2022 年 18 巻 1 号 p. 103-110
Objective: The perfect O sign is often evaluated in carpal tunnel syndrome but there are no clear criteria. The purpose of this study is to develop a tool for quantifying the perfect O sign and to investigate the values of the perfect O sign in healthy subjects using this method.
Methods: Participants are healthy 20- to 30-year-old volunteers (n = 13) without any clinical symptoms of carpal tunnel syndrome. Surface electromyogram was used to measure the amplitude of the abductor pollicis brevis (APB), first dorsal interosseous muscle (FDI), flexor digitorum superficialis (FDS), and extensor digitorum communis (EDC) while performing the perfect O sign in three different wrist positions: neutral, dorsiflexion, and palmar flexion. The roundness of the perfect O sign in healthy subjects was measured by approximating a circle using 7 points in the photo captured by a smartphone and imported to a personal computer.
Results: The FDI/APB ratio was significantly lower in the dorsiflexion position than that in the palmar flexion position, and the FDS/APB ratio had a significantly lower dorsiflexion position than that of the other two wrist positions. Based on these results, a device was developed that holds the wrist in the dorsiflexion position. The mean roundness of the perfect O sign using the device in 13 healthy volunteers was 80.46 ± 9.47%.
Conclusions: Dorsiflexion of the wrist can minimize the effect of other muscles while performing the perfect O sign. The perfect O sign can be quantified by calculating the roundness.
