Effects of antebrachial torsion on the measurement of angulation in the frontal plane: A cadaveric radiographic analysis

Objectives: To quantify the effect of ante- brachial torsion on the miscalculation of radi- al valgus measured radiographically and to assess a radiographic positioning method used to mitigate torsion-associated artifac- tual miscalculation of concurrent frontal plane angulation. Methods: A canine cadaveric forelimb was used to model different combinations of val- gus and external torsion. Valgus was induced in the limb in increments of five degrees, radiographic images were taken at each in- crement, and the observed radiographic val- gus was measured. Various angles of torsion were then induced and the process was repeated for a range of torsional angles at 15° increments. For the second objective, the study was repeated with the forelimb rotationally re-positioned to mirror the degree of the induced torsion of the deformity at each valgus and torsion iteration. Results: Both zero degrees and 15° torsional iterations possessed mean artifactual valgus (AV) values between zero and five degrees for every valgus increment. With torsion of 30° and higher, mean AV values varied widely and did not fall within the zero to five degree ac- cepted range. Rotationally re-positioning the limb in an attempt to alleviate the AV discrep- ancies resulted in the 30° torsional group hav- ing acceptable AV values for valgus values be- tween zero and 20°. Clinical significance: Increasing ante- brachial torsion interferes with accurate radiographic measurement of frontal plane deformities. Radiographically repositioning the limb allows the accurate calculation of more valgus and torsion combinations, but still results in miscalculations of more com- plex deformities.