 Let's move on to the hip. This is a six-year-old boy with right hip pain. Here's a radiograph, frontal projection. Let's look at what we can see. First, I look at the congruity of one hip joint versus the other. I look at the density. I look at soft tissues, and I look to see if there is a joint effusion. What immediately grabs my attention is the density on one side versus the other. You notice this is quite a bit brighter than on the contralateral side. In addition, there is a linear thin lucency just under the contral surface on the right, as you see over here. On the left, there's no similar lucency. Now, let's take a look at some of the soft tissues around this joint and compare it to this joint. I'm going to draw a line for you. This is the obturator-internus muscle. This here is the obturator-internus muscle. Okay? The distance, if we will, from here to here is bigger than the distance from here to here. So that tells me there is some elevation or displacement of that soft tissue structure. Also, the distance between here and here is going to be larger than the distance between here and here. Let's go ahead and measure that. That's about 1.1, and here it's about 0.73. So all that tells me is that there is a joint effusion on the right side, the increased sclerosis, and the lucency tells me that there's a little bit of collapse happening, and these are the classic findings of leg cavae perthes, or a form of avascular necrosis, if you will. Some people call it an osteocondrosis. Some people call it avascular necrosis. You know, there's no great answer, but it's an area where there's not enough perfusion happening to that femoral head. In the next vignette, we're going to show you what this looks like on MR imaging.