So, we'll get started without further ado, and it's a real pleasure to invite Dr. Christine Chung from San Diego to deliver the first talk, and she's going to be focusing on the shoulder. Good morning, everyone. It's really a pleasure to be here, and I wanted to thank Andrew and the organizing committee for the opportunity to share the podium with such a group of experts. So, we'll go ahead and get started. As we think about tips and tricks for the evaluation of shoulder radiographs, I've set out a few potential points for us to consider here. So, initially, as you consider approaching the radiograph, similar to MR, we have to have really a dedicated way to do that, so an ABC-type system. I've chosen alignment bones, excuse me, cartilage, soft tissues. While we don't see cartilage when we're looking at radiographs, that will be sort of our buzzwords for looking for joint space preservation or narrowing. We want to be able to assess the whole articulation with the views that we are acquiring, so you have to see the whole picture. Maybe not the A to Z, but the AP view to the scapular Y view. In our practice, the internal rotation, the external rotation, and the axillary views are the standard radiographic assessment. The one-view study is a no-view study, or is it? Clearly, we want to have a full evaluation of the articulation, but when we identify findings on only a single view, don't discount those because you're not seeing them on another view. Really try to holistically assess the radiographic study. And the eye sees what the mind knows. So, this is a bit of a double-edged sword. You want to be an insider. You want to know what you're looking at, but you don't want to be overly biased. So, as we consider the approach of the radiograph, know what you're going to be looking for. Observe actively. Use all the information you have, including looking at comparison studies. Be sure you know the history. Take a quick look at the EMR. I know you're thinking, this is a radiographic study. How much time can I spend going back to look at all of these things? But if you have the luxury to be able to do that, it markedly increases your accuracy and your ability to detect these subtle findings. So, no normal. External rotation view on the left, internal rotation view in the middle, axillary-wide view. Look at the alignment. And we're going to focus here on glenohumeral joint alignment today. You want, of course, that articular surface of the humerus to be contacting the glenoid. Look at your osseous landmarks. The lesser and greater tuberosity is an external rotation with the bicipital groove between. When you're in internal rotation, of course, you're going to remember that you're looking at two crescents. The crescent below all of this is the greater tuberosity, the articular surface above it. Here, your lesser tuberosity bicipital groove over the anterior aspect of the greater tuberosity. And those landmarks in the real estate that you are assessing on these radiographs. And of course, in the axillary view, giving us another way to look at the joint space. Remember in the shoulder that the alignment with respect to that humerus articulating with the glenoid is giving you secondary information about the integrity of the rotator cuff. So another way that we're looking at the soft tissues. And knowing normal happens with time and repetition. The more cases you see, the more that's imprinted in your understanding of the pattern of what a normal shoulder looks like. That serves as the template for you to then identify what is abnormal. So let's apply these findings to our first case. As we look at the external rotation view here and consider alignment, humerus articulating with glenoid. Of course, remember now, no high-riding humeral head. The secondary implication here is that in this case of OA, our rotator cuff should not have a massive tear. When we look at osteostructures, remodeling of the greater tuberosity, subchondral sclerosis, osteophyte formation, moving to that axillary view and identifying asymmetric joint space narrowing, possibly even with a little mechanical erosion at the anterior margin of the glenoid. We get so much information from the radiographs. And when we move to an MR imaging study, we see that our conclusions were fairly correct. Intact rotator cuff degenerative change and the localization of the joint space narrowing accurately depicted from the plain film. Well, let's move on to another case assessing this alignment. Superior subluxation of the humeral head with respect to the glenoid. Anchor sutures in place here in remodeling of the greater tuberosity, giving you the hint that this person has had rotator cuff repair and previous pathology. You are expecting, in this case, a massive rotator cuff tear based on the alignment. Looking at the osteostructures, osteophyte formation, moving to the axillary view, looking at the joint space narrowing here, you see the distribution of joint space narrowing and even here, again, mechanical erosion with some loss of bone stock. You're getting a massive amount of information from the plain film study. Moving to the MR and corroborating those findings, again, fairly accurately to the level of the joint space narrowing. Here you're seeing, because of that superior subluxation of the humeral head, now it's articulating with the superior half of the glenoid and the coracochromial arch. You see the significant superior joint space narrowing, asymmetric joint space narrowing at the inferior margin of the glenohumeral articulation. Well, as you look at this view in external rotation, looking at the alignment, the overall morphology of the joint, you may think that it's normal. Subtle finding, a little bit of sclerosis here. One view, looking at the second view, having the whole picture, we're unmasking here significant pathology in the form of this Hill-Sachs lesion. We need all the images. If we knew that this person had a previous anterior dislocation, we would, of course, be cued into those findings even before we opened the study. Of course, that Hill-Sachs lesion nicely profiled on the axillary MR view. Well, alignment, again, a key thing that we're looking at. In this case, the patient in internal rotation. No overlap of the humerus with respect to the glenoid. And as you look at the contour or the bones again, with our organized and systematic approach, we see a defect there that were we told the patient had had a posterior dislocation, we would be looking for those findings. But they are there before us. As we then look at the post-reduction images, we can find the same findings. We see the area of impaction along the anterior margin of the humerus and posterior margin of the glenoid with the corticated ossicle. The MR showing us those exact findings. So now, again, looking at our humerus in external rotation, the alignment looks OK here. Let's look closely at the osseous