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Large Population Study Of Meniscal Extrusion By MRI

Ozgur TOSUN, Aliye Kapukıran Tosun, Mustafa Karaoğlanoğlu

Ankara Ataturk Education and Research Hospital,

Address for Correspondence:
Mustafa Kemal Mah. Barıs Sitesi. 2091. Sok.
No:11  Bilkent 06800/ANKARA.


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Objective:The aim of this study was to asses the relationship between meniscal extrusion and  the joint space loss with meniscal tears in patients under 60 years old

Materials and methods:The study group consisted of 108 of 623 patients ( 73 female, 35 male) (mean age 43.14 ± 7.01) with meniscal extrusion and  60 patients (29 female, 31 male) (mean age 47.04 ±7.8) without meniscal extrusion as control group  under 60 years old.

Results:A statistically significiant association was found  between the medial meniscal extrusion and the posterior horn of medial  meniscal tear  in the study group. Statistically significant medial  joint space  narrowing  was found in both the study and the control group. Statistically significiant lateral joint space widening was detected in the study group when compared to control group. Also lateral joint space widening was found to have been directly affected from the degree of meniscal extrusion.

Conclusion: Medial meniscal extrusion greater than 3 mm is significantly associated with radial and oblique tears which results in disruption of meniscal stability. Also as in occur in menisectomies,  medial meniscal extrusion may results in tendency to varus alignment that results in an increased stress in the medial compartment which is known to be a major factor in the development of medial gonarthrosis.

J.Orthopaedics 2010;7(4)e2


MRI; Meniscal Extrusion;  Joint space


The meniscus is essential for distributing  axial forces on the knee through its hoop mechanism.  The absence of the meniscus increases the peak pressure in the knee joint. Resection of as little as 15–34% of the meniscus increases contact pressures by more than 350%(1,2).

Medial meniscal extrusion (MME) has been defined as pathologic displacement (>3 mm) of the peripheral edge of the medial meniscus beyond the central margin of the medial tibial plateau(3).  MME has been demonstrated to occur with tears of the medial meniscal root, radial tears, complex tears, meniscal degeneration and degenerative joint disease(4). In the setting of MME, the meniscus is no longer able to redistribute and transmit load. Increased stresses are transferred to the femorotibial articular cartilage, leading to degenerative articular cartilage wear, flattening of the femoral condyles and osteophyte formation. The aim of this study was to asses the relationship between meniscal extrusion and  the joint space width  and also correlate with meniscal tears in  a large patient population younger than 60 years old.   

Materials and Methods:

An experienced musculoskeletal radiologists retrospectively reviewed the 1.5-T MR scans of 9568 knees in 9148 consecutive patients between April 2008 and June 2009.  All study procedures were approved by the local ethical committee. Of the 623 patients with medial meniscal extrusion, 108 patients ( 73 females and 35 males; mean age 43.14 ± 7.01 years) were included in the study group. Control group was consisted of  60 patients (29 females and 31 males; mean age 47.04 ±7.8 years) without meniscal extrusion. Exclusion criterias were the presence of severe osteoarthritis, complex meniscal tears, chondrocalcinosis or signs of trauma and acute or chronic infections. All MR imaging were performed using one of the two 1.5 T MR scanner (Integra and Achieva, Philips Medical Systems, Netherland) equipped with dedicated knee coil. All studies were performed using coronal oblique  fat supressed T2 (TR range / TE range , 4500-5000/60-92),   and proton dansity (PD) weighted image (TR range / TE range , 3000-4500/25-35), sagittal proton dansity (TR range / TE range, 1200-1500/6-12) and  T2 weighted (TR range / TE range , 1200-1500/80-95) dual spin echo, axial fat supressed PD images (TR range / TE range , 4500-5000/25-35) with a 4 mm section thickness and 0,4 mm gap. The total acquisition time was between 15 and 20  minutes. A field of view of 16-18 cm with a matrix size of 256x256 was used for all images.  Three measurements were done and the mean of these three measurements was recorded for each patient.

In the coronal plane, extrusion measurements were made using the technique described by Breitenseher et al (5). The criterion for meniscal extrusion was a distance of 3 mm or more between the peripheral border of the meniscus and the central margin of the tibial plateau as measured in the coronal plane (Figure 1). A distance of less than 3 mm was not considered as meniscal extrusion. Also the medial and lateral tibiofemoral joint spaces of the knees of each  patient were measured separately at the level of tibial medial eminencia (Figure 1). Cartilage was scored as being either normal or abnormal (partial or full thickness  defects as abnormal) on both the femoral and tibial sides of the joint by the review of T2 and  proton density images.

