Use of positive contrast radiography to identify synovial involvement in horses with traumatic limb wounds

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The diagnostic value of positive contrast radiography in the work-up of suspected synovial infection in horses with limb wounds near synovial structures has yet to be systematically evaluated.


To determine the specificity, sensitivity and positive and negative predictive values of positive contrast radiography for identification of synovial infection in a population of horses with limb wounds.

Study design

Retrospective case study comparing the performance of positive contrast radiography to the gold standard of synovial fluid cytology in horses presenting with limb wounds in the vicinity of synovial structures.


Case records of horses presenting to the Royal Veterinary College Equine Hospital between 2010 and 2015 with limb wounds that may have compromised adjacent synovial structures were analysed. Synovial fluid cytology results were used to categorise synovial structures in infected and noninfected groups. Positive contrast radiography results were compared between infected and noninfected groups and sensitivity, specificity, positive and negative predictive values were calculated.


Fifty horses with 66 synovial structures were included in the study. Positive contrast radiography had a high specificity (86.4%), but only a moderate sensitivity (59.1%) for the identification of synovial infection. In addition, a low positive predictive value (68.4%) and high negative predictive value (80.9%) were observed in this population of horses.

Main limitations

Sensitivity, specificity and predictive values may differ between different synovial structures and cases. Different conclusions may be drawn from the results in a single population. Sensitivity and specificity of positive contrast radiography may also be influenced by different techniques used by examiners and by inherent characteristics of individual cases.


Positive contrast radiography should be used for the investigation of potential synovial infection in horses with limb wounds, particularly if no synovial fluid sample for laboratory analysis can be obtained. However, it appears that positive contrast radiography is best used in combination with other tests to ensure that a correct and timely diagnosis is made.

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