INTRODUCTION

Joint ill is a real problem on stud farms and for the smaller breeder- it has an estimated prevalence of 0.5-1 % in Thoroughbreds. It can result in loss of the foal for future athletic performance, and in the most serious cases, euthanasia may be the end result.

DEFINITION

Joint ill is an infection of the joint +/- adjacent bone, caused by a variety of bacteria. The term ‘ joint ill ‘ is thus somewhat misleading, because the infection can, and often does, spread to the bones on either side of the joint, resulting in an osteomyelitis - an infection of the bone. Most commonly, more than one joint is involved

ANATOMY

To understand how we go about diagnosing, treating and preventing joint ill, it is useful to know a bit about the anatomy of a joint. A joint is the union between two or more bones. It is surrounded by a fibrous joint capsule, and filled with lubricating joint or synovial fluid. The bone ends which make up the joint are lined by a special type of cartilage called articular cartilage. There are thus different types of joint ill which are classified according to which areas of the joint are infected . In the most simple type, there is no involvement of the bone, and there is usually a better response to treatment, but if the bones of the joint do become involved, then treatment becomes more difficult, and the prognosis for a return to normal becomes more guarded.

PREDISPOSING FACTORS

Joint ill is most commonly preceded by septicaemia - a systemic bacterial infection. The sources of the bacteria include the genital tract of the mare, the skin of normal horses , and the environment. These organisms gain access to the blood stream by a variety of routes, including the respiratory tract, the gastro-intestinal tract, the umbilicus and the placenta. The bacteria then enter the joint, establishing a focus of infection.

Failure to acquire sufficient colostral immunity is probably the leading contributory cause of neonatal infection. Other factors which predispose to the development of septicaemia, and thus joint ill, include

So you can see by these factors which increase the likelihood of joint ill occurring that there are several management strategies that can be implemented to decrease the likelihood of joint ill occurring.

DIAGNOSIS

" A lame foal has joint ill until proven otherwise "

Lameness
Joint ill is one of the most common cause of lameness in foals. Other causes include fractures , kicks, bruises to the foot, developmental abnormalities eg tarsal collapse, contracted tendons. While foals with joint ill are commonly systemically unwell, this is not always the case, and the disease should be suspected in any lame foal.

The degree of lameness can vary. It ranges from very subtle - just not moving quite right, or stepping short, to non weight bearing fracture lame. While the foals that are very lame may be easy to diagnose, those with subtle lameness's can be more difficult. Foals that are unable to stand, either because they are too weak, systemically unwell or have angular limb deformities, will not , however, be recognised with a lameness.

So lameness is often the first recognised sign. In addition, infected joints can become hot , painful and swollen and the tissues around the joint can also be swollen, indicating the infection is present in the bone. All foals, especially those at increased risk, should routinely be monitored for signs

of disease. Palpation of the joints and monitoring of rectal temps are important so that an early diagnosis and initiation of treatment can be instigated. An increase in rectal temperature does not always occur with joint ill, and indeed the foals temperature can be sub-normal. However, an elevated temperature is a good indication of infection, and is thus a useful tool for diagnosis

Joint Fluid Examination
If there is a suspicion that a foal does have joint ill, a sample of joint fluid should be taken, preferably before antibiotics have been started. However, if there is a delay in sampling, antibiotics should be started regardless. Analysis of the joint fluid can aid in diagnosis, and also treatment options. Normal joint fluid is clear, with low cell and protein levels. Gross examination of the sampled joint fluid is sometimes diagnostic - ‘pus ‘ = infection. Further analysis includes protein and cell levels, which are elevated in infection. Culture and sensitivity ( c and s ) can also be performed. The purpose of culturing joint fluid is to identify the bacteria causing the infection and then find the antibiotic that would be most effective for treatment. While c and s is often helpful in the treatment of joint ill, it is not the be all and end all for diagnosis, as the results take several days , and a negative culture i.e. no bacteria grown, does not rule out infection. Previous antibiotic treatment, sampling methods, and the low number of bacteria which can be present in the joint can all result in a negative result, as can infections of the adjacent bone, with no spread of the bacteria to the joint.