Figure 1:  Measurement of meniscal extrusion, lateral and medial joint space in 45 years old woman. Coronal Turbo spin-echo (  TSE) T2 weighted image (TR/TE, 4620/72) of right knee obtained through mid portion medial femoral condyle.  Vertical line (yelllow line) is drawn intersecting margin of medial tibial plateau at the site of transition from horizontal to vertical. Extrusion is measured from this line to outer edge of meniscus. At the same slice, Medial and lateral joint spaces are measured separately   approximately 1 cm away from outer edge of tibia. Horizontal tear at posterior horn of medial meniscus and ostechondral lesion in the lateral plateau of tibia (arrow)  are seen.

An internal meniscal signal extending  to the articular surface was considered as meniscal tear. Meniscal tears  were classified into one of five configurations using previously described criteria (6) (Figure 2, 3). A tear parallel to the tibial plateau separating the meniscus into upper and lower parts was considered as horizontal tear; which  is vertical (perpendicular to the tibial plateau) and propagating parallel to the main (circumferential) axis of the meniscus as longitudinal tear; which is vertical and propagating perpendicular to the main axis as radial tear and which are intermediate tears between horizontal and  vertical as oblique,flap or parrot-beak tears.


Figure 2:  53-year-old man with radial root tear of posterior horn of medial meniscus on coronal PD  image with fat saturation (TR/TE 3948/30) and (b) sagittal  PD image ( TR/TE 1692/6)


Figure 3:  24 year old man with oblique tear of posterior horn of medial meniscus on coronal PD  image with fat saturation (3948/30) and (b) sagittal  PD ( TR/TE 1692/6) image.

Medial and lateral joint space width was seperately  compared with meniscal extrusion level, meniscal tears and cartilage defects. Results of of study group was also compared with the results of control group.

Statistical analysis was performed by using SPSS for Windows release 11.5 ( Chicago IL, USA ) software. Chi-square test is used for categorical data and Student’s t test is used for comparing independent groups. A paired t test was used  to compare  the joint space width between medial and lateral sides in each group. Statistical significance level was set  as P value < 0.05.

Results :

In 92% of patients of the study group, meniscal tears were detected. 55 (50,9%) radial (mostly root tear), 29 (26,9%) oblique, 6 (6.5%) bucket handle, 2 (1.9%) longitidunal and 2 (1.9%) horizontal tear were detected in the study group (Table 1). Mean extrusion value  was  4.1417 mm (± 0,778) in study group (Table 2).  A statistically significiant association was found  between the medial meniscal extrusion and the radial and oblique tears at posterior horn of medial  meniscus  in the study group (in 88% of the knees)  (P<0,001). No association was found between the anterior horn  and  the body tear.




Meniscal tear


Oblique or Flap



Bucket Handle




(% 88)


 (% 50.9)


(% 26.9)


 (% 1.9)


(% 1.9)


 (% 6.5)




(% 21.6)


(% 5)


( % 8.3)


(% 6.6)




Table 1: Number of Patients  and Frequency of  Meniscal Tear Type in Both Groups

Mean medial and lateral joint space width were 3.27mm (±0,93) and 4.26 mm (±1,12) respectively  in the study group, and 3,61mm (±0,85) and 3,86 mm ( ±0.77) respectively in the control group. Statistically significant medial  joint space  narrowing and  lateral joint space widening  was found  in the study group in comparision to that of control group. . Statistically significant narrowing was detected in medial joint space in comparison to lateral joint space both in the study (p<0,001) and in the control group (p <0,01). Correlation coefficients were as 0,692 in the study and 0,652 in the control group. No correlation was found between medial joint space narrowing and MME degree. Statistically significiant lateral joint space widening was detected in the study group when compared to the control group (p < 0.05). Lateral joint space widening was also found to be directly affected from the degree of meniscal extrusion (Table 2). (r=0,206) (p<0,05).

Cartilage defects  was detected in 28 of 108 patients of the study group. There was no statistically significant relation between the joint space narrowing and the cartilage defects or thinning in the femur medial condyle.


Extrusion Degree


Medial Joint Space (mm)

Lateral Joint Space










Table 2:   Mean Value of extrusion degree , Medial and Lateral Joint Space

Discussion :

In this study we found an asymetric joint space narrowing (JSN), as narrowing of the medial compartment and widening of the lateral compartment, due to the meniscal extrusion. A  significiant association was found  between the medial meniscal extrusion and the posterior horn of medial  meniscal tear  in the study group. Joint space narrowing  was not seemed to be affected by the cartilage defects.

