MR imaging of meniscal cysts: incidence, location, and clinical significance.

OBJECTIVE: The purpose of this study was to determine the incidence of medial versus lateral meniscal cysts as seen on MR imaging. MATERIALS AND METHODS: A total of 2572 knee MR imaging reports were retrospectively reviewed for the presence of meniscal tears and cysts. Two musculoskeletal radiologists reviewed all images with reported cysts. The type and location of meniscal tear and the presence and location of meniscal cysts were recorded. RESULTS: A total of 1402 meniscal tears were reported in 2572 MR examinations (922 [66%] of 1402 in the medial compartment; 480 [34%] of 1402 in the lateral compartment). Meniscal cysts were present in 109 (4%) of 2572 knees. Of the 109 cysts, 72 (66%) were in the medial compartment, and 37 (34%) were in the lateral compartment. Meniscal cysts were found in association with 72 (7.8%) of the 922 medial meniscal tears and 37 (7.7%) of the 480 lateral meniscal tears. Meniscal cysts showed direct contact with an adjacent meniscal tear in 107 (98%) of 109 cases, with the tear showing a horizontal component in 96 (90%) of 107 cases. CONCLUSION: Meniscal cysts occur almost twice as often in the medial compartment as in the lateral compartment. Medial and lateral tears occur with the same frequency. These findings, when viewed in the context of the historical literature on meniscal cysts, suggest that MR imaging detects a greater number of medial meniscal cysts than physical examination or arthroscopy, and that MR imaging can have an important impact on surgical treatment of patients.     

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.     

Meniscus root repair

Root tears are a subset of meniscal injuries that result in significant knee joint pathology. Occurring on either the medial or lateral side, root tears are defined as radial tears or avulsions of the posterior horn attachment to bone. After a root tear, there is a significant increase in tibio-femoral contact pressure concomitant with altered knee joint kinematics. Previous cadaver studies from our institution have shown that root repair of the medial meniscus is successful in restoring joint biomechanics to within normal limits. Indications for operative management of meniscal root tears include (1) a symptomatic medial meniscus root tear with minimal arthritis and having failed non-operative treatment, and (2) a lateral root tear in associated with an ACL tear. In this review, we describe diagnosis, imaging, patient selection, and arthroscopic surgical technique of medial and lateral meniscus root injuries. In addition we highlight the pearls of repair technique, associated complications, post-operative rehabilitation regimen, and expected outcomes.     

Magnetic resonance diagnosis of meniscal tears in patients with acute anterior cruciate ligament tears

OBJECTIVE: To evaluate the accuracy of magnetic resonance imaging in the diagnosis of meniscal tear in patients with acute anterior cruciate ligament tears. METHODS: Magnetic resonance images obtained from 41 patients imaged within 6 weeks of injury who had acute anterior cruciate ligament tears identified at arthroscopy were retrospectively reviewed for meniscal tear. RESULTS: With MR imaging the sensitivity, specificity and accuracy for diagnosing meniscal tears in the presence of acute anterior cruciate ligament tears were 71%, 93%, and 88%; for the lateral meniscal tears were 57%, 100% and 85%; and for the medial meniscal tears were 100%, 88%, 90%. All false negative cases (n = 6) involved the posterior horn of the lateral meniscus. CONCLUSION: In the presence of acute anterior cruciate ligament tears, MRI imaging has relatively low sensitivity for detecting meniscal tears due to missed tears in the lateral meniscus.     

Analysis of meniscal and chondral lesions accompanying anterior cruciate ligament tears: relationship with age,time from injury,and level of sport

