Effect of Limb Rotation on Radiographic Measurements of Carpal Parameters in the Equine Carpus

Radiography is an important diagnostic tool to evaluate limb deformities but is sensitive to changes in orientation of object, cassette or radiography machine. Influences of limb rotation on radiographic measurements of dorsopalmar carpal radiographs have not been reported. This study measured effects of limb rotations around vertical and horizontal axes on 10carpal parameters and identified an acceptable range of rotation where those parameters experienced a minimum change. Fifteen forelimbs from 9 adult equine cadavers were transected at the distal third of the radius, fixed vertically, then digitally radiographed 13 times. The first radiograph was aligned to a specific set of landmarks (ZDP) and subsequent radiographs were rotated through -15˚ to +15˚ in both axes with 5˚ intervals. Parameters were measured on the 195 radiographsand analysed using a random effects model. Percentage change for a 5˚ increase in rotation calculated as (slope x 5/absolute predicted value at zero degrees) x 100.Most of the parameters showed significant alterations during vertical and horizontal rotations. Using rotational angles of Vertical±5° and Horizontal±5° or 10° in only one axis as the maximum acceptable range of rotation from ZDP would offer the best potential to avoid significant effects of rotation on these measurements.