MR diagnosis of recurrent tears in the knee: value of intraarticular contrast material

After surgical resection or repair of a torn meniscus, the healed area may have areas of abnormal signal intensity on MR images. Consequently, routine MR imaging is not reliable for detecting recurrent meniscal tears. As a result, we studied the efficacy of MR imaging with intraarticular contrast material (MR arthrography) for detecting recurrent tears of the meniscus. Thirty-seven patients who previously had a meniscal tear treated by either meniscal resection or repair had conventional MR imaging and MR arthrography with 40-50 ml of a 1:100 solution of gadopentetate dimeglumine in saline. All patients had arthroscopy shortly after the MR studies. Follow-up arthroscopic surgery was performed within an average of 6.6 weeks after the MR arthrograms. The routine MR images and MR arthrograms were reviewed separately and randomly, and these results were compared with the arthroscopic findings. Meniscal morphology, signal intensity, and the presence of joint fluid tracking into recurrent tears were evaluated. The overall accuracy in diagnosing recurrent meniscal tears in the post-operative meniscus was 66% when conventional MR imaging was used and 88% when MR arthrography was used. In patients who had only minimal meniscal resection, both methods had an accuracy of 89%. In patients who had more extensive meniscal resection, accuracy was 65% with conventional MR imaging and 87% with MR arthrography. In four patients who had only a small meniscal remnant, the accuracy was 50% with routine MR imaging and 100% with MR arthrography. On conventional MR images, the presence of an effusion tracking into a meniscal tear had a sensitivity and positive predictive value of 90% for detection of recurrent meniscal tears; however, the sensitivity was only 41%. Our results show that the sensitivity of MR imaging in detecting meniscal tears after surgery varies with the extent of the resection. Sensitivity was considerably improved when intraarticular contrast material was used. MR arthrography should be considered as an alternative to arthroscopy in patients who have had resection or repair of the meniscus.