INFECTION INVOLVING SYNOVIAL STRUCTURES, JOINTS, BURSAE AND TENDON SHEATHS.

Transcription

1 INFECTION INVOLVING SYNOVIAL STRUCTURES, JOINTS, BURSAE AND TENDON SHEATHS. Owners often find it difficult to understand why vets get so concerned about certain small wounds. This is when the wound is potentially involving a synovial structure. Wounds causing infection in these structures can be life threatening if the infection cannot be controlled. For various reasons, explained later, antibiotics alone will not successfully treat the infection. As a rule of thumb, if the level of lameness is much worse than the wound looks like it should warrant, then the vet should be called immediately to assess the horse (see info sheet: emergencies and when to call the vet). This client sheet will provide information on the management of synovial wounds and try to explain why they are so serious. WHAT ARE SYNOVIAL STRUCTURES? Synovial structures are specialized sterile cavities within the horse s body that form joints, tendon sheaths and bursae. Tendon sheaths form protective socks that cover the tendons. The most commonly infected tendon sheaths are the distal digital tendon sheath which runs down the back of the cannon and contains the superficial and deep digital flexor tendons, the tarsal sheath which runs down the inside of the hock and the carpal sheath which runs down the inside of the knee. Bursae are fluid filled sacs which act as pulleys to alter the angle of pull of certain tendons. The most commonly infected bursae are at the point of the hock (the subcutaneous, calcaneal and gastrocnemius bursae) and within the foot, the navicular bursa. These structures are most commonly affected due to their superficial positions within the horse s body. I.e. they are the most prone to injuries from wounds and foot penetrations.

2 Diagram showing position of joints and bursae in the distal limb (blue) and the distal digital tendon sheath (red) These synovial structures are sterile and filled with synovial/joint fluid. They are lined by synovium, which is a lining of many finger like projections. This provides an ideal place for bacteria to hide and combined with a poor blood supply makes it incredibly difficult for antibiotics alone to treat the wound and infection. Synovial lining of the joint seen during keyhole/arthroscopic surgery. This is similar in sheaths and bursae too. HOW DO SYNOVIAL STRUCTURES BECOME INFECTED? There are three main ways in which synovial structures can become contaminated with bacteria, which leads to infection: 1. Wounds directly into the structures. The wounds can vary from large lacerations where synovial involvement is obvious, to small pin prick/ thorn puncture wounds where the actual wound is tiny, but a vital synovial structure has been involved. These are the wounds that will catch you out. When there is severe lameness but a small wound, then synovial infection/sepsis must be considered.

3 2. Haematogenous spread. This is blood born infection and is most common in young foals, known as joint ill. Bacteria circulating in the bloodstream settle out and colonize the synovial spaces, setting up infection. This is not as common in adult horses, but it can happen. 3. Post surgery/ joint injection. Any horse having joint surgery or medication of joints/ sheaths and bursae is at risk of developing infection. The synovial structures are sterile. This is why when your horse undergoes joint surgery, full aseptic conditions are strictly adhered to. When your horses joints are treated, the joints to be treated undergo a full surgical scrub, the vet wears sterile gloves and performs the procedure under aseptic conditions. Anitmicrobials are also often mixed with the joint treatments as an extra precaution. A horse about to undergo arthroscopic surgery into the knee joints, under full aseptic/sterile conditions WHY ARE SYNOVIAL INFECTIONS SO SERIOUS? Synovial infection of joints or tendon sheaths by bacteria and other organisms can result in a potentially catastrophic inflammatory reaction. This results in permanent degenerative changes to the synovium, joint capsule, articular cartilage, tendons and surrounding structures, and can lead to permanent loss of athletic function or a life-threatening lameness. Early diagnosis and aggressive therapy are essential for achieving a successful resolution. HOW DO WE DIAGNOSE SYNOVIAL INFECTION? In some cases, the involvement of synovial structures may be obvious, for example in big open wounds where the vet can see the exposed joint or tendon sheath. Smaller wounds are harder to assess. A good knowledge of the horse s anatomy is vital for the vet to recognize when synovial structures might be involved. If synovial involvement is suspected then the vet will want to take a sample of the synovial fluid for analysis. This SYNOVIOCENTESIS is a vital and potentially life saving, yet simple procedure to perform. It involves the vet placing a needle into the suspected structure and taking a sample of the fluid. Whilst the needle is in the synovial space, sterile fluid and antimicrobials are injected. If these are seen to exit the wound, then this tells the vet immediately that the synovial structure is involved.

4 Joint fluid being sampled from a fetlock joint Infection in the synovial structure can be confirmed by laboratory tests where PROTEIN levels and WHITE BLOOD CELL levels are analyzed. The synovial fluid can also be cultured to see exactly what bugs are growing and what antimicrobials will be effective. HOW DO WE TREAT SYNOVIAL INFECTION? Once synovial infection has been confirmed, aggressive therapy needs to be instituted to provide the best chance of a successful outcome. 1. The gold standard treatment is for the horse to undergo arthroscopic/keyhole surgery under general anaesthesia. This is by far and away the most successful way of treating synovial sepsis. The infected joint is visualized by camera under keyhole surgery and large volumes of sterile fluid are flushed through the joint to remove the infection and debris. Because the synovial structure can actually be seen, debris can be physically removed, along with infected and damaged synovial lining. The horse is also placed on antibiotics. After surgery, the horse will remain on antibiotics. The affected synovial structure may also be directly medicated with antibiotics, or a procedure called IVRP performed. IVRP is intravenous regional perfusion. This involves injecting antibiotics into a vein close to the involved structure with a tourniquet placed, so that the antibiotics stay TRAPPED within the infected site. It is not unusual for synovial septic structures to require more than one surgery. Keyhole surgery being performed

5 IVRP being performed 2. The next level of treatment is to flush the synovial structure with the horse under standing sedation only. This has the advantages of removing the risk of general anaesthesia and the cost involved in that process. But is has many disadvantages including not visualizing the joint with the camera, therefore debris may be left behind in the structure which will continue to drive infection. The horse also has to be of the right temperament and the synovial structure involved be easily accessible in the standing horse. A standing through and through flush being performed in a septic navicular bursa 3. The third level of treatment is to not flush the joint but to try a combination of antibiotics and IVRP. This is rarely successful in serious infections, and is only recommended if there are serious financial restrictions. Owners must be aware of the limitations of this treatment. WHAT CAN YOU AS AN OWNER DO TO IMPROVE THE CHANCES OF YOUR HORSE SURVIVING SYNOVIAL INFECTION? It cannot be reiterated too many times how serious synovial infection in a horse is. The chances of successful treatment though can be improved by undertaking the following advice: 1. Call the vet sooner rather than later

6 If your horse has a small wound but is very lame, CALL THE VET! If the wound is over a tendon sheath or joint, CALL THE VET! If your horse has stood on a nail and there is a foot penetration, CALL THE VET! Early recognition and prompt treatment of synovial infection will dramatically improve the chances of a successful outcome. 2. Be aggressive in your treatment choice If financially possible, choose option one as the treatment plan. Aggressive treatment early on in the disease process results in much higher success rates.