The effect of multiplanar distal radius fractures on forearm rotation: in vitro biomechanical study.

PURPOSE: Many patients develop distal radioulnar joint (DRUJ) pain and loss of forearm rotation after distal radial fractures. Residual distal radial deformity is one potential cause of DRUJ dysfunction; however, the parameters of distal radial fracture alignment that lead to an acceptable functional outcome are poorly defined in the literature.

METHODS

We used 8 fresh-frozen cadaveric specimens in this in vitro study to examine the effect of simulated distal radius fracture misalignment on forearm rotation. A distal radial osteotomy was performed just proximal to the DRUJ and a custom-made, 3-degrees-of-freedom modular implant designed to simulate distal radius fracture deformities was secured in place. This allowed for accurate simulation of dorsal angulation, dorsal translation, and radial shortening, both independently and in combination. We examined the effects of distal radius deformity in the setting of both an intact and sectioned triangular fibrocartilage complex.

RESULTS

Pronation was not significantly affected until dorsal angulation reached 30 degrees . Dorsal translation of up to 10 mm or radial shortening up to 5 mm had no effect on forearm rotation. Combined deformities had a greater effect on forearm motion than isolated malpositions. Dorsal angulation of > or =20 degrees combined with 10 mm of dorsal translation or 20 degrees of angulation with 2.5 mm of radial shortening resulted in a significant decrease in forearm pronation. There was no effect of distal radial deformities, either isolated or combined, on the magnitude of forearm rotation after sectioning the triangular fibrocartilage complex.

CONCLUSIONS

This study demonstrates that a broad range of distal radius fracture malpositions can be tolerated before a notable loss in forearm range of motion is evident. Combined deformities are more likely to result in a clinically important loss of forearm rotation, and this should be considered when choosing the optimal management of patients with displaced distal radial fractures. Disruption of the triangular fibrocartilage releases the tether on the DRUJ, allowing for preservation of forearm motion even in the setting of marked osseous deformities.