contour when we're assessing the bone. Very careful assessment, running your eyes along the articular surface, identifying subtle areas of cortical irregularity. As you look closely at the greater tuberosity here, sclerosis with a bit of lucency. Subtle are these greater tuberosity fractures. Of course, they're very prominent on the MR images. As we look at another example, same kind of findings. You see a subtle lucency, areas of sclerosis, impaction, very subtle contour irregularity at the junction of the greater tuberosity to the articular surface. Looking at the alignment, looking at the bones, you're noticing the subtle change in contour, the sclerosis, potentially the lucency. Now, notice the imperative nature of having true external and internal rotation. With external rotation, you're profiling the greater tuberosity. Even with a little bit of internal rotation, you markedly decrease your ability to really assess the quality and contour of that bone. And then, of course, here with another external rotation view at the two-month follow-up, we can profile the remodeling that resulted from that greater tuberosity fracture. So now, we have a patient who is limited from the standpoint of their ability to really comply with all of the different views needed. And this is common in people who are coming for radiographs. They're in pain, particularly the ones who have had a traumatic injury. We may not get perfect views. As you look at this view, internal rotation, the arrows pointing out the cortical discontinuity, fairly obvious. So, we know when we have a surgical neck fracture that we want to keep looking to see if that fracture has extended to other parts of the humerus. In this case, very common to have the surgical neck fracture extend through and isolate the greater tuberosity. That wasn't called on the initial image, to be fair, osteopenic patient, limited views, but something that you should be looking for and became evident on the follow-up films. So, look at the whole picture, know what you should be looking for in potential complications to be able to raise the possibility or detect. As you're looking at these series of images, here focusing on the scapula, subtle lucency here in the region of the scapular spine, that's a normal variation. So, know the variations that we can see in the different osseous structures as well as osseous morphology. Here, you can see a lucency again, but now we're in the body of the scapula, away from the area where we see those normal variations, that lucency is larger. You're seeing an accompanying cortical defect. Your observation of the osseous findings help you make the correct diagnosis. And just a reminder that when you're thinking about fracture, often we think about lucency, but particularly in the scapula. In many cases, the fracture actually has overlap, so it may look like sclerosis instead of lucency. Remember that, that's something you need to know. And also, as you assess the osseous structure, look at the subtle cortical step-off there that's going to help you. Looking holistically at the images, you know this patient had trauma, because in this case, you're also seeing a clavicle fracture. Where there's one, there can be more, so be sure that you keep looking. Now, if we think about, again, looking at the alignment, it's intact as we're thinking about the glenohumeral articulation. Look at the osseous structures, identifying an area here of sclerosis. Single view, could it be inside the bone, or is it outside the bone? Comparing then to your other views, a scap-y axillary view, you identify that area of sclerosis and can accurately say that that's hydroxyapatite. Because you know the osseous morphology, you can localize it. Here you are, you know that in internal rotation of the humerus, you're at the posterior aspect of that greater tuberosity in the region of the oblique facet. That's confirmed as you're looking at the axillary view. This is in the region of the infraspinatus. You look closely at that area of sclerosis. Well, let's look at another example. Again, looking at the initial frontal radiograph, here's the area of increased density. Moving to the second view that tells you this is outside the bone, not inside the bone, here you're identifying that area of increased density. Now, in contradistinction to the one you previously saw, this isn't homogeneously dense. Rather, you're seeing a focal area of lucency there. That suggests that you've got crystalline calcifications here. And the location looks like it's outside of the expected position of where your subscapularis may be attaching. That's borne out as we look at the MR image with this intense inflammatory response. In this case, a calcific bursitis with that crystalline component of the calcification. You have localized. You have characterized the soft tissue finding. And through your observation, not only identified the fact that you have something in the bursa, but the fact that it's crystalline in nature. So, an immense amount of information coming from the radiograph. So, in our time together today, hopefully I've given you some tips and tricks to help depth, deepen your ability to kind of ferret information out of the radiographs. And honestly, looking at radiographs is one of my favorite things to do. Although our trainees are often really focused on the CT, the MR, the cross-sectional imaging, as Andrew indicated, it really is an art that you can gain so much information from. Thanks for your attention. Thank you. It is a privilege for me to be here and to be able to talk about something that I love, both conventional radiography and arthritis. I have one particular objective. We're going to review the distribution of common and a few not so common articular diseases that involve the joints of the hands and wrists. And we'll come up with particular target areas that are affected in each of these articular disorders. I call this the target area approach. Let's start with the hand. And this is my drawing. I would admit it's not the best drawing. The thumb didn't come out quite the way I wanted. But you recognize these joints, the proximal and interphalangeal joints, the distal interphalangeal joints, the metacarpophalangeal joints, and the interphalangeal joint of the thumb. In rheumatoid arthritis, we deal with the disease that's bilateral symmetrical with predominant abnormalities involving the metacarpophalangeal and proximal interphalangeal joints. The most common joints that are initially involved are shown in orange, the second and third metacarpophalangeal joint, and the third proximal interphalangeal joint. This is a classic example of rheumatoid arthritis showing you the early radiographic findings at a typical target site. Soft tissue swelling, that is fusiform, osteopenia, that is periarticular, joint space narrowing, that is diffuse, and erosions that are marginal in distribution. At the