 Hello everyone. I'm Dr. Chaitani Pare, Consultant, Musculoskeletal Interventional Radiologist, practicing at Palestine of Diagnostic Centres and Utec Diagnostic Centres in Mumbai. Today, we are going to begin with a complete session on the meniscal MRI imaging, which is actually divided into three sessions or three videos. Today's session is particularly on the meniscal anatomy, followed by normal radiance and what normal structures can mimic a tear. Now, this is important because when we label a meniscal signal as a tear, there are likely chances that the patient will land up with an arthroscopic surgery. So, we need to be really sure before labeling something as a tear. And for this, it is important to know the normal structures which can mimic a tear. So, that is what we'll be discussing in today's session. The next session is on the meniscal tears, what are the types of meniscal tears and what are the important points that you need to mention in a report so that the orthopod can take a further decision on the line of management. And the third session is a difficult one, which is on the post-operative meniscus. Now, this is a topic with multiple gray zones. So, we'll be predominantly discussing on when to call a meniscal signal as a post-operative signal and when to label it as a tear, which is actually very important from the management point of view. So, in order to understand the meniscus in detail, please stay tuned for today's session as well as the videos which are going to come in very soon. Thank you so much. Today, we'll be discussing about meniscal variants that is when not to call a meniscal tear. In today's session, we won't be concentrating on the sequences and as far as the anatomy goes, we'll only be discussing about the meniscal anatomy. For all those who are interested in knowing the sequences and MRI knee joint anatomy in detail, you can go back to the MRI knee joint anatomy video, which is there on the Indian Radiologist YouTube channel. After that, we'll be discussing about normal structures that look like a tear, that is, tear mimics and finally, we'll look at the normal meniscal variants. As far as the meniscal anatomy goes, all of us know that there are two meniscus in the knee joint, the medial and the lateral. Both the meniscus have got five parts. So, you have an anterior root and a posterior root, then there is an anterior horn and a posterior horn and finally, there is a longer structure, which is nothing but the central part of the meniscus, which is the body of the meniscus. Now, if you imagine or if you just think about it, whenever you look at the axial cuts of an MRI knee and if luckily you have a section that's going through the meniscus, the meniscus will have an appearance like this. So, this is exactly when you're looking at the meniscus from above. Now, whenever you want to take sagittal images, the first image that you'll cut, so this is through the periphery of the meniscus or the periphery of the medial or the lateral compartment, whichever you're concentrating on and whenever you cut through this particular plane on a sagittal image, you'll see the meniscus in the form of a box or a rectangle. Next, when you come further towards the midline in the joint, you get a bow tie appearance of the meniscus, which is when you are cutting through this section of the body and finally, when you come further more towards the midline, what you can see is two triangular structures and these are nothing but your anterior and posterior horn. So, if you'll see, this is your anterior horn and this is your posterior horn and there is nothing in between. So, this is what is the appearance of both medial and lateral meniscus on a sagittal image. So, this is the MRI me sagittal image to show you how it looks like. So, this is the most peripheral section where you'll see the meniscus in the form of a rectangle. Then you begin to see a bow tie appearance of the meniscus, which is nothing but the body again. And finally, you see two triangular structures, which is nothing but your anterior horn and posterior horn. Now, on coronal images, so why on coronal images it is important to look at the body because as you've seen on the sagittal images, we could see the body in the form of a rectangle or a bow tie, but when you want to see the body in the form of a triangle, that will be seen on a coronal image. So, here you can see that whenever you are cutting on the coronal image, this particular section of the body, you will see the body in the form of a triangle. So, this is what is the appearance of the body on a coronal image. So, the triangular appearance for the anterior and posterior horn is on a sagittal image, whereas for the body, it is on the coronal image. Now, let us just know more about the medial and lateral meniscus and the differences between the two. So, the medial meniscus has an open C-shaped or a semi-circular appearance. An important point to note is that