Role of MRI Evaluation in Knee Injuries

BACKGROUND Knee is a major weight bearing and largest joint that provides mobility and stability during physical activities as well as balance while standing. Due to its wide range of functions it is exposed to forces beyond its physiological range, and thus bone and soft tissue of knee are at risk of injuries. We wanted to study MRI appearances of cruciate ligaments and meniscal tears in cases of knee injuries and correlate the MRI findings of knee injury with clinical observations/other radiological investigations/arthroscopic findings. We also wanted to evaluate the sensitivity, specificity, PPV, NPV and accuracy of MRI in detecting knee injuries taking arthroscopy as gold standard (wherever performed). METHODS This prospective diagnostic descriptive study was conducted in the Department of Radiodiagnosis of Maharishi Markandeshwar Institute of Medical Sciences and Research, MMDU, Mullana, among 100 patients presenting with knee injuries referred to Department of Radiodiagnosis for MR imaging. MR scans were carried out on 1.5 tesla MR machine Achieva (by Phillips Medical System) and studies were performed with the sense extremity coil. Arthroscopic knee surgery was performed in 39 patients. MR findings were correlated with clinical and arthroscopic findings wherever possible. RESULTS MR diagnosis of 100 cases was as follows: in ACL tear 50%; PCL tear 19%; MCL tear 17%; LCL tear 16%; MM tear 49%; LM tear 31%; Sensitivity, specificity, NPV, PPV and accuracy of MRI in detecting the knee injuries taking arthroscopy as gold standard are as follows ACL-100%, 90.9%, 100%, 96.5% and 97.4 %; lateral meniscus-100%, 94.5%, 100%, 50% and 94.8%; medial meniscus 90.4%, 66.7%, 85.7%, 76% and 79.5% respectively. Correlation between MRI and arthroscopic findings regarding presence and absence of posterior cruciate ligament tear was highest with sensitivity-100%, specificity-94.5%, NPV-100% and accuracy-94.8%, There were 6 false positives for meniscus tear on MR examinations accounting for low positive predictive value (72%) of MR examination. Posterior horn tears of menisci are likely to be missed on arthroscopy. Out of 6 false positive cases of meniscus tear, 4 were located predominately in the posterior horn and 2 in the anterior horn. Thus, acceptance of MRI findings as false positive is controversial. CONCLUSIONS MRI is a useful non-invasive modality having high diagnostic accuracy, sensitivity and negative predictive value making it a very reliable screening test for diagnosis of internal derangements of knee joint. Thus, MRI saves many knees from unnecessary arthroscopies.