metacarpophalangeal joints, the erosions in rheumatoid predominate on the radial aspect of the metacarpophalangeal heads, at least initially, as shown in this example. We turn our attention now to osteoarthrosis and inflammatory osteoarthritis, where the major abnormalities occur in the proximal and distal interphalangeal joint. In osteoarthrosis, there are two fundamental radiographic features. Diffuse joint space lines and osteophytes typically at the margins of the joint. What's nice is the way the two bones fit together snugly like the pieces of the puzzle. This is very, very characteristic of ordinary osteoarthrosis of the digits. At the metacarpophalangeal joints in osteoarthrosis, there's one fundamental radiographic feature, and that is diffuse loss of joint space. Therefore, if you see erosions, you're not dealing with this disease. And if you see prominent osteophytes at this particular location, it may be another disease that you ought to consider. In inflammatory osteoarthritis, we paint a picture of inflammation on one or two of the joints involved in ordinary osteoarthrosis. Here, things look a little bit more aggressive. The degree of collapse, subchondral bone collapse, essentially, is more prominent. It looks a little bit like a broken pencil. And indeed, what can occur is deviation of the digits in a radial or ulnar direction that can be quite dramatic at these joints that have inflammatory osteoarthritis. As opposed to the symmetry of rheumatoid, psoriatic arthritis is asymmetrical in many cases. More than that, it is unilateral. More than that, it is ray-like in distribution. It may involve multiple articulations of one or two fingers and spare the others. It may also produce significant erosive abnormality of the distal interphalangeal joints. I show you an example of psoriatic arthritis with a ray-like distribution. You can appreciate here the involvement of multiple joints in a single finger, marginal erosions, and joint space loss. Let's see if I can get that to, okay. Calcium pyrophosphate crystal deposition disease is an interesting entity. It's a very common articular disease in middle-aged and elderly persons. We think of this particularly with the crystal calcium pyrophosphate. We look for cartilage calcification known as chondrocalcinosis. And we look for structural joint disease pyrophosphate arthropathy that looks a lot like OA but differs in terms of morphology and distribution. Here's the classic appearance of pyrophosphate arthropathy in the hand, typically bilateral symmetrical, predominantly involving the second and third metacarpophalangeal joints as shown here. If you're lucky, as in this case, one of the arrows showing you there is calcification. But indeed, in some of these cases, you get pyrophosphate arthropathy without calcification. There are a number of diseases that are associated with calcium pyrophosphate crystal deposition. I provide you with a list at the bottom left. I illustrate one of those, hemochromatosis. The arthropathy of hemochromatosis is very similar to idiopathic pyrophosphate arthropathy. It's bilateral, it's symmetrical, it involves the metacarpophalangeal joints. But here, all of the metacarpophalangeal joints may be involved. And one of the characteristic morphologic features shown at the bottom right are beak-like osteophytes that may be seen on the radial aspect of the metacarpal heads. Although we don't think of septic arthritis that often in the hand, it may involve the metacarpophalangeal joints as in this case with marginal erosions and joint space loss. When you see this, you can almost predict what's occurring. This is the fist fight. This is the person who is struck in the mouth, okay? And you can see the damage that may occur following that. And long after the supposed loser's mandibular fracture has healed as shown here, the winner may have a septic arthritis of the metacarpophalangeal joint. The diagnosis made easy when there is dental material adjacent to the involved joint, as in this case. Let's move on now in the last part of this lecture to the second target site. Here we deal with more complex articulations. I'm showing you those on a couple of drawings, my drawing in the bottom right, the easier one to see these articulations. The major joint is the radiocarpal RC joint between the distal radius and the proximal carpal row. The second, labeled IRU, is the infraradioulnar joint, separating distal portions of the radius and ulna. The third is a meandering joint between the proximal and distal carpal rows, known as the midcarpal MC joint, and I separate off the triscathy portion of the midcarpal compartment. More distally, we have the common carpometacarpal joint and the first carpometacarpal joint. And peeking from one of those images, the top, you can see the pisiform triquetral compartment. In rheumatoid arthritis at an early stage, bilateral involvement, pancompartmental involvement, that is classic even in early rheumatoid arthritis. I show you that in cadaveric sections on your right, showing you here in a cadaver with rheumatoid arthritis, pancompartmental involvement. Now, as I look out, I imagine some of you are pretty good at this. And if you're good at this, you'll sometimes diagnose rheumatoid arthritis with more selective involvement of the radiocarpal and distal radioulnar compartment. We all know to look for the ulnar styloid erosions and the swelling that can occur around it. But soon, the rule is pancompartmental disease in rheumatoid. When we deal with gout, we deal with pancompartmental involvement also. It may be asymmetrical, but there's an important distribution rule. If you see pancompartmental involvement with the predominant abnormalities at the common carpal metacarpal joint with erosions of the metacarpal base, think of gout. The second pattern we deal with is what we see in osteoarthrosis and inflammatory osteoarthritis with involvement of the radial aspect of the rift, the first carpal metacarpal joint or the triscaphe joint or both joints together, very, very typical. Here I show you an example at the bottom right, radiographs OA, first carpal metacarpal and triscaphe joints. The third pattern is what we see in pyrophosphate arthropathy, bilateral, yes, symmetrical, yes, dominant involvement of the radiocarpal and midcarpal compartments. And the most characteristic finding is narrowing shown on the bottom right between the radius and the scaphoid with excavation of the scaphoid fossa of the distal radius. There's also disorganization in the midcarpal joint often with abnormal tilting of the lunate and there's abnormal calcification in many of these cases. Bottom right, you can see the calcification in the triangular fibrocartilage. Now pyrophosphate arthropathy can look like two post-traumatic abnormalities that occur in the wrist. But this occurs at patients of any age, even young people and typically unilateral. The