the posterior horn of the medial meniscus is larger than the anterior horn. So, it's nearly double the size of the anterior horn. Now, why this is important? Whenever there is a meniscal tear and there is a displaced meniscal flat in the posterior horn, you will find that the posterior horn is attenuated or smaller in size. And if the posterior horn appears of the same size of anterior horn, you know that there is a tear in the posterior horn because the posterior horn of the medial meniscus has to be nearly double the size of the anterior horn. And the third point is that it is less mobile because it is attached to the deep fibres of medial collateral ligament and because it is less mobile, medial meniscus is more prone to tears. Similarly, lateral meniscus has a tight C-shaped appearance. So, you can see it is more C-shaped while this is an open C-shaped thing. This is more like an incomplete circular appearance. Now, again, an important point to note is that the anterior horn and posterior horn they are similar in size. So, whenever on a sagittal image, if you will compare the anterior horn and the posterior horn, you will find that both of them are same in size for a lateral meniscus. But again, remember, for a medial meniscus, the posterior horn is double the size of the anterior horn on the sagittal image. So, in case of a lateral meniscus, if you find that the posterior horn is smaller as compared to the anterior horn, you know that there is a tear in the posterior horn. And the lateral meniscus is loosely attached to the joint capsule, that is because between the meniscus and the joint capsule, you have a popliteal hiatus through which your popliteus tendon passes and goes out of the joint. So, as we all know, the popliteus tendon is an intraarticular structure and then it passes through the capsule and goes out. So, therefore, it is loosely attached to the joint capsule. Now, hematomy of the meniscus. So, again, we are looking at the sagittal image and first we will be looking on the medial meniscus. So, this is nothing but your medial compartment, medial femurothebul compartment and what we will be doing is we will be going from periphery towards the midline. So, the structure that you see over here, this black structure, that is nothing but your medial collateral ligament. Now, as you go, sorry, as you go further towards the midline, you begin to see a jet black structure, right? So, this bone is your femur. One section inside, you begin to see the TBR as well and between the femur and the TBR, you see this jet black structure and this is nothing but your medial meniscus. So, initially, it has a more of a rectangular appearance, okay, which is nothing but the body and then as you go further inside, you begin to see two structures. So, this is one triangular structure and this is another triangular structure and these are nothing but your anterior and posterior horns and as I have stressed upon even before, the posterior horn of medial meniscus is double the size of the anterior horn. So, this is how a normal medial meniscus will look on a sagittal image. If you find that the posterior horn and anterior horn are similar in size, you have to think about a posterior horn turn and look for a displaced meniscal flap. As we go further towards the midline, we begin to see the anterior root and the posterior root attachment of the medial meniscus. Now, same thing we will be doing for the lateral femurothebal compartment. So, we are going from periphery to the midline on a sagittal PD image and as you go, so first structure that you see over here, these are nothing but your, this is nothing but your then biceps tendon. So, this is a conjoined tendon which will go attached to the fibular head. Now, as you go further towards the midline, you begin to see the lateral femur and the lateral tibia and again a rectangular shaped meniscus between them which is nothing but your lateral meniscus. As you go further inside, you begin to see the classic bow tie appearance, and this is again nothing but the body of the lateral meniscus and finally, you begin to see two triangular structures which is your anterior horn and posterior horn and now if you will have a look closely the anterior and the posterior horn of the lateral meniscus are similar in size. So, this is a point to remember and further towards the midline you begin to see the anterior root and the posterior root of the medial meniscus and just one more point to remember is normally the anterior root attachment of the lateral meniscus has a striated appearance. So, here if you see there are striations in it and it has a slight hyper intense signal. So, there is intrinsic hyper intense signal within the anterior root attachment of the lateral meniscus and that is normal. So, you should not label this as a degeneration or a tear. So, remember the anterior root attachment of lateral meniscus has a normal striated appearance with hyper intense