VAIL, COLO. – Four simple criteria are useful in distinguishing septic arthritis from transient synovitis in a child with an inflamed hip.
The criteria are known as the Kocher criteria, for Dr. Mininder S. Kocher, associate director of sports medicine at Children’s Hospital Boston, who was first author of the study that introduced the criteria and an associated evidence-based, predictive algorithm.
The criteria are inability to tolerate weight bearing, fever greater than 38.5° C (101.3° F), an ESR (erythrocyte sedimentation rate) in excess of 40 mm/hour, and a peripheral WBC count greater than 12,000 cells/mm3.
Dr. Kocher and his coworkers showed in a retrospective study that a child who meets none of these four criteria has just a 0.2% chance of having septic arthritis. With one criterion present, there’s a 3% chance. With two criteria, it’s 40%. With any three, the probability of septic arthritis jumps to 93%. And when all four criteria are present, the probability of septic arthritis is 99.6% (J. Bone Joint Surg. Am. 1999;81:1662-70).
"Looking back on our own cases, this has been really helpful," Heather R. Heizer said at a conference on pediatric infectious diseases sponsored by Children’s Hospital Colorado.
Heather Heizer
The Kocher criteria deserve to be more widely known. Septic arthritis is an orthopedic emergency. Delayed treatment can lead to irreversible joint damage. And septic arthritis occurs more often in childhood than at any other period of life, observed Ms. Heizer, a physician assistant in the department of pediatrics at the University of Colorado at Denver.
The most common site for septic arthritis is the hip, followed by the knee, then the ankle. Together these three sites account for 80% of all cases.
In addition to the Kocher criteria, other signs and symptoms of septic arthritis include limb pain, joint effusion, and a strong tendency for the patient to hold the affected joint in the position of maximal intracapsular volume in order to minimize discomfort. Neonates and infants may present with pseudoparalysis in response to the joint pain.
The log-roll technique is an effective way to detect hip effusion on clinical examination. With the patient lying supine on the examination table, the examiner places one hand at the ankle and another on the thigh and rolls the leg back and forth. Hip effusion can also be detected by ultrasound or MRI. However, it’s important to recognize that the presence of hip effusion doesn’t distinguish septic arthritis from transient synovitis.
Diagnosis of septic arthritis is based upon a combination of clinical findings and analysis of synovial fluid obtained via joint aspiration. Septic arthritis is suggested by an opaque, yellow-to-green synovial fluid with an elevated WBC, at least 75% polymorphonuclear leukocytes, and a glucose concentration of only about 30% of that in blood.
The initial antibiotic therapy should be selected before synovial fluid culture results are available. The child’s age is an important consideration, as the causative organisms vary. Haemophilus influenzae was the most common pathogen in children younger than 5 years of age until the vaccine entered wide use. Now Staphylococcus aureus is No. 1 in all age groups, and community-acquired MRSA (methicillin-resistant S. aureus) is an important consideration.
In neonates, other organisms include group B streptococcus, Streptococcus viridans, Streptococcus pneumoniae, Neisseria gonorrhoeae, gram-negative enteric bacteria including Escherichia coli and group A streptococcus.
An important and underappreciated cause of septic arthritis in non-neonates younger than age 5 years is Kingella kingae. It is typically culture-negative but can be detected by polymerase chain reaction. In addition, Neisseria meningitidis is a consideration in this age group and all the way through adolescence, as well.
Ms. Heizer declared having no financial conflicts.