The high signal intensity meniscus of the knee. Magnetic resonance evaluation and in vivo correlation

This study describes the different appearances of meniscal abnormalities on magnetic resonance (MR) images and correlates macroscopic and histologic findings. Twenty-three of 40 cadaveric menisci with MR signal abnormalities were examined macroscopically; five of the 23 were studied histologically. In addition, MR studies of seven patients (14 menisci) were examined and findings were correlated arthroscopically. Histologic analysis was performed on two of these menisci. The two major findings on MR images were: (1) abnormal, high, centrally located signal intensity within the meniscus and (2) disruption of the peripheral meniscal contour. Macroscopically evident meniscal degeneration correlated well with findings on MR images in all cases. Histologic abnormalities included microcyst formation and separation of collagen bundles. Four menisci with intact outer contour lines on MR images had macroscopically identifiable tears. In addition, two meniscal tears were appreciated only after intra-articular injection of gadolinium-DTPA. We conclude that MR imaging is superior to macroscopic examination as performed by arthroscopy or arthrotomy for the detection of degenerative meniscal lesions. The technique also accurately identifies meniscal tears, a capability that might be enhanced by prior intra-articular injection of MR contrast agents.     

Detection of meniscal tears and marrow lesions using coronal MRI

OBJECTIVE: The usefulness of coronal images in addition to sagittal images for detection of additional meniscal injuries or bone lesions has been questioned. Some authors believe meniscal tears are rarely seen only in the coronal plane. We performed a retrospective review of coronal and sagittal MR images of the knee to determine whether coronal imaging resulted in the detection of any additional meniscal tears or bone lesions when compared with sagittal MRI of the knee alone. MATERIALS AND METHODS: Two musculoskeletal radiologists retrospectively reviewed 200 consecutive sets of MR images of the knee by consensus. Both observers recorded their retrospective findings on sagittal proton density images, sagittal and coronal T2-weighted images, and coronal T1-weighted images. Findings recorded were those of meniscal tears, bone marrow abnormalities, and bone lesions. RESULTS: On these 200 consecutive sets of MR images of the knee, 114 meniscal tears were shown. Ninety-three meniscal tears were shown on sagittal proton density images only. One hundred fourteen meniscal tears were seen on sagittal proton density and coronal T1- and T2-weighted images. Use of coronal images resulted in the confident detection of 21 additional meniscal tears not well seen on sagittal proton density images alone. Twelve of the 21 additional meniscal tears were seen on coronal T1- and T2-weighted images. Nine of the 21 additional meniscal tears were seen only on coronal T1-weighted images. Most of these additional meniscal tears were in the body of the meniscus. These 21 additional meniscal tears were confirmed arthroscopically. Eight marrow lesions were well characterized only on coronal T1-weighted images. Five were osteochondral lesions, one was an intraosseous hemangioma, and two were microfractures. CONCLUSION: Coronal MR images of the knee allowed better detection and characterization of some meniscal tears than sagittal images alone. Radial meniscal tears, bucket-handle tears, and horizontal tears in the body of the meniscus may be difficult to characterize in the sagittal plane alone. Use of coronal T1-weighted images, rather than coronal T2-weighted or sagittal proton density images alone, allows accurate characterization of some additional marrow lesions. The addition of a T1-weighted sequence in the coronal plane adds only 1 min 30 sec to the scanning time.     

MR imaging of meniscal tears with discoid lateral meniscus

Objective: To study MR findings of meniscal tears with discoid lateral menisci (DLMs) and to evaluate the incidence and accuracy of MRI compared to arthroscopical surgery. Material and methods: MR appearances of surgically proved torn discoid lateral menisci (DLM) were studied in 57 knees (40 patients). They were all performed with a 1.5T MR before surgery. MR sequences included T1- and T2* weighted images on both coronal and sagittal planes and 3D-axial images with a slice thickness of 0.7 mm. Result: Of 57 DLMs, there were 32 complete DLMs and 25 incomplete DLMs. Twenty-five of 32 complete DLMs had tears; including seven with intrasubstance tear, five with radial tear, five with other kinds of tears and eight with severe tears involving whole meniscus. On the other hand, 13 of 25 incomplete DLMs had tears; including two with intrasubstance tear, six with radial tear, four with other kinds of tears and one with severe tears. All DLMs were correctly diagnosed on MR images. Twenty-seven of 38 tears with DLM were correctly identified on conventional 2D MR images. This yielded 71.1% sensitivity, 100% specificity and 80.7% overall accuracy. When adding axial 3D MR images to 2D MR images, 36 of 38 tears were correctly diagnosed. A combination of both techniques yielded a sensitivity of 94.7% and a specificity of 100%. Ten of 11 radial tears with DLM were correctly identified on 3D axial images, where only three of them could be diagnosed on conventional 2D images. Eight of nine intrasubstance tears were correctly identified on 3D axial images, where six of them could be diagnosed on conventional 2D images. Conclusion: DLMs had a much higher incidence of meniscal tears than normally shaped lateral menisci and MR is the only modality of choice to evaluate them before surgery. Especially 3D axial MR images were quite useful in the detection of intrasubstance and radial tears often associated with DLMs.     

