In vivo fluoroscopic kinematography of dynamic radio-ulnar incongruence in dogs

Aim of the study was to investigate dynamic radio-ulnar incongruence (dRUI) in the canine elbow joint comparing orthopedic healthy and dysplastic dogs in a prospective in vivo study design. In 6 orthopedic sound elbow joints (5 dogs, median age 17 months & mean body weight 27.9 kg) and 7 elbow joints with medial coronoid disease (6 dogs, median age 17.5 months & mean body weight 27.6 kg) 0.8 mm Ø tantalum beads were surgically implanted into radius, ulna and humerus for dynamic radiosteriometric analysis (RSA) using high-speed biplanar fluoroscopy with the dogs walking on a treadmill. dRUI, in the form of proximo-distal translation of the radius relative to the ulna, was measured for the first third of stance phase and compared between groups using unpaired t-testing. Healthy elbow joints exhibited a relative radio-ulnar translation of 0.7 mm (SD 0.31 mm), while dysplastic joints showed a translation of 0.5 mm (SD 0.30 mm). No significant difference between groups was detected (p = 0.2092, confidence interval -0.6 – 0.2). Based on these findings dRUI is present in every canine elbow joint, as part of the physiological kinematic pattern. However, dysplastic elbow joints do not show an increased radio-ulnar translation, and therfore dRUI cannot be considered causative for medial coronoid disease.