Session I - Upper Extremity

Rotational Malreduction of Distal Radius Fractures as Seen on Plain Films: A Cadaver Model

Paul Tornetta, III, MD; Andrew Stein, MD; Mark Desmond, MD, Boston Medical Center, Boston, MA

Purpose: Several factors have been shown to have prognostic significance in the treatment of distal radius fractures and are currently used as the main criteria by which to assess the adequacy of reduction. These criteria include articular congruity, radial length and radial angulation, all of which are easily measured with plain radiographs. Little attention, however, has been paid to malrotation at the fracture site. We hypothesized that this may be due to an inherent difficulty in appreciating rotational malalignment on plain radiographs. The purpose of this study was to determine the amount of rotation that may occur at a metaphyseal distal radius fracture before it is appreciated on plain PA and lateral radiographs.

Methods: Nine wrists in 5 preserved cadavers were used. The skin and extensor tendons overlying the distal radius were removed. The radio-carpal and distal radio-ulnar joint capsules were preserved. A Kirschner wire was drilled into the radius perpendicular to its long axis just ulnar to Lister's tubercle, and a second Kirschner wire was placed parallel and 1 cm proximal to the first. A transverse osteotomy was then made in the distal radial metaphysis in the typical location of a distal radius fracture between the two K-wires. A fluoroscopic image intensifier was used to obtain a true lateral view of the radio-carpal joint. The distal fragment was then pronated relative to the proximal fragment in increments of approximately 5 and a true lateral view of the radiocarpal joint was obtained at each increment. The angle between the K-wires was measured with a goniometer to determine the precise amount of rotation at the osteotomy site. This was continued until a step-off could be appreciated at the osteotomy site and the amount of rotation was recorded. A PA image of the wrist was also obtained with the fragments at the final rotation.

Results: An average of 38 (range 30-46) of rotation at the osteotomy site was required before the malalignment could be appreciated radiographically as a step-off on a true lateral view of the radio-carpal joint. PA images of the wrist with the fragments at this rotation did not reveal malalignment or step-off. However, there was a more subtle finding that indicated rotational malalignment identified during the study. As the distal fragment was pronated with respect to the proximal fragment, the ulna was seen to take a more volar position on the true lateral of the radiocarpal joint. Likewise, a lateral in the plane of the radioulnar axis demonstrated an oblique view of the radiocarpal joint when the osteotomy was rotated. In the preosteotomy lateral, the ulna was slightly dorsal to the midline of the radius, but with pronation at the fracture site, it moved volar.

Discussion: Despite the frequency of fractures of the distal radius a consensus on the best treatment options and the best measures of an acceptable reduction remains elusive. Many authors have suggested that an anatomic reduction is the best predictor of long-term outcome. Articular step-off, loss of radial height and dorsal angulation have been associated with poor results. These parameters are easily measured with plain radiographs. Rotational malalignment has received little attention, and we hypothesized that this might be due to an inherent difficulty in appreciating its presence with plain radiographs or fluoroscopy. Our results demonstrate that a significant amount of rotation (avg. of 38) is necessary at the fracture site before it is apparent radiographically as a stepoff. This may be relevant in the clinical setting as there is a tendency during external fixation of distal radius fractures to obtain a reduction with the forearm in pronation. We observed that a true lateral view of the radio-carpal joint should also show complete concomitant overlap of the radius and ulna. A more volar location of the ulna on the true lateral radiograph of the radiocarpal joint or an oblique view of the radiocarpal joint on a lateral in the radioulnar plane are the first signs of malrotation on plain radiographs.

Conclusion: Rotational malalignment of distal radius fractures is not seen on plain radiographs until it reaches an average of 38. Restoration of the normal relationship of the ulna to the radius on the true lateral of the radiocarpal joint is necessary to avoid malrotation in the treatment of distal radius fractures.