The purposes of this multi-center study were: (a) to document the location and type of meniscal and chondral lesions that accompany anterior cruciate ligament (ACL) tears, and (b) to test for possible relationships between these lesions and patient age, time from initial injury (TFI), and sports level (i.e., recreation, amateur, professional, and national). The cases of 764 patients with ACL tears who underwent arthroscopy for the first time were retrospectively analyzed. The group included 684 males and 80 females of mean age 27 years (range 14–59 years). The mean TFI was 19.8 months (range 0.2–360 months). Eighty-seven percent of the group engaged in regular sporting activity. Thirty-seven percent had medial meniscal tears, 16% had lateral meniscal tears, and 20% had tears of both menisci. The most common tear types were longitudinal tears in the posterior and middle horns of both menisci. Tears of the lateral meniscus were more centrally located than those of the medial meniscus. Incomplete tears and radial tears were significantly more common in the lateral meniscus. Nineteen percent of the knees had one or more chondral lesions. Sixty percent of the chondral lesions were located in the medial tibio-femoral compartment. Patient age was statistically associated with presence of a medial meniscal tear, presence of a grade 3 or 4 chondral lesion, and presence of a complex tear of the medial meniscus. Sports level was not statistically related to any of the parameters studied. The odds of having a medial meniscal tear at 2 to 5 years TFI were 2.2 times higher than the odds in the first year post-injury, and the odds at >5 years were 5.9 times higher than at 0 to 12 months TFI. The frequency of lateral meniscal tear remained fairly constant at 2 years TFI. The odds of having a grade 3 or 4 chondral lesion were 2.7 times greater at 2 to 5 years TFI than they were at 1 year post-injury, and these odds increased to 4.7 when patients at >5 years TFI were compared to those in the 2 to 5 years category. Multivariate analysis demonstrated that TFI and age were equally important predictors of lateral meniscal tears and of grade 3 or 4 chondral lesions; however, TFI was the better predictor of medial meniscal tear.This multi-center study was performed by the Turkish Society of Sports Traumatology, Arthroscopy and Knee Surgery. It was presented as a poster at the ESSKA 2000 Congress in London, UK     

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.     

Patterns of meniscal injury associated with acute anterior cruciate ligament injury in skiers.

To determine if the incidence and patterns of meniscal injury associated with acute anterior cruciate ligament injury in skiers are different from those seen in individuals injured in nonskiing athletic activities, we reviewed the records of 150 patients with acute anterior cruciate ligament injuries. All patients had undergone arthroscopic evaluation within 21 days from the time of injury. There were 75 individuals who were injured while skiing and 75 individuals who sustained an injury in some other high-load athletic activity. Associated meniscal injury was documented at the time of arthroscopy and characterized by location, region, zone, depth, shape, size, and stability. Thirty-one of 75 skiers had an associated meniscal injury as compared to 47 of 75 of the nonskiers. This suggested a strong trend of decreased incidence of meniscal injury in the skier group, but the nonskiers had a higher incidence of major meniscal tears that required repair or partial meniscectomy. The location of the meniscal tear was also significantly different. The incidence of isolated lateral meniscal injury in skiers was higher than in nonskiers. There was a strong trend of increased incidence of medial meniscal involvement in the nonskiers than in the skiers. While there was no difference in the zone or region of tear between the two groups, the skier group was more likely to have a longitudinal tear of the posterior horn of the lateral meniscus. In both groups, lateral meniscal tears were more likely to require conservative treatment or partial meniscectomy while medial meniscal tears were more likely to be repaired than excised.     

Meniscal tears on knee arthrography: Patterns of arthrographic abnormalities

The presence or absence of a meniscal tear was established in 340 out of 475 consecutive patients who had double contrast knee arthrograms. The accuracy in these 340 cases was 95% for both the medial and lateral menisci although the specificity for lateral tears was only 0.64. Analysis of the pattern of arthrographic abnormalities revealed that both medial and lateral tears usually involved the posterior horn of the meniscus. Posterior horn abnormalities rarely caused a false positive diagnosis of a meniscal tear. In contrast, isolated blunting of the anterior horn of either the lateral or medial meniscus was an unreliable sign of a tear and accounted for many of the false positive diagnoses. It is concluded that careful attention to the posterior horn of each meniscus is essential for accurate arthrographic diagnosis of a meniscal tear.     

Relationship between bone bruise volume and the presence of meniscal tears in acute anterior cruciate ligament rupture

Purpose

To determine whether there is a relationship between the size of the bone bruise volume after an acute anterior cruciate ligament (ACL) rupture and the presence of meniscal tears in the medial and lateral compartment.