As found in our study, Kesmezacar et al. reported that narrowing of medial compartment and widening of lateral compartment of knees in which medial menisectomy  was done.  Also they  stated that significiant increase in the varus of knees  was observed after partial menisectomy(7). Also significant narrowing of medial joint space  was observed  in the study of rabbit model of total menisectomy which was conducted  by Mesner et al. They reported that removal of the medial meniscus led to a permanent narrowing without resulting in any cartilage changes(8). The degree of varus (bowing) present in a knee joint is a combination of the geometric alignment of the femur and tibial (congenital), and the degree of narrowing in the medial compartment (due to loss of cartilage and/or bone), and/or widening of the other joint space compartments (due to ligament laxity or injury to other soft tissue structure.  Any medial displacement occurring in the gravity center of the body results in an increased stress in the medial compartment, which is known to be a major factor of medial gonarthrosis (9,10). Sharma et all reported that varus  alignment increases the risk of medial osteoarthritis progression, that valgus alignment  increases the risk of lateral osteorthritis progression. Also they stated that severity of varus was correlated with greater medial joint space loss, severity of valgus was correlated  with lateral joint space loss in a 18 month period (11). We didn’t measure varus and valgus angle which was one of limitation of our study but theoretically, the decrease in the medial and the increase in the  lateral joint space which was detected in our study will probably increase the varus alignment which can increase   osteoarthritis progression at the medial joint space.

Widening of lateral compartment is also seen in knees with discoid lateral meniscus. Discoid lateral meniscus was not detected in our patientss

Asymetric joint space narrowing (JSN) was detected in our study. When JSN is detected, it is important to differentiate inflammatory from degenerative causes. Asymetric JSN is seen in osteoarthritis, especially involving medial femorotibial compartment. In the previous studies, joint space narrowing of knee has been linked to loss of articular cartilage. However meniscal damage also contributes to joint space narrowing (12,13,14). Previous studies have reported that changes in the articular cartilage in the medial tibiofemoral compartment were less marked, even where there was a linear correlation between mean cartilage volume and radiographic JSN. Radiographic JSN is not a reliable tool for assessing cartilage status in patients with early osteoarthritis. Joint space narrowing  was not affected by the cartilage defects in our study as reported in some previous studies. Adams et al,  who conducted a study in  patients older than 60 years with osteorthritic knees, reported  that early narrowing of the joint space observed on conventional radiographs (Kellgren 1-3) appears to be a function of meniscal extrusion rather than loss of articular cartilage, but joint space narrowing in advanced disease (Kellgren 4) was appears to be  related primarily to loss or changes in articular cartilage (15).

Also significant association was found between the medial meniscal extrusion and the tear of posterior horn of medial meniscus, especially of  radial  and  oblique. In a study of Costa et al, which was conducted in patients aged between 34- 83 years (mean age 56 years), it was reported that major medial meniscal extrusion (>3mm) was associated with  a tear   of medial meniscus especially of radial tear(4).  Kenny  published a study relating radial displacement of medial meniscus and “Fairbank’s” signs. These concern three radiographic abnormalities in the knee after meniscectomy, as a result of loss of meniscal function: an anteroposterior osseous ridge projecting downward from the femoral condyle, generalized flattening of the marginal half of the femoral articular surface, and narrowing of the joint space. Kenny concluded that these abnormalities could develop in knees with radial displacement (i.e., extrusion) of the medial meniscus and loss of meniscal function. Also, unstable meniscal tears have been associated with development of osteoarthritis ( 16, 17). As detected in our study, Mage et al and Lerer et al found that radial or root tear was strongly associated with meniscal extrusion (3,18). However no association was found between oblique tear and meniscal extrusion in these studies. Only in a study of Costa it was found that oblique tears was associated with minor extrusion that was less than 3 mm. Contrary to the previously reported findings , we found a statistically significant association with oblique tear and MME. Oblique or flap tears which represent a composite of a longitudinal and radial tear, start on the free edge of the meniscus and will extend to the meniscal fibrocartilage. They are the most common type of meniscal tear (19,20), Flap tear frequently develops after  minimal meniscal trauma superimposed on a degenerative process resulting from chronic shear forces. Usually, they have either a predominantly horizontal or vertical component with  some degree of distruption of meniscal structure, which can result in meniscal subluxation.

There are some limitations in our study.  Since our study was a retrospective study, we had no reference or gold standard because MRI was used as the surrogate documentation of the abnormality. The absence of arthroscopic confirmation of our findings could also represent a limitation. A selection bias exists because these cases were selected on the basis of the presence of some degree of extrusion.

To conclude, medial meniscal extrusion is significantly associated not only with radial tears and also with oblique or flap tears which results in disruption of meniscal stability. Also as in occur in menisectomies,  decrease in medial and increase in lateral comparment of knee joint was found in our study.  These changes may results in tendency to varus alignment that results in an increased stress in the medial compartment which is known to be a major factor in the development of medial gonarthrosis. Also widening of lateral comparment was directly affected by extrusion degree but narrowing of medial comparment wasn’t affected.


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This is a peer reviewed paper 

Please cite as: Ozgur TOSUN: Large Population Study Of Meniscal Extrusion By MRI

J.Orthopaedics 2010;7(4)e2





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