first shown there is scapholunate advanced collapse, we call it the slack wrist. It's a form of scapholunate dissociation associated with multiple ligamentous abnormalities of the wrist. The second shown on the bottom center image is the snack wrist, a chronic non-united fracture of the scaphoid with narrowing between the radial styloid and distal pole of the scaphoid. They look a little bit like pyrophosphate arthropathy, but the major difference, patients of any age, not just older people, typically unilateral, often a history of trauma and there may not be calcification. We'll finish up in the last couple of minutes here, just showing you a couple of the patterns. If you see selective involvement of the base of the thumb, that is the first carpal metacarpal joint, osteoarthrosis, of course, but I want to also point out scleroderma. You will get subluxation at this particular joint. You'll get joint space narrowing and you may, as shown on the bottom right, get hydroxyapatite calcification in and around the joint. And then the final pattern is isolated involvement of the triscaphe portion of the midcarpal compartment. Yes, we see this in osteoarthrosis, but we also see it in pyrophosphate arthropathy. In this example, chondrocalcinosis in the triangular cartilage and disease involving the triscaphe portion of the midcarpal compartment. So what I've done in my allotted period of time to show you how the target area approach works, we've looked only at the hands and wrists. Remember the patterns, the distribution, better shown, I think, with conventional radiography than with MR imaging. I thank you for your attention. Thank you, Andrew. And to the other speakers, I've been talking about the hip and I realize this is a terrible title that I picked. Sorry. But the radiographs of the pelvis and hip are really straightforward. There's just one or two lines and landmarks to look at. So I'm listing them here. We'll go through all these, obviously. You may want to throw in a couple of measurements. And for good measure, there's several different projections to look at too. And Andrew's giving me 10 minutes, so this shouldn't be a problem. But what I'm going to do is concentrate on one very small part, and that is thinking about the hip as a ball and socket joint. And you know what a ball and socket is. You get a lot of motion there. And the ball, obviously, is going to be the femoral head and the socket is going to be the acetabulum, two round circles. Now, they're not complete circles because we have the femoral neck and the acetabulum is open inferiorly and laterally. And frankly, even the acetabulum is not a great circle because we have this inner part, the acetabular fossa, where there's no articular cartilage. So to simplify it even more, instead of two circles, let's just look at two arcs, okay? So we have two arcs in the normal hip joint. They're parallel to each other. They're about the same distance apart. And obviously, what's inside there is articular cartilage, which is going to be invisible. Immediately, it's going to look wider because of the acetabular fossa. Now there's one other part of the joint that sometimes you get a chance to see. So when we do a frog leg lateral, we're still looking at an AP of the pelvis, but we've rotated the femoral head. We can now see a different part of the femoral head, and we can see the posterior inferior joint space. And just like superiorly, that should be two parallel lines about the same distance apart. So now that we have these two lines or two circles, and that's our normal pattern, we could look at a couple of different patterns. And each of these has a pretty small differential diagnosis. Uniform narrowing, the two are close together. Non-uniform narrowing, widening. Or we could have the two circles move with respect to each other, what we call subluxation. Or the acetabulum can be bulged inwardly, what we call protrusion. Or we could even lose the nice round circle and have collapse of, say, the femoral head. So starting with that uniform pattern, which is what we see here, this really has a small differential diagnosis. And frankly, you've heard about it already this morning. It's inflammatory arthritis, like rheumatoid or seronegative arthritis, uniform cartilage loss, or septic arthritis. This patient happens to have rheumatoid arthritis. So notice, just by looking at two lines, we had a small differential. We didn't talk about erosions. Is there osteoporosis? Is it symmetric? Anything like that. Two lines, and you're already on the right path. Same thing here. Now again, we have uniform joint space narrowing. This patient happened to have a fever, and this was septic arthritis. You can see on the MRI the amount of inflammation in the soft tissues, bone, and joint. Now I could tell you these are two different patients with hip pain, and the surgeon was convinced. There was FAI, which I said I wasn't going to talk about. But you could see why, because there is this acetabular overcoverage. There's this bump there. But you guys are way smarter than our surgeon, because you're looking at that and saying, well, wait a minute. There's uniform narrowing. There's another reason. And your best friend, when you're looking at the hip, is the sacroiliac joint. So in this case, where we have fusion of the sacroiliac joint inflammatory arthritis, this is ankylosing spondylitis, this other patient has psoriatic arthritis with narrowing of the SI joint. And really, everyone needs a best friend, right? Whether you're Paris and Nicole. At my house, it's Pirate and Augie. Oh, right, exactly. Thank you. And the hip and the SI joint, in this particular case, the SI joint is very sad, because his friend the hip has an acetabular fracture. Now sometimes you'll see uniform narrowing, but those two white lines are gone. That's an important clue. If those white lines are invisible, they've been erased, that means there's erosions. And all those diseases I just talked about can have erosions. So when you see those white lines gone, this is what you're picturing. This is the same patient, a million tiny erosions all along that surface. And you can also use that pattern to help when there's another pattern. Say there's acetabular protrusio, and you're trying to figure out what's causing that. Well, we can, again, look at the superior part of the joint, see there's uniform narrowing, and this was a patient with rheumatoid arthritis. So the pattern of protrusio, where the acetabulum is bulged inward and the femoral head moves again with it, is really due to bone softening. And that has a small differential diagnosis. Diseases like osteomalacia, the inflammatory arthritis we've been talking about because of hyperemia, and diseases that change the structure of bone, like pageant disease and fibrous dysplasia. Now non-uniform narrowing is really what, as you heard about already, is the hallmark of