Fluoroscopic and magnetic resonance cross-sectional imaging assessments of radial and ulnar torsion profiles in volunteers.

Purpose: Planning an osteotomy to correct rotational malunions of the forearm is difficult because the uninvolved side is the only available reference to assess radial and ulnar torsions. This study was designed to compare the reliability of 2 methods for the determination of the torsion profile of both forearm bones and to assess side differences further in volunteers.

Methods: Fluoroscopy in combination with goniometry and magnetic resonance (MR) cross-sectional imaging were used to determine torsion profiles of the radius and the ulna in 24 asymptomatic volunteers. Interrater and interside reliabilities were assessed.

Results: For the radius, interclass correlation coefficients were less than 0.65 with fluoroscopy and greater than 0.80 with magnetic resonance imaging (MRI). For the ulna, both methods had an interclass correlation coefficient of greater than 0.90. Maximum side-to-side differences assessed with fluoroscopy and MRI were 25 degrees and 34.5 degrees for the radius and 20 degrees and 32 degrees for the ulna, respectively. There were no statistical differences between sides using both methods for both forearm bones.

Conclusions: Fluoroscopy coupled with goniometry is a valuable method for assessing the torsion profile of the ulna. MR cross-sectional imaging is better to assess the torsion profile of the radius; however, a side difference in torsion profile of up to 35 degrees for the radius and of up to 20 degrees for the ulna should be considered physiologic. Hence, only side differences greater than these limits may serve as an indication for an axial osteotomy in the clinical setting.