal canal, The position of the wrist was measured simultaneously with use of a two-axis electrogonio meter, Aided by a computer monitor that displayed a moving line of rea l-time carpal-tunnel pressure, each subject was instructed to move the wrist throughout the range of motion and to adjust it to the position that corresponded to the lowest carpal-tunnel pressure, For the contr ol subjects, the lowest carpal-tunnel pressure averaged 8 +/- 4 millim eters of mercury (1.07 +/- 0.53 kilopascals), and the average position of the wrist associated with the lowest pressure was 2 +/- 9 degrees of extension and 2 +/- 6 degrees of ulnar deviation, For the patients who had carpal tunnel syndrome, the average position of the wrist (2 /- 9 degrees of flexion and 1 +/- 9 degrees of ulnar deviation) associ ated with the lowest pressure was similar to that in the control group , but the average lowest carpal-tunnel pressure (19 +/- 2 millimeters of mercury [2.53 +/- 0.27 kilopascals]) was more than twice as high (p < 0.003), For all of the subjects, the carpal tunnel pressure had a p arabolic relationship,vith the position of the wrist: it increased wit h greater deviation from neutral, These data indicate that splints tha t immobilize the wrist in a functional position of extension do not mi nimize carpal tunnel pressure.