The Role of MRI in the Diagnosis of Intra Articular Knee Derangement: a Prospective Study

Conclusion: MRI represents the optimal imaging tool in the evaluation of internal knee derangement as it showed high sensitivity, specificity, diagnostic accuracy for meniscal and cruciate ligament injury, in addition to associated derangement like articular cartilage damage and synovial effusion. The Role of MRI in the Diagnosis of Intra Articular Knee Derangement: a Prospective Study ORIGINAL


Introduction
The knee is a complex structure and one of the most stressed joints in the body.It is a large joint, vital for movement, and susceptible to injury.Knee injuries represent roughly 6% of all acute injuries    treated at emergency department and approximately one-third of these have been reported to be sports related [1].The principal intra articular structures in knee are the two menisci, the two cruciate ligaments, and the two collateral ligaments.The injury to these intra articular structures is generally termed as "Internal derangement of knee" which was first coined by British surgeon leeds William Hey in 1784 [2].Although clinical examination is most important for the diagnosis of ligament injury, painful stress examinations are not always accurate in the acute phase of the injury.For that reason, magnetic resonance imaging (MRI) is indicated for early diagnosis of the acutely injured knee [3].While the use of arthrography and arthroscopy improves the accuracy of the diagnosis, both are invasive and can cause complications.MRI scanning has often been con-sidered as an alternative to diagnostic arthroscopy in evaluating internal architecture of the knee as it is non invasive, painless and provides excellent soft tissue contrast [4] .
Meniscal tear and degeneration are manifested as increased signal intensity on T1 & T2 weighted images within the substance of meniscus.Meniscal abnormalities on MRI have been classified by grading system [5,6] into 4 grades as in figures 1-4.Clinical significant of intra meniscal signal uncertain, it likely that MRI is more sensitive than arthroscopy and the decision to perform menisec-tomy currently is based exclusively on the presence of a surface tear.
The normal anterior cruciate ligament (ACL) should have a taut, low to intermediate signal intensity with continuous fibres in all planes and sequences.Tears of ACL typically occur in the middle portion of the ligament.The diagnosis of ACL tear is made on MRI by either Identifying disruption of the ligament along its normal course (figure 5) or as a focus of increased signal intensity within the substance of the ligament often best seen by T2weighted image [7][8][9][10][11].
Tears of the posterior cruciate ligament (PCL) are diagnosed by disruption along the course of the ligament or by areas of increased signal intensity within the substance of the ligament.Most of PCL tears involve the mid substance of the ligament [12,13].

Aim of the study
To assess the role of MRI in the evaluation of intraarticular knee derangement.

Patients and Methods
This prospective study was conducted at MRI unitdepartment of radiology in Al-kindy teaching hospital during the period from April 2015 to March 2016.We studied 30 patients who were referred from orthopedic department with suspected intraarticular derangement (meniscal and or ligmenteous tear).Patients with prior arthroscopy or surgical intervention or with known joint disease like neoplasm, inflammatory or infectious disorder were excluded from the study.MR scan were performed on all patients included in this study using a Siemens 1.5 Tesla MR machine.The following images were obtained for all patients: T1-weighted images in the sagittal plane, T2-weighted images in the sagittal and coronal plane, T2-SPIR in the sagittal and coronal plane.All images were interpreted by two qualified radiologists for any intra articular lesions and NPV: true negative/true negative + false negative = % of the true negative to all negative cases.
Accuracy: true positive + true negative/total.

Results
The average age of the population studied was 33 years.The age group 20-39 years is being the most referred to the clinic; because of their marked daily & athletic activities.High male preponderance noted and this may probably reflect the out patient population (figure 6).
Most medial meniscus tears are noted in the posterior horn while most lateral meniscus tears are noted in the anterior horn (figure 8).

Discussion
MRI of the knee has become a dependable device in the depiction of knee injuries.Injuries to menisci and cruciate ligaments can be detected on MRI with a high degree of sensitivity and specificity, but accuracy of MRI decreases in patients with multiple injuries [14].Although arthroscopy has been regarded the gold standard in diagnosis of meniscal and ligament injuries, MRI remains a reliable, non-invasive tool, which can reduce the use of diagnostic arthroscopy.
Zairul-Nizam et al. studied patients with knee injuries and concluded that the MRI is very sensitive in diagnosing meniscus and ligamentous injuries [15].However, in other studies there were inconsistent findings, Madhusudhan et al. in the UK studied 109 injured knees.In their study, the physical examinations, with the exception of meniscus tears, were superior to MRI results [16].In a study in Mashhad on 92 patients with knee injuries, Mazlomy et al. noted similar results and reported a high accuracy for clinical examinations [17].Behairy et al. is an Egyptian study of 70 patients that noted high diagnostic accuracy of both physical examination and MRI, and in most cases, only small differences existed between the two methods, which was also confirmed in a study by Thomas et al. [5,18].Major causes for the differences in the results were related to different skill levels of staff involved in MRI interpretation, arthroscopy and clinical examination.The difference in technique used for the MRI is of importance.Studies have shown that if the examination is performed by a skilled technician, the results will be accurate [19].
In our study, MRI showed that the sensitivity of medial meniscal injury was 94.1% with false positive results in 2 patients (11%) and false negative results in 1 patient (5.5%) of the medial meniscal injuries and these results in agreement with Kuikka et

