Corpus: Flexor digitorum profundus muscle

The flexor digitorum profundus muscle, abbreviated as FDP, belongs to the deep layer of the flexor muscles of the forearm. It is completely covered by the flexor digitorum superficialis muscle.

2.1. Origin

The muscle originates from the anterior surface of the ulna and the palmar side of the interosseous membrane of the forearm.

2.2. Insertion

The four tendons of the muscle run beneath the flexor retinaculum through the carpal tunnel. Before their insertion, they pass through the tendinous chiasm. They insert into the distal phalanges (end segments) of fingers II - V.

For the flexion of the 2nd and 3rd fingers, the anterior interosseous nerve from the median nerve with fibers from segments C7, C8, and Th1 is responsible. The flexion of the 4th and 5th fingers is under the domain of the ulnar nerve.

The flexor digitorum profundus muscle is responsible for the palmar flexion (bending) of the metacarpophalangeal, proximal interphalangeal (PIP), and distal interphalangeal joints (DIP) of the 2nd to 5th fingers and the wrist. It is one of the most important finger flexors. Furthermore, the lumbrical muscles of the hand use the tendons of this muscle as their origin.

For functional testing, the finger to be examined is fixed at the PIP, and the patient is asked to flex the finger at the DIP. Since this movement is not facilitated by the flexor digitorum superficialis muscle, an isolated injury of the deep flexor tendon can be demonstrated. Additionally, the Lumbricalis-Plus test can be used to assess an injury distal to the origin of the lumbrical muscles.