[1] The mechanism of injury is thought to be forceful extension of a flexed digit. Avulsion of an isolated flexor digitorum superficialis (FDS) tendon is rare, and the exact pathology is uncertain.

and the flexor digitorum superficialis flexes the proximal interphalangeal joints of digits 1 to 4. The flexor carpi radialis flexes and radially deviates the wrist. 1 Neurovascular injury ...

and rupture of flexor digitorum superficialis tendon (long arrow) at level of proximal phalanx. Distal stump of flexor digitorum superficialis tendon ruptured through decussation (arrow).