| Abstract|| |
Objective: To study MR appearances in various conditions affecting the knee and to identify the common lesions. Materials and Methods: One hundred and fifteen patients with knee complains and suspected to have meniscal, ligamentous or other pathology were studied using Sigma contour 0.5 T (GE) MR machine. Images were obtained in sagittal, axial and coronal planes using SE, GRE and STIR sequences. Slice thickness of 4mm, FOV of 17 x 17 cm & 192 x 160 matrix were used. Results: Anterior cruciate ligament (ACL) tears accounted for the major cases (36.5 percent) followed by Medial meniscal tears (MM)(36.5 percent and Lateral meniscal tear (17.3 percent). Hyperintensity, discontinuity and nonvisualisation were primary signs of ACL tear. Secondary signs like Posterior cruciate ligament (PCL) buckling, PCL index of greater than 0.5 and uncovered lateral meniscus (LM) were also noted in certain areas. Meniscal tears seen commonly are grade III in medial meniscus and Grade 1in lateral meniscus. Cases of meniscal cyst, synovial chondromatosis, quadriceps tendon tear, osteochondritis dissecans are clearly demonstrated on MR scans. The exact extent of the tumor in the marrow and soft tissues and involvement of joint space was demonstrated with great degree of accuracy. Conclusions: MR imaging of knee is an excellent modality that detects lesions not evident on arthroscopy and helps in planning the treatment of meniscal and ligament injuries. It demonstrates extent of marrow and soft tissue involvement of tumors with great degree of accuracy.
Keywords: MR Imaging Knee, meniscal tears, cruciate ligament
|How to cite this article:|
Shetty D S, Lakhkar B N, Krishna G K. Magnetic resonance imaging in pathologic conditions of knee. Indian J Radiol Imaging 2002;12:375-81
|How to cite this URL:|
Shetty D S, Lakhkar B N, Krishna G K. Magnetic resonance imaging in pathologic conditions of knee. Indian J Radiol Imaging [serial online] 2002 [cited 2020 Aug 8];12:375-81. Available from: http://www.ijri.org/text.asp?2002/12/3/375/28488
| Introduction|| |
The most significant advances in knee imaging have been made in the realm of MR imaging. The reports in 1983 by Kean and coworkers  and Moon and associates  were the first to describe the potential of MRI in assessing the knee. Since then because of its improved signal to noise ratio (SNR), higher resolution, reduced artifacts, shorter imaging times and improved accuracy, MRI has clearly emerged as the primary imaging tool in the workup of knee joint pathology. The main indication of MRI is in assessment of meniscal and ligament injuries. However it is useful in demonstrating other knee joint abnormalities involving articular cartilage, bone marrow, synovium, patellofemoral joint and adjacent soft tissue.
The main aim of this study is to assess the diagnostic usefulness of MRI in patients with suspected pathologies of the knee and to identify the common lesions affecting the knee-joint.
| Materials and Methods|| |
One hundred and fifteen patients with knee complaints and suspected to have meniscal or ligament tears or other pathology related to the knee joint were studied using Signa Contour (GE) MR machine with a superconducting magnet and field strength of 0.5 T using a QD extremity coil. The patient population consisted of 70 men and 45 women, majority in the age range of 11-30 yr.
Patient was placed in supine position with the knee in a closely coupled extremity coil. The knee was externally rotated 15-20°, in order to facilitate the visualization of ACL completely on sagittal images . The knee was flexed slightly 5-10°, to increase the accuracy of assessing the patellofemoral compartment and patellar alignment . Excessive flexion or hyperextension does not permit accurate evaluation of patellar alignment.
Pulse sequences used were SE, FSE, GRE and STIR in three standard imaging planes namely coronal, sagittal and axial. Slice thickness of 4mm, FOV of 17x17 cm and 192x 160 matrix were used.