Methods

Following Institutional Review Board approval, 50 patients with an acute ACL rupture and MRI imaging within 30 days of injury were identified. Two musculoskeletal radiologists evaluated the lateral and medial menisci and graded them as one of the following: no meniscal tear, tear of one meniscus (medial or lateral) or tear of both menisci (medial and lateral). Sagittal T2 fat-suppressed images were used to calculate bone bruise volume. The relationship between bone bruise volume and the presence of a meniscus tear was calculated.

Results

Forty-three (86 %) patients had a bone bruise, 16 (32 %) patients had no tear, 7 (14 %) patients had lateral meniscus tear, 13 (26 %) patients had medial tear and 14 (28 %) patients had medial and lateral tears. There was a statistically significant difference in femoral bone bruise volume when comparing no meniscal tear to medial and lateral tears as well as when comparing medial or lateral tears to medial and lateral tears.

Conclusion

There is a statistically significant relationship between femoral bone bruise volume and the presence of meniscal tears in ACL injury, especially in the setting of medial and lateral pathology.

Level of evidence

Retrospective cohort study, Level III.     

MR IMAGING OF DISPLACED MENISCAL TEARS OF THE KNEE: Importance of a "disproportional posterior horn sign"

Purpose: Meniscal tears associated with displaced fragments are clinically significant. We propose the "disproportional posterior horn sign" as a supportive criterion to identify a posterocentrally displaced meniscal fragment on MR imaging studies. If the meniscal posterior horn in the central portion appears larger than that in the peripheral section, it is considered positive for "disproportional posterior horn sign".Material and Methods: MR images obtained in 42 patients with 43 lesions, confirmed to have displaced meniscal tears, were included in this study. The MR images were retrospectively evaluated for the presence of the "disproportional posterior horn sign", as well as the other known signs.Results: The "disproportional posterior horn sign" was seen in 9 (20.9%) of 43 lesions, including 1 lateral discoid meniscal tear, 5 lateral meniscal tears and 3 medial meniscal tears. Five of them also had other signs of a displaced meniscal fragment. However, the remaining 4 cases only exhibited the "disproportional posterior horn sign". For the other MR signs, the "absent bow tie sign" was detected in 40 (93%) of 43 lesions, the "flipped meniscus sign" in 27 (62.8%) of 43 lesions, the "double posterior cruciate ligament sign" in 17 (39.5%) of 43 lesions and the "notch fragment sign" in 22 (51.2%) of 43 lesions.Conclusion: The "disproportional posterior horn sign" is helpful in demonstrating a posterocentrally displaced meniscal fragment, especially when other characteristic signs are unremarkable or absent.     

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.     

Abnormal superior popliteomeniscal fascicle and posterior pericapsular edema: indirect MR imaging signs of a lateral meniscal tear

OBJECTIVE. Because MR diagnosis of lateral meniscal tears can be difficult, indirect signs may be useful when a tear is suspected. We studied whether an abnormality of the superior popliteomeniscal fascicle or pericapsular edema was associated with lateral meniscal tears and thus may be an indirect MR imaging sign of a lateral meniscal tear. MATERIALS AND METHODS. We identified 59 consecutive patients who underwent both knee MR imaging examinations and knee arthroscopy. Thirty patients had lateral meniscal tears, and 29 had intact lateral menisci. We reviewed paired sagittal proton density- and T2-weighted MR images from these 59 patients for abnormal superior popliteomeniscal fascicles and edema surrounding the posterolateral capsule. RESULTS. The superior popliteomeniscal fascicles were abnormal in nine of the 30 patients with torn lateral menisci but were normal in all 29 patients with intact menisci (p = 0.001). Abnormal fascicles were apparent only when the lateral meniscal tear involved the posterior horn. Posterior pericapsular edema was seen in 10 patients with a torn posterior horn and in one patient with an anterior horn tear of the lateral meniscus, but in only two patients with intact menisci (p = 0.006). CONCLUSION. The presence of superior popliteomeniscal fascicle abnormalities and of posterior pericapsular edema is significantly associated with a tear of the lateral meniscus, most commonly in the posterior horn. Noting the presence of these findings may help improve the accuracy of MR diagnosis of lateral meniscal tears.     

