 Hi, I am Malini Lavande, Musculoskeletal Radiologist at InnoVision Imaging and Nanavati Super Speciality Hospital in Mumbai. Along with my colleague Aditya Daftari at InnoVision Imaging, we have set up a sub-speciality Musculoskeletal Imaging practice both locally as well as with tele-radiology. Both of us are passionate about teaching and we conduct a number of conferences and teaching sessions throughout the year. I am very happy to be part of Indian Radiologist because I think they are doing a great job in making sure that radiology teaching and education is reaching everyone. These are very tough and crazy times and I am optimistic I believe together we shall overcome this and meanwhile stay safe and take care. Today we are going to talk about the role of MRI in shoulder instability. The anatomy has already been covered but a quick recap. The shoulder joint is a joint meant more for mobility than stability. So you have a very shallow glenoid fossa articulating with a spherical humeral head. The fibrocartilaginous labrum forms a rim around the glenoid deepening it. In addition there are other static stabilizers like the superior middle and the inferior glenohumeral ligament which are thickenings of the capsule. Especially the inferior glenohumeral ligament has an anterior band, a posterior band and an inferior hammock like structure and these add to the stability of the shoulder joint. We also have the rotator cuff muscles which are not only mobilizers but also dynamic stabilizers keeping the humeral head in place. Before we begin just a little bit of discussion about how we describe the labral tears. Some people use the clock position where they take the anterior labrum as 3 o'clock, posterior as 9 o'clock, here 12 o'clock and 6 o'clock the inferior labrum. But the problem with this is depending on the right or the left shoulder these would get inverted. Some people follow that the anterior labrum is always called 3 o'clock no matter which shoulder it is. But we prefer to use the quadrant method where we talk of the superior, posterior superior, posterior inferior, inferior, anterior inferior and anterior superior quadrants of labrum. So for example I will describe a tear as, tear involving entire anterior labrum extending across 12 o'clock up to posterior equator. So this will give the surgeon the entire extent of the labral tear so that he can plan the surgery accordingly. Instability could be following an initial episode of trauma or it could be at times congenital because of the lack supporting structures. It could be unidirectional more often anterior or sometimes posterior but it could also be multidirectional when it becomes more difficult to diagnose. Usually patients do not come to us for imaging in the first time immediately after acute trauma but more often they come for imaging following recurrent episodes of dislocation. Whenever we evaluate instability the three main structures that we are looking at is the labrum, the capsule and the bone. The bone on the glenoid side as well as on the humeral side. Now the most common type of instability is the anterior instability and in this what happens is the humeral head which is normally in this position gets dislocated anteriorly and inferiorly. So as you can see when the humeral head gets dislocated in this direction the anterior inferior labrum here gets torn. And also if we can see here the posterior superior humeral head will impinge against the glenoid especially when it relocates and this will lead to anterior inferior labral tear and an impaction fracture along the posterior superior humeral head which is the hill sacs lesion. On an axial image this is how the normal labrum is seen in relation to the glenoid. If there is a tear of the anterior inferior labrum and the periosteum which is attaching here to the bone is also torn it is a cartilaginous bank cartilation or a fibrous bank cartilation. Here are some examples. So we do not do our thrograms anymore since quite a number of years because with high resolution imaging especially with 3 tesla it is possible to get these very high resolution proton density images which can show the labral tear very well. So here you can see the posterior labrum is normal labrum being fibrocartilaginous structure looks hyper intense on all the sequences and here you can clearly see an anterior inferior labral tear. This is a coronal image again depicting the tear well. This is another case again compare it with the normal posterior inferior labrum and here you have got a tear of the anterior inferior labrum. This is a sagittal image so we do not use sagittal images really for diagnosing labral tears we diagnose them on coronal and axial but we use the sagittal image to get an idea of the extent. So here you can see it is from just above the anterior equator going almost up to the 6 o'clock position. Now depending on the force with which the dislocation happens if the force is more a piece of the glenoid may also come out along with the labrum and this is called as the bony bankard lesion. So here in this patient again very important to look at the non-fat saturated images because on fat saturated sequences everything