All right, I'd like to thank the forum as well as Anna and AOSSM for allowing me to present my study looking at how post-traumatic osteoarthritis progression is diminished by early mechanical unloading in a mouse model. So we've been talking a lot about ACLs, right? So the idea is that we know that ACL is a traumatic injury to the joint that often causes degenerative joint disease. Sometimes going up to even up to 80% within the literature. So we know that this is a sequelae of an ACL injury. We know that the inflammatory cascade is from injury to inflammation to joint degeneration, whether that be also with alternate mechanical loading and cartilage damage. This occurs fairly often in our younger population, so we know that this is a problem with post-traumatic osteoarthritis. When we look at ACL tears, we don't really have... We see this inflammatory response, we see this bone bruising, but we don't necessarily have any clinical consensus with regards to activity modification post-injury. So the interesting idea about how this came about was that we had a Grand Rounds within our department, and we were talking about ACL tears, and one of our basic scientists came up to me and said, well, why don't you guys unload them? And I thought, could it be that easy? Or... But number one. But number two is like, I don't know if I have an answer. I don't think we clinically say that we ever unload our ACLs post-acute injury. Just for an ACL alone, rather than fracture pattern or meniscus or whatnot. If we think about the basic science about how injury occurs within the joint, this is kind of a graphic of what happens. So in the acute period, you had this high, high, high inflammatory response within the first three days. This is where you have inflammation, you have apoptosis, you have cell death, you have matrix degradation, all the bad things that happen to a joint. And then usually after about a week, five to seven days, you start seeing initiation of that anabolic phase. So the question is, can unloading, can that mitigate that inflammatory response? Can we change the progression of post-traumatic osteoarthritis from the beginning molecular level? So our hypothesis was to look at unloading following joint injury will reduce inflammation, protease activity, all the degradative enzymes, and mechanical damage to the joint. And over time, will reduce long-term articular cartilage degeneration and osteophyte formation. So we thought that this could make a difference. So that being said, I know mice are not people. Mice are these animals that will forever run on an injured limb and you'll have no idea because that's part of their survival, right? That being said, humans will, once they have an injury, potentially will mitigate and try to kind of protect the joint for at least a couple of days until the joint feels a little bit better. So maybe it does occur during that acute inflammatory period. So this is a model that was developed in our lab, actually I should say Dr. Christensen's lab, where there is an axial load. I know there's a great sound effect with this, but I took the volume out. So the idea is that we will load a, it's not, sorry, it's not horrible, but the idea is that you will load slowly an axial load to the tibia and then it overloads the joint and basically it will take out the ACL. So that's it. It's an isolated ACL injury, relatively traumatic only to the ACL and not to the other structures. And these are the force displacement curves to kind of show what's going on. And then we decided, we looked in the literature and tried to figure out how do you unload a hind limb? And NASA actually has this great data about suspending these mice from their backsides. So what we did was we put some tape around the backside of a tail of a mouse and hook it up to a pulley and swivel system so that the mice can get around everywhere on their front limbs, but they completely unload their hind limbs so that we're not torturing them. They can get to food, they can get to water and they live their mice lives. So the idea then was we took our study. So we did skeletal mature female mice that were 12 weeks old, and this correlates roughly to about 20 to 30 year old human adult. We did ACL rupture or sham injury. So anesthetize them, put them in the machine, but didn't actually rupture their ACLs. And then we divide them into two groups. We either would do, we call it GC, which is ground control, allow them to run around freely after the injury, or we would unload them for seven days and then allow them to run around up to 14 to 28 days. And then, so the first imaging that we looked at was looking at protease activity. So this is a fancy way of looking at infrared fluorescent dyeing. And so this makes really cool pictures, right? So the idea is that we have this molecule called procense, and in the native phase, it's quenched, meaning it doesn't release any of its fluorescence. And then when it comes into contact with protease, so any of the inflammatory cytokines that break things down, it will actually release that fluorescence. And this is where infrared camera captures it. So you can see on the top images here, day one, three, and seven, we have the uninjured limb on the left, and then we have the injured limb on the right. And you can see that on day one, there's a little bit of inflammatory response. There's swelling and whatnot. Day