Meniscal bucket handle tears: a retrospective study of arthroscopy and the relation to MRI

In this study, we aim to evaluate the arthroscopic findings of meniscal bucket handle tears and to correlate them with the proposed MR imaging signs of meniscal bucket handle tears suggested in the literature. Thirty-six patients who had a diagnosis of bucket handle tear in arthroscopy, in either medial or lateral meniscus, were included in our study (32 males and 4 females). Meniscal tears were evaluated in arthroscopy according to Dandys classification. The MRIs were retrospectively analyzed regarding the following findings: absence of bow tie sign, presence of double posterior cruciate ligament (PCL) sign, double anterior horn sign, flipped meniscus sign, disproportional posterior horn sign, and fragment within the intercondylar region. Locked types I and II fragment of medial meniscus and half-length, whole-width and whole length–half-width fragment of lateral meniscus in arthroscopy were basically correlated with fragment within the intercondylar notch and absent bow tie signs in MRI. We did not find the double PCL sign in any of the patients with a lateral meniscal bucket handle tear. The most common signs in MR images of meniscal bucket handle tears were the fragment in the notch sign and the absent bow tie sign. They were observed with equal frequency of 88.8%. The presence of double PCL sign, double anterior horn sign, flipped meniscus sign, disproportional posterior horn sign were less common (41.66, 33, 25, and 27.7%, respectively). We conclude that the presence of at least two of the six MRI signs should be regarded as highly suggestive for bucket handle tears of menisci.     

Meniscal tear characteristics in young athletes with a stable knee: arthroscopic evaluation

BACKGROUND: There has been great interest in the literature regarding meniscal tears in unstable knees, but there is not as much information available on stable knees. PURPOSE: To report the characteristics of isolated meniscal tears (type and location) in athletes with intact cruciate ligaments. STUDY DESIGN: Case series; Level of evidence, 4. METHODS: Arthroscopic surgery was performed on 314 (83.1%) knees in the acute phase ( < 6 weeks) of injury and on 64 (16.9%) knees more than 6 weeks after injury for a total of 364 athletes (378 knees). Cooper's classification was used to classify the meniscal tears according to the type and location. RESULTS: Overall, 262 of 378 tears (69.3%) were located in the medial meniscus and 116 (30.7%) in the lateral meniscus. Vertical tears (77.5%) were significantly more frequent than were horizontal tears (22.5%; chi(2) test, P < .001). A total of 23.2% of tears involved the peripheral zones (zone 0 or 1), and tears that extended into the posterior horn accounted for 75.7%. Regarding the tear shape between male and female athletes, on both sides there were no statistically significant differences in the percentage of horizontal, bucket-handle, longitudinal, or radial tears. CONCLUSION: The characteristics of isolated meniscal tears differ with regard to the sport, sex, and tear location and type from those seen in unstable knees. This knowledge is useful in knee injury management.     

半月板大桶柄样撕裂的关节镜下联合修补技术

目的:介绍关节镜下自内向外缝合技术联合全内缝合技术修补半月板的手术方式(联合修补技术),探讨修补半月板大桶柄样撕裂的安全、可靠方法。方法:2002年5月~2006年1月,采用关节镜下联合修补技术修补93例患者的96个半月板大桶柄样撕裂,均累及半月板后角至前角与体部交界处(前体部)区域。手术适应症:红-红区及红-白区损伤、具备可复位性、半月板组织无复合撕裂及明显变性、前十字韧带(ACL)完整或同时重建。手术技术:撕裂的后角与体部交界处(后体部)至中、前1/3区域采用标准的自内向外缝合技术:在半月板上、下表面交错进行垂直褥式缝合,膝后内侧或后外侧作辅助安全切口保护血管神经,伸膝位将缝线在关节囊浅层打结固定;撕裂的后部区域采用全关节内缝合技术:经两个后内侧或后外侧入路在关节内完成垂直褥式缝合、打结及剪线。单纯的红-白区撕裂修补后局部植入血凝块促进愈合,合并前十字韧带损伤者同时行韧带重建手术。术后对93例患者中的49例共51个半月板进行了平均20·1个月(9·2个月~54·2个月)的随访。随访时均进行了临床评估,包括交锁、积液、关节间隙压痛、McMurray试验。随访结果显示:49例患者中,无症状者46例(93·9%),关节间隙压痛者2例(4·1%),交锁复发1例(2%)。51个半月板中的44个(86·3%)经MRI复查,结果为:30个(68·2%)完全愈合,13个(29·5%)部分愈合,1个(2·3%)不愈合。38例患者共40个半月板(78·4%)经过二次手术探查,完全愈合者36个(90%),部分愈合者2个(5%),不愈合行半月板切除者2个(5%)。膝关节活动度检查显示3例伸膝受限>10°。结论:对于发生在红-红区或红-白区的大型半月板撕裂,采用自内向外与全关节内两种缝合技术可以保证撕裂的全长区域获得有效、稳定的修补,并且与ACL重建同期进行,可以获得很好的主、客观临床疗效。联合修补技术是安全、可靠的半月板大桶柄样撕裂的修补方法。     