An axial acquisition through patellofemoral joint was used as an initial localiser for subsequent sagittal and coronal plane images. The coronal plane optimally evaluates the collateral ligaments and body of the menisci. The sagittal plane reveals the cruciate ligaments, menisci and synovial anatomy especially the suprapatellar pouch. Overall the bones, muscles, tendons, neurovascular structures were fully evaluated with integration of all three planes.
| Results|| |
In our study group of 115 patients over a period of 24 months, the common conditions encountered were ACL tears, MM tears and LM tears [Table I]. The common age group was in the range of 21-30 yr and men predominated over women. ACL tear accounted for the major number of cases (36.5%) Hyperintensity in the ligament was noted in 28 cases [Figure1], discontinuity in 10 cases and nonvisualization of ACL was seen in six cases [Figure - 2] Secondary signs such as PCL buckling [Figure - 3], PCL index of >0.5 [Figure - 4] and uncovered LM [Figure - 5] were noted.
PCL tears accounted for only a small percentage of cases (4.34%). Discontinuity in mid-substances was seen in two cases [Figure - 6] and hyperintensity in three cases.
MM tear was commoner than LM tear accounting for 36.5% of cases. Grade III tear where hyperintensity extended upto the articular surface [Figure - 7] was the most common followed by grade II tears [Figure - 8]. Grade I tear was most commonly observed in LM tear. Bucket handle tear of MM was clearly evident on sagittal images as double PCL sign [Figure - 9].
Discoid menisci were seen in six cases, where there was the characteristic appearance of noting the bowtie appearance in more than two contiguous slices on sagittal imaging [Figure - 10]. The exact extent of the tumor in the marrow and soft tissues and involvement of joint space was depicted clearly on sagittal and coronal scans [Figure - 11] and [Figure - 12].
The hyperintense meniscal cyst and ganglion cyst with their relation to the meniscus and ligaments respectively were well demonstrated on T2W1, [Figure - 13] and [Figure - 14]. Popliteal cyst was clearly demonstrated with its neck extending into the knee joint [Figure - 15]. Focal defects in the femoral condyle in osteochondritis dissecans was well demonstrated on coronal T2W1 [Figure - 16]. Quadriceps tendon tear with bleed was seen as hyperintense signal on Sag. T1W1 [Figure - 17]. Coronal T1W1 clearly showed characteristic bone infarcts as areas surrounded by hypointense serpiginous borders in osteonecrosis [Figure - 18].
Conditions such as synovial plicae, synovial chondromatosis and chondromalacia patellae were also clearly demonstrated [Figure - 19],[Figure - 20],[Figure - 21].
| Discussion|| |
Multiple imaging modalities are currently used to evaluate pathologic conditions of the knee. Over the past several years, the role of MRI in knee imaging has steadily increased and is often the main or only imaging tool for evaluation of suspected internal derangements . Complete evaluation of the capsule, collateral ligaments, menisci and tendons about the knee has been difficult with conventional and CT arthrography. Multiplanar MR images provide significant improvement in assessing these structures.
In our study we found that positioning knee with 5 - 10° of flexion and 15 - 20° of external rotation was optimal. If ACL was incompletely seen repeat oblique images were obtained. T2W1 was preferable, as acute lesions were seen as high signal intensity with great degree of accuracy which correlated with study by Mink et al .
In our study ACL tear was the commonest condition accounting for 42 patients (36.5%) which correlated with study by Sonnin et al . Mid substance tear in the form of hyperintensity was noted in 30 patients (71.4%). Berquist et al  reported in their study mid-substance tear as the most common type (90). Hyperintensity in the ligament was seen in 28 patients (61.9%) and discontinuity in 10 patients (23.8%). Six patients (14.3%) with ACL tear showed non-visualisation of ACL which correlated with study by Gentili et al . Secondary signs such as PCL buckling, anterior tibial displacement, uncovered meniscus sign and bone contusions assisted in diagnosis in indeterminate case. Associated meniscal tear was seen in 32 patients (76.2) which correlated with 70% incidence reported by Robertson et al . PD and T2WI revealed abnormality with great degree of accuracy.