is suppressed looking homogeneously dark and you may not be able to identify the bony fragment well. So here you can see there is a osceus fragment coming off the anterior inferior glenoid which is seen in this sagittal and coronal images well. We need to give dimension of this osceus fragment. If there is a very thin slender flake of bone coming off CT would be better than MR to demonstrate that but having said that to the surgeon it does not really matter. If it is a very thin flake then he is going to probably along with the labrum reattach it back. The thin flake is not something that he would be dealing with separately. If the labrum is torn but the periosteum is still intact it is a perthes lesion. As we can see here the anterior inferior labrum is torn but the periosteum is clearly intact. Now our surgeon says that all this differentiation of the different type of tear does not matter to him. His main questions to us always are is the labrum intact or not. If it is not intact, if it is torn what is the quality of this labrum? The torn labrum is it good or due to chronic recurrent dislocation is this labrum worn off degenerated? And the other question he is interested is in the glenoid bone loss which we will come to later. Alpsa, anterior labral periosteal sleeve avulsion is a condition in which you can see the labrum torn. So the periosteum is still intact and this labrum kind of gets bunched up, displaced inferiorly and medially like a rolled up shirt sleeve. So here is an example this is the torn anterior inferior labrum which is got displaced medially and inferiorly. Glad glenoid labral articular disruption. Here you can see a tear of the labrum and a piece of the adjoining glenoid cartilage has also come off along with it. Here you can see there is a piece of the cartilage which has come off along with the labral tear. Now this was a patient whom we scanned when the shoulder was in anterior dislocation and as you can see here this is the shoulder dislocated anteriorly. So this labrum here is torn and you can see the glenoid impacting into the humeral head and so you will end up getting an impaction fracture along posterior superior humeral head which is the hill sacs lesion. When we see hill sacs lesion it can be very shallow flattened kind of hill sacs as we see here or it could be more deep and wet shaped like here. We need to give the dimension especially this transverse dimension and the depth. This transverse dimension is what is used to determine whether the lesion is engaging or not engaging which will come to slightly later. Do not get confused with this appearance for a hill sacs lesion. A hill sacs lesion will always be seen in the superior most sections where the humeral head begins or above the level of the coracoid process and then it may be large and may be extending below. But if you see something like this which is only in the lower humeral head then it is a normal anatomic groove and we should not get confused with the hill sacs lesion. Coming to the next kind of instability which is posterior instability less common than the anterior instability but usually the patients with anterior instability come to us saying a history of I could feel the shoulder popping out. Here the history may not always be forthcoming the history could be just pain during certain moments and we need to look at the constellation of findings on MRI to diagnose this. So here this is the normal position and now the humeral head is getting dislocated posteriorly and inferiorly. So the posterior inferior labrum gets torn as the humeral head dislocates posteriorly and the impaction injury is seen along the anterior humeral head. So this is called reverse bankard lesion the labral tear and the impaction injury here is the reverse hill sacs lesion. Again a patient who was scanned while his shoulder was in a posteriorly dislocated position and you can clearly see there is an impaction fracture along the anterior humeral head which is the reverse hill sacs lesion and when the humeral head dislocates posteriorly you get a tear here in the posterior inferior labrum which is the reverse bankard lesion. So here is the classic appearance where you have a slightly flattened reverse hill sacs lesion there is marrow edema there suggesting this is an acute event and here you can clearly see the intact anterior inferior labrum while the posterior inferior labrum is torn. Again the sagittal images shows here the extent of the posterior inferior quadrant labral tear. But sometimes the history would not be that of a dislocation it can just be some pain and discomfort. And here what do we see there is posterior labral tear the anterior labrum is seen normal there is a clear posterior labral tear. Also what you see is there is bony osceus remodeling look at the anterior glenoid and here if you see there is osceus remodeling and then this capsule here is lax. So putting these findings together we can suggest that it is possible there is posterior instability for which clinical correlation with the instability test would need to be done. Another structure we need to look carefully at is the inferior glenohumeral ligament. So this here