Diagnostic performance of ultrasonography, bursography and standing magnetic resonance to detect navicular intrabursal pathology in horses with foot pain.

Background: Navicular intrabursal pathology (NIP) is a common cause of forelimb lameness in horses. An accurate diagnosis of which structure is involved is essential for therapy and prognosis.

Objectives: The study aimed to compare the diagnostic performance of ultrasonography, bursography and standing magnetic resonance (MRI) imaging as diagnostic tools of the proximal NIP using bursoscopy as the gold standard.

Study design: Prospective blinded study.

Methods: A total of 21 feet from 17 horses were included. The feet underwent ultrasonography, followed by MRI, and thereafter bursography and bursoscopy. The images were interpreted blindly to document the presence or absence of the podotrochlear lesions. The lesions of interest were dorsal fibrillations (DF) and splits of deep digital flexor tendon (DDFT), adhesions and fibrocartilage defect (FD) of the navicular bone. The accuracy, specificity, sensitivity, positive predictive values and negative predictive values were calculated. Furthermore, the kappa test was used to calculate the inter-observer agreement.

Results: Bursoscopy revealed lesions in 95% (20/21) of the feet. Eighteen DF and 11 split lesions in the DDFT, 19 FD and 8 adhesions were identified. MRI showed accuracy of 94% (17/18, 95% CI 76.2%-99.9%) for DF and 81% (9/11, 95% CI 63.6%-97%) for split lesions in the DDFT, whereas the accuracy for FD was 58% (11/19; 95% CI 36.1%-80.8%). Adhesions with MRI were predicted correctly in only 37.5% (3/8; 95% CI 43%-85.4%) of the feet. Bursography showed with MRI similar accuracy regarding the adhesions. Bursography had accuracy for FD of 68% (13/19; 95% CI 52.8%-91.8%) and DDFT lesions were detected in 85% (17/20, 95% CI 34%-78.2%) of the feet. Ultrasonography predicted DDFT lesions in 65% (13/20, 95% CI 63.6%-96.9%) of the feet, whereas its adhesions' accuracy was 25% (2/8, 95% CI 14.5%-56.9%). The inter-observer agreement was the lowest for ultrasonography compared to MRI and bursography.

Conclusions: A combination of ultrasonography and bursography can be an alternative to standing MRI when the latter is not an option or is used as complementary tests.