The quadruple cruciate sign of simultaneous bicompartmental medial and lateral bucket-handle meniscal tears

We report the second known case of bicompartmental bucket-handle tears of the medial and lateral menisci and the first documented case of the bucket-handle tears occurring simultaneously following trauma, which occurred after a motorcycle accident. Both bucket-handle fragments were displaced into the intercondylar notch. An anterior cruciate ligament tear was also present. Coronal images demonstrated four structures in the intercondylar notch: the anterior and posterior cruciate ligaments and the medial and lateral bucket-handle meniscal fragments.     

Meniscal tears: role of axial MRI alone and in combination with other imaging planes

OBJECTIVE: The purpose of this study was to determine the reliability of standard axial MR images alone in the diagnosis of meniscal tears of the knee and in combination with other imaging planes. MATERIALS AND METHODS: Sixty-two patients (55 men, seven women; age range, 23-68 years) with a prior MRI examination who underwent arthroscopic surgery of the knee during a 1-year period were included in the study group. Images were independently reviewed for identification of meniscal tears by two musculoskeletal radiologists blinded to arthroscopic findings. Sequences for meniscal evaluation included axial fat-saturated fast spin-echo proton density, coronal fat-saturated fast spin-echo proton density, and sagittal fast spin-echo proton density with 4- to 5-mm slice thicknesses. Imaging groups for evaluation were axial, coronal, sagittal, axial and sagittal, axial and coronal, and coronal and sagittal. Observers reported a confidence level for the presence or absence of meniscal tear in all imaging groups based on a 5-point scale. Statistical analysis considered medial and lateral menisci separately. RESULTS: Forty patients had medial meniscal tears, and 16 had lateral meniscal tears at arthroscopy. For medial and lateral meniscal tears, the accuracy (79% and 71%, respectively) of imaging in the axial plane was comparable to other imaging groups but the mean confidence levels (2.82 and 3.00, respectively) were low. In one patient, the axial plane alone correctly showed that no tear was present. No statistically significant difference was observed between imaging plane groups of both menisci in the diagnosis of meniscal tears (p > 0.05). The axial plane increased the accuracy of sagittal and coronal planes of lateral meniscus when combined. CONCLUSION: In standard knee MRI examinations, the axial imaging plane may be valuable for the detection and characterization of meniscal tears.     

Medial meniscus extrusion on knee MRI: is extent associated with severity of degeneration or type of tear?