three, you can see much more, kind of a brighter response, which correlates with that graphic, with that spike around three days. And then it kind of calms down a little bit more at seven days. And then this is the hind limb unloaded. So you can see that the uninjured and injured limb looks fairly similar. It's really cool. And then as you go into the day three, then you can start seeing some of the inflammatory response, some of that protease activity coming up. So then this is a graphic looking at basically the pictures. So what we see is that at day seven, we looked at... We compared it against a normal limb and found that this radiant efficiency, or this fluorescence that we see, is increased about 83% compared to control in the ground control mice. So the ones that we just allowed to run around. It was only increased by 22% in the hind limb unloaded. So there's a big difference in how we can change the protease activity just by unloading that limb. Another marker that we looked at was looking at synovitis. So synovitis, we graded it within a six-point system. And the picture on the left is the injured unprotected limb, and the one on the right is more the protected limb. So you can see that the inflammatory response is much more robust in terms of there was a lot of hypercellularity, a lot of density. So just really boggy synovitis within the mouse within that first seven days. And then once we loaded the unloaded ones, we actually saw it return back to normal. So you can see that the synovitis on the right is for the unloaded at seven days. So big difference in terms of how thick that synovitis is. This is an interesting concept, and I still haven't quite wrapped my head around it in terms of what this means. But the idea is that we did micro-CTs on these animals to look at trabecular bone as well as osteophyte formation. So within the trabecular bone, I want you to pay attention to the two bar graphs at the bottom of the solid lines. So what we see is that there is more trabecular bone loss in the loaded limb as compared to the unloaded limb compared to controls. So that means that inflammatory response does affect the trabecular bone and how much that bone absorbs. And it's a smaller effect, but certainly it's statistically significant. So we look at 15% trabecular bone resorption versus 22% in the... So 15% in the unloaded, hind limb unloaded, as opposed to 22%. And then this, I think, is really... This is the more remarkable part of this study, I think, is looking at the osteophyte formation. So again, micro-CT to look at actually the bony osteophyte formation throughout the joint. And what we see is... So again, we unloaded the mice for about seven days, then we let them start walking on it, and then we start seeing the change within the osteophyte formation. So at day 21, 14, there's no difference, but at day 21, we start to see a 36% difference. And then that progresses and gets more remarkable at day 28, where there's a 46% difference. So there is a clear difference in terms of how much osteophyte formation occurs if you've unloaded this limb in the acute period. So this is some more histology of it. So on the left side here, you have the uninjured limb. So just to orient you, condyles on top, tibias on the bottom, meniscus in between. And so I'm going to talk to you about the top pictures here, which is the ground control mice. And you can see on day 14, so two weeks after injury, you see a tremendous amount of... So this is a posterior horn of the meniscus flipped up. So it's almost a buck and handle tear, but you see a tremendous loss of that articular cartilage on the femoral side, some of that bone, subracular bone loss also. And also you see hints of it on that posterior tibia. This is much more marked in day 28, so you can see almost that tibia is really shifted anteriorly from loss of that ACL. You can see that that bone and cartilage is tremendously worn. If you look at the hind limb unloaded, you can see at day 14, it's relatively, I mean, you still have some preservation of that articular cartilage. You have preservation of some of that trabecular bone. But then you see at day 28, you see some of that kind of wear down also, but not nearly as bad as what we see on the ground control mice. So in summary, we look at unloading. So unloading diminishes joint inflammation and mechanical damage during the unloading period. So in that seven days, definitely there's a big difference. But we know that inflammation and trabecular bone remodeling return to control levels when you reload them again. But there is potential long-term reduction in osteoarthritis formation and post-traumatic osteoarthritis progression in the long term. And I think this is where that's the exciting part of this study. So in conclusion, our mechanical unloading or resting during the early phase after joint injury can reduce early inflammation and may have long-term effects for reducing post-traumatic osteoarthritis progression. So I'd like to thank AOSSM, actually, because we did get a grant to look at post-traumatic osteoarthritis. And from there, we've actually translated that into a DOD and an NIH R01 to further study this. So I'd like to thank the Christensen Lab and everyone else involved. So thank you. Thank you.

post-traumatic osteoarthritis

early mechanical unloading

ACL injuries

inflammatory cascade

joint degeneration