半月板可疑撕裂的MRI与关节镜对照研究

研究半月板可疑撕裂的出现机率及其临床意义。材料和方法：回顾性分析了１２６个膝关节的ＭＲ扫描资料，当二位放射科医生均不能肯定半月板内的高信号是否延伸至半月板表面时，诊断为半月板可颖撕裂，并与关节镜检查结果进行对照。结果：１２６例中有２２例诊断为半月板可疑撕裂，占１７．５％。１２例位于内侧半月板的后角，４例位于外侧半月板的前角，６例位于外侧半月板的后角。２２例中１８例作了关节镜检查，只有２例发现有撕裂     

Magnetic resonance imaging findings of surgically proven medial meniscus root tear: tear configuration and associated knee abnormalities

OBJECTIVE: To evaluate magnetic resonance imaging (MRI) findings of medial meniscal root tear and the correlation of medial meniscal root tear with other associated knee abnormalities. METHODS: We retrospectively assessed preoperative magnetic resonance images of 39 patients with arthroscopically confirmed medial meniscal root tear. Magnetic resonance imaging findings were retrospectively reviewed by 2 experienced musculoskeletal radiologists for consensus. We evaluated the configuration of meniscal root tear and the other associated knee abnormalities on MRI for direct correlation with arthroscopic findings. RESULTS: At arthroscopy, there were 36 radial tears and 3 complex tears involving the medial meniscal posterior horn roots. All 36 radial tears could be correctly diagnosed by MRI, with findings showing ghost sign on sagittal images in 100% (36/36), vertical linear defect on coronal images in 100% (36/36), and radial linear defect on axial image in 94% (34/36). However, all 3 complex tears were misdiagnosed as radial tears on MRI. Medial meniscal root tears displayed a strong association with degenerative joint disease in 97% (38/39). Medial meniscal root tears were also found in association with cartilage defects of the medial femoral condyle and medial meniscal extrusions (> or =3 mm) in 89% (34/38) and 67% (26/39), respectively. CONCLUSIONS: Medial meniscal root tears were usually posterior horn root radial tear. A high association with degenerative joint disease, cartilage defects of the medial femoral condyle, and medial meniscal extrusions (>/=3 mm) were also noted.     

Iliotibial band friction syndrome: MR imaging findings.

Six patients with clinical histories and physical examination results consistent with iliotibial band friction syndrome (ITBFS) were examined with magnetic resonance (MR) imaging. Ill-defined decreased signal intensity on T1-weighted images and increased signal intensity on T2-weighted images was present deep to the iliotibial band, adjacent to the lateral femoral epicondyle. Axial fast imaging with steady-state precession (FISP) gradient-echo sequences were essential in differentiating the ill-defined signal intensity abnormality associated with ITBFS from fluid in the lateral knee joint. None of these patients were found to have lateral meniscal tears, and all responded to conservative measures directed at treating ITBFS. The authors conclude that MR imaging may be useful in confirming or establishing the diagnosis of ITBFS in patients with the appropriate clinical history and distal lateral thigh or lateral knee pain.     

New method for fast MR imaging of the knee

Thirty-five patients with suspected internal derangements of the knee were examined with conventional two-dimensional (2D) spin-echo magnetic resonance (MR) imaging techniques and a new rapid three-dimensional (3D) method called 3D FASTER (field echo acquisition with a short repetition time and echo reduction). A 9-minute 3D FASTER data acquisition achieves nearly isotropic voxels for the calculation of any desired image plane without a significant loss in image quality. Image contrast is optimized for visualization of knee anatomy in a single sequence. An image-processing workstation is used to speed the multiplanar image calculation and display for more efficient analysis of the complex 3D data set. The 3D FASTER images were superior or equal to 2D images (which took three times longer to acquire) in demonstrating meniscal tears, ligament tears, bone marrow disease, and osteochondral defects. The combined advantages of improved imaging capability and efficiency could make 3D FASTER imaging a routine MR method for knee imaging.     