PCL tear accounted for only a small percentage of patients (4.34%) and the signs were hyperintensity in 3 patients and discontinuity in 2 patients. Sonnin et al  in their study found an incidence of 2-23% as PCL injury.
The MM tear was more common (36.7%) than LM tears (17.3%) in our study which corresponded with study by La Prade and colleagues . Grade III tear (increased signal intensity extending to articular surface) was most common followed by grade II (linear intrasubstance tear) and grade I (focal/globular intrasubstance tear). The degeneration of menisci demonstrated high signal intensity due to imbibed synovial fluid. In our study we found that T2* weighted GRE images clearly depicted the meniscal tears than FSE images, as supported by Rubin et al . Normal anatomical structures such as transverse and meniscofemoral ligaments, popliteus tendon, genicular artery and other artifacts such as capsule attachment, bursae of MCL, can cause pseudo-tears in the menisci which have to be taken note of.
Discoid meniscus is a dysplastic meniscus with a broad disc like configuration. These are seen best on sagittal images as appearance of bowtie in more than 2 contiguous slices. In our study there were six patients (5.2%) and incidence of lateral discoid meniscus was more than medial discoid meniscus. This correlated with reports by Weiner et al .
The cystic lesions encountered were meniscal cyst, ganglion cyst and popliteal cyst. Meniscal cyst can be intrameniscal, parameniscal or synovial. We had one case of MM cyst which was seen to communicate with the horizontal degenerative tear in the meniscus. Similar MR appearance was reported by Burk et al . This was clearly seen on coronal T2W1 and STIR images. Ganglion cysts have been distributed both on surface and within substance of ACL and are thought to represent mucinous degeneration of connective tissue or herniation of synovial tissue through capsular defect. We had encountered one case of ganglion cyst attached to ACL demonstrated on Sagittal T2W1. The relation of popliteal cyst to the muscle and its communication with joint was clearly demonstrated on axial images.
Synovial plicae are embryological remnants of septal division of knee into compartments. Four cases were noted in our study. Two were superior, one superior medial and one inferior synovial plicae. On MR imaging, plicae appear as low signal intensity bands on all sequences. In our case, the plicae was well demonstrated in contrast to the joint effusion.
Osteonecrosis is well depicted on MR imaging earlier than radiographic appearance. The characteristic appearance of altered signal intensity areas with well defined serpiginous hypointense margins involving tibia and lower femur were clearly demonstrated in our case correlating with the findings designed by Lotke et al .
In our study, five patients of tumors were studied, MR was found to demonstrate internal haemorrhage, intraarticular, marrow and soft tissue extension, with a great degree of accuracy correlating with study by Dooms et al .
In conclusion, MRI is an excellent noninvasive modality in imaging of the knee and a noninvasive replacement for arthrography and nontherapeutic arthroscopy. It is useful in conditions where arthroscopy cannot detect peripheral meniscal tears, inferior surface tears, osteochondritis without apparent damage to cartilage. Being noninvasive, MR does not involve morbidity associated with arthroscopy and helps in planning the treatment of meniscal and ligament injuries. It is nonspecific in determining the histologic nature of bone masses however. It is the only method for imaging marrow invasion, bone infarcts and subtle fractures. Many anatomic variants can mimic tears on MRI.
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D S Shetty
C/o "Anugraha", Hayagreeva Nagar 1st Road, Udipi 576 102, Karnataka
Source of Support: None, Conflict of Interest: None
[Figure - 1], [Figure - 2], [Figure - 3], [Figure - 4], [Figure - 5], [Figure - 6], [Figure - 7], [Figure - 8], [Figure - 9], [Figure - 10], [Figure - 11], [Figure - 12], [Figure - 13], [Figure - 14], [Figure - 15], [Figure - 16], [Figure - 17], [Figure - 18], [Figure - 19], [Figure - 20], [Figure - 21]
[Table - 1]