2020 年 20 巻 1 号 p. 1-11
This study aimed to clarify the contribution of the dorsal interosseus (DI) muscles to proximal interphalangeal (PIP) joint extension function. Six healthy males were included in the study. PIP joint extension angle and torque were measured upon electrical stimulation of the 2nd and 3rd DI muscles; furthermore, an electromyogram of both muscles during active maximum PIP joint extension was obtained. Six positions were measured between metacarpophalangeal (MP) joint flexion of 80° and hyperextension (MPH) of 20° (MP80, MP60, MP40, MP20, MP0, and MPH20).
The average PIP joint extension angle upon electrical stimulation of the 2nd DI muscle was almost constant within −60° to −70° regardless of MP joint position. Although it was 0° for MP40 and MP20 upon stimulation of the 3rd DI muscle, it was around −30° and −50° for MPH20 and MP80, respectively (p < 0.01). PIP joint extension torque was measured at MP40 and MP20, where full extension was possible, and 0.03 Nm at MP40 and 0.05 Nm at MP20. Muscular activity during finger extension motion by the maximum effort was approximately 30% of the maximum activity at MP40 and approximately 70% at MP80 and MPH20 as a peak value for both muscles (p < 0.01).
This study revealed that the 3rd DI muscle governs PIP joint extension function; its degree of effect is influenced by MP joint position. Moreover, muscular activity in PIP joint extension motion fluctuates with MP joint position, and the muscles are activated at positions where PIP joint extension is not efficiently obtained. This increased activity is caused by suppression of MP joint extension, which increases the PIP joint extension function via the extensor digitorum muscles.
