AUTHOR AND EDITOR INFORMATION

Section 1 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

INTRODUCTION

Section 2 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Background

Septic arthritis (SA) results from the presence of microbial agents in a joint space. SA 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 SA 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 SA 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 SA 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

SA 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 SA 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 SA has been observed. Large population-based studies to prove this trend are lacking. 

Subgroups of children who are at high risk for SA 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 SA 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

SA occurs in children of all races.

Sex

A higher incidence of SA 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 SA 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

Section 3 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

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 SA 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 SA 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 SA, most had a low-grade fever, but one third were afebrile at presentation.³ Absence of fever should not sway the clinician from the diagnosis.
  • The presence or absence of fever may be used to distinguish SA 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 SA 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/μL, were independent variables that best distinguished SA from transient synovitis.¹ The probability of SA 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 SA (1975-1985), over 90% had involvement of a single joint of a lower extremity.³ One notable exception is gonococcal SA. 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 was the most common cause prior to the widespread use of vaccines. In a series of 61 children diagnosed with a known pathogen between 1975-1985, H influenzae type B caused the infection in about half of the children.³ Because of the success of immunization programs, the incidence of SA has dramatically declined. S aureus is now the most likely etiologic agent in children of all ages, followed by group A streptococci and Streptococcus pneumoniae. MRSA-CA is an increasingly common cause of SA 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 SA 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.

DIFFERENTIALS

Section 4 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Other Problems to be Considered

The differential diagnosis of a painful monoarthritis is rather extensive. In contrast to children with septic arthritis (SA), children with transient synovitis appear well and are usually afebrile with just a mild limp. In adolescents, a slipped capital femoral epiphysis may manifest as a painful hip, thigh, or knee. Most patients are afebrile and the onset of pain may be preceded by minor trauma. Legg-Calve-Perthes disease, which is most common in boys, afflicts children aged 4-8 years. In contrast to SA, the pain is subacute with a more indolent onset, and these children do not have fever.

Aside from gonococcal arthritis or SA in the neonate, polyarthritis is not typically caused by bacteria within the joints. The differential for polyarthritis in children is broad and includes Lyme disease, acute rheumatic fever, serum sickness, Kawasaki disease, systemic lupus erythematosus, and Henoch-Schönlein purpura.

WORKUP

Section 5 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Lab Studies

Diagnosis is established by a combination of clinical findings and results of synovial fluid analysis.

• When septic arthritis (SA) is suspected, synovial fluid should be obtained for CBC count, glucose, Gram stain, and culture. Synovial culture has poor sensitivity (60-70%), and the data that establish the typical characteristics of synovial fluid in SA were collected in the era of widespread H influenzae type B infection. How these characteristics will change in the current era remains to be seen. Similarly, although blood cultures should be obtained, they have relatively low yields.
• A synovial fluid WBC count of more than 50,000/mL suggests SA, especially if the count exceeds 100,000/mL or if a predominance of polymorphonuclear cells is observed. Still, counts are often lower, and high counts may be associated with other conditions.
• The synovial fluid glucose concentration averages 30% of that in the serum, a finding unique to SA.
• Erythrocyte sedimentation rate is typically elevated, but in one series, fewer than one half of children with SA had peripheral WBC counts above 15,000 cells/μL.
• Although often elevated, a peripheral WBC count within the reference range does not rule out SA.
• The C-reactive protein (CRP) is a more sensitive marker for SA than is the peripheral WBC count. In one study, a CRP of more than 2 mg/dL was found to be a strong independent risk factor for SA of the hip among children presenting with hip pain.²

Imaging Studies

• Radiography
• • Although plain radiography may reveal an effusion as widening of the joint space with displacement of fat planes, it is insensitive in the diagnosis of SA.
  • Radiography may be most helpful in screening for etiologies other than SA as a cause of joint pain. For example, it may reveal bony changes suggestive of osteomyelitis, bony tumors or fractures as the source of swelling, and Legg-Perthes disease and slipped capital femoral epiphysis, which are diagnostic considerations in a child with an irritable hip.
• Ultrasonography
• • Ultrasonography is a simple, sensitive, and relatively inexpensive technique for detecting a hip effusion.
  • This test has a greater sensitivity than plain radiography and is becoming the modality of choice to reveal hip effusions. Ultrasonography is also used to guide the aspiration needle if an effusion is detected.
  • In a study of 96 children suspected to have SA of the hip, 40 had normal ultrasonography findings and no SA.
  • Ultrasonography has several advantages over CT in this setting, including eliminating radiation exposure and guiding the aspiration of deep joints such as the hip.
• Scintigraphy: This has a limited role in most cases but may be helpful if multifocal disease is suspected in neonates. It also assists with the detection of an associated osteomyelitis.