is the inferior glenohumeral ligament the axillary recess region and during dislocation you can have injury to this. And for the surgeon when he goes in arthroscopically this is an area which is difficult to visualize. So he would want to know beforehand if the inferior glenohumeral ligament is intact or not. Here in this patient you can see the normal inferior glenohumeral ligament is seen as a well defined thin hypo intense band but here at the humeral attachment it is torn. So this is what is called as haggle, humeral avulsion of glenohumeral ligament. You can have a similar injury at the glenoid side and that would be called as gaggle, glenoid avulsion of glenohumeral ligament. Sometimes you can have osceus avulsion either from the glenoid attachment or from the humeral attachment. Next coming to the most important question that the orthopedic surgeon is interested in and it is is there anterior inferior glenoid bone loss and if so how much is it? Now if you look at articles there are a number of methods that one can use but the one which we use is the best fit circle method. So this is the normal glenoid if you look at it the anterior inferior quadrant has a convex anterior margin. Something which looks like a pear shaped or as Dr. Resnick says he calls this the avocado shape and with recurrent dislocation this portion of the glenoid with every dislocation some portion of the bone is getting worn off and you start seeing a straight line like this where you know that there is glenoid bone loss and we need to measure how much this is. So the method we follow is for this you need to get a good sagittal plane proton density image and then you draw a line along the axis of the glenoid a longitudinal line this yellow one. Then draw a circle which best fits the posterior inferior and the inferior margin of the glenoid. So this portion should be fitting well into the circle now the anterior and the posterior diameters of this circle should be of the same size. If there is bone loss then we can calculate the percentage this is how we calculate the bone loss. So after having drawn that circle here this is the diameter of the expected intact glenoid and this here is the bone loss. So the bone loss divided by this actual glenoid diameter multiplied by 100 will give you the percentage of the bone loss. A 3D CT is supposed to be the best method to measure the bone loss and when you do CT since you obtain images of both the shoulder you can compare both sides and you can measure the glenoid bone loss. Now why is this so important to the surgeon because if the glenoid bone loss is significant then just repairing the labrum reattaching the labrum is not enough because the glenoid itself has lost its normal pear shape the surgeon needs to do a procedure called as lethargy surgery and this lethargy is usually done as open surgery. You take a piece of the coracoid process and attach it to the glenoid trying to make the glenoid more pear shaped. So this is something the surgeon wants to know beforehand so that he can plan his surgery accordingly. Now is there an absolute figure that about 20% he is going to operate about 25% he is going to operate? No. The surgeon would keep in mind the status of the labrum, the capsule and the bone loss altogether and before deciding on lethargy procedure but usually about more than 20-25% is when they consider it more significant. A new concept is on track versus off track lesion. So if you imagine this hill sack lesion if this hill sack lesion is very large much larger than the glenoid then during abduction and external rotation it will lock itself against the glenoid and this will lead to recurrent dislocation. So in this situation it is not enough to only repair the glenoid labrum and the glenoid bone but it is also important to address this hill sack lesion. So when we talk of on track versus off track the glenoid track means the part of the glenoid which is in contact with the humeral head during abduction and external rotation and that is 83% of this intact glenoid expected diameter. So from here till here or twice of ab is what would have been the expected glenoid diameter 83% of that from that you subtract the bone loss this measurement from anterior margin to the circle this and that gives you the glenoid track. It is called on track or non engaging lesion when the glenoid track is larger than the hill sack interval which is the transverse dimension of the hill sack lesion the maximum transverse dimension. It is called off track or engaging lesion when the hill sack interval is larger than the glenoid track. So when the hill sack lesion is large to prevent recurrent dislocation one needs to do a procedure called as REMPRISAGE where this infraspinatus tendon is attached to the hill sack lesion by a suture anchor so that it fills up this concavity. So to conclude we need to know the anatomy very well we need to give the information which will decide the management that is the status of the labrum the status of the capsule and the status of the bone if there is any bone loss on the humeral side as well as on the glenoid side. We need to be aware of normal variants and pitfalls. Thank you.