All right. So now we're going to change it up a little bit and we're going to talk about small breed dogs. We're going to talk a little bit about avascular necrosis of the femoral head. 

So this one we actually do know about the pathophysiology. So unlike some of our other juvenile bone diseases where you know we suspect that it's probably multifactorial. With avascular necrosis of the femoral head there's actually been some really good, you know, information that's come out about why they develop this disease process. So essentially what happens is that there is loss of vascular supply to the head of the femur. In the juvenile the femoral epiphysis is going to be entirely dependent on these little delicate epiphyseal arteries. So this is a picture of an adult femur and you can tell because there is no physeal scar remaining. So the physis actually forms a barrier to blood supply in the juvenile. You know, normally the metaphysis is very richly supplied with blood. And in the adult, blood vessels can travel within the, the bone itself, so that the, the femur, the, the entire head and neck of the femur is well supplied with blood. But in the juvenile, the physis is going to be going to be running basically right here, kind of where I'm indicating with my mouse. And so all of this rich blood supply from the metaphysis gets the feces and it cannot cross that physis is a barrier. Additionally, in dogs, the ligament of the head of the femur does not supply blood to the ephiphysis. That's different in cats, which is why we don't really see this disease process commonly in cats. Because in that species, the, blood supply coming in with the ligament of the head can supply, can help to provide kind of some redundancy in blood supply. So, both of those are no longer an option in our juvenile dogs. We can't get blood from the metaphysis. We can't get blood from the ligament or the head. And so instead, there's going to be these small little epiphyseal arteries that come off extra capsularly and then penetrate the epiphysis directly. And so what we have observed, there's been some cool anatomic, studies that have been done. There's actually an anatomic difference between how these epiphyseal vessels, run in small breed dogs versus large breed dogs. In large breed dogs these arteries have some redundancy. They've got some slack to them. And so they're able to run kind of right along the side of the bone to penetrate the epiphysis. And so they're relatively protected there. You know, they're laying right against the bone. There's, you know, some redundancy to them. So if the dog does something that kind of, you know, jerks the the joint space a little bit they're not put under too much tension. In small breed dogs that's not the case. The arteries are described as having a suspended bridge, anatomy. And so essentially there's little there's very little slack in them. And they, they kind of veer away a little bit from the bone. So they're kind of traversing the joint space, relatively unprotected. You know, they're not laying right on the bone and there's not much redundancy. And so there's the chance that if the dog does, you know, some little small dog thing, like, jumps off the couch or you know, runs after a cat, you know, if there's, you know, something that kind of, puts some tension on those arteries it's a part of normal range of motion of the hip that could potentially cause it to avulse, to snap, to potentially thrombose. And so they're more at risk for, injury as compared to the epiphyseal arteries in large breed dogs. 

If that happens, if we do thrombose or snap or you know, avulse, whatever, one of those little epiphyseal arteries then the bone that should be supplied by it begins to die. And so necrotic bone is going to be quite brittle. And so, as that bone dies and the organic component of it kind of goes away, we're left with just the mineral component of that bone, which is then going to begin to collapse just under the stresses of weight bearing. So these animals are not, you know, doing anything particularly traumatic they're just doing normal young dog things. They're running around playing and living their happy little lives. But since that bone is more brittle than it should be, it begins to crumble and kind of collapse and fragment in on itself. And remember, this bone that we're talking about is the epiphysis. So this is the part of the head of the femur that is right up against, that forms the joint space. This is the subchondral bone that we're talking about. And so as that subchondral bone begins to collapse, the articular cartilage laying over the top of it is now poorly supported, it begins to buckle, the joint surface is disrupted. And so with time, you know, now that we have this disruption of the joint surface, we don't have that nice, smooth moving, surface that we should have, we begin to get joint degeneration as a secondary change on top of it. And so if you look at this, this image here, this is actually dog with hip dysplasia, which we're going to talk about in a little bit. But you can see how this femoral head is remodeled. This acetabulum is remodeled. If you compare it to the normal looking hip over here, this hip is, showing signs of degenerative, degenerative change. And so the same thing will happen in these dogs with avascular necrosis. And so eventually, you know, if this goes on long enough, we can see that these animals end up with end stage DJD. 

So, like I said, this tends to be a small breed dog disease process. Usually it is unilateral. And so these guys will typically come in, quite painful and lame on one of their back legs. In rare animals, it can be bilateral. I think like 11% or something. Usually this is kind of subacute to a more chronic lameness. Every once in a while you get the owner who brings in their little toy breed dog the second that she sees it limping. But most of the time, it's something that's kind of been gradually getting a little worse over a period of days to weeks. And so, the other thing that I have noticed with these little toy breed dogs, they get around great on three legs. And so I've had a lot of these guys come in and they're, you know, painful and lame in one of their back legs instead of, you know, showing a lameness, a lot of times they just hike it up. They'll just hike it up and they'll actually come in and they'll be non weight bearing because they get around so well on three legs that if it hurts them to use the leg they just don't. They just pull it right up. So not uncommon to see a non weight bearing lameness in these guys which is different than most of the other disease processes that we're talking about today. They're also usually quite painful on hip manipulation. You'll appreciate frequently prepudice, restricted range of motion. kind of general signs of, hip discomfort and hip disease. 