Procedures

• Clinicians should have a low threshold for performing an arthrocentesis, especially for children with a painful monoarthritis, significantly limited range of motion, and no plausible noninfectious explanation.
• Emergency department physicians are usually adept at performing arthrocentesis of most joints. The knee joint, for example, can usually be entered fairly easily using either a medial or superolateral approach. However, aspiration of fluid from the hip typically requires the involvement of a radiologist and an orthopedic surgeon.
• General practices that help to ensure the safety and success of arthrocentesis include liberal use of sedatives and analgesics, joint immobilization, sterile technique, and local anesthesia. Use of a needle large enough (18-20 gauge) to aspirate the viscous synovial fluid is necessary.

TREATMENT

Section 6 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Medical Care

• Splint the affected joint in a functional position for the first few days after diagnosis. Encourage early passive range of motion to stretch tendons and prevent contractures.

Surgical Care

• For uncomplicated septic arthritis (SA) involving joints other than the hip or shoulder, serial needle aspirations are indicated. This may be discontinued once fluid no longer reaccumulates. Failure to reach this goal is an indication for arthrotomy and open drainage.
• Urgent arthrotomy and open drainage is indicated in SA of the hip or shoulder, SA of other joints if no improvement occurs within 3 days of starting antimicrobial therapy, or if a large amount of pus or debris is aspirated during diagnostic arthrocentesis.

Consultations

• Orthopedic surgeon: SA of the hip requires emergent irrigation and drainage to minimize risk of aseptic necrosis of the femoral head.
• Infectious diseases specialist: This consultation is particularly indicated if the diagnosis is uncertain or if the microbiology is unusual.

Activity

• After 2-3 days of immobilization, encourage early passive range of motion.

MEDICATION

Section 7 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Typically, a clinician chooses an antibiotic before synovial fluid culture results are known. Thus, the child's age and risk factors, as well as Gram stain results, should all influence initial antibiotic coverage. Neonates are at risk for infection with gram-positive organisms, such as S aureus or group B streptococci, and gram-negative organisms such as E coli.

In the absence of meningitis, a semisynthetic penicillin (eg, oxacillin) plus an aminoglycoside (eg, gentamicin) may be used. Neonates with concomitant meningitis and septic arthritis (SA) present a therapeutic challenge. Oxacillin does not penetrate the blood-brain barrier well, and ampicillin, although it offers better cerebrospinal fluid levels, does not provide adequate coverage against S aureus. In this case, a combination of both vancomycin and a third-generation cephalosporin, such as ceftriaxone, is a reasonable choice for initial coverage.

S aureus is the most common cause of SA among nonneonates. Oxacillin alone should provide adequate coverage in older children who are immunocompetent, assuming that they are immunized for H influenzae type B. However, in communities in which MRSA-CA is prevalent, clindamycin is a better initial choice. A third-generation cephalosporin is the initial therapy for an adolescent possibly infected with gonococcus. Once culture results and sensitivities are known, antibiotic selection can be more specific. For example, a child with group A beta hemolytic streptococcus (GABHS) infection could be treated with penicillin, whereas one growing anaerobes would need clindamycin.

Drug Category: Antibiotics

Empiric antimicrobial therapy must be comprehensive and should cover all likely pathogens in the context of the clinical setting.

