Tuesday with Tony – Joint infections

Have you noticed that when my docs and techs do a sterile scrub on your horse’s joint prior to an injection, it feels like 5 hours of scrubbing for about 15 seconds of actual injection? And have you noticed that my docs get a lot more uptight about a half inch wound over your horse’s hock than a big dramatic looking wound on his chest? Like with real estate, location is everything, and this week we are talking about infections in a location that we take very seriously – joints.

In its most basic sense, a joint is a place where 2 or more bones meet, along with the cartilage that covers the bone ends, and a joint capsule with a synovial membrane that secretes fluid to lubricate the joint. Most types of joints have movement of some sort – hinging like your knee or moving in multiple directions like your shoulder. It’s the same for your horse. Think about the joint capsule like a protective balloon around the joint. It’s a really important place, sealing the joint space and providing nutrition and lubrication to the cartilage. When infection gets inside that space, there can be career ending or life-threatening consequences. That’s why my docs don’t mess around when a joint infection is on the line.

These locations that are surrounded by a fluid-secreting synovial lining are called synovial cavities. There are so many synovial cavities in a horse, especially in the legs! And it’s not just joints, but tendon sheaths and bursae too, which are similarly worrisome if they get infected. That’s why my docs’ knowledge of anatomy is so important. A wound in one spot might not be that big of a deal, but a wound an inch away could be in a synovial cavity. The treatment and prognosis could be vastly altered by just a tiny difference in location.

How do joint infections happen?

The answer is a bit different depending on whether it’s a mature horse or a foal. In foals, bacteria usually get into the joint through the bloodstream. The infection starts somewhere else in the foal, like the umbilicus or the lungs, and then bacteria travel in the blood until they arrive in the joint. This is especially problematic when foals don’t get enough immunity by suckling high quality colostrum right after birth, causing failure of passive transfer.

Adult horses most commonly get joint infections from wounds that enter the joint space, bringing debris and bacteria inside. Since it’s the same for a tendon sheath or bursa infection, we’ll just use joints as our example from here on. The wound could be an obvious laceration leaving little doubt that the joint has been compromised, but it could also be a tiny puncture wound that leaves no evidence of the injury.

Joint infection can also rarely be seen as a complication of joint surgery or joint injection. That’s why you see all the scrubbing we do before joint injections. It’s not common to have a problem, but my docs will still be very careful with sterility.

Signs of infection

The first and most important thing is if your horse has a wound anywhere near a joint, call my doc immediately. This is not the time to take a wait and see approach – it could turn into a real CATastrophe. Besides the wound itself, you might see lameness starting within hours to days, swelling in and around the joint, or sometimes fluid draining from the wound. It’s important to remember though, that if the joint has an open wound and is draining fluid, it may not show lameness or swelling yet. That doesn’t mean it’s not a big problem, so don’t put off calling my doc! If it’s been going on a while, the horse may have a fever. In a foal, the fever may be the first thing that occurs even before the joint swells up. No matter which of these you see first, the moral of the story is to call my doc and not mess around trying home remedies.

How we diagnose a joint infection

When there is a wound near a joint, my doc will clean the wound and then explore it to find out if it communicates directly with the joint. She may put on a sterile glove and feel within the wound itself. She may insert a sterile instrument into the wound to track which direction it goes. An x-ray can be used to look for bone abnormalities caused by infection or to help with determining if the wound communicates with the joint.

A fluid sample can be collected from the joint to test for infection. Normal, healthy joint fluid is clear, pale yellow in color, and somewhat stringy rather than thin like water. Fluid from an infected joint may turn cloudy, watery, and sometimes change color. There are several lab tests that can be used to determine normal from infected joint fluid.

My doc may inject the joint with sterile saline from a site distant from the wound to pressurize the joint. If there is communication between the wound and the joint, the pressurized fluid will leak from inside the joint out through the wound. If there is no current communication, no leakage will occur.

If any of these methods determine your horse has an infected joint, you’ll have to start treating quickly and aggressively.

How an infection is treated

Your horse will need his joint flushed out with large volumes of sterile fluid. This is best done under general anesthesia at a hospital. The gold standard is to use an arthroscope to inspect the joint surfaces, look for debris, and deliver a high flow of fluid to rinse out infection. He’ll also need powerful antibiotics given through his vein. Antibiotics are often injected directly into his joint or the region of infection as well. It’s important for the horse to be comfortable enough to bear weight on his injured leg and prevent too much stress on his other legs, potentially causing laminitis, so he’ll receive anti-inflammatory medication to reduce swelling and pain.

A joint infection can be difficult to treat, especially if the infection has been present for a while before treatment begins, or the bone or soft tissue structures are involved. So when there’s a wound on your horse’s leg, calling my doc quickly will give your horse the best chance to get the treatment he needs.

Until next week,

~Tony

P.S. Don’t forget to head on over to our podcast page to learn more about joint infections and so much more. Click here to go to the podcast page.