eMedicine Specialties > Pediatrics: General Medicine > Infectious Disease

Arthritis, Septic

Author: Richard J Scarfone, MD, Associate Professor, Department of Pediatrics, University of Pennsylvania School of Medicine; Attending Physician and Director of Emergency Preparedness, Division of Emergency Medicine, The Children's Hospital of Philadelphia
Contributor Information and Disclosures

Updated: Apr 29, 2009

Introduction

Background

Septic arthritis (SA) results from the presence of microbial agents in a joint space. Septic arthritis of the hip is a true orthopedic emergency; delay in diagnosis or treatment may result in irreversible damage to the joint. In recent decades, the relative frequency with which specific microbial agents cause infection dramatically decreased, resulting in a decline in the overall incidence of septic arthritis and a modification in the presumptive medical therapy.

Pathophysiology

The most common route by which microorganisms enter a joint is by hematogenous spread to the synovium. Less commonly, entry occurs directly following a penetrating trauma or contiguously from an adjacent osteomyelitis. Because of their unique anatomy, neonates and young children often have coexisting septic arthritis and osteomyelitis. The bony cortex is thin, and the periosteum is loose. Blood vessels that connect the metaphysis and epiphysis serve as a conduit by which bony infection may easily reach the joint space.

Proteolytic enzymes released by inflammatory cells can damage joint cartilage. In addition, inflammatory mediators, bacteria, and pus increase pressure within the joint, compress intra-articular vessels, and impair blood supply to the cartilage and adjacent bone. Pressure necrosis within any joint may destroy synovium or cartilage, but septic arthritis of the hip is a true orthopedic emergency. In the hip, if the condition remains undiagnosed and untreated, contiguous spread may cause ligamentous damage, avascular necrosis of the femoral head, dislocation, and osteomyelitis.

Frequency

United States

Septic arthritis is more common in children than adults, but the actual incidence is unknown. From 1979-1996, a tertiary-care children's hospital reported just 82 children with either confirmed or suspected septic arthritis of the hip.¹ More recently, 34 such cases were diagnosed at a tertiary-care children's hospital from 2000-2004.² Data from older studies are somewhat obsolete because effective vaccines have virtually eliminated the most common etiologic agent, Haemophilus influenzae type B.

With the dramatic increase in community-acquired methicillin-resistant Staphylococcus aureus (MRSA-CA), the clinical impression of pediatricians and pediatric emergency medicine physicians is that a corresponding increase in the incidence of septic arthritis has been observed.³ Large population-based studies to prove this trend are lacking. 

Subgroups of children who are at high risk for septic arthritis include neonates, individuals with hemophilia who are subject to hemarthrosis, and individuals who are immunocompromised, such as those with sickle cell anemia or human immunodeficiency virus (HIV) infection or those treated with chemotherapy.

Mortality/Morbidity

Because of the availability of antibiotics, children rarely die from septic arthritis or its complications. Although chronic arthritis is uncommon, the short-term morbidity and costs, in terms of prolonged antibiotic therapy and hospitalizations, may be substantial.

Race

Septic arthritis occurs in children of all races.

Sex

A higher incidence of septic arthritis is reported among boys than among girls; some series report that boys are affected twice as frequently as are girls. However, a series of 82 children with septic arthritis of the hip found no sex predilection.¹

Age

SA occurs among all age groups but is most common in younger children, peaking in those younger than 3 years.