osteoarthritis, DJD, and that could be either primary or secondary. And where the narrowing is can be anywhere it wants along that surface. So for example, this patient with primary osteoarthritis has the most narrowing straight superiorly. You can compare it to what it looks like more medially and more laterally. A patient like this has osteophyte formation, so we think, well, there's probably going to be osteoarthritis. Where's the non-uniform narrowing? Eh, maybe, but remember, there's another part of the joint that's easily accessible. So on the frog lateral of the same patient, we could see the posterior inferior joint narrowed compared to superior. Again, that's non-uniform narrowing. This is a patient with hemophilia and secondary osteoarthritis. Now sometimes with OA, what you'll see is that the hip will sublux. So in this particular patient, the hip is subluxed laterally with respect to the acetabulum. And you might say, well, we're, you think of that subluxation diseases like developmental dysplasia, for example, when the acetabulum is not completely formed, but it can happen in osteoarthritis. Now, why is that? Well, in this particular case, the narrowing is superolaterally. So we've lost cartilage there. Bone moves against bone. And we have something else going on. Remember I said the acetabular fossa should be empty. In this case, we have a white rock inside there. That's a medial osteophyte that's pressing the femoral head outwardly. And where the hip moves in osteoarthritis depends on where the narrowing is. So if the non-uniform narrowing is superomedially, in this case now the femoral head moves centrally or axially. And again, you'll say, well, wait a minute, I was told that rheumatoid arthritis, that's how it works. And true, that is how it works in rheumatoid arthritis. If you have uniform narrowing, concentric narrowing, the femoral head moves along its long axis, which is also centrally. So realize that the idea of subluxation is actually nonspecific. You have to step back and not just blindly apply a rule, but rather think of what else is going on that explains the subluxation. Now what about widening? Widening is typically due to some sort of entrapped tissue, often a fracture fragment, although sometimes we see it with femoral head bone loss. So in this case, clearly widening. You could use the other side for comparison. Hopefully you didn't need to. And we see there's a fracture of the posterior acetabular wall. Right away we say, aha, there's going to be a fracture fragment inside the joint. And that's when we're going to go ahead and do a CT and identify that fracture fragment. Obviously now this patient needs open surgery to fix that. And we want to detect this preoperatively. This is what we do not want to see. So this is a patient who had a femoral head fracture, a Pipkin fracture, underwent internal fixation, and postoperatively we have widening in the joint. You know what that means. They missed a fracture fragment inside the joint at the time of surgery. Again, we can show that with CT. And unfortunately this patient now requires a second operation, open dislocation, removal of the fracture, and they had to refix the posterior wall as well. Now here's a young patient, no trauma, but again with a widening of the joint. We can compare one side compared to the other. But in this case, the problem is not the joint, but it's the ball, right? The round ball is no longer round. If we look at the height of the epiphysis on the affected side versus the other, we could see that that has collapsed down. And this is a patient with leg Perthes disease. So widening together with collapse is another pattern to look for. Again, this patient clearly has uniform widening, no trauma. But if you look at the ball and socket, let's look at the ball. It should be a nice round circle. We're missing a big crescent of that top of the circle. We have bone loss here. To figure out why we have bone loss, we can look back a couple of months. This patient had severe osteoarthritis, and this is what we call rapidly progressive or rapidly destructive hip arthritis, one of the patterns of osteoarthritis where you actually have predominantly bone loss. That brings us to our last pattern, which is collapse of the femoral head. So we already said you could see that with bone loss, but by far the most common cause of collapse is going to be osteonecrosis. So you take a patient like this, and what catches your eyes obviously is there's sclerosis, indistinct trabeculae, there's some rarefaction. But just take a step back. Is there a ball? Is there a socket? And if you look at the ball, it's not round, right? We're missing the top of the ball. Again, that top of the femoral head has collapsed down due to the osteonecrosis. So just looking at these two lines and applying some very simple rules, you can very rapidly come to a differential diagnosis. And I'm going to give you here just the most common causes of uniform narrowing is going to be an inflammatory or infectious arthritis, non-uniform narrowing. I don't use the word symmetric, by the way. I notice Christine does, because symmetric to me means right to left. But you get the idea. It's within the right, within the joint, osteoarthritis, widening, typically in a trapped fracture, subluxation, remember, is nonspecific, a lot of different things can cause that, protrusio going to be due to a softening and then collapse, most commonly due to osteonecrosis. We're going to talk about the lower limb, sorry, we're going to talk about the knee. And I've sort of thought about the fact that I only gave myself 10 minutes for this talk. So what am I going to talk about? And I thought, well, let's focus our attentions on the lateral radiograph. I could have talked about trauma, I could have talked about arthritis, but actually when I spoke to my residents back at home, they said that what they really took from one teaching session I did was about the lateral radiograph. So let's talk about it, because whenever you look at a radiograph of a joint, everybody has their favorite view. You know which is your favorite view, because that's the one you look at first. And most people with the knee look straight at the AP, and then they look at the lateral and they have a quick scan, check there's not an effusion, check there's not a lipohemothorosis, maybe comment on a loose body, and if they're really going for it, the alignment of the patella. But there's so much more we can say about a lateral radiograph. So the first thing I'd like to consider is that the femoral condyles are not uniformly smoothly curved, as we can see here. There's a depression highlighted here on the lateral femoral condyle. If we get a better idea of the anatomy, we can look at these two sagittal knee CT reconstructions, which I've taken through the lateral tibial plateau, or lateral side of the knee, I should say, and the medial side of