Anterior interosseous nerve palsy mimicking rupture of the index flexor digitorum profundus after volar locking plate fixation of a distal radius fracture

Abstract

We describe the case of a patient with distal radius fracture who became unable to flex the distal interphalangeal joint of the index finger after internal fixation using a volar locking plate. There was palpable crepitus with active thumb motion, and wrist radiographs showed prominence of the volar plate at the watershed line. Therefore, our initial diagnosis was plate-induced closed rupture of the flexor digitorum profundus tendon of the index finger. However, upon surgical removal of the plate, no tendon rupture was found. Magnetic resonance imaging after plate removal showed diffuse increased signal intensity in the index flexor digitorum profundus on T2-weighted fat-suppressed images, which indicated muscle denervation. Based on the above findings, we changed the diagnosis to anterior interosseous nerve palsy with isolated paralysis of the flexor digitorum profundus of the index finger. Finger flexion disability following volar plate fixation of distal radius fracture should always be investigated carefully..

Keywords: anterior interosseous nerve palsy; distal radius fracture; flexor digitorum profundus; index finger; volar locking plate.

Fig. 1

The patient was unable to perform active flexion of the distal interphalangeal joint of the left index finger (A), but encountered no difficulty with active thumb flexion (B)

Fig. 2

Posteroanterior and lateral radiographs of the affected wrist showing prominence of the volar plate at the watershed line.

Fig. 3

Axial (A) and sagittal (B) computed tomography images showing that the ulnar distal end of the plate was located 4 mm above the volar surface of the cortical bone.

Fig. 4

Magnetic resonance imaging of the forearm showing diffuse increased signal intensity in the flexor digitorum profundus muscle (arrow) of the index finger on T2-weighted fat-suppressed images.