The purpose of this study is to evaluate the pronator quadrates muscle in patients who underwent internal fixation with a volar locking plate for unstable distal radius fractures.

Forty patients who underwent internal fixation with a volar locking plate for unstable distal radius fracture were enrolled. We evaluated the clinical results according to the Mayo wrist score, the wrist range of motion, and the grip strength at the last follow-up. Using ultrasonography, muscle thickness of the pronator quadrates was compared between injured and uninjured arm.

Bone union was achieved in all cases. The mean Mayo wrist score was 82.79 points. The grip strength of the injured arm was decreased to 89.1% of the uninjured side. The decrease of pronation range of the injured wrist motions was significant (82.3°, p=0.004). There was significant atrophy of the pronator quadrates muscle on the injured side (injured side: 3.19 mm, uninjured side: 4.72 mm, p=0.001); and the decrement of muscle thickness in pronator quadrates showed an association with the Mayo wrist score (r=-0.35, p=0.042).

These results suggest that continuity of the muscle is maintained after use of the volar locking plating for unstable distal radius fractures with repair of pronator quadrates; however, there is atrophy of pronator quadrates muscle and limitation of pronation in the injured wrist.