Transcript:

[0:01]

Hi everyone, welcome back to Mad Barn Academy, and if you're new here today, then welcome — we hope to earn your subscription. I’m Dr. Fran Row, one of the veterinary nutritionists here at Mad Barn, and today’s topic of osteoarthritis is going to be piggybacking a little bit off of our last video on lameness examination. Osteoarthritis, or OA, is one of the most common causes of lameness in horses, particularly our older horses or our performance horses, so it’s an issue that owners are usually all too familiar with.

[0:39]

Today will be part one in a two-part series on osteoarthritis. We’ll cover an overview of what OA actually is, and then in the part two video we’ll cover more on diagnosis and management strategies. So, let’s get started.

[1:02]

To begin, let’s review some terms. Arthritis, which is a general medical term, is defined simply as inflammation of a joint. Now, there are many recognized causes of arthritis, which can help us further classify that arthritis into different subcategories. In horses, the three main causes of arthritis include: traumatic arthritis — in which inflammation is due to injury to the joint or joint structures; septic arthritis — in which inflammation is due to an infection within the joint, usually bacterial; and, third, the topic for us today — osteoarthritis, in which there’s inflammation that is both the cause and effect of cartilage damage or cartilage degeneration within the joint.

[2:07]

Osteoarthritis, or OA, can also be referred to as degenerative joint disease, or DJD, so you might hear those terms interchangeably. Our focus for today is OA specifically, so let’s talk more about what actually happens inside the joint when there’s degenerative change.

[2:31]

A joint is anywhere that two bones meet. Joints allow our rigid skeletons to move — they flex, they extend, and they allow for some type of action to take place. In horses, we tend to differentiate joints as either being high motion, in which there’s a lot of bending or action taking place, versus low motion, which is the opposite — minimal bending or action, and more weight-bearing or loading on the joint. Some examples of high motion joints are the knee (carpus), the fetlock, the stifle, and the coffin joint. Some examples of low motion joints include the pastern joint and the two lower hock joints — the distal intertarsal joint and the tarsometatarsal joint.

[3:30]

In order to understand how osteoarthritis affects the joint, we first have to understand the normal anatomy of a joint. In this diagram, we have two bones meeting, making a joint. The space between these bones is the joint space, which is surrounded by a capsule. This capsule has a fibrous outer layer and an inner lining called the synovial lining, or synovium. The synovium produces joint fluid, which fills the space between bones. Joint fluid is viscous — thick — and its job is to nourish the cartilage, reduce friction during movement, and act as a shock absorber.

[4:40]

Each bone is padded with a special type of cartilage called articular cartilage. This provides shock absorption during movement or compression, and allows for frictionless movement when the bones oppose each other. The bone directly beneath the articular cartilage is the subchondral bone — important because osteoarthritis can cause changes here. Every joint also has associated soft tissue structures — tendons and ligaments — that provide stability and allow it to bend, flex, or extend. These lie mostly outside the joint capsule but are critical for function and stability.

[5:57]

Some joints, like the stifle, have additional pads of cartilage inside the joint called the meniscus — two in the stifle, equivalent to our knee — that add extra padding and shock absorption. Some joints, like the stifle or hip, also have intracapsular ligaments that reside inside the joint capsule, attaching the bones together for extra stability.

[6:59]

Osteoarthritis is defined as arthritis characterized by cartilage degeneration within a joint, but the degenerative process actually involves all joint components. While cartilage damage gives OA its definition, ultimately the entire joint undergoes degenerative change. This is because cartilage injury incites inflammation, and that inflammation perpetuates a cycle of more degeneration throughout the joint.

[7:56]

Osteoarthritis can develop in any joint, but in horses it’s most common in high motion joints of the limbs, and also in the neck. There are many ways OA can develop, but it’s easiest to break them into two main categories: a normal joint experiencing abnormal stress, and an abnormal joint experiencing normal stress.

[8:31]

In the first case — a normal joint with abnormal stress — the joint is anatomically normal to start with, but cartilage becomes damaged under abnormal circumstances. Examples include a joint infection (septic arthritis), joint injury (traumatic arthritis), excessive use, or improper loading due to poor conformation.

[9:07]

In the second case — an abnormal joint with normal stress — the joint has abnormal cartilage and can’t withstand what would be considered a normal workload. The cartilage will sustain damage even with mild forces during normal use. Two examples of an abnormal joint are developmental orthopedic disease (DOD) in young, growing horses, and age-related cartilage degeneration in senior horses.