signal within. Now, let us look at tear mimics that is normal structures that look like a tear but they are not a tear. So, as you can see this is your lateral meniscus because your anterior horn and posterior horn are similar in size. While we are just playing this video I need you to concentrate on this tiny black structure. I have already labelled it. If you will see closely on this still image you will feel that there is a tear. So, there is a tear between this lateral meniscus and this superior margin of the lateral meniscus anterior horn. Now, let us look at the entire sequences. So, if you will see this tiny jet black structure. So, this structure which will go and attach to the anterior horn of medial meniscus. Now, again we are coming back and this is the jet black structure which is coming and attaching to the anterior horn of lateral meniscus. I will again play this video for you. So, you can see this jet black structure is going and attaching to the anterior horn of medial meniscus. Again we will be coming back. So, if you feel that there is a tear but it is coming and attaching to the anterior horn of lateral meniscus as well. So, this is nothing but your transverse meniscus ligament. So, this is a ligament that attaches the anterior horn of lateral meniscus to the anterior horn of medial meniscus. Whenever you look only on a sagittal image and on a still section or one particular image, you will see that at the point where it goes and attaches to the medial meniscus or the lateral meniscus, it looks like a tear but it is not a tear. So, just trace the entire sequence and you will understand that it is not a tear along the superior margin of the meniscus but instead it is a transverse meniscus ligament. Again we are looking at the lateral femurothevil compartment, your anterior horn and posterior horn are similar in size. So, as you go towards the midline, here you can see that at the superior daughter of the posterior horn of lateral meniscus, there is this thin jet black structure. Now, if I will give you this one single image, you will feel that there is a tear. There is a tear which is reaching up to the superior margin of posterior horn of lateral meniscus. Now, as you go further towards the midline you will find that you can still appreciate this gap. Okay, further again here, again you can appreciate the gap and this is the black structure. Sorry, this is that black structure. This is the black structure. You can again appreciate here it looks like completely like a longitude milter in the periphery of the posterior horn of lateral meniscus. And further on, what you see is that this structure and plus there is another black structure. So, this particular black jet black structure this particular structure is nothing but your posterior cruciate ligament and there is a jet black structure which appears like a dot which is posterior to the posterior cruciate ligament and then there is one dot that is anterior to the posterior cruciate ligament. Now, these are nothing but your meniscus femoral ligaments. The anterior one is ligament of hump free and the posterior one is ligament of brisbur. Now, how do you remember? Just remember that in alphabetical order H comes before. So, H is anterior. So, the first thing the most anterior one is the first in the alphabetical order and W comes later. So, W is posterior. So, this is how we remember the names. Obviously, it is not much important to remember the ligament of hump free but you need to remember the ligament of brisbur. I will tell you in a while why it is important and as the name suggests it is nothing but a meniscus femoral ligament. So, it is a ligament that connects the meniscal or the posterior hump of the lateral meniscus to the femur. So, again we will go back sorry, okay. So, here you can see that it looks like a turd but when you completely trace the image you will find that it is nothing but the meniscus femoral ligament. Now, I told you to specifically remember ligament of brisbur and that is important because in anterior cruciate ligament injuries you get a posterior hump lateral meniscal tear which is called as the brisbur grip tear. Now, normally what happens is this hyper intense linear signal that you see in the posterior hump of lateral meniscus it is only restricted up to the medial most one-third or half of the posterior hump. So, if on a just I will show you so if this is your lateral meniscus okay. This is your anterior root and this is your posterior root and this is your intercondylar notch fine. So, this is the midline which is the intercondylar notch and this is your peripheral part. So, whenever there is a ligament of brisbur, whenever you see this on a sagittal image and you are correlated on the axial images you will find that the hyper intense signal is restricted like this. So, this is your hyper intense signal here okay. And this hyper intense signal is present only up to the medial one-third or half