3-Dimensional deformity analysis of malunited forearm diaphyseal fractures.

PURPOSE

Several biomechanical studies using cadavers have revealed that axial rotation deformity of the forearm bones reduces forearm motion. However, little information is available on the 3-dimensional deformity patterns, including axial rotation deformity in malunited diaphyseal fractures of the forearm. The complex deformity of both forearm bones is difficult to assess on plain radiographs or cross-sectional images. Therefore, we assessed osseous deformity in malunited diaphyseal fractures of the forearm using 3-dimensioinal analysis.

METHODS

We examined 21 patients (16 malunions of both forearm bones and 5 isolated radial malunions). Three-dimensional computer models of bilateral radius and ulna were created from computed tomography data. We evaluated deformity by superimposing the mirror-image bone model of the contralateral normal bone onto a model of the affected bone.

RESULTS

In 21 radial malunions, extension (n = 17) and pronation (n = 16) deformities were common. This tendency was seen particularly in proximal malunions. Average extension, valgus, and pronation deformities were 18°, 2°, and 16°, respectively. In 16 ulnar malunions, valgus (n = 15) and pronation (n = 12) deformities were common. Average flexion, valgus, and pronation deformities were 1°, 11°, and 6°, respectively. Extension deformity of the radius and valgus deformity of the ulna were correlated with restriction of forearm motion.

CONCLUSIONS

Malunited diaphyseal fractures of both forearm bones showed complex deformities, which suggests that 3-dimensional modeling may be a more effective method than standard computed tomography or radiographs. Pronation deformity of the radius may be caused by the supinator and pronator muscles. In addition, the deformity pattern of both bones may indicate that valgus and internal rotation force in the neutral forearm position is applied to both forearm bones after injury.

CLINICAL RELEVANCE

Three-dimensional forearm osteotomy, including rotational realignment, is necessary to obtain anatomical reduction.