6
There are several explanations for the misleading results of MRI regarding the menisci.These pitfalls in interpreting meniscal tear includes: some of false positive MRI findings were in fact false negative arthroscopic results, some of these tears detected on MRI were intrameniscal tears that did not communicate with arthroscopic visible meniscal surface.Delay between MRI and arthroscopy or surgery also result in false positive MRI diagnosis if the delay is being long enough to allow the meniscus to heal, that's to say some false positive results may reflect healed tear.
Mackenzie et al. summarized the four most common reasons for false positive diagnosis; wrong diagnosis due to variable anatomic structures, overestimation of pathology countered as meniscus tear (for example chondral injuries that mimic meniscus tears), false negative arthroscopic findings and tears within the meniscus without expansion to the articular surface [22].Jee et al. concluded that MRI in the presence of ACL tears has lower sensitivity for detecting meniscal tears due to missed lateral meniscal tear, and this may represent one of the causes of the misinterpretation of meniscal injures in this study [23].MRI specificity for medial meniscal injury in this study was 84.6% which agrees with the study of Kuikka et al. and Ramnath et al. which reported 87.1% specificity [20,21].
In this study we noted that the posterior horn of medial meniscus is most frequently involved and this may be attributable to its anatomical arrangement and being less mobile than the lateral one.
The sensitivity and specificity for ACL injuries in this study were 85.7% and 91.3% respectively, which agree with Khanda et al. as they observed in their study sensitivity and specificity for ACL injuries of 86.67% and 91.43%, respectively [24].Rayan et al. presented similar results, as they report 81% sensitivity for ACL injuries [25].This low sensitivity probably secondary to the criteria used by radiologist and orthopedic surgeon to distinguish between normal, partially, & completely ruptured ACL.MRI finding of an ACL tear apart from abnormalities of ACL proper are termed secondary signs, sensitivity of these signs are limited thus the absence of these signs are not exclude ACL disruption, consequently these signs may allow confidant diagnosis with high specificity for ACL injury, these include bone bruises and osteochondral fractures, anterior translocation of tibia, anterior tibial spine fractures and their associated bone bruises, so these signs might lower sensitivity of MRI for ACL tears.
Regarding the PCL, Witonski and Vaz et al. reported that both the sensitivity and specificity of MRI in making the diagnosis of PCL tears were 100% [26,27].In our study we evaluated no PCL injuries as these not encountered during the study period and this was one of the limitations in this study.Some authors reported that specific imaging sequences improve the sensitivity and specificity for detecting meniscal and ligamentous tears [28].In our work, we noted that T2-SPIR sequence was the best to detect meniscal tear.
The value of our work was that we studied the accuracy of MRI and its agreement with arthroscopy and surgery as it is actually done without using a specific imaging protocol.Despite the fact that this study has a limitation in terms of the small number of patients, we believe that the groups studied are representative of the population normally attending the orthopedics clinics and this study could become a baseline and give guidance for further studies.

Conclusion
MRI is non invasive imaging technique and has been shown highly accurate in the diagnosis of tears of the menisci and cruciate ligaments, making diagnostic arthroscopy unnecessary in most patients.
Familiarity with normal knee joint anatomy and common imaging pitfalls reduces but does not completely eliminate MRI imaging interpretation errors so more experience is needed for MRI observer to avoid the error in the diagnosis.
MRI proved to give good results in the diagnosis of tear in the posterior horn of the meniscus, which might create difficulties in diagnostic arthroscopy.

Figure 1 :
Figure 1: Knee MRI image show grade I meniscal injury which appear as single round or punctate high signal focus (arrow) within meniscal substance.

Figure 2 :
Figure 2: Knee MRI image show grade II meniscal injury which appear as linear high signal focus (arrow) with meniscal substance that does not abut the articular surface.

Figure 3 :
Figure 3: Knee MRI image show grade III meniscal injury which appear as linear hyperintense signal (arrow) with meniscal substance that communicating with the inferior articular surface.

Figure 4 :
Figure 4: Knee MRI image show grade IV meniscal injury which appear as meniscal fragmentation (arrow).

Figure 5 :
Figure 5: Knee MRI images a) partial tear of ACL appear as increased signal intensity and irregularity of its fibers (red arrows).b) complete tear of ACL appear as disruption along its fibers (white arrow).

Figure 6 :
Figure 6: Age distribution of study population.

Figure 7 :
Figure 7: MRI findings in 30 patients with internal knee derangement .

Figure 8 :
Figure 8: Distribution of different types tear according to their site in final diagnosis .

Table 1 .
al. and Ramnath et al. which reported sensitivity of MRI of 91.7% [20, 21].Index values of MRI findings for medial meniscus injuries.

Table 2 .
Index values of MRI findings for lateral meniscus injuries.

Table 3 .
Index values of MRI findings for ACL tears.