 So without wasting any time, let's begin with today's topic which is the MRI anatomy of the knee joint. So in today's short session, we will be discussing about the sequences, the approach to the knee MRI scan, how to look at a normal scan and normal MRI anatomy of the knee joint. As far as the sequences go, you've got the common sequences that we take for a knee MRI are T2 fat saturated sequence, proton density sequence. So these two sequences are particularly important for internal derangements, whereas T1 weighted sequence is not an important sequence in internal derangement because as you can see, the cartilage is not well visualized, also it is difficult to identify meniscal and ligament injuries on a T1 weighted image, but T1 weighted images are required when you are suspecting infections and tumors, particularly when you're suspecting any marrow abnormality. So in order to look at the MRI knee scan, you can use the compartment approach which comprises of, first you look at the medial compartment followed by the lateral and patellar femoral compartment, then the midline structures that is the cruciate ligaments followed by miscellaneous structures like joint effusions, baker's system, neurovascular bundles. So if you follow this compartment approach, you won't miss anything while looking at the scan. Before we look at the MRI images, just a short discussion on menisci. So we have got the medial and the lateral meniscus. The medial meniscus has a larger C appearance, whereas the lateral meniscus has a smaller C appearance. The parts of the meniscus comprise of anterior root, anterior horn, body, posterior horn and posterior root. And when you take sagittal sections of the meniscus, so when you are cutting the meniscus at this level, you will see the body in the form of a rectangle shape. At this level, you will see the body in the form of a bowtie appearance and at this level, where you will be cutting both the posterior horns and you will have a triangular appearance of the posterior horn on the sagittal images. So now we begin with the compartment approach and the first compartment is medial compartment. We look at the medial femur and tibia, the joint and the cartilage between the two bones, medial meniscus and the posterior meniscocapsular junction, medial collateral ligament, breast tendons and posterior medial corner. Now ideally you should begin looking at the scan by using the T2 fat saturated images to look for the site of marrow edema and the soft tissue edema. This will help you to localize as to which compartment is involved and where you need to concentrate. But for the anatomy sake, we will start with the sagittal pd image and this is the medial most image of the sagittal images of the knee and what we will be doing is we will be going from the medial most image towards the midline. So the most peripheral medial image will show a jet black structure which is the medial collateral ligament as you go towards the midline you start to see two bones this is the medial femur and this is the medial tibia. The medial tibia has a triangular appearance on the sagittal image and as you go further towards the midline the first thing that you need to look at are the bones and the bone marrow edema pattern. So the common sites of marrow edema first one is this which is peripheral medial femur and posterior medial tibial. Now this marrow edema pattern happens in pivot shift injury and which involves anterior cruciate ligament injuries. The second site to look for edema is the proximal metadiphyzol region on the medial side and this edema happens in medial tibial stress edema or fracture. This edema will be seen at the edge of the film so make sure you don't miss this edema and next we look at the subcontral bone marrow edema. The subcontral region is the region of the bone that is just underneath the cartilage. So this is the subcontral region of edema and this is the subcontral region of tibia. And if you see the jet black line is the cortex of the bone this is the cortex of the bone and the gray zone that is overlying the jet black line this is your femoral articular cartilage this is your tibial articular cartilage. So after the bones you look at the articular cartilage and you see this white line between the two gray zones this white line is nothing but the thin fluid between the joint and so this will help you to differentiate the femoral from the tibial articular cartilage. Now the femoral articular cartilage is divided into a weight bearing cartilage and a non-weight bearing cartilage and the demarcation is peripheral aspect of anterior horn of medial meniscus and peripheral aspect of posterior horn of medial meniscus. So this entire zone is the weight bearing cartilage and this is the non-weight bearing cartilage. While reporting it is important to mention that which cartilage is involved because the management varies when the weight bearing cartilage is involved while on the other hand the tibia if you appreciate the entire cartilage is the weight bearing cartilage. So in tibia you do not have the differentiation of the weight bearing and non-weight bearing. Furthermore the weight bearing cartilage on the medial femur can be divided into three zones which is the anterior central and posterior so you can better report whether which particular cartilage is involved. Once you've looked at the bones in the cartilage the next structure to look is at the medial meniscus. So again we are at the peripheral most section where you can see the medial collateral ligament. Now we will be going towards the midline and what you can appreciate is a jet black structure in the joint space which is nothing but the body of the medial meniscus and as you go further towards the midline you can see two triangular structures so this is the anterior horn and this is the posterior horn of the medial meniscus and if you appreciate the posterior horn is double the size of the anterior horn and this is important for medial meniscus because if the posterior horn of the medial meniscus is of the same size as that of the anterior horn it means that there is a posterior horn tear and a flap that is displaced and so you need to look for it. The next structure is the posterior meniscocapsular junction and tear in this region is nothing but the ramp lesion which can happen with anterior cruciate ligament injuries. So now as you go further towards the midline you can appreciate the anterior and the posterior root of the medial meniscus and if you'll see the posterior root of the meniscus is attaching to the TBR just anterior to the TBL