Septic Arthritis in the Newborn Foal

Septic arthritis is a bacterial infection of a joint. It is often combined with osteomyelitis, infection of the bone. Lameness or increased joint swelling (effusion) in a neonatal foal should be attributed to a septic arthritis/osteomyelitis process until proven otherwise. Many owners mistakenly believe that the mare must have stepped on the foal to make her lame but in fact the foal has a septic joint. This is important because septic joints need emergency treatment.

Septic arthritis is commonly referred to as joint ill, septic polyarthritis, septic epiphysitis and septic physitis, and is associated with infection of the umbilicus (navel ill).

• Usually foals have failure of passive transfer of maternal antibodies.
• Clinically, the foal may present with multiple problems related to septicemia (a wide spread bacterial infection) or they may be normal with the exception of a hot, swollen joint.
• Because septic arthritis is a painful condition, foals spend more time laying down. Pressure sores may develop over the bony prominences.
• Fifty percent of the foals with septic arthritis have umbilical abscesses (navel ill).
• Because the bacteria are spread through the blood stream, a single joint or multiple joints may be affected in a foal.
• The short term outcome of septic arthritis/osteomyelitis depends on the promptness of treatment, the number of joints involved, the amount of bone destruction and the other body systems that may be involved. Approximately 60 percent of the foals survive the neonatal period.

Diagnosis

Lameness and joint swelling in the neonatal foal is an emergency situation. A veterinarian should be called to examine the foal and perform certain diagnostic tests and therapeutic procedures. Tests may include:

• Complete blood count
• Chemistry profile
• Immunoglobulin levels (measure of colostrum intake)
• Arthrocentesis (collecting a sample of joint fluid)
• Joint fluid analysis
• Culture and sensitivity of joint fluid
• Blood culture
• Radiographs of the affected joint
• Ultrasound examination of the umbilical structures of the foal

Treatment

• Broad spectrum antibiotics for 3 to 4 weeks
• Plasma transfusion if immunoglobulins (colostral antibodies) are less than 800 mg/dl
• Wash the joint every other day until joint fluid is normal and foal is more sound
• Stall rest for 3 to 4 weeks

Home Care and Prevention

It is somewhat difficult to provide the initial care of the foal with septic arthritis at home. Joint lavage (washing or irrigation) needed to be performed by a veterinarian in a clean area under heavy sedation or anesthesia. Because of these factors and the fact that the procedure must be repeated several times, it is probably best done in a hospital situation. Once the joint lavages are completed the foal can continue the antibiotic treatment at home.

The most important aspect of preventive care is to make sure the foal receives good quality colostrum at birth. This is done by having the birth attended and making sure the foal stands and nurses by 3 hours after birth. If there is any deviation from this pattern or the mare has experienced premature lactation (dripped milk before the foal was born), then this foal is at high risk for septicemia, which could lead to septic arthritis/osteomyelitis.

Septic arthritis is a bacterial infection of a joint. It is often combined with osteomyelitis, infection of the bone. Septic arthritis is commonly referred to as joint ill, navel ill, septic polyarthritis, septic epiphysitis and septic physitis. In the neonatal foal it is secondary to septicemia, which is a wide spread infection that is in the blood system of the animal. Septicemia is usually secondary to the foal not receiving enough good quality colostrum at birth. Colostrum is the antibody-rich first milk that gives the foal protection against bacteria in the environment. Infection can enter the foal's body through ingestion, inhalation or through the umbilical stump. About 50 percent of the foals with septic arthritis have umbilical abscesses.

In one study it was found that over 25 percent of septic foals have joint or bone infection. Anatomically, the blood vessels in the bones adjacent to joints and the growth plates, make a sharp turn. It is believed that the blood flow through these natural hairpin turns actually slows down, allowing the bacteria time to settle out and multiply in these regions.

Lameness or increased joint swelling (effusion) in a neonatal foal should be attributed to a septic arthritis/osteomyelitis process until proven otherwise. Many owners falsely believe that the mare must have stepped on the foal to make it lame but in fact the foal has a septic joint. This is important because septic joints need emergency treatment. (In humans, it is believed that septic joints must be treated within 24 hours to obtain complete recovery.)