Drug Name	Gentamicin (Garamycin)
Description	An aminoglycoside with good gram-negative activity. Dosing regimens are numerous; adjust dose based on CrCl and changes in volume of distribution.
Adult Dose	1.5-1.8 mg/kg/dose IV Dosing intervals based on CrCl: >60 mL/min: Administer q8h 40-60 mL/min: Administer q12h 20-40 mL/min: Administer q24h 10-20 mL/min: Administerq48h <10 mL/min: Administer q72h
Pediatric Dose	2.5 mg/kg/dose IV q8h
Contraindications	Documented hypersensitivity
Interactions	Potentiates the effects of neuromuscular blockers; amphotericin B, cyclosporine, cephalosporins, and furosemide may increase the risk of renal toxicity; coadministration with loop diuretics may increase auditory toxicity of aminoglycosides; possible irreversible hearing loss of varying degrees may occur (monitor regularly)
Pregnancy	D - Fetal risk shown in humans; use only if benefits outweigh risk to fetus
Precautions	Nephrotoxicity and ototoxicity may be associated with prolonged elevated trough concentrations; monitor levels to minimize the risk of toxicity and to optimize therapy

Drug Name	Ceftriaxone (Rocephin)
Description	A third-generation cephalosporin with broad-spectrum, gram-negative activity; lower efficacy against gram-positive organisms; higher efficacy against resistant organisms. Arrests bacterial growth by binding to one or more penicillin-binding proteins.
Adult Dose	1-2 g IV/IM q24h
Pediatric Dose	Neonates <7 days: 50 mg/kg/d IV/IM q24h Neonates >7 days: <2000 g: 50 mg/kg/d IV/IM q24h >2000 g: 75 mg/kg/d IV/IM q24h Infants and children: 50-75 mg/kg/d IV/IM q24h
Contraindications	Documented hypersensitivity; hyperbilirubinemic neonates
Interactions	Probenecid may increase ceftriaxone levels; coadministration with ethacrynic acid, furosemide, and aminoglycosides may increase nephrotoxicity
Pregnancy	B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals
Precautions	Caution in those allergic to penicillin antibiotics; more common adverse drug reactions include skin rashes, diarrhea, and pain at the site of injection; caution with history of gallbladder, biliary tract, or hepatic disease

Drug Name	Penicillin G (Pfizerpen)
Description	Active against most gram-positive organisms except S aureus as well as some anaerobes. Interferes with synthesis of cell wall mucopeptide during active multiplication, resulting in bactericidal activity against susceptible microorganisms.
Adult Dose	1-2 million U IV q4-6h
Pediatric Dose	Neonate: Postnatal age <7 days: 100,000 U/kg/dose IV q8h Postnatal age >7 days: 100,000 U/kg/dose IV q6h Infants and children: 25,000-60,000 U/kg/dose IV q6h (not to exceed 4.8 million U/24 h)
Contraindications	Documented hypersensitivity
Interactions	Probenecid can increase effects of penicillin; coadministration of tetracyclines can decrease effects of penicillin
Pregnancy	B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals
Precautions	Cross sensitivity to cephalosporin antibiotics; caution with renal impairment, impaired cardiac function, or seizure disorders

Drug Name	Clindamycin (Cleocin)
Description	Active against most gram-positive organisms and anaerobes. Inhibits bacterial growth, possibly by blocking dissociation of peptidyl t-RNA from ribosomes causing RNA-dependent protein synthesis to arrest.
Adult Dose	600-1200 mg/d IV divided q6-8h
Pediatric Dose	Neonates <7 days: <2000 g: 5 mg/kg/dose IV q12h >2000 g: 5 mg/kg/dose IV q8h Neonates >7 days: <2000 g: 5 mg/kg/dose IV q8h >2000 g: 7.5 mg/kg/dose IV q8h Infants and children: 10 mg/kg/dose IV q8h
Contraindications	Documented hypersensitivity; regional enteritis, ulcerative colitis, antibiotic-associated colitis
Interactions	Increases duration of neuromuscular blockade induced by tubocurarine and pancuronium; erythromycin may antagonize effects of clindamycin; antidiarrheals may delay absorption of clindamycin
Pregnancy	B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals
Precautions	Pseudomembranous colitis has been associated with the use of clindamycin; dose adjustment may be necessary in patients with severe hepatic dysfunction; conversely, no adjustment is necessary in patients diagnosed with renal insufficiency; administer capsule with a full glass of water