Tears of cruciate ligaments and menisci: evaluation with cine MR imaging

A cine magnetic resonance (MR) imaging technique, involving the acquisition of kinematic sagittal images during knee movement, was used to evaluate 52 symptomatic knee joints. Results were compared with those obtained by means of static three-dimensional (3D) MR imaging. Twenty-seven of the 28 anterior cruciate ligament (ACL) tears and 22 of 24 normal ligaments were correctly identified at cine MR imaging for a sensitivity of 96% and a specificity of 92%. Static 3D MR imaging yielded a sensitivity of 71% and a specificity of 88%. All four posterior cruciate ligament tears were identified at cine and 3D MR imaging. For meniscal tears, cine MR imaging yielded a sensitivity of 48% and a specificity of 96%; the sensitivity and specificity for 3D MR imaging were 71% and 96%, respectively. Cine MR imaging proved to be more useful than static MR imaging in assessing the tightness of cruciate ligaments, especially of those that were partially torn, and in assessing the movement of meniscal-free fragments. The increased information obtained with cine MR imaging may warrant continued investigation and clinical application.     

Meniscal tears: comparison of half-Fourier technique and conventional MR imaging

PURPOSE: To determine whether half-Fourier MR image acquisition technique can provide similar information to that of conventional MR acquisition technique for evaluation of meniscal tears. MATERIALS AND METHODS: We studied 101 menisci in 52 patients who were referred for evaluation of meniscal tears. Sagittal MR images of the knee were obtained for all patients by using proton density and T2-weighted SE sequences on a 1-T clinical system. The half-Fourier technique and conventional technique were used for all patients. All other imaging parameters were identical for both sequences (TR/TE=2400/20,70; 3 mm slice thickness; 200 x 256 matrix; field of view, 200; one signal acquired). Both sets of images were filmed with standard window and level settings. Images were randomised and interpreted independently by two radiologists for the presence of meniscal tears. Images were also subjectively assessed for image quality using a five-point grading scale. RESULTS: On half-Fourier images, Reader 1 interpreted 23 menisci as torn, compared to 28 for Reader 2. On conventional images, Reader 1 interpreted 24 menisci as torn, compared to 26 for Reader 2. Agreement between interpretation of the conventional and that of the half-Fourier images was 99% for Reader 1, and 98% for Reader 2. Agreement between readers for the half-Fourier images was 95%, and for the conventional images 96%. No statistically significant difference was found in the subjective evaluation of image quality between the conventional and half-Fourier images. CONCLUSION: The half-Fourier acquisition technique compares favourably with the conventional technique for the evaluation of meniscal tears.     

Do asymptomatic marathon runners have an increased prevalence of meniscal abnormalities? An MR study of the knee in 23 volunteers

Excessive repetitive musculoskeletal loads and stresses associated with intense physical activity may lead to deterioration of the menisci of the knee. Therefore, MR imaging was performed on the knees of 23 asymptomatic marathon runners (eight men, 15 women; average age, 40 years; average number of years training, 10; average training distance per week, 41 miles) to determine the prevalence of meniscal signal abnormalities. None of the runners had previous knee injuries or surgery and each of them regularly competes in 26-mile, 50-mile, or 100-mile marathon races. T1-weighted coronal MR images and proton density-weighted and T2-weighted sagittal images were obtained with a 1.5-T MR system and a transmit/receive extremity coil. The medial and lateral menisci were divided into four portions, or horns, and a total of 92 horns were evaluated (i.e., four horns per knee: medial posterior, medial anterior, lateral posterior, and lateral anterior). Two meniscal horns (2%) had grade 3 signal (grade 3 indicates a meniscal tear), 12 (13%) had grade 2 signal, 29 (32%) had grade 1 signal (grades 1 and 2 are indicative of meniscal degeneration), and 49 (53%) had grade 0 signal (grade 0 is normal). Overall, the prevalence of meniscal tears was 9% (two meniscal tears found in 23 runners). This is lower than the prevalence of MR signal abnormalities indicative of meniscal tears reported for asymptomatic, nonrunner athletes (20% of 20 athletes) and for asymptomatic nonathletes (16% of 74 subjects). Fifty-three percent of the meniscal horns of the nonrunner athletes had grade 1 or 2 signal, indicative of meniscal degeneration. Our results indicate that the prevalence of meniscal tears in marathon runners is no higher than the prevalence reported for sedentary persons, and the runners have the same amount of meniscal degeneration as do nonrunner athletes.     