Clinical

History

• Joint pain or swelling
  • Acute joint inflammation marked by severe pain and swelling is the hallmark of septic arthritis (SA). Joint pain results from stretching of the fibrous joint capsule. If lower extremity joints are involved, parents often report that children can not bear weight and that they resist all efforts to move the involved joint.
  • Children typically have involvement of a single joint; lower extremity joints, especially the knee and hip, account for most cases. The elbow is the most common upper extremity joint to become infected.
  • Neonates are more likely to have infection in multiple joints (polyarticular disease).
• Pseudoparalysis
  • A septic joint is so painful that most children do not tolerate any range of motion, resulting in pseudoparalysis. If the knee or hip is involved, an ambulatory child refuses to walk or bear weight on the affected limb. Among 82 children with septic arthritis of the hip, 78 (95%) were unable to bear weight on the affected limb at presentation.¹
  • If supported by a physical examination of the joint, this history helps to distinguish septic arthritis from other less painful causes of arthralgia, such as transient synovitis of the hip, postinfectious or reactive arthritis, or traumatic hemarthrosis.
• Fever
  • In a series of 95 children with septic arthritis, most had a low-grade fever, but one third were afebrile at presentation.⁴ In a more recent study, 83% of children with septic arthritis had a recent fever, but only half were febrile at ED presentation.⁵ Absence of fever should not sway the clinician from the diagnosis.
  • On the other hand, the presence or absence of fever may be helpful in distinguishing septic arthritis from transient synovitis of the hip.
    • Each condition presents as an acutely irritable hip in a young child and may be associated with an effusion.
    • In general, children with septic arthritis have greater impairment with more diminished range of motion than those with transient synovitis.
    • One retrospective series determined that a history of fever and difficulty of bearing weight on a limb, along with an erythrocyte sedimentation rate greater than 40 mm/h and a peripheral WBC count of more than 12,000 cells/μ L, were independent variables that best distinguished septic arthritis from transient synovitis.¹ The probability of septic arthritis was 99.6% for children with all 4 factors and 93.1% for those with any 3 factors. In another series, none of the children with transient synovitis had fever, and fever was found to be the most influential predictor in distinguishing between the 2 conditions.²

Physical

• Decreased or absent range of motion, joint tenderness, swelling, warmth, and erythema are common physical signs. However, because of the deep location of the hip joint, there may be no erythema or swelling noted. Children orient an affected joint in such a way as to minimize the pain. The hip is flexed, abducted, and externally rotated. The knee, ankle, and elbow are partially flexed, whereas the shoulder is adducted and internally rotated.
• Diagnosis is suspected in children who present with monoarthritis of a lower extremity. In a series of 95 children with septic arthritis (1975-1985), over 90% had involvement of a single joint of a lower extremity.⁴ One notable exception is gonococcal septic arthritis. This results from the hematogenous spread of the organism with fever, chills, rash, tenosynovitis, and migratory polyarthritis, which often leads to monoarticular infection.

Causes

• Neonates (aged <2 mo): S aureus is the most common cause, but Escherichia coli, group B streptococci, and other gram-negative bacilli also cause SA. 
• Children (aged 2 mo to 5 y): H influenzae type B had been the most common cause prior to the widespread use of vaccines. In a series of 61 children diagnosed with a known pathogen from 1975-1985, H influenzae type B caused the infection in about half of the children.⁴  In contrast, among 46 children diagnosed with septic arthritis from 2000-2006, S aureus was the cause in 31 (67%).⁵  Other etiologies include group A streptococci and Streptococcus pneumoniae. Community-acquired methicillin-resistant S aureus (MRSA-CA) is an increasingly common cause of septic arthritis in children.
• Adolescents: Neisseria gonorrhoeae is the suspected cause for those with either polyarticular or monoarticular disease.
• Others
  • Group A streptococcus is reported in numerous children with active varicella-zoster infection.
  • Salmonella is suspected in individuals with sickle cell anemia.
  • Mycobacterium tuberculosis is a rare cause of chronic pyogenic arthritis. If identifiable risk factors are present, then a purified protein derivative (PPD) should be placed for the child with culture-negative disease.
  • Kingella kingae has been noted to cause septic arthritis in children younger than 5 years in Israel and is an emerging pathogen in the United States. Rarely, fungi or anaerobes may be found within a septic joint. A common cause of reactive arthritis is the spirochete Borrelia burgdorferi. Children typically present with a monoarthritis, in the absence of fever, weeks to months after being bitten by a tick. Less common causes of reactive arthritis include mycoplasma and viruses.

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