Diagnostic accuracy of plain radiography to identify synovial penetration in horses with traumatic limb wounds.

Background: The diagnostic value of plain radiography for diagnosing synovial penetration in limb wounds near synovial structures has not been determined.

Objectives: To assess diagnostic accuracy of plain radiography to identify synovial penetration in horses with traumatic limb wounds.

Study Design: Retrospective case study.

Methods: Case records of horses presented to the Faculty of Veterinary Medicine of Ghent University (2011-2021) with limb wounds near synovial structures were categorised in groups with and without synovial penetration using results of synovial fluid analysis and surgical findings. Plain radiographic images were evaluated retrospectively. Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) were calculated for the total study sample and for the cases with and without use of a metallic probe in the wound during radiographic evaluation.

Results: Based on the total sample of 141 horses with synovial penetration and 75 cases without synovial involvement, plain radiography presented a sensitivity of 61% (95% CI: 52%-69%), a specificity of 81% (95% CI: 70%-89%), a PPV of 86% (95% CI: 79%-90%) and a NPV of 53% (95% CI: 46%-58%). With the use of a metallic probe, a sensitivity of 54% (95% Cl: 39%-69%), a specificity of 88% (95% Cl: 64%-99%), a PPV of 93% (95% Cl: 78%-98%) and a NPV of 41% (95% Cl: 32%-49%) were obtained.

Main Limitations: Sample size did not allow comparing different synovial structures. Results can be influenced by individual case characteristics.

Conclusions: If findings of a series of plain radiographs suggest synovial penetration in horses with a wound near a synovial cavity, then synovial penetration is likely, but the absence of plain radiographic findings does not rule out synovial penetration. The use of a metallic probe during radiography may be helpful. However, plain radiography should be interpreted cautiously, and clinical decision making should also include other techniques.