Clinically, the foal may show multiple problems related to septicemia, such as shock, pneumonia, diarrhea and meningitis, or they may be normal with the exception of a hot, swollen joint. A single joint or multiple joints may be affected in a foal. The most common joint involved is the stifle followed by the hock, carpus, fetlock and shoulder.

Septic arthritis/ osteomyelitis in the foal has been described as four different types depending on where the infection is located. The S-type denotes synovial infection with no evidence of bony involvement. The synovia is the inside lining of the joint itself. This type is usually seen in young foals, a few days old, that have other systemic signs of illness. More than one joint may be affected. Joint distension is present and the animal is in extreme pain. The second type is the E-type or epiphysitis type, which involves osteomyelitis (bone infection) of the epiphysis, the bone that underlies the cartilage of a joint. The clinical signs are similar to the S-type, but the foals may be slightly older. The P-type occurs when there is osteomyelitis of the physis or growth plate of the bone. The P-type is usually seen in older foals and affects only one joint. A fourth type of infectious arthritis has been described as the T-type, which involves the small bones of the hock (tarsal bones).

Because septic arthritis is a painful condition, foals spend more time laying down. Pressure sores may develop over a bony prominence, such as the hip, hock or elbows. A pressure sore starts off as a thickening or leathery feel to the skin. This skin then sloughs off leaving a raw open wound. The presence of these sores should alert an owner that the foal is laying down more that he should and a source of pain should be investigated.

The short-term outcome of septic arthritis/osteomyelitis is dependent of the promptness with which treatment is initiated, the number of joints involved, the amount of bone destruction and the other body systems that may be involved. One study reported that approximately 60 percent of the foals with just the S-type septic joint survive the neonatal period. The presence of bone infection (osteomyelitis) decreases the short-term survival to less than 40 percent. The septic joint does not cause death of the foal, rather the owners often reject further treatment and elect euthanasia. Long-term full recovery is possible but some arthritis may remain.

The presumptive diagnosis of septic arthritis/osteomyelitis in the neonatal foal is made on the physical appearance of lameness in the foal, joint swelling and a history of possible failure of passive transfer of colostral antibodies. Certain diagnostic tests will help to confirm the diagnosis.

• Complete blood count. A newborn foal with signs of septicemia will usually have a lower than normal White Blood Cell (WBC) count. This is generally due to the infection overwhelming the immune system and using up the white blood cells faster than they can be produced. If the foal is slightly older (2 to 3 weeks old) and has septic arthritis, the WBC count is usually higher than normal. The slower onset of the problem allows for the body to recruit white blood cells to fight the infection.
• Chemistry profile. A chemistry profile is a series of blood tests that check various organ systems, electrolytes and protein levels. Foals with septicemia may have abnormalities in renal function and protein levels but there is nothing specific to indicate septic arthritis.
• Immunoglobulins. Most foals with septic arthritis/osteomyelitis have the infection because of inadequate protection from colostral antibodies. This is called failure of passive transfer (FPT). The immunoglobulin (antibody) levels in the foals blood can be measured by many different methods. One of the most common tests is called the CITE test. This is a semi-quantitative test that can be performed stall side in approximately 20 minutes. The ease and speed of the test makes it valuable in obtaining a quick answer to the foal immunologic status. Foals that receive adequate colostrum generally have levels of greater than 800 mg/dl. Foals with septic arthritis/osteomyelitis generally have levels less than 400 mg/dl and sometimes less than 200 mg/dl.
• Arthrocentesis and fluid analysis. If a foal has a swollen, painful joint, it is important to obtain a sample of the joint fluid. The joint is clipped and scrubbed clean (surgically prepared). A sterile needle is then inserted into the joint and synovial fluid (joint fluid) is aspirated. Normal synovial fluid is pale yellow, clear and viscous. Synovial fluid from an infected joint is cloudy and watery. Fluid analysis of normal synovial fluid generally has less than 250 WBC per microliter, and the protein is less than 2 mg/dl, while the cytology from an infected joint has a WBC count in the thousands and a protein level greater than 2. These results indicate a severe inflammatory response to the infection.
• Joint fluid and blood cultures. Joint fluid culture of a septic joint will only grow bacteria in approximately 50 percent of the cases. You are more likely to have a positive culture from foals with osteomyelitis and just synovitis. A negative culture does not negate that diagnosis of a septic joint. Bacterial growth may be inhibited by the inflammatory response or by previous antibiotic administration. Blood cultures are sometimes helpful in determining the cause as well. Organisms cultured from these foals (from blood, synovial fluid, umbilicus, etc.) include E. coli, Klebsiella, Streptococcus, Enterobacter, Actinobacillus, Staphylococcus epidermis and Pseudomonas. Sensitivity patterns are important in deciding the antibiotic that would be most effective against the causative organism. Because cultures may take several days before they grow bacteria it is important to start the foal on antibiotics that have a wide range of effectiveness (broad spectrum antibiotics), no matter what.
• Radiographs of the affected joint. It is important to take radiographs of the affected joints to determine the presence and extent of any bone involvement. Early in a bone infection (e.g. first 21 days) you may not see any bone destruction but it will give you a baseline by which you can compare future radiographs. If the swelling and pain persist, radiographs should be repeated every 4 to 5 days to evaluate progression of the lesions. If osteomyelitis bone infection) is present, your treatment may become more aggressive than if you are dealing with a synovitis alone.
• Ultrasound of the umbilical structures. Fifty percent of the foals with septic arthritis/osteomyelitis have an infection of the umbilical structures suggesting that this may be a common port of entry for the bacteria. Usually, the external umbilicus looks normal, despite the fact that the deeper structures such as the umbilical arteries and vein, are to be enlarged and infected. The only way to evaluate these structures is through the use of ultrasound. Enlargement of any of the structures is highly suggestive of infection.