[9:53]

DOD occurs when cartilage and subchondral bone fail to develop normally in the growing foal. This results in abnormal subchondral bone and/or abnormal cartilage that is missing in areas or forms a flap, which interferes with normal joint loading and the frictionless movement required for proper joint function.

[10:43]

So, kind of the two big examples of DODs that most people are familiar with are osteochondrosis dessicans, or OCD, and then subchondral bone cysts. Now, the opposite for our senior horses is just age-related degeneration of the joint cartilage. With age, joints are less able to cope with the normal stresses of life and movement, and they’re less able to repair those really minor microdamages that occur in the joint. You can think of this as wear and tear on a joint, and that wear and tear is just going to become more apparent with age.

[11:31]

Okay, now let’s switch gears and talk about the opposite — a normal joint that is undergoing some type of abnormal stress situation. The first on the list is going to be infection. Bacterial infection causes very significant and often irreparable damage to a joint just because of the massive inflammatory process that takes place to try and control that infection. In most of these cases, especially for adult horses, this is usually going to occur by way of some type of penetrating wound that involves a joint. But septic joints can happen in foals, particularly if that foal was a failure of passive transfer foal and did not receive enough colostrum immediately after birth.

[12:23]

Now, last on the list — injuries, excessive use, and poor conformation — are a little bit more intuitive in terms of how those scenarios result in degenerative change within a joint. Injuries will result in joint instability and/or directly damage the structures and cartilage within the joint, setting off the inflammatory process. Excessive use is what allows all of these really small traumas to accumulate in a joint, accelerating that wear and tear we talked about earlier. Some horses with wear-and-tear osteoarthritis might start showing arthritis earlier in life, especially if they’ve had a lot of miles — racehorses coming off the track, for example, or horses that have been heavily used as athletes. Their joints are going to show that. Lastly, poor conformation results in abnormal joint loading. These horses have some type of conformational defect; they’re not standing or moving in a physiologically or biomechanically normal way, and that’s going to affect joints over time as well.

[13:57]

Regardless of how the osteoarthritis starts in a joint or multiple joints, the outcome is generally the same. We see the following degenerative changes: cartilage thinning or erosion of the articular cartilage; joint swelling, termed effusion; thinning of the joint fluid — which is normally very viscous — making it more watery; bony remodeling, including osteophytic change and hardening of the subchondral bone beneath the cartilage; and, lastly, thickened synovium and a thickened joint capsule.

[14:51]

All of these degenerative changes lead to reduced function by way of a narrowed joint space, increased friction during movement, reduced range of motion, reduced ability to absorb concussive forces during movement, and ultimately all of this culminates in pain. This is why osteoarthritis is so important — it can really affect the performance and quality of life of our horses by causing pain and lameness.

[15:27]

Here’s a really excellent diagram that puts into visual form all those degenerative changes I just listed, so you can really appreciate the major changes to this joint and how they perpetuate the cycle of inflammation.

[16:09]

The real challenge with osteoarthritis is that it’s a cycle of degeneration that feeds into itself. Degenerative changes incite inflammation, which leads to more degenerative change, which leads to more inflammation, and so on. One of the biggest ways that we address osteoarthritis is by interrupting this cycle of inflammation and trying to stop it from happening.

[16:37]

That is going to lead us into the part two video for osteoarthritis, where we’ll do a deeper dive into the diagnosis and management strategies for horses with osteoarthritis.

[16:54]

All right, you guys — here are the references for today, and thanks so much for listening. Don’t forget to like and subscribe, and be sure to explore the other videos on our channel — we have lots of new videos being added all the time. If you haven’t seen the lameness exam video I posted previously, go ahead and watch that because it’ll give you an idea of what’s going to happen when you call your vet out if you think you have a horse with osteoarthritis that needs to be addressed or diagnosed.

[17:26]

Additionally, I’ve included some links in the description below — there are supplemental materials on degenerative joint disease or osteoarthritis, and a great article on how to assess pain in horses, since they are often very stoic and it can be difficult to determine if horses — especially senior horses with osteoarthritis — are uncomfortable and if it’s affecting their quality of life.

[18:04]

All right, you guys — check back next time for that part two video, it’ll be coming out shortly. Thanks so much, bye!