Question

The patient is unable to make the "OK" sign. Which muscle is involved?

• A. FDS (Flexor Digitorum Superficialis)
• B. FDP (Flexor Digitorum Profundus)
• C. FIC (Flexor Indicis Proprius)
• D.

Hint:

The FDP is responsible for flexion of the distal phalanx, and its weakness can lead to difficulty making the "OK" sign.

Answer 1

The Correct Option is B

When a patient is unable to make the "OK" sign, it typically indicates an issue with the muscles responsible for flexing the distal phalanges of the thumb and index finger. The "OK" sign requires the flexion at the distal interphalangeal joint of the index finger and the interphalangeal joint of the thumb.

The muscle primarily responsible for flexing the distal phalanx of the index finger is the Flexor Digitorum Profundus (FDP). This muscle forms the deep layer of the flexors and is unique because its action extends to the distal phalanges, whereas the Flexor Digitorum Superficialis (FDS) mostly acts on the proximal phalanges and does not affect the ability to create the "OK" sign as directly.

The Flexor Indicis Proprius (FIC) aids in index finger movements but is not the primary muscle for distal flexion. Therefore, when the "OK" sign cannot be performed, the dysfunction is most directly linked to the Flexor Digitorum Profundus.

Thus, the muscle involved is the Flexor Digitorum Profundus (FDP).