Morphologic evaluation of chronic radial head dislocation: three-dimensional and quantitative analyses.

BACKGROUND: Treatment of chronic radial head dislocation is controversial, considering whether to reduce and reconstruct the proximal radioulnar joint. The anatomic alteration that influences the decision to reduce the dislocation is not completely understood.

QUESTIONS/PURPOSES: We attempted to clarify the changes of the proximal radioulnar joint that occur in chronic radial head dislocations to clarify how they might influence the decision to perform repair.

PATIENTS AND METHODS: We evaluated 15 patients with chronic radial head dislocations categorized by duration of "early" (< 3 years) (n = 8) and "longstanding" (> 3 years) (n = 7) groups. We measured the angle and depth of the radial notch of the proximal ulna and evaluated radial head deformity using 3-D bone models created from CT data.

RESULTS: For the early group, no differences were observed in the shape of the radial notch between affected and normal sides. For the longstanding group, the radial notch angle was greater on the affected side (mean +/- SD, 45.5 degrees +/- 9.7 degrees ) than on the normal side (29.7 degrees +/- 6.3 degrees ), and the radial notch depth was smaller on the affected side (0.2 +/- 1.6 mm) than on the normal side (2.3 +/- 1.3 mm). The shape of the radial head was nearly normal in the early group, whereas the longstanding group had a dome-shaped deformity.

CONCLUSIONS: In longstanding chronic radial head dislocation, deformation develops in the radial head and radial notch of the ulna, which is remodeled in a manner corresponding to the dislocated position of the radial head.

LEVEL OF EVIDENCE: Level III, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.