the knee, as we can see there. And we can see that both the femoral condyles have a flattening on them. There's a difference though, notice that the lateral side, that flattening is more posterior compared to the medial side, where it's more anterior. This is the terminal sulcus. Terminal sulcus actually represents the junction between the patellofemoral joint and the tibiofemoral joint. And we can see them on this schematic and also on this dry specimen. I took so much time photographing that dry specimen, so appreciate it, okay? Getting the light to show those sulci is virtually impossible. I was sat in my room for a long time doing that. Anyway, here we go. There's the lateral sulcus, there's the medial sulcus. Notice the medial one is more anterior. So if we go back to our lateral radiograph, we can use these sulci to demonstrate which femoral condyle is which. If we bear in mind the medial femoral condyle outlined here has the more anteriorly located sulcus, whereas the lateral has the more posterior aligned one. Now, one of the problems we have is it's actually quite unusual, I got lucky with this radiograph. It's quite unusual to see both sulci. Usually you can see the lateral one. It's harder to see the medial one. So what can we do? Well, we've got a way we can deal with that. Remember when we look at our MRI or our CT scan, we're familiar with this roof of the intercondylar notch that we can see just there. We call that Blumenstatt's line when we're looking at a MRI for some reason. When we're looking at a radiograph, we have the same line. We just don't call it Blumenstatt's line, it's somebody else's line. I don't know. But if we continue the line of that like that, it crosses the lateral femoral condyle at about the point where that sulcus is. Do you see that on that radiograph? So we know that when we see a sulcus roughly in line with that line, it's going to be the lateral one because the medial one is going to be more anterior to that line. I use that a lot. Go back to the CT that we had before though and notice that the tibial plateau has different shapes. You know this because you read MRs, but we don't always appreciate that on a radiograph. So if you remember, the medial tibial plateau has a concavity to it, as we see here, whereas the lateral one is flat, or even, as in this case, slightly convex. I remember it as lat is flat, because that's easy to remember. And we can see that we can apply this to the lateral radiograph, where we normally just see a complex pattern of overlapping lines, and people sort of look at it and go, yeah, that's about okay. But if we actually analyse that lines, we can see we've got a convex or slightly flat lateral tibial plateau, and a concave medial tibial plateau. And in this case, again, I got lucky. It's reasonably easy. Notice you can still see the lateral femoral condyle sulcus there. But I got lucky with this radiograph, because due to the excellent skills of my radiographers or techs in my department, they got it slightly oblique. You can see the femoral condyles aren't overlapping. And that makes it very clear where we see here. But actually, if we go to a much better lateral radiograph, as we see here, we can see exactly the same distinction. There's the lateral. It's flat or convex. And there's the medial. It's concave. You've got to analyse these lines. Now why is that important? When you're reading a knee radiograph, particularly for trauma, it's really important to follow these lines. So here's an example of a trauma radiograph. In this case, the AP radiograph, which I'm not going to show you, didn't show any fracture. But using what we know about the lateral, we can follow the flat lateral tibial plateau. There it is. It looks okay. Now we can do the same thing with the medial one. And uh-oh, there's a fracture there. So not only can we say that there's a posterior tibial plateau fracture here, but we can say it's a fracture of the posteromedial tibial plateau. And of course, we can confirm that with CT. But that breaks my heart to have to do that when you've diagnosed it on a radiograph. Now there's another couple of lines that I just wanted to highlight, and that's the relationships of the bones around the proximal tib-fib joint, tibiofibular joint. Notice here that on this coronal and lateral CT reconstructions, how the articular surface of the tibia at the joint extends over the proximal fibula. It forms a roof over it, something we can appreciate on the radiograph. There it is. And if we want to look for disease at the proximal tib-fib joint, this represents the tibial articular surface of that joint. Now going back to our CT, if we take an axial section at this level, we can appreciate that the medial side of the tibia lies posterior to the lateral side. That's quite important. Why is that important? Well, if we look at our radiograph, we should see two more lines overlapping the fibular head, representing the more anterior-posterior border of the lateral tibia and the more posterior border of the medial tibia. So you see those two lines beautifully there, and you can see how they match up nicely with the CT on that axial. Notice also how the line, particularly of the lateral tibia, should pass through the shadow of the proximal fibula. That tells you you've got a normal alignment at that proximal tib-fib joint. And notice also that if we continue that line that I've told you is the lateral border of the posterior tibia, it joins up with what we've already seen is the convex surface of the lateral tibial plateau. Now I couldn't finish my lateral knee talk without saying something about fat pads, because we see them very beautifully on a lateral radiograph. On this case, we've got a T1-weighted sagittal image, and we can appreciate superior to the patella, the suprapatellar fat pad, the pre-ephemeral fat pad, and if we go down below the patella, we can appreciate the hoffus fat pad, the infrapatellar fat pad. And hey, we see the same things on the radiograph. We look at this radiograph and we say, oh, great, the suprapatellar recess or bursa isn't distended containing fluid, but actually what we're seeing, we're seeing that recess because we can see the pre-ephemeral, the suprapatellar, and the infrapatellar fat pads. It all matches up perfectly. And there is our recess representing where we will see the effusion. Notice also we can see the quadriceps tendon here. People ignore the quadriceps tendon at their peril, I have to say. The quadriceps tendon not only looks like the quadriceps tendon that we'd expect to see on ultrasound and MR, because it has those three lines to it, because we know that the quadriceps tendon is receiving contributions from a lot of muscles in our quadriceps, four, in fact. So we know that the normal suprapatellar stripe is an undistended bursa. I take five millimetres as my thickness, but I was told by a much wiser radiologist than