Summary
Objectives: To quantify the effect of antebrachial torsion on the miscalculation of radial valgus
measured radiographically and to assess a radiographic positioning method used to
mitigate torsion-associated artifactual miscalculation of concurrent frontal plane
angulation.
Methods: A canine cadaveric forelimb was used to model different combinations of valgus and
external torsion. Valgus was induced in the limb in increments of five degrees, radiographic
images were taken at each increment, and the observed radiographic valgus 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 accepted range. Rotationally re-positioning the limb in an attempt to
alleviate the AV discrepancies resulted in the 30° torsional group having acceptable
AV values for valgus values between zero and 20°.
Clinical significance: Increasing antebrachial 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 complex deformities.
Keywords
Angular limb deformity - radioulnar torsion