MR enteroclysis protocol optimization: comparison between 3D FLASH with fat saturation after intravenous gadolinium injection and true FISP sequences

The aim of this study was to introduce the true fast imaging with steady-state precession (FISP) sequence for MR enteroclysis and compare it with the already used T1-weighted fast low-angle shot (FLASH) sequence. Twenty-one patients underwent both MR and conventional enteroclysis. The MR enteroclysis examination was performed after administration of an iso-osmotic water solution through a nasojejunal catheter and the following sequences were included: (a) true FISP; and (b) 3D FLASH with fat saturation after intravenous injection of 20 mg Buscopan or 1 mg glucagon and 0.1 mmol/kg gadolinium chelates. The true FISP sequence provided images with significantly fewer motion artifacts, whereas 3D FLASH was less sensitive to susceptibility and chemical shift artifacts. The homogeneity of endoluminal opacification, wall conspicuity, and distention of the small bowel were very good to excellent and the two sequences presented no statistically significant differences here. True FISP provided significantly better overall image quality than did 3D FLASH. The true FISP sequence can provide good anatomic demonstration of the small bowel on T2-like images and could be combined with T1-weighted FLASH images for an integrated protocol of MR enteroclysis.     

MR imaging of the knee: preliminary results with a 3DFT GRASS pulse sequence

The knees of 17 patients (18 extremities) with possible meniscal, cruciate ligament, and articular cartilage abnormalities were examined with a three-dimensional Fourier transform (3DFT), gradient-refocused acquisition in a steady state (GRASS) pulse sequence. Arthroscopic confirmation was available in all cases and was the standard for comparison. Thirteen of these extremities were also examined by using a two-dimensional Fourier transform spin-echo pulse sequence with a 2000-msec repetition time and 20- and 80-msec echo time. In these 13 cases, both pulse sequences correctly identified seven of eight meniscal abnormalities. However, interpretation of the 3DFT GRASS images resulted in fewer false-positive meniscal tears (three vs six). Cruciate ligament tears were detected more readily on the 3DFT GRASS images (six vs three with two possible tears on the spin-echo images). These preliminary findings suggest that the overall accuracy of MR imaging of the knee could be improved by including 3DFT gradient-refocused pulse sequences.     

Contribution of thin-slice (1 mm) axial proton density MR images for identification and classification of meniscal tears: correlative study with arthroscopy

Objective To evaluate the diagnostic efficacy of thin-slice (1 mm) axial proton density-weighted (PDW) MRI of the knee for meniscal tear detection and classification. Methods We prospectively assessed pre-operative MR images of 58 patients (41 males, 17 females; age range 18-62 years) with arthroscopically confirmed meniscal tear. First, we evaluated the performance of the sagittal and thin-slice axial MR images for the diagnosis of meniscal tears. Second, we compared the correlation of tear types presumed from sagittal and axial MRI with arthroscopy and tear classification from axial MRI. Tears were classified on the sagittal plane and the axial plane separately. The diagnostic performance and tear classification were compared statistically with arthroscopy results, which is accepted as the standard of reference. Results 8 of 58 patients were removed from the study group because they had complex or degenerative tears. A total of 62 tears were detected with arthroscopy in 50 patients. On the sagittal images, sensitivity and specificity values were 90.62% and 70.37%, respectively, for medial meniscus tears and 72.73% and 77.14%, respectively, for lateral meniscus tears. The corresponding values for axial images were 97.30% and 84.00%, respectively, for medial meniscus tears and 95.65% and 80.50%, respectively, for lateral meniscus tears. There was no significant difference in tear classification between the arthroscopy results and the thin-slice axial PDW MRI results (p>0.05). Conclusion thin-slice axial PDW MRI increases the sensitivity and specificity of meniscal tear detection and especially classification, which is important for surgical procedure decisions.     