Treatment In-depth

• Supportive care of the foal with septic arthritis includes fluid therapy, adequate nutrition, environmental temperature control and plasma transfusion to increase immunoglobulin levels.
• The antibiotic choice usually consisted of penicillin or ampicillin combined with gentocin or amikacin. This provides protection against the most common pathogens – E. coli, Klebsiella and Streptococcus. Because of an increasing resistance to gentocin, our drug of choice to treat gram negative is amikacin. Antibiotic therapy should be continued for a minimum of 7 days after the resolution of clinical signs. This is generally 3 to 4 weeks.
• Joint lavage. When infection occurs in or around a joint, inflammation of the synovial membrane takes place. There is an increase of fluid, white blood cells and protein within the joint. Degradative enzymes are released and cartilage degeneration can then ensue. Joint drainage and lavage are important adjuncts to the effective therapy of the infected joint. It allows for the removal of the enzymes from the joint and decreases the pressure of the effusion. Several methods of joint drainage have been suggested. Simple drainage alleviates the high intra-articular pressure but does not effectively remove all of the inflammatory products. Joint lavage can be done by a "through and through" method, by distention irrigation, by arthrotomy or arthroscopy. This is best accomplished under general anesthesia. The affected joint is clipped and sterilely prepped with povidone iodine and alcohol. An 18-16 gauge needle is placed into the joint and connected to a liter bag of normal saline or lactated ringers solution. The joint is distended under pressure and then another needle is placed in the opposite side of the joint and the fluid is allowed to drain out. A 3-way stop-cock can be placed on the egress needle to allow multiple distensions of the joint capsule. This provides a thorough flushing of the infected joint. This procedure should be repeated every other day until the joint fluid becomes more normal with decreased WBC and protein.
• Surgical intervention may be necessary in osteomyelitis. This may involve surgical removal of the infected bone.
• The foals were confined to their stalls with minimal exercise. Support wraps were utilized on some of the cases, but immobilization of the joint was not done.

The survival rate of foals with septic arthritis often depends on factors other than the joint itself,such other complicating problems of septicemia. In one study 66 percent of the foals with the synovitis type survived, but if you eliminate two animals that died within 24 hours of admittance due to septic shock, then this percentage increases to 80 percent. Forty-four percent of the foals with osteomyelitis survived. Long term studies have not been conducted to answer the question of long term soundness after the animals have been placed in work. In all circumstances, septic arthritis should be treated as a medical emergency. In humans with bacterial arthritis, it has been found that a delay in treatment of a few days drastically decreases your chance of complete recovery.