of the posterior hump of lateral meniscus. But instead if this hyper intense signal is extending up to the posterior horn poly junction or in the peripheral one-third of the lateral meniscus. So, this entire thing is looking like this okay. So, this entire thing is having a hyper intense signal then you call it as a brisbur grip tear. And to further understand the brisbur grip tear we will be discussing it in further videos when we come down to the meniscial tears. So, just remember normally your hyper intense signal between the posterior horn and the brisbur ligament is only restricted up to the medial one-third or half of the posterior horn of lateral meniscus. When this signal extends further towards the periphery that is nothing but your brisbur grip tear. And another thing do not over call brisbur grip tear it only happens when there is a anterior cruciate ligament injury. Okay. Now the next thing what you need to see is here. So, there are two things if you will if you closely watch first thing I wanted to look at is there is a black structure here. This is your medial femurative compartment. On the lateral side you don't see a significant black structure. So, all you see is something hyper intense strands. So, this medial black structure in the interpondylar notch is your posterior cruciate ligament. So, this is your PCL. Okay. And here what you don't see a significant black structure but just you think strand this is actually the location of a ACL. But in this particular patient there has been a ACL tear and there is no healthy ACL remnant. So, these are the two normal structures that you see in the interpondylar notch. Now, if you look you are able to see two more structures over here. So, there is one jet black structure which is a small one this and there is another jet black structure. Okay. Now, there are two different structures. So, there are two or four structures in the interpondylar notch. Now, again we will come from anterior to posterior from front to back that is anterior to posterior. This is the lateral compartment. This is your anterior on of the lateral meniscus. Now, as you go posteriorly you see that this structure is actually this structure is actually arising from the anterior horn of the lateral meniscus. Further on you will see that this structure is actually coming from the body. So, this is nothing but the bucket handle tear of the natural meniscus and if you will see that this structure is the displaced meniscal flat in the interpondylar notch and if you closely look even the body is blunted. So, normally a body should have a triangular appearance right. So, this is how we have discussed that on a coronal image the body will have a triangular appearance. But here you will see the body has a more of a blunted appearance right and so this blunting is because this particular meniscal flat has displaced in the interpondylar notch. Further on as you go posteriorly you will see that this flap goes and attaches to the posterior horn of the lateral meniscus. So, again we will come from posterior to anterior now. This is your posterior horn and if you closely look in this region you will see a flap is arising from there going in the interpondylar notch and coming and attaching to the anterior horn and anterior root of the lateral meniscus. So, this is surely a bucket handle tear of the lateral meniscus. Now, what is the second structure? So, again if you will see the second structure is arising from here which is nothing but the anterior root of medial meniscus right. So, this is your structure ok. Now, as you go further posteriorly this is the structure this one again this is the structure this is the structure. It goes and attaches to the posterior root of lateral meniscus ok. So, again we will come back. So, it is arising from when you I will just get it completely anteriorly ok. So, again it is arising from the anterior root of medial meniscus and goes posteriorly and attaches to the. So, this is your structure attaches to the posterior root of lateral meniscus. So, now what are these both structures? So, this structure which we saw is arising from the anterior horn of lateral meniscus and going to the posterior horn of lateral meniscus that is your bucket handle tear and this is a normal structure within the joint it is not always visible but when visible it can cause confusion with bucket handle tear and this is nothing but oblique menisco meniscus ligament. So, it arises from the anterior horn of the anterior root of medial meniscus goes and attaches to the posterior horn or posterior root of lateral meniscus. So, if you see a extra structure in the intercondylar knot which is attaching to the anterior and posterior horn of the same meniscus that is your bucket handle tear if you see a structure that is arising from one meniscus and going to another meniscus that is your oblique menisco meniscus ligament. So, just remember this and it will be sorted. So, this