Characteristics of displaceable and nondisplaceable meniscal tears at kinematic MR imaging of the knee

PURPOSE: To prospectively determine if kinematic magnetic resonance (MR) imaging of the knee may demonstrate displacement of menisci with tears and, if so, to characterize displaceable and nondisplaceable meniscal tears. MATERIALS AND METHODS: The study was approved by the hospital's review board, and informed consent was obtained. Forty-two patients (30 men, 12 women; mean age, 36.9 years) with 43 arthroscopically documented meniscal tears visible at 1.5-T MR imaging underwent kinematic MR imaging with an open-configuration 0.5-T MR imager with their knees in supine neutral, supine with 90 degrees flexion and external or internal rotation, and upright weight-bearing positions. Analysis of meniscal movement was performed in different knee positions in the coronal MR imaging plane. Meniscal displacement--that is, meniscal movement of 3 mm or more (in the medial direction for the medial meniscus, in the lateral direction for the lateral meniscus)--was compared with the patient's pain level as assessed with a visual analog scale by using analysis of variance. RESULTS: Between the different knee positions, meniscal displacement of 3 mm or more (displaceable meniscal tears) was noted in 18 (42%) of 43 menisci with tears. Simultaneous occurrence of grade II or III ipsilateral collateral ligament lesions was present in all 18 displaceable meniscal tears, whereas a normal-appearing collateral ligament or collateral ligament lesion (grade I) was present in 22 of 25 nondisplaceable tears (P < .05). Displaced menisci most commonly had complex, radial, or longitudinal tear configurations (16 of 18, 89%). Patients with displaceable meniscal tears had significantly more pain than did patients with nondisplaceable meniscal tears (P < .001), independent of the concomitant knee abnormalities. CONCLUSION: Displaceable meniscal tears usually have longitudinal, radial, or complex configurations; such tears are associated with substantial ipsilateral collateral ligament lesions and pain.     

Fat-suppressed volume isotropic turbo spin echo acquisition (VISTA) MR imaging in evaluating radial and root tears of the meniscus: Focusing on reader-defined axial reconstruction

Objective

To assess the diagnostic value of fat-suppressed (FS) three-dimensional (3D) volume isotropic turbo spin echo acquisition (VISTA) imaging in detecting radial and root tears of the meniscus, including the reader-defined reformatted axial (RDA) plane.

Materials and methods

Twenty-three patients with arthroscopically confirmed radial or root tears of the meniscus underwent magnetic resonance imaging (MRI) with 2D and FS 3D VISTA sequences. MRIs were reviewed independently by two musculoskeletal radiologists blinded to the arthroscopic findings. Sensitivity, specificity, accuracy, and interobserver agreement were calculated for radial and root tears. Both radiologists reported confidence scale for the presence of meniscal tears in 2D axial imaging, 3D axial imaging, and RDA imaging, based on a five-point scale. Wilcoxon's signed rank test was used to compare confidence scale.

Results

The sensitivity, specificity, and accuracy of FS 3D VISTA MR imaging versus 2D MR imaging were as follows: 96%, 96%, and 96% versus 91%, 91%, and 91%, respectively in reader 1, and 96%, 96%, and 96% versus 83%, 91%, and 87%, respectively, in reader 2. Interobserver agreement for detecting meniscal tears was excellent (κ = 1) with FS 3D VISTA. The confidence scale was significantly higher for 3D axial images than 2D imaging (p = 0.03) and significantly higher in RDA images than 3D axial image in detecting radial and root tears.

Conclusions

FS 3D VISTA had a better diagnostic performance in evaluating radial and root tears of the meniscus. The reader-defined reformatted axial plane obtained from FS 3D VISTA MR imaging is useful in detecting radial and root tears of the meniscus.     

Meniscal tears with fragments displaced in notch and recesses of knee: MR imaging with arthroscopic comparison