attachment of posterior cruciate ligament. So now we've looked at all the structures on medial compartment. Now let's look at the lateral compartment. The lateral compartment consists of the lateral femur and the lateral tibia, lateral femurotibial joint and cartilage. Then there is the lateral meniscus and popliteo meniscal fascicles. From anterior to posterior you have the imliotibial band, antrilateral ligament, fibular collateral ligament, popliteus tendon, bicep tendon and conjoined tendon. So again this is the lateral host sagittal pd image where you can see the fibula, the biceps femurus muscle and the conjoined tendon inserting onto the fibula subsequent images and last you look at the posterior lateral corner. So again this is the lateral host sagittal pd image where you can see the fibula, the biceps femurus muscle and the conjoined tendon inserting onto the fibular head. So as you go towards the midline again you start to see the lateral femur and the lateral tibia. If you see the lateral tibia has more of a squarish or a rhomboid appearance and then first is again you look at the bone marrow edema pattern and so the common sites of bone marrow edema is this region which is called as the sulcus terminalis. Sulcus terminalis is present in the anterolateral femur just anterior to the anterior horn of lateral meniscus. So edema in this region and edema in the posterior lateral tibia these two edema patterns again indicate anterior cruciate ligament injury. The second edema pattern is anterolateral femur. Edema in this region indicates lateral patellar dislocation and the third edema pattern is obviously your again your subcontral edema pattern which happens in osteoarthritic needs. So once you've looked at the edema look at the cartilage so this is the lateral femural cartilage this is the lateral tibial cartilage and just like the medial femuril the lateral femural cartilage is divided into weight bearing and non weight bearing and weight bearing is further divided into anterior central and posterior weight bearing. Now once you've looked at the cartilage and the bones the next structure are the soft tissue structures. Now this is the conjoined tendon and the biceps as you go again towards the midline the next structure that you see this is the popliteus tendon. The rest of the structure that is the eotibial band the fibular collateral ligament all of those are better seen on the coronal and axial images and so we discuss it there. So as we go now further towards the midline we look at the meniscius and this jet black structure within the joint is the lateral meniscus which is the body of the meniscus and as you go towards the midline you can see posteriorly here this is the popliteus tendon and these are the two thin tiny hypo intense lines which is present between the posterior horn of the lateral meniscus and the popliteus tendon and these are nothing but the popliteus meniscus so you do not have a meniscocapsular junction on the lateral side instead you have a popliteum meniscal fascicle and the popliteus passes between the meniscus and the capsule so these fascicles they provide stability to the lateral meniscus and as you go further towards the midline you can see the two triangular structures which are nothing but the anterior and the posterior horn and if you appreciate the anterior and posterior horn of the lateral meniscus out of the same size unlike that of the medial meniscus now one important thing in lateral meniscus is something called as a discoid meniscus so if you see a bowtie appearance of the body on the third image then it is a normal appearance which is a normal bowtie sign if you do not see the normal bowtie sign on the third image it indicates that there is a discoid meniscus so how to look at it again from the peripheral most section we are going towards the midline this is your first section this is your second section and here you can see that a bowtie appearance has begin to be seen so this is the normal bowtie sign and hence this is a normal lateral meniscus if you would not see a bowtie sign in this region but instead a rectangular meniscus it would mean that there is a discoid meniscus so again you can see the bowtie sign here and this is the normal meniscus now as you go towards the midline you can see this thin hypo intense structure which is arising from the anterior horn of the lateral meniscus this is not an anterior horn tear if you'll trace it further you'll see that this structure goes and attaches to the anterior horn of the medial meniscus if you'll see on the axial image this is this entire linear structure connecting the anterior horn of both the menisci and this is nothing but the transverse meniscal ligament and as you go further towards the midline you can appreciate the anterior and the posterior root and if you see the anterior root has a intrinsic hyper intense signal and a striated pattern this should not be mistaken for a degeneration or a tear this is a normal appearance of the anterior root of lateral meniscus now another next structure to keep an eye on is this thin structure which is attaching to the posterior horn of the lateral meniscus and as you trace it further you'll see there are two structures one anterior and one posterior to the posterior cruciate ligament the posterior structure is the ligament of Rizberg and the anterior structure is the ligament of Humphrey and these are menisco femoral ligaments which will go and attach to the femur now we look at the third compartment which is the patella femoral compartment which comprises of patella trochlea the cartilage between that the patella femoral ligaments the quadriceps tendon and the patella tendon and the fat pad and the bursa so this is your patella femoral compartment where this is the quadriceps tendon this is the patella this is the patella tendon and this is femur and the tibia so this is the trochlea of the femur important is to look at the position of the patella to see if there is any patella alta or baha for which you can use the insal salvati ratio as well next obviously is to look for the bone marrow edema pattern so this is a medial image and if you see edema in the inferior medial patella that is again indicative of lateral patella dislocation so you should look for the signs of lateral patella dislocation as far as the cartilage is concerned the patella cartilage is better visualized on axial images so we will discuss it there the trochlea cartilage is well seen on sagittal images and it is particularly important to look at the inferior trochlea cartilage because the inferior