over here you'll see this is your oblique menisco meniscus ligament which is arising from one meniscus and going to another meniscus. Now, the third structure which is normal but can look like a tear are the menisco fascicles. So, here you'll feel that there is some tear between the you know the periphery and the this thing. So, this is something but the papyrite menisco fascicles. So, there are about 3 papyrite menisco fascicles you do not need to know the name of each of it but just remember that they are thin linear hyper intense bands which connect the posterior horn of lateral meniscus to the papyrite tendon sheath. So, and there is normal fluid signal over here. So, this again should not be mistaken for a tear. Important is to remember that with cruciate ligament injuries there can be injury to the papyrite menisco fascicle and you need to report them. So, you need to report them as a papyrite menisco fascicular injury or a posterior lateral capsule injury whatever wordings you want to use but it should be reported. Now, we have looked at those structures which are normally present in the knee joint but look like a tear. So, we will be looking at normal variants. So, these are meniscal variants which are seen in asymptomatic individuals and they do not indicate tear. So, the first is a discoid meniscus and there are 3 types of discoid meniscus a complete discoid incomplete discoid or a Riesberg variant. Second is meniscal flounds and then we look at meniscal ossicles. Now, this is your normal. So, first thing you know to know is discoid meniscus is more common on the lateral than on the medial side. So, this is your normal lateral meniscus which is the body. If you will see on a coronal section, the body has a clean triangular appearance. Now, here also the body has a proper triangular appearance but it is longer. So, here this is your partial discoid and this is your complete discoid. So, if your meniscus the lateral meniscus is extending towards the midline. So, this is your entire body and if it is involved if it is extending more than 80% of the tibial articular surface. So, this is your 80% and this is the rest 20%. So, if it is involving more than 80% of the tibial articular surface that is when you call it as a complete discoid. If it is involving less than 80% of the tibial articular surface that is when you call it as a partial discoid. Now, the important thing is when to call it a discoid in the first place. So, it is very easy to ignore a complete discoid. There is always a confusion with partial discoid. Do not over call partial discoid or incomplete discoid meniscus. Remember, whenever first thing is obviously on eyeballing so you can just open any other normal knee joint and look at a normal body and then you can just take a call. So, eyeballing is what we usually use. If it is too much dicey you can go by a criteria which is that the discoid meniscus, the thorough discoid meniscus on the coronal section if the body is more than 15 millimeters. But, using an exact mathematical criteria is not ideal because it can vary depending upon the built of the person. So, the second which is more viable way of diagnosing a discoid meniscus is absent bowtie sign. So now, as we have seen that normally as you go towards the midline, the body takes a bowtie appearance. Now, if this bowtie appearance is not seen for three consecutive sections. So, if you see that the body is in the form of a rectangle for three consecutive sections that is when you call it as a discoid meniscus. Now, again this criteria has some particular rules before you follow it. So, it is when you are using approximately 3 millimeter thickness section with a zero slice gap. So, if you are using a 5 millimeter thickness section then obviously you will never identify a partial discoid meniscus because it won't be that much longer because the difference between the two slices is 5 millimeters. So, the criteria is when the difference between the two slices is 3 millimeter which is the routine protocol that we use in any knee joint MRI. So, 3 millimeter slice thickness with a zero slice gap. Now, here if you see this is the first section and you can see the rectangular appearance of the body of the meniscus. Again second section you should see the rectangular body. Now, on the third section I should get a bowtie appearance but still I am not getting a bowtie appearance in this patient. It is still pretty much rectangular. Still it is rectangular. Now, it is somewhat begin to develop a bowtie appearance. So, if you see there is a curve that is begin to appear. So, it is somewhat rectangular with a bowtie appearance. Now, you can still see. Okay, and by now actually you should be seeing the anterior and the posterior horns separately. There shouldn't be an attachment between the two but still you can see that there is a meniscal tissue which is connecting the anterior and the posterior horns. So, and now you can appreciate