PURPOSE: To retrospectively evaluate magnetic resonance (MR) imaging for the depiction of meniscal tears with partially detached meniscal fragments displaced in the intercondylar notch or in the meniscal recesses of the knee. MATERIALS AND METHODS: The institutional review board required neither its approval nor informed patient consent for the retrospective review of patient data; however, informed patient consent had been obtained before the MR imaging examinations were performed. The presence of meniscal tears with notch and recess fragments was determined at MR imaging and at subsequent arthroscopy in 101 consecutive knees to determine the value of MR imaging for the depiction of these lesions. Initial reports were reviewed to evaluate results of initial interpretations. MR images were retrospectively analyzed to determine the value of several MR image signs for the detection of displaced tears with notch or recess fragments. RESULTS: At arthroscopy, 37 (41%) of 91 torn menisci had partially detached fragments. Twenty-six torn menisci had notch fragments, and 14 had recess fragments; three torn menisci had one notch and one recess fragment each. At initial MR image analysis, 38 (36%) of 105 torn menisci had partially detached fragments. Twenty-eight torn menisci had notch fragments, and 13 had recess fragments; one torn meniscus had two recess fragments, and three torn menisci had one notch and one recess fragment each. At initial analysis, sensitivities and specificities were, respectively, 69% and 94% for detection of tears with notch fragments and 71% and 98% for detection of tears with recess fragments. At retrospective analysis of sagittal MR images, the presence of at least one sign indicative of meniscal tear with a notch fragment had sensitivities and specificities, respectively, of 65% and 78% for observer 1 and 77% and 73% for observer 2. The presence of at least one sign indicative of a meniscal tear with a recess fragment had sensitivities and specificities, respectively, of 64% and 77% for observer 1 and 64% and 76% for observer 2. CONCLUSION: Meniscal tears with notch and recess fragments are frequently seen at arthroscopy and can be depicted at knee MR imaging with moderate sensitivity and high specificity.     

MRI of the knee: value of short echo time fast spin-echo using high performance gradients versus conventional spin-echo imaging for the detection of meniscal tears

Objective. Fast spin-echo (FSE) sequences reduce imaging time compared with conventional spin-echo (CSE) sequences, but may result in blurring. High-performance gradients permit shorter interecho spacing and use of the second echo as the effective TE (20 ms); both improvements reduce blurring. This randomized observer study compared a short TE, second-echo FSE sequence obtained using high-performance gradients and a CSE sequence with similar TR/TE for the detection of meniscal tears in the knee. Design and patients. One hundred consecutive MR examinations of the knee using FSE and CSE sequences at 1.5 T were evaluated. The FSE sequence used an effective TE of 20 ms (centered on the second echo at 2 times minimal interecho spacing) and an echo train length of 4. FSE and CSE parameters were otherwise similar. Four independent, masked readers reviewed randomized sagittal FSE and CSE sequences. Results. Cases were assessed for the presence or absence of meniscal tears and, if present, whether tears were medial or lateral and anterior or posterior. Sequence concordance was 93.5% (1496 of 1600 meniscal segments); the intermethod kappa value was 0.78. Sequence quality was graded from 1 to 5. Average quality of CSE images was slightly but statistically significantly preferred by three of the four readers. Conclusion. There was no statistically significant difference between CSE imaging and FSE imaging centered on the second echo (20 ms) using high-performance gradients for the detection of meniscal tears in the knee. There was a small preference for the quality of CSE images. Received: 22 July 1999 Revision requested: 27 October 1999 Revision received: 7 February 2000 Accepted: 21 March 2000     

Meniscal extrusion in young athletes: associated knee joint abnormalities

OBJECTIVE: The objective of our study was to assess the rate of meniscal extrusion and its connection with common meniscal and joint abnormalities. MATERIALS AND METHODS: MR signs of meniscal extrusion were evaluated retrospectively in 24 rugby and soccer players (40 knees) who are currently free of pain in the knee, impaired mobility, and joint swelling. The control group consisted of 23 consecutive active individuals (36 knees) with no history of knee problems. The criterion for extrusion of the meniscus was defined as a distance of 3 mm or more between the peripheral border of the meniscus and the edge of the tibial plateau measured on coronal images. RESULTS: Forty-eight percent of the athletes' knees and 30% of the control subjects' knees showed evidence of meniscal extrusion. Among the athletes, a significant association between meniscal extrusion and joint effusion (11 cases), meniscal tears (seven cases), and anterior cruciate ligament (ACL) tear (four cases) was found (p < or = 0.004). In the control group, no significant association was found between meniscal extrusion and joint effusion (three cases), meniscal tears (four cases), and ACL tears (two cases) (p = 1.00). A significant association was not found between degenerative change and meniscal extrusion in either the athletes (p = 0.23) or the control subjects (p = 1.00). The most commonly associated knee abnormality was joint effusion in 73% of knees with meniscal extrusion in athletes. CONCLUSION: Meniscal extrusion is a common finding on MRI of athletes' knees. Meniscal extrusion in association with meniscal tear and joint effusion is postulated as a significant injury in athletes and its recognition as such in this group is important because it may prompt orthopedic intervention.