OBJECTIVE: The meniscus is considered "extruded" when it extends beyond the tibial margin. We hypothesize that severe degeneration, large radial tears, complex tears, and tears involving the meniscal root would alter meniscal stability and cause more substantial extrusion. MATERIALS AND METHODS: The knee MRI database at Thomas Jefferson University Hospital was searched for reports describing meniscal extrusion; MR images were reviewed retrospectively. On mid coronal images, extrusion of the medial meniscus was quantified in millimeters. A separate, independent review of the meniscus evaluated degeneration severity and tear (type and extent). Radial tears were divided into those involving more (large) or less (small) than 50% of the meniscal width. Tears that involved the "root" at the tibial spine were recorded. Chi-square analysis compared these findings with extrusion extent, divided into minor ( 3 mm) extrusion. RESULTS: One hundred five knees were reviewed (12 men and 93 women; age range, 34-83 years; mean age, 56 years). Distribution of medial meniscus extrusion was 2 mm (n = 17), 3 mm (n = 17), 4 mm (n = 27), 5 mm (n = 14), 6 mm (n = 16), and 7-10 mm (n = 14). Mild, moderate, or marked degeneration was seen in 47%, 26%, and 27% with minor extrusion, respectively, and in 17%, 41%, and 42% with major extrusion, respectively (p = 0.003). Tears were seen in 59% (20/34) with minor extrusion versus 89% (63/71) with major extrusion (p = 0.001). Tears involved one third, two thirds, or all of the meniscus in 75%, 25%, or 0%, respectively, with minor extrusion and 46%, 40%, or 14% with major extrusion, respectively (p = 0.014). Longitudinal (nonradial) and horizontal tears were not associated with extent of extrusion (p = 1.0). Oblique tears were significantly associated with minor extrusion (minor, 26% [9/34]; major, 4% [3/71]; p = 0.003). Radial tears were seen in 9% (3/34) with minor extrusion versus 21% (15/71) with major extrusion (p = 0.20). All three radial tears with minor extrusion were small; conversely, 87% (13/15) of radial tears with major extrusion were large (p = 0.019). Complex tears were seen in 18% (6/34) with minor extrusion versus 59% (42/71) with major extrusion (p < 0.001). Tears involving the meniscal root were seen in 3% (1/34) with minor extrusion and 42% (30/71) with major extrusion (p < 0.001). CONCLUSION: Substantial medial meniscus extrusion (> 3 mm) is associated with severe meniscal degeneration, extensive tear, complex tear, large radial tear, and tear involving the meniscal root.     

MR of the knee: the significance of high signal in the meniscus that does not clearly extend to the surface

On MR images of the knee it is sometimes impossible to determine with confidence if a focus of high signal in the meniscus is confined to the substance of the meniscus or if it extends to involve the surface. This is a critical differentiation because the latter represents meniscal tears that can be found and treated at arthroscopy, whereas the former represents degeneration, tears, or perhaps normal variants that cannot be detected or treated arthroscopically. We make an equivocal diagnosis of a tear when it is difficult to decide if signal in a meniscus involves the meniscal surface. We studied MR scans of the knee in 142 consecutive patients for the presence of such equivocal tears. Their prevalence was 14% (20/142); 17 were in the posterior horn of the lateral meniscus and three were in the posterior horn of the medial meniscus. In 13 cases with arthroscopy/arthrotomy correlation, no tears were found. In one of the 20 patients in whom the meniscus was removed during arthroplasty, histologic examination of the meniscus showed separation of collagen bundles, which was caused by meniscal degeneration confined to the substance of the meniscus. These results suggest that a meniscal tear is unlikely when MR scans show a focus of high signal in a meniscus that does not unequivocally extend to involve the surface of the meniscus.     

The flipped meniscus sign

Meniscal fragments may be difficult to detect on magnetic resonance (MR) imaging and yet are clinically significant. This paper describes and illustrates the MR appearance of an easily overlooked meniscal fragment. Ten knees, each appearing to show an abnormally large anterior meniscal horn (8 mm or more in height) were prospectively identified on MR images. In each case demonstrable large tears of the ipsilateral posterior horns were present (same meniscus as had large anterior horns). The lateral meniscus was involved in nine cases and the medial in one. Two of the ten patients imaged had surgically proven bucket-handle meniscal tears as well as meniscal fragments overlying the ipsilateral anterior horn. In one case previous MR imaging at our institution had demonstrated the affected anterior horn to be of normal caliber. The striking MR appearance of an abnormally enlarged anterior meniscal horn in association with a tear of the ipsilateral posterior horn suggests the presence of a meniscal fragment or of a posteriorly detached bucket-handle tear of the posterior horn of the meniscus.Presented at the Fifteenth Annual Skeletal Symposium of the Hospital of the University of Pennsylvania at Sun Valley, Idaho, USA, on 3 March 1992