the bowtie as well. So, this is what is nothing but a discoid meniscus. So, you are not able to see the bowtie on the third sequence or the third image and if you find that you have pretty much gone towards the midline but still the anterior and the posterior horns are connected by the meniscal tissue. So, that was a discoid meniscus. Now, this is a second form of this is a second normal variant which is nothing but the Riesberg variant of discoid meniscus. So, if you remember I had told you that in a normal individual, you will see topical meniscal fascicles here. So, this is your posterior horn of lateral meniscus. This is your popliteous tendon. Okay, so this is going to be your capsule and the popliteous tendon sheath. So, between these two what you will see is the popliteous meniscal fascicles. Now, whenever you don't see any fascicle and you see more than that, more important is if you see a clear fluid filled gap in this region. This is nothing but the Riesberg variant. So, if the person does not have a history of trauma, you shouldn't label this as a tear. Okay, if the person does have intact cruciate ligaments and everything do not label this as a tear. But instead this is nothing but the Riesberg variant of the discoid meniscus. So, you can put it as Riesberg variant of discoid meniscus with lack of visualization of popliteous meniscal fascicles. And these patients will classically have a clinical history of snapping knee. So, whenever you get this history and you see this finding please report it. Okay, now the next meniscal variant is the meniscal flounce. Now, what is a meniscal flounce? It is nothing but this wavy appearance of the free margin. So, if you see this is nothing, this is your apical free margin or the apex of the meniscus, right? Which is a triangular shaped meniscus. Now, if you see here, there is a wavy appearance of the apex of the meniscus. And this is normal. This should not be labeled as a tear. This is nothing but a meniscal flounce. It does not have any much clinical significance but the important thing to remember is not to label it as a tear. And the last meniscal variant that we are going to discuss is meniscal ossicle. Now, meniscal ossicle is ossification that usually happens towards the posterior root attachment of the meniscus. More often, they are involving medial meniscus. And with the, why does it happen if there is no particular theory but there are a couple of theories that it could be secondary to trauma or degeneration. The important is not the cause. Again, it is not clinically significant. You do not have to operate this patient and that is where the importance lies. Now, if, sorry if we look on the proton density image, it appears hyper intense. It is within the substance of the meniscus. Do not label this as a degeneration or a tear of the meniscus. How to differentiate it? Always look at the fat saturated image. Since this is a bone or an ossification, you will find that it will completely suppress on a fat saturated image. Second, look at the x-ray. You will see it on a lateral view of the x-ray. Third, if you have a CT cut, you can look at the classification of the ossification in this region. So, remember meniscal ossicle will be nearly the shape of the meniscus within the substance of the meniscus but do not label it as a tear because it does not require any intervention, any surgical intervention. And how to identify it? Look at your fat saturated image. Look at the x-ray and look at the CT if you have. Do not get the CT cut done for this person, for this purpose. Look at the x-ray first but if you are still in doubt, then maybe you can go for it. So, just to sum up, things which are not to be mistaken for a tear, transverse meniscal ligament, remember they connect that to anterior haunts of the menisci. Menisco femurin ligaments which is ligament of Humphrey and Risberg. Risberg is important. You have to differentiate the normal ligament from Risberg rib tear. Oblique meniscal-meniscal ligament this is very important. If it is seen, it can create a confusion with bucket-handled tear. So, look at it carefully. Populity of meniscal fascicles. Identify them in case of cruciate ligament injuries. Look at them because you need to report populity meniscal fascicular injury or posterior lateral capsular injury. Meniscal flounce do not label it as a tear and meniscal ossicle please use other modalities like radiographs to differentiate it from a tear. I hope you've liked today's session and now I'm sure that none of you is going to label a normal structure as a meniscal tear. If you really liked today's session, please hit the like button and you can put in your comments in the comment section and if any of you have any queries regarding the topic, please feel free to ask them in the comment section and I'll revert back to you. And please stay tuned for the next videos to come in on the meniscal tear and post-operative meniscal. Thank you.