Efficacy of Routine Magnetic Resonance Imaging (MRI) in Evaluation of Knee Joint Pathologies

Background: Imaging modalities like ultrasonography (USG), magnetic resonance imaging (MRI) and magnetic resonance arthrography (MRAr) provide different form of information about the joint space and tendons related to the knee joint. Knee is the most frequently examined joint by MRI / MRAr as it is relatively non-invasive and highly accurate in assessing joint structures, saving majority of patients from non-therapeutic arthroscopy procedures. The main objective of this study is to understand the comparative role of routine MRI and MRAr in our hospital settings. Subjects and Methods: Twenty-five patients included in the study underwent both MRI and MRAr on the same day. Results were interpreted by radiologists and data was tabulated with the final diagnosis established on MRAr. Results: Efficacy of MRI was inferior in evaluation of Anterior Cruciate ligament, meniscal and capsular tears. In patients, where MRI was normal, MR Arthrography revealed significant findings. Conclusion: Routine MRI misses significant outcome information when compared to MRAr in evaluation of knee joint. Hence, MR Arthrography should be done for optimal evaluation of knee joints in all patients especially those with clinicoradiological discordance.


Introduction
Imaging modalities like ultrasonography (USG), magnetic resonance imaging (MRI) and magnetic resonance arthrography (MRAr) provide information about the joint space and tendons around the joint which is useful to the clinician. [1] MRI was introduced in 1980's and has since then gained popularity as a relatively accurate and safe tool for diagnosing musculoskeletal disorders. [2] Knee is the most frequently examined joint by MRI and MRAr as they are not only accurate and relatively non-invasive method for its evaluation but also saves the patient from non-therapeutic arthroscopy procedures. [3] Multiple studies have already quoted the superior performance of MRAr over conventional MRI in joint pathologies especially on 1.5T; however the disadvantage being that it is a relatively invasive procedure. [4] Even though MRAr is an invasive procedure it is relatively less cumbersome when compared to conventional contrast-arthrography and it also enables the evaluation of extra-articular anatomy helping in a satisfactory preoperative analysis of the joint space increasing the confidence of both the radiologist and treating orthopedician. It also helps in reducing nontherapeutic arthroscopic procedures. [5] MRAr is minimally invasive when compared to arthroscopy and provides nearly the same detection accuracy as arthroscopy. [6] Aim & Objectives Aim: Efficacy of routine magnetic resonance imaging (MRI) in evaluation of knee joint pathologies Objectives: • To evaluate the role of MRI in assessment of knee joint abnormalities related to cruciate ligaments, capsule and menisci • To evaluate the role of MRAr in assessment of knee joint abnormalities related to cruciate ligaments, capsule and menisci • Efficacy of routine MRI in evaluating various knee joint abnormalities related to cruciate ligaments, capsule and menisci • Assessing pathologies where MRAr provides information critical to management.

Subjects and Methods
• A study was conducted on 25 knee joints in 25 patients above the age of 21 years with clinical indication of MRI knee.
• An informed consent was obtained from the patients before the procedure about the procedure-related risks.
• After a thorough inspection with a metal detector, surgical history and history of allergy to Iohexol or Gadolinium, all patients underwent MRI followed by MRAr. Contrastsolution used for MRAr contained 4ml of 2% lidocaine, 0.1ml Gadolinium, 5ml Iohexol and 6 ml of normal saline.
• The patients were examined using 1.5T (Siemens Magnetom Avanto system). Images were acquired in a sequence for knee (Meniscal, ligamentous and Capsular tears) analysis.
• The findings of conventional MRI and MRAr were recorded in a double-blinded manner.
• The findings of MRI were compared with MRAr as a gold standard. After acquisition of images, they were interpreted and the findings were recorded on a predefined proforma. The data was analyzed statistically by "Cohen's Non-Parametric Kappa test" and a p value was obtained for the same. In addition the sensitivity, specificity, positive & negative predictive values (PPV & NPV) and accuracy were also calculated.

Results
[ Table 1] shows mean and standard deviation of age in years among patients with knee joint pathologies.
[ Table 2] shows degree of agreement of MRI with MRAr in diagnosing various knee joints pathologies in 25 patients included in our study. The data presented in [ Table 2] was assessed by "Cohen's Non-Parametric Kappa test". The "degree of agreement judged using criteria proposed by Landis and Koch the agreement excellent (co-efficient K=0.81-1), good (co-efficient K=0.61-0.80), moderate (co-efficient K=0.21-0.60), poor (co-efficient K=0-0.2) and very poor (co-efficient K< 0)".
[ Table 3] shows the sensitivity, specificity, positive & negative predictive values and accuracy of MRI for various findings using MRAr as Gold-standard.

Discussion
The total sample size was 25 and the majority of the sample was above the age of 30 years (52%), and the knee joint         From this study we can conclude routine MRI is inferior to MRAr in meniscal and capsular tears. Also, false positive results are seen with routine MRI especially when there is scarring of meniscus. Previous studies have shown better performance of Arthrography in operated meniscal tears if the meniscal tear repair is more than 25% of meniscal substance with 89% reliability over 63% of MR. [7] However, postoperative work-up was not included in our study.

Conclusion
• Accuracy & Sensitivity of routine MRI is inferior to MRAr in cases of anterior cruciate ligament & meniscal tears with partial-thickness tears being commoner.
• Meniscal pathologies were most common among knee joint pathologies followed by anterior cruciate ligament tears which had higher detection rate on MRAr.
• Routine MRI is inferior to MRAr in detection of knee joint capsular tears due to joint distension &visualisation of extracapsular contrast extravasation.
• Routine MRI was equivalent to MRAr where significant joint effusion was present.
• Routine MRI over-graded the meniscal tears as Grade III.

Summary
Since the results of MR Arthrography are superior to routine MRI in evaluation of knee joint pathologies, hence MR Arthrography should be preferred in patients with higher clinical suspicion of knee joint pathology or when there is clinicoradiological discordance related to routine MRI. Also, MR Arthrography should be preferred whenever invasive Arthroscopy or knee joint surgery is contemplated.