The position of x‐ray beam‐centring affects radiographic measurements of palmar angle and sole thickness on radiographs of the equine thoracic distal limb

Abstract

SummaryBackgroundDifferent locations of x‐ray beam centring on the equine distal limb for lateromedial and dorsopalmar radiographs of the equine digit may affect clinically relevant radiographic measurements.ObjectivesTo evaluate the effects of two different locations of x‐ray beam centring on lateromedial and dorsopalmar radiographic measurements of the equine digit and to assess intra‐ and inter‐observer variability of measurements.Study designProspective, observational and method comparison.MethodsComparisons were made of nine measurements on orthogonal radiographs acquired from 24 unshod equine feet at two locations of x‐ray beam centring: coronary band and hoof–ground interface. Radiographic measurements were obtained by three observers of varied equine veterinary experience and made in triplicate by a board‐certified veterinary radiologist.ResultsRadiographs acquired with x‐ray beam centred at the coronary band and hoof–ground interface produced differences in the mean measurements of palmar angle, defined as the angle created by the palmar processes of the distal phalanx relative to the ground surface, on the lateromedial projection (p = 0.002), and medial (p < 0.001) and lateral (p < 0.001) sole thickness on the dorsopalmar projection. There was less variability of palmar angle (p = 0.039) and more superimposition of the palmar processes (p < 0.001) with the x‐ray beam centred at the hoof–ground interface.Main limitationsThe study population was homogeneous and only included horses without outwardly visible abnormalities of the foot. Anatomic measurements were not used for comparison due to the nonterminal nature of the study.ConclusionsCentring the x‐ray beam at the hoof–ground interface produces more repeatable and smaller radiographic measurements of palmar angle and sole thickness when compared to centring the x‐ray beam centred at the coronary band. The distal phalangeal palmar processes are more superimposed with the more distal x‐ray beam centring. The strong inter‐ and intraobserver variability support the use of these nine radiographic measurements by practitioners of all levels of experience.