When you take your radiographs it's a little variable depending on how long things have been going on, exactly what you see. But in the majority of these cases, we identify that something has gone wrong well into the disease process. So, again, the bone has become necrotic, we've kind of passed through that necrosis phase. And usually when we get these guys in is when we've reached what we call the fragmentation phase. So the bone is actually beginning to kind of crumble and collapse. And so usually when we take our radiograph we see something like this left sided picture here. So this is showing a femoral head that is obviously like very distorted like this barely even looks like a femoral head anymore. It looks like some sort of weird mushroom and so we'll often see this like distortion of the femoral head and frequently associated degenerative changes secondary degenerative changes in the acetabulum, too. You can see this acetabulum also doesn't look normal. It's also been remodeled as a result of articulating with this very abnormal femoral head. So that's how many of them will look. We'll see this, distinctive, distortion, and collapse of the femoral head. However, like I said, every once in a while you do get the owner who notices that their dog is limping and that day brings it in to the veterinarian. And so in those cases, we might identify them more in the necrosis phase. So, we can see on the right sided radiograph this isn't perfect. You know, it's really rare that we would actually catch one of these dogs in the necrosis phase because it's just a very short window of time. And honestly like this dog, you can see this femoral head doesn't quite look normal. It's it looks a little bit irregular. You know we have had undoubtedly some fragmentation. But it still looks basically like a femoral head, unlike the picture over on the left. But what you can appreciate is that even though it still looks basically like a femoral head, it's got all these, like, irregular areas of lucency within it. So that's again, because this bone is dying. And so we're getting this, osteolysis that is occurring secondary to this necrosis. So this is a fairly early image of a dog with avascular necrosis. There's been minimal fragmentation. That's going to get worse with time. But eventually we do tend to end up with a lot of collapse of the femoral head and secondary DJD, degenerative joint disease. 

So how do we treat them when we find them? There are theo, there is theoretically the option for non-surgical treatment. It doesn't tend to work out. The idea is if we identify these dogs in the necrosis phase, you know, before there's been a change to the anatomy of the femoral head, we can actually take them and put them in a non weight bearing sling. Like I said, these little guys get around great on three legs and so many of them will tolerate wearing the sling. And then they stay in that sling, you know, with you know, of course taking it down at least weekly to do, range of motion with them, before putting it back up and ideally more frequently. We'll get to that in a second. But for weeks we maintain them in this non weight bearing sling with the idea that we can get them through the necrosis phase and eventually to the point where the bone can reossify. That's not going to be a fast process. Like that is going to be quite a while before that is able to happen. And so during that time if that animal starts using its leg, you know, begins to put weight on that leg, the concern is that that dead brittle bone, if it hasn't had adequate time to reossify, could begin to crumble and then we get worsening DJD longer term. So in the meantime again they have to stay with their sling. There are commercial slings that make it a little bit easier to take the leg down and, you know, manipulate them. But they're, it is challenging for sure to maintain this, maintain them in the sling in this length of time. And additionally, there's a lot of concern if you, you know, if you're not using one of the commercial slings, there's a lot of concern with bandage morbidity with non weight bearing slings. You know, we see it a lot with emurs where animals will get skin lesions. Sometimes if the sling is too tight we can end up with ischemic injury to the distal limb to the toe. I've seen animals lose toes, lose limbs entirely sometimes from, emer sling complications. And so, you know, it's it's challenging to do. Again it requires that very early identification. And I do think that even with the non weight bearing sling, a lot of these guys are going to end up with some degree of fragmentation, will be at risk for some degree of DJD development in the future as well as the loss of range motion, loss of muscle mass that are associated with, maintaining the limb in a non weight bearing sling for a long period of time. So hopefully I've convinced you that the nonsurgical option isn't really a great one. But that's okay because we have some excellent surgical options here. In general for these cases, we recommend a salvage of the hip with either an FHO or a total hip replacement. So the picture on the bottom left here is showing an FHO. That's a common abbreviation that we'll use to describe a surgical procedure that removes the head and the neck of the femur, which is I personally prefer FJNE, so a femoral head and neck excision because it is very important that the entire neck be removed as well as the head, so that we don't end up with painful continued bone to bone contact between the femoral remnant and the acetabulum. The idea with an FHO is that they will, develop a pseudarthrosis a false joint of scar tissue in between those two bones. And then weight transfer will occur instead of across the hip joint it will ocur across the muscles of the hind limb. So that can be a very successful option in small breed dogs. They do, since they lose that, you know, rigid contact between the femur and the acetabulum, they do lose a little bit of athletic function. But especially if this is a unilateral case again, small breed dogs tend to do really well despite that. Plus, you know, I don't know how many small breed dogs you guys have, you know wherever you are that are actually you know, doing a lot of walking and being their owners hiking partner and things like that. A lot of the small breed dogs where I work, you know get carried a lot of the time. And so a little loss in athletic function tends to be something that they can tolerate. However, if you have an owner who wants to have a sport papion or something they do make nano total hip implants and so even are very, very toy dogs can likely receive a total hip replacement. If you have an owner who is interested in that as an option. Personally, if it were my own dog, I'd probably just do an FHO because I think they do great with them. But again, if you do have an owner who has specific desire to preserve their animals, athletic function as much as possible, a total hip replacement can be an option as well. Both these should be effective at controlling the discomfort, associated with bone necrosis and DJD that we see in these avascular necrosis cases. 

So once again, good outcomes with surgery not so good outcomes probably wouldn't bother it with, nonsurgical management. Alright.