Value of Low-Field Magnetic Resonance Imaging in Diagnosing Meniscal Tears in the Canine Stifle: A Prospective Study Evaluating Sensitivity and Specificity in Naturally Occurring Cranial Cruciate Ligament Deficiency with Arthroscopy as the Gold Standard

Objective To evaluate the sensitivity and specificity of low-field magnetic resonance imaging (lfMRI) for detection of meniscal tears in the canine stifle. Study Design Double-blinded prospective clinical study. Animals Forty-two consecutive stifles of dogs (>= 20 kg; n=34) with clinical and radiologic signs suspicious for cranial cruciate ligament (CCL) insufficiency. Methods Each stifle had 7 predefined lfMRI sequences using a 0.5 T magnet with a human knee coil. After lfMRI, diagnostic arthroscopy was performed by 1 surgeon unaware of the MRI findings. After completion of the study MRI images were read by 1 investigator, unaware of the intraoperative findings. Results At arthroscopy, 22 stifles had meniscal tears requiring subtotal meniscectomy. Of these only 14 were identified by lfMRI. Overall sensitivity and specificity of lfMRI for detection of meniscal tears were 0.64 (95% confidence interval [95% CI]=0.43, 0.80) and 0.90 (95% CI=0.70, 0.97), respectively. Positive and negative predictive values were 0.88 (95% CI=0.64, 0.97) and 0.69 (95% CI=0.50, 0.83), respectively. Neither the state of dislocation of vertical longitudinal tears nor the amount of CCL rupture had an influence on lfMRI accuracy (P=1.00). Conclusion lfMRI was of low diagnostic accuracy in detecting meniscal tears, when compared with arthroscopy. Especially negative lfMRI findings should be interpreted with caution. Clinical Relevance When using lfMRI as a noninvasive preoperative screening tool for the diagnosis of meniscal tears, a high percentage of missed meniscal tears has to be expected.