Position of the Wrist Associated with the Lowest Carpal-Tunnel Pressure: Implications for Splint Design (*)


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Abstract

Increased carpal-tunnel pressure has been implicated in the pathophysiology of carpal tunnel syndrome, but it is not known whether splints that immobilize the wrist in a functional position of extension minimize 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 use of a new, dynamic method that continuously measures carpal tunnel pressure throughout the range of motion of the wrist. The pressure was measured by means of a pressure transducer connected to a flexible catheter that had been inserted into the carpal canal. The position of the wrist was measured simultaneously with use of a two-axis electrogoniometer. Aided by a computer monitor that displayed a moving line of real-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 control subjects, the lowest carpal-tunnel pressure averaged 8 plus/minus 4 millimeters of mercury (1.07 plus/minus 0.53 kilopascals), and the average position of the wrist associated with the lowest pressure was 2 plus/minus 9 degrees of extension and 2 plus/minus 6 degrees of ulnar deviation. For the patients who had carpal tunnel syndrome, the average position of the wrist (2 plus/minus 9 degrees of flexion and 1 plus/minus 9 degrees of ulnar deviation) associated with the lowest pressure was similar to that in the control group, but the average lowest carpal-tunnel pressure (19 plus/minus 2 millimeters of mercury [2.53 plus/minus 0.27 kilopascals]) was more than twice as high (p < 0.003).For all of the subjects, the carpal tunnel pressure had a parabolic relationship with the position of the wrist:it increased with greater deviation from neutral. These data indicate that splints that immobilize the wrist in a functional position of extension do not minimize carpal tunnel pressure.

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