Quantitative examination of isolated finger flexion associated with function of the flexor digitorum superficialis

[Purpose] Isolated finger flexion associated with function of the flexor digitorum superficialis has been qualitatively assessed using standard and modified tests. The purpose of this study was to quantify isolated finger flexion in healthy participants. [Participants and Methods] We assessed 100 volunteers (mean age: 44.6 years) without upper limb dysfunction using the standard and modified flexor digitorum superficialis tests. The sum of the isolated active flexion angles of the metacarpophalangeal and proximal interphalangeal joints of the test finger was also calculated, with the other three fingers held in an extended position with our original jig. [Results] The mean isolated flexion angles were, respectively, 152.4° and 154.8° for the right and left index fingers, 161.1° and 160.4° for the middle fingers, 160.6° and 158.2° for the ring fingers, 129.4° and 134.6° for the independent flexor digitorum superficialis function, 85.8° and 74.7° for the common flexor digitorum superficialis function, and 75.8° and 71.2° for absent flexor digitorum superficialis function in the small finger. The functional variations of the flexor digitorum superficialis of the small fingers showed symmetry in 65.0% of the fingers but asymmetry in 35.0%. [Conclusion] The data obtained in this study provide normal reference values for the examination of independent movement disorders of the fingers.