Validation of a technique to assess radial torsion in the presence of procurvatum and valgus deformity using computed tomography: a cadaveric study.

Objective - To validate a technique to assess radial torsion with and without procurvatum and valgus deformity using computed tomography (CT). Study Design - Anatomic study. Animals - Radii (n=3) from normal dogs. Methods - Three cadaveric radii were scanned using CT (3 mm slices). Transverse image sections were assessed at the distal and proximal physeal scar parallel to the joint surface in both sagittal and dorsal planes. Anatomic landmarks of the radius were identified and torsion was measured. A hinged Ilizarov circular external skeletal fixator was constructed to create known procurvatum, valgus, and torsional deformities. Results - Between observers results were highly correlated for calculation of torsion (r=0.972, r(2)=0.9448, P <.00001). Mean baseline torsion of the radius in the construct was 4.88 degrees. At 20 degrees procurvatum and valgus, mean calculated torsion was 5.07 degrees (confidence interval [CI]=4.6-5.6 degrees). At 20 degrees procurvatum and valgus with 22.5 degrees-induced torsion, mean measured torsion was 25.4 degrees (expected=27.38 degrees; CI=22.7-28.1 degrees). At 40 degrees procurvatum and valgus and 45 degrees-induced torsion, mean measured torsion was 51.1 degrees (expected=49.88 degrees; CI=-49.2 to 53.0 degrees). Conclusion - Assessment of radial torsion by CT is reproducible and accurate in the presence of procurvatum and valgus antebrachial angular limb deformities in the dog. Clinical Relevance - Despite complex presurgical planning, current measurements only allow for measurement of valgus and procurvatum deformities in the sagittal and dorsal planes, this method allows for more precise measurements of radial torsion in the transverse plane. (C) Copyright 2008 by The American College of Veterinary Surgeons.