Septic or Infective Arthritis

Infections in joints and tendon sheaths are all too common conditions in horses and ponies.  Unfortunately if treated incorrectly they are often career threatening and occasionally, if the infection is not brought under controlled, can result in the horse being put down.   The key to a successful outcome is prompt recognition and aggressive treatment, and following this many horses return to full athletic function.

Wounds are the most common cause of joint infection.  These often occur following a kick or the horse getting trapped in wire. Bacteria may also enter a joint via a blood borne route (haematogenous spread), which particularly happens in foals when they have not received enough colostrum in the first few hours of life.  On very rare occasions infection can also be introduced following the injection of drugs into a joint.

The most commonly infected joints in the horse are the hock, fetlock, elbow, knee, coffin, and stifle joints.  The digital sheath (windgall), extensor tendon sheaths (over the front of the knee and hock) and the tarsal sheath (thoroughpin) are the most commonly infected tendon sheaths.

In the early stages following a penetrating wound, the joint may merely be contaminated by the introduced foreign material (e.g. hair, grit) and the bacteria. The horse very quickly mounts an acute inflammatory reaction in response to this but unfortunately, the bacteria readily overcome these defenses and colonises the various parts of the joint.  The presence of the bacteria and foreign material also leads to activation of various mediators that stimulates a rapid influx of the horse’s own white blood cells into the joint.  These then start to release destructive enzymes that result in damage to the articular cartilage and synovial membrane (the lining of the joint).   This leads to further release of enzymes and so a continuing cycle of joint destruction occurs.  It has been found in some infected joints that 45% of some articular cartilage components are lost within 2 days.   If left untreated a total loss of articular cartilage and osteomyelitis (infection of the adjacent bone) quickly follows.   Often more than one type of bacteria can be involved in an infected joint.

Horses with an infected joint tend to be very painful and are often virtually non-weight bearing on the affected limb. The joint is usually very distended and synovial fluid may emerge from the wound edges. 

There are several things that a vet can do to confirm whether a joint has been penetrated, including the detection of joint penetration on the examination of the wound, (indicated by the emergence of synovial fluid from the wound), if this is not present the vet may distend the joint with saline, at a site distant to the wound, and look for fluid coming from the wound, or he/she may also take a sample of joint fluid and have it analysed. The latter is the most accurate way to determine joint infection.  Occasionally X-rays and/or ultrasound scanning may be used to help detect joint infection.

Treatment should be started as soon as possible following the diagnosis of an infection. The aims of treatment are: to eliminate the bacteria that are causing the problem; to remove any introduced foreign material; to restore a normal joint environment as quickly as possible (infected joints are more acidic than normal joints); to avoid any resultant joint degeneration; and to prevent spread of infection, both locally and systemically throughout the body.  The two most important parts of treatment are the use of antibiotics and lavage (flushing) of the infected joint or sheath. Antibiotics are usually given either intravenously or intramuscularly. 

In addition to this sponges or beads or adjacent local veins may to used to get higher concentration of antibiotics into the affected joint. Antibiotics alone to treat a joint infection are very rarely effective because insufficient levels end up in the acidic environment of an infected joint and because antibiotics are is not particularly good at penetrating the surrounding damaged tissues.   Obviously antibiotics alone cannot remove the grit, hair and dirt that are found in many infected joints.

The other vital part of treatment is lavage of the joint.  Lavage removes much of the introduced bacteria, foreign material and the excessive protein build up (in many cases pus) and it also restores the pH in the joint to a normal level, allowing the antibiotics to work.   Joint lavage should ideally be carried out by arthroscopy (keyhole surgery) because this provides the best technique to visualise the joint, remove debris, deliver high volumes of fluid, and to breakdown adhesions.  With the use of keyhole surgery the surgeon can also use small-motorised equipment (less than 4.5 mm in diameter) to treat any damaged or diseased tissues.  The design of the keyhole equipment means that virtually all areas of the joint can be inspected and fluid can be delivered at rates of up to ¾ litre per minute.  This creates an excellent way to remove damaged and infected tissues.  Rather than keyhole surgery lavage can occasionally be undertaken through needles or via the use of drains.  These methods have largely been superseded by the use of keyhole surgery because of its greater ability to view the entire joint and the ability to use the hand and motorised equipment.  They are a lot less successful. Following the joint flush the vet will monitor the response to treatment by walking and trotting the horse at regular intervals and possibly taking repeat samples of joint fluid.  The antibiotic may well be changed and/or a second joint flush undertaken if the horse does not improve in 3 to 4 days.   The prognosis for septic arthritis in the horse is dependent on prompt recognition, aggressive therapy, quick alteration of the treatment based on close monitoring and good nursing.  With the use of keyhole surgery and newer antibiotics many more horses return to a full and healthy life with no significant long term problems than ever occurred 10-15 years ago.


The material contained in this website is presented for information purposes only . The material is in no way intended to replace professional veterinary care or attention from a professional veterinary surgeon. 

The advice given in any of our web pages cannot be used as the basis for a diagnosis or choice of treatment.

Clyde Vet Group advises that you should always consult a veterinary surgeon about any queries with animals under your care.

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