trochlea cartilage is not well appreciated on the axial images so this is the superior trochlea and this is the inferior trochlea cartilage now next we look at the midline structures which comprise of the anterior and the posterior cruciate ligaments and the neurovascular structures so again you're going from medial to lateral and the first dead plaque structure that you see is the posterior cruciate ligament which is just posterior to the posterior root of medial meniscus and the next structure that you see is the anterior cruciate ligament and if you'll appreciate again there is an intrinsic hyper intense signal and a striated appearance at the tibial attachment of anterior cruciate ligament and this is again a normal appearance this should not be mistaken for a tear or a spring and here you can see the femoral attachment of the anterior cruciate ligament now we look on the coronal images and we are going from anterior to posterior so the first structure anteriorly that you see is a triangular bone which is the patella with the quadriceps and the patella tendon attaching to it now first we look at the medial compartment and on the medial side the first structure that you see is the anterior horn of the medial meniscus as you go posteriorly you can appreciate the medial femoral tibial cartilage very nicely this is the body of the medial meniscus body appears triangular in appearance on coronal images also look for any extrusion of the body of the medial meniscus which where the body will be displaced outwards and the next structure is this jet plaque ligament which is the medial collateral ligament so this is the femoral attachment and here will be the tibial attachment the entire medial collateral ligament can be seen on a single image so as you go posteriorly you can see two to three hypo intense structures towards the tibial side and these are nothing but your best tendons the next structure is the posterior horn and this is the posterior horn and this is the posterior root of the medial meniscus so if you see the posterior root actually dips down and attaches to the intercondyla remnants of the tibia adjacent to the posterior cruciate ligament now we look at the lateral structures and the first structure that you see is a hypo intense vertical band which is the eliotibial band which attaches to the anterolateral tibia next is the anterior horn of the lateral meniscus next is the lateral femoral tibial articular cartilage which is very well seen on the pd images then you have the body of the lateral meniscus and again this has a normal triangular appearance if you see body longer than this or almost reaching up to the intercondyla or notch then that means there is a disquiet meniscus the next is this thin hypo intense structure which is the anterolateral ligament and this is the tibial attachment of the anterolateral ligament this is the side where you're supposed to look for saigon's fracture in case of anterocruciate ligament injuries this is the fibular collateral ligament and if you see you cannot appreciate the distal half of the fibular collateral ligament this doesn't mean there is a tear fibular collateral ligament is the oblique ligament and so as you go posteriorly you can appreciate the mid and the distal fibular collateral ligament so it is the oblique ligament and visualized on sequential images this is the biceps femoris tendon and fibular collateral ligament and biceps femoris together join to form the con joint tendon which attaches to the fibular head the next structure that is deep to the fibular collateral ligament is the popliteus tendon which arises from the notch on the lateral femur so now as you go further posteriorly you can appreciate the posterior horn of the lateral meniscus and the posterior root of the lateral meniscus and here this is the popliteus tendon and this is the popliteus myotendinus junction another structure is this black structure which is nothing but the posterior lateral capsule and archivate ligament is nothing but the thickening of the posterior lateral capsule so posterior lateral corner mainly comprises of the archivate ligament the popliteus tendon and the muscle and the fibular collateral ligament with other small structures. So now we have looked at the coronal images, we will look at the axial images which is particularly important to look for the patylofemoral compartment. So this is the femur, this is the podriceps tendon which attaches to the patella. As you go further inferiorly, this is the lateral patella cartilage, the medial patella cartilage and the central patella cartilage. Here lateral trochlear, medial trochlear and central trochlear cartilage. This is the lateral patylofemoral ligament. This is the medial patylofemoral ligament and medial patylofemoral ligament is slightly thin as compared to the lateral and if you see you cannot appreciate the inferior trochlear cartilage and that is why you need to look at the inferior trochlear cartilage on the sagittal images. Then you have the patella tendon which goes and attaches to the tibial tuberosity. Some discussion on cruciate ligaments. So both the cruciate ligaments comprises of two bundles and it is important to identify each of the bundles because single bundle injuries are common. The key to remember is ample. So ACL you can just remember ample where ACL comprises of anterior medial and posterior lateral bundles and just invert it and you will have anterior lateral and posterior medial bundles for the PCL. So again you are going from cranial to cordil and you can see the femoral attachment of anterior cruciate ligament and here you can appreciate the anterior medial and the posterior lateral bundles individually. This is the femoral attachment of the posterior cruciate ligament and here you can see the anterior lateral and the posterior medial bundle of the PCL. And this is the tibial attachment of ACL and this is the tibial attachment of PCL. And here posterior you can appreciate the popliteal vessels, the tibial nerve and this thin nerve is nothing but the common peroneal nerve and when you trace it it goes close to the fecibular neck. So take home points, have a compartment uproar so that you do not miss anything. Identify bone marrow edema pattern so you know which soft tissue structures would be injured. Just remember that anterior root of lateral meniscus and tibial attachment of anterior cruciate ligament have a normal striated appearance. Do not label them as injury and please correlate all the structures in all three planes when you are doubtful whether it is injured or not. Thank you.