myself that whenever you see a radiologist with a ruler in his hand, you've got a radiologist who's probably in trouble. So I use my eyeballs to look at this. This is clearly a distended one. This is a joint effusion. Notice how we can still see the quadriceps tendon, despite the fact that we've got a joint effusion there. Notice also we can still see our fat pads, despite the fact we've got a joint effusion there. Follow the fat pads, they're our friend. We learn about the lipohemarthrosis here on a horizontal beam lateral radiograph, and as we expect, we see a lot more. We see still the pre-femoral fat pad. Anterior to that, we can see the suprapatellar recess containing fluid, in this case probably blood. However, floating on that fluid, we've got fat, and notice how we get a nice straight line between the fat and the fluid. That's what we expect. Notice also as we zoom in a little bit, we've got another line here. That's the anterior surface of the joint capsule, probably with a bit of synovial thickening as well. And guess what? Ahead of that, we've got our suprapatellar fat pad, and ahead of that, we've got our quadriceps tendon. And I've given you enough time looking at this radiograph for you to tell me why there's a lipohemarthrosis there. Of course, we've got a fracture. It's an avulsion of the ACL in this case. Last thing to say is we've clearly here got a big joint effusion. In this case, it was a hemarthrosis, and you can see the suprapatellar distended bursa there, but we just don't see the joint capsule distended there. Notice we can see it as well in an infrapatellar location. It's bulging into Hoffer's fat pad. Hoffer's fat pad is our friend, and again, there's a fracture in this case, and you probably spotted this on the lateral view of the patella. We did confirm it on the AP, but I hope I've shown you that the lateral radiograph really is our friend. You take nothing else away from this. If you didn't already know, know how to tell which condyle's which. Know how to tell which plateau's which. Also, try to understand the lines that we're seeing around the posterior tibia that are projected over the proximal tib-fib joint. Understand how that 3D anatomy works in two dimensions that we look. And I couldn't leave the lateral radiograph without saying the fat pads are important. Thank you for your attention. So, I, before I start, I would like to acknowledge and give a shout out to my former colleague, Dr. Connie Chang from Mass General, who provided some of the examples. Okay, so I would like to start with the most important thing. Don't miss foot and ankle trauma. So here we have a 20-year-old woman, rollover car accident. Not a diagnostic mystery. There is a little fragment here of the lateral talar dome, and this is an osteochondral defect. So osteochondral defects can be due to direct trauma. Typically it's high-impact trauma where you can see an osteochondral fracture, as we saw in our case, or cartilage delamination on MRI. This causes altered biomechanics and then can lead to progressive osteoarthritis and cartilage loss. But osteochondral defects can also be due to repetitive microtrauma on the subchondral bone and cartilage leading to OA. So what does the surgeon want to know if you're looking at a radiograph like this? They want to know the stability of the fragment. And this is the corresponding MRI of our patient. And you can see that this fragment is displaced, it's actually rotated. You see that the cortical bone is on the bottom. And they want to know the exact location and the extent involvement of underlying bone and associated injuries. Another case, 27-year-old man, status post-MBA. You see an obvious avulsion fracture of the medial malleolus. Also a fracture of the medial talus. But as Dr. Cheng earlier mentioned, don't stop looking. You should know where to look with this type of trauma. Please look at the talar dome. And there it is. There is another osteochondral defect of the lateral talar dome. And here we see it on CT. There it is, the little fragment. And again, the surgeon wants to know is it displaced, is it loose, and as it is here. Different case, 25-year-old woman with a twisted ankle. We see a lot of soft tissue swelling over the lateral ankle. But it's a little bit more distal than what you typically see with an inversion injury. And let's map this up. So there we see it again. If you look carefully, there is a little piece of bone. And this is a typical injury of an extensor digitorum brevis avulsion. And many always look at this if you see soft tissue swelling over the lateral ankle. And the EDB is one of the intrinsic foot muscles. It originates from the anterior calcaneus, as you can also nicely see on the graphic. And patients with an EDB avulsion typically have very distinct point tenderness on the lateral ankle. It's about 2 centimeter distal from the point where you typically have the inversion injury. And here's the corresponding MRI showing the avulsion fracture of the anterior calcaneus. A 30-year-old man with lateral ankle pain after a fall. A little bit more of an eye test. And here you see subtle linear lucency of the anterior process of the calcaneus. So this is an anterior process calcaneal fracture. And this was a little bit more difficult to see. And it's actually one of the most commonly missed ankle fractures. It has the same mechanism as a lateral ankle sprain, inversional implantar flexion. And therefore, often it can be missed because people just think it's an ankle sprain. Also has a similar presentation. Again, the tenderness is also a little bit more distal compared to a typical ankle sprain. Treatment is walking boot, a cast for four weeks. And if you don't, if you miss it and there is delayed treatment, it can lead to persistent symptoms and sometimes requires surgical intervention. Here we see a subacute injury. There is a little bit sclerosis and edema here on the MRI. So carefully look at the anterior process of the calcaneus. 25-year-old man, pain after fall. This is a little bit more difficult to diagnose because of the overlying cast. But take a look at the subtalar joint. There is a little bit of irregularity. And this was a talus lateral process fracture. So on the right, you see the normal subtalar joint. So look how smooth and round it is. Maybe I can go back here. And now take a look at the occasion with a fracture. You see it's irregular. So this is an area should always scrutinize in the setting of ankle trauma. And now let's take a look at the CT. So that's the corresponding CT, so much worse. And they are also referred to as snowboarders' fractures. And there is sudden dorsiflexion and inversion on a fixed foot. So it's typically the foot that is in the back of the snowboard. Or there are other mechanisms are typically fall from height. Also with significant trauma, as in this case, or MVAs. So they can be difficult to visualize on routine radiographs. And that contributes to the high miss rate. So if a patient has had high energy trauma, a negative X-ray, just have a low threshold to proceed to a CT. But always look at the subtalar joint and see whether it's smooth. 