Blood Samples
Blood samples can also be helpful in the diagnosis of joint ill. Blood can be cultured to identify a septicaemia. An increased white cell count may occur, and indicates infection. Packed cell volume and protein levels can help in the assessment of dehydration, and Ig should be measured to check for Failure of Passive Transfer.

Radiographs
X rays are useful not only for initial diagnosis, but also for monitoring the progression of the disease and the effectiveness of treatment. They can also be used initially out rule out a fracture, and to identify any accompanying osteomyelitis, if present. Initial rads are also useful to provide a baseline for further x rays eg if no bony involvement is evident initially, but response to treatment is slow, then follow up rads may subsequently show osteomyelitis. Radiographic examination can be helpful in assessing a foals prognosis - a foal with multiple joint involvement and evidence of osteomyelitis on rads has a poor prognosis for use as a performance animal.

TREATMENT

Treatment of choice depends on how early treatment is initiated, the number of joints involved, whether bone involvement is suspected / confirmed, and the severity of the disease.

Antibiotics
Antibiotics should be started as soon as joint ill is suspected, but preferably after joint and blood samples have been taken for culture.. A wide range of bacteria, including Salmonella, E coli and Actinobacillus equuli are commonly found in infected joints, and thus initial antibiotic is ‘ broad spectrum ‘ i.e. effective against a wide range of bacteria which can cause the disease for eg penicillin and gentamicin. When and if culture results become available, the antibiotic regime can be altered accordingly. Foals should be kept on antibiotics for at least three weeks after clinical signs eg lameness, joint swelling, have stopped.

Assess foal’s status
Many foals with joint ill are also systemically unwell. It is important to fully evaluate the foal clinically, especially to look for other sites of infection eg scan the umbilicus. The foal may be dehydrated, need IV fluids, helped to nurse or stomach tubed with milk to maintain nutrition and hydration. If the foal has a history of FPT then colostrum or plasma may be indicated.

Drainage
The aim of draining affected joints is to remove debris and inflammatory mediators which can potentiate and prolong the infection. If the disease is caught early, and antibiotics started, joint aspiration, by removing joint fluid with a needle, may be sufficient. However, if the disease has been present for more than 24-48 hrs, or the foal has not responded to joint aspiration, then more aggressive therapy is warranted.

Distension-irrigation and through and through lavage are two techniques which can be used to more completely drain and flush the joints. Both require the foal to undergo GA, and the number of treatments depend on the foal’s response to each treatment.

The use of arthroscopy where you put a camera into the joint to drain joints and evaluate cartilage damage is becoming more popular. Open drainage can also be used.

Exercise Restriction
The foal must be box rested for a significant amount of time, to minimize the potential damage of excessive weight bearing on inflamed joints. Some foals are bandaged or put in casts to restrict movement

Nursing
Good nursing is critical for a successful outcome. Foals need to be kept warm, hydrated and with attention to nutritional needs - hand feeding, IV fluids if necessary. Regular monitoring of the foal’s clinical status eg rectal temp, palpation of joints, follow up radiographs and bloods can help in the assessment of response to treatment .

Other
Non steroidal anti-inflammatories eg finadyne are important both for their anti-inflammatory effects and also for pain relief. Sometimes these foals are so painful that they wont feed, so its important that we make them more comfortable.

Anti-ulcer medication can be important

PROGNOSIS

Improves with prompt recognition and aggressive treatment . Foals that respond quickly to treatment have a better prognosis . Foals with several joints involved can be a nightmare to treat, and often are euthanised.

PREVENTION

Farm management
Farm management is the key to preventing joint ill, and because it can be such a difficult disease to treat, prevention is certainly better than cure. It is important to rotate and rest foaling paddocks and yards, so that contamination eg faecal is kept to a minimum, thus minimizing the potential for foals to become infected by environmental bacteria. Preventing overcrowding by reducing the stocking rate will also help decrease environmental contamination. Good ventilation and sanitation in foaling boxes is important.

Foal monitoring
Ideally foals should be monitored to ensure that they have sufficient intake of colostrum within the first 6-12 hours. Foals should also be checked regularly after this so that early signs of septicaemia and joint ill can be detected, and treatment initiated sooner rather than later.

Antibiotics
Antibiotics can be used to prevent infection, although their routine use is debatable. Situations where they may be warranted include in the face of an outbreak, or where there is limited personnel to monitor foals.