30-year-old woman with an inversion injury, we see a lot of lateral soft tissue swelling also at the dorsal aspect of the foot. There is the little bulging injury here at the capsule of the talon avicular joint. But if you continue looking, there is also a fracture of the base of the fifth metatarsal. And the reason why I'm showing you this is that often in the ED, they might only order an ankle radiograph. So the lateral view is the only one where you can see the base of the fifth metatarsal. So just make sure that you always scrutinize the base of the fifth on your lateral views. Here's a 30-year-old man, status post-MVA. We can see a lot of dorsal soft tissue swelling. Here are the frontal views and the oblique views. And you see, hopefully, all that there is some malalignment of the TMT joints, the first and second. So this is a list rank injury. So the list rank injuries are one of the leading causes for medical malpractice litigation against ER docs and radiologists. And it's estimated that up to 20% of these injuries are initially missed. And 50% of patients with list rank injuries pursue, actually, litigation up to two years after the injury. So the list rank joint complex is an articulation between nine bones, the five metatarsals and the three cuneiforms and the cuboid. And there are also the list rank ligament complex, as you can see on these cadaver images. Mechanism include high-velocity trauma, MVA, where you also often see fractures, but can also occur after low-velocity trauma. For example, plantar faction, axial load, forced abduction can occur just after running, jumping, or tripping off a curb. And they can also be purely ligamentous or have small fractures. These injuries can have serious complications or consequences. They can lead to rapid osteoarthritis or loss of the longitudinal arch. So let's take a look at normal radiographs. So the medial border of the second metatarsal should align with the intermediate cuneiform like this. And there should be less than 2 millimeter gap. So here on the left, you can see that the bones do not line up. There is a little step off. It's not very obvious, but that's how these injuries often present. So this is a list rank injury with subluxation. Take a look on the image on the right. So here, there is normal alignment. There is no subluxation. However, if you look carefully, you see these multiple comminuted bone fragments, and there's actually a fracture of the base of the second metatarsal. So you have to look at everything, not just malalignment, but also these small fracture fragments. So here, a question list rank injury, we see one side. And sometimes, comparison with the contralateral side can be helpful. So here, we see the other side. Now it's very obvious that there is something wrong, and there is some malalignment. So if you're not really sure, you can always ask for the contralateral side. Dorsal soft tissue swelling, does it help? You see the image on the left. There is a lot of dorsal soft tissue swelling, not on the right. Unfortunately, both had a list rank injury. So if soft tissue swelling is present, it can confirm it. But if it's absent, do not exclude a list rank injury. When in doubt, get an MRI. Forty-two-year-old man, status post-MVA. We only had an ankle series. If this is an osteoporoneum, the prior images saved the day. You can see it wasn't there previously. So this was a cuboid fracture. They can be difficult to diagnose on radiographs. Here is the corresponding MRI showing the fracture. A 35-year-old man with heavy object fell on the foot. Cuboid looks a little funny. There's some sclerosis lucency. That's the corresponding MRI showing a communoidic cuboid fracture. So when in doubt for these midfoot fractures, get an MRI or a CT. This is a 25-year-old professional ballroom dancer with sudden onset of lateral foot pain trying a new stance move on toes. So here we see a linear lucency at the base of the fifth metatarsal. And the location is really important. It's not like the one I showed you earlier on the lateral ankle radiograph. This is between the metathesis and the diaphysis of the metatarsal. And that's called a Jones fracture. So why do we care? Well, here, this is a month later. Now you see progression of the fracture. It looks actually worse. Two months later, it almost looks like non-union. There is now sclerosis at the fracture margins. And then the patient was made completely non-weight-bearing. And now it's finally healing. So these fractures occur in a watershed area between the metathesis and the diaphysis where there is poor blood supply. And there's a very high rate of non-union. So they need to be treated very aggressively with non-weight-bearing. And often they require surgery. So that's why important for you as a radiologist to say exactly where these fractures are. Now I just want to spend a couple of minutes on stress fractures, just because we are often asked to look for them on ankle radiographs or foot radiographs, 40-year-old man, runner with heel pain, subtle sclerosis, and that is a calcaneal stress fracture, and any bent-like sclerosis that is perpendicular to the orientation of the trabecula consistent with stress fractures. Here we see another one here on the other side right there. And this is the corresponding MRI. Here's another example of a tibial stress fracture. What about in the metatarsals? Because we are often asked to look for stress fractures and runners in the metatarsals, this patient has an obvious fracture of the second proximal phalanx. But don't stop looking. Maybe because of the altered biomechanics, there's very subtle linear sclerosis and lucency at the base of the fourth metatarsal, and that's consistent with a stress fracture. This is another patient with foot pain, very subtle periosteal reaction or periostitis, and which can be the only sign of a stress fracture or stress reaction. And the last case, this is a patient who actually suffered a fracture of the medial hallux sesamoid, and we had his radiographs 10 years later where you now see sclerosis of the sesamoid with abnormal morphology consistent with osteonecrosis confirmed on the MRI and the CT. So especially for these sesamoid fractures, or question is often sesamoiditis or osteonecrosis, sometimes it's helpful to get cross-sectional imaging. So just want to conclude with a checklist. Always look for the osteochondral defects, especially if the mechanism is right. Know the avulsion fractures and have a low threshold for talus, Lisfranc, and midfoot fractures to recommend cross-sectional imaging and know your stress fractures. Thank you very much.

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