Drug Name	Vancomycin (Vancocin, Lyphocin, Vancoled)
Description	For treatment of infections due to suspected or documented MRSA or serious or life-threatening infections due to S aureus.
Adult Dose	2 g/d IV divided q12h
Pediatric Dose	Neonates: Postnatal age <7 days: 10 mg/kg/dose IV q12h 7-30 days: 10 mg/kg/dose IV q8h Infants >30 days with CNS infection: 15 mg/kg/dose IV q6h
Contraindications	Documented hypersensitivity; previous severe hearing loss
Interactions	Erythema, histaminelike flushing and anaphylactic reactions may occur when administered with anesthetic agents; taken concurrently with aminoglycosides, risk of nephrotoxicity may increase above that with aminoglycoside monotherapy; effects in neuromuscular blockade may be enhanced when coadministered with nondepolarizing muscle relaxants
Pregnancy	C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Precautions	Caution in renal failure, neutropenia; red man syndrome (ie, erythema-multiforme like reaction with rash involving face, neck, and upper trunk, pruritus, urticaria, and hypotension) is caused by too rapid IV infusion (dose given over a few minutes) but rarely happens when dose given IV over 2 h administration or as PO or IP administration; red man syndrome is not an allergic reaction

FOLLOW-UP

Section 8 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Further Inpatient Care

• Hospitalize all children presumed to have septic arthritis (SA) for empiric intravenous antibiotic therapy.

In/Out Patient Meds

Once an organism is identified, an appropriate antibiotic is selected, and the child is demonstrating a good clinical response, continue outpatient therapy with either high-dose oral antibiotics or parenteral antibiotics. Antibiotics readily enter the joint fluid in high concentrations after oral administration. Frequent revisits to the physician, to ensure compliance and good clinical response, are essential.

• An S aureus infection usually clears after 3-4 weeks of antibiotic therapy.
• Antibiotic therapy for 3 weeks for H influenzae type B or S pneumoniae infections is usually sufficient.
• Gonococcal infections require 7-10 days of antibiotic therapy.

Complications

• Meningitis (10-30%), osteomyelitis (5-10%), cellulitis (10-30%), and pneumonia (5%) are potential complications in young children with SA resulting from hematogenous spread of H influenzae type B.
• Osteonecrosis, growth arrest, and sepsis are potential complications from SA of any etiology.

Prognosis

• Time to diagnosis is the most important prognostic factor in SA. Early institution of therapy helps to prevent degenerative arthritis. Diagnosis may be delayed in young infants, which leads to a poorer outcome.
• Other poor prognostic factors include infection of the hip joint, which may lead to aseptic necrosis of the femoral head; infection with S aureus; and a prolonged passage of time before the synovial fluid is sterilized.

Patient Education

• Nontraumatic joint pain with evidence of arthritis, such as swelling, warmth, or redness, requires emergency medical attention.
• For excellent patient education resources, visit eMedicine's Arthritis Center. Also, see eMedicine's patient education article Knee Pain.

MISCELLANEOUS

Section 9 of 10  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

Medical/Legal Pitfalls

• Failure to perform an arthrocentesis
• Delay in diagnosis, leading to a poorer prognosis for joint function

REFERENCES

Section 10 of 10

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• References

1. Kocher MS, Zurakowski D, Kasser JR. Differentiating between septic arthritis and transient synovitis of the hip in children: an evidence-based clinical prediction algorithm. J Bone Joint Surg Am. Dec 1999;81(12):1662-70. [Medline].
2. Caird MS, Flynn JM, Leung YL, et al. Factors distinguishing septic arthritis from transient synovitis of the hip in children. A prospective study. J Bone Joint Surg Am. Jun 2006;88(6):1251-7. [Medline].
3. Welkon CJ, Long SS, Fisher MC, Alburger PD. Pyogenic arthritis in infants and children: a review of 95 cases. Pediatr Infect Dis. Nov-Dec 1986;5(6):669-76. [Medline].
4. Dagan R. Management of acute hematogenous osteomyelitis and septic arthritis in the pediatric patient. Pediatr Infect Dis J. Jan 1993;12(1):88-92. [Medline].
5. Frank G, Mahoney HM, Eppes SC. Musculoskeletal infections in children. Pediatr Clin North Am. Aug 2005;52(4):1083-106, ix. [Medline].
6. Kratz A, Greenberg D, Barki Y, et al. Pantoea agglomerans as a cause of septic arthritis after palm tree thorn injury; case report and literature review. Arch Dis Child. Jun 2003;88(6):542-4. [Medline].
7. Shetty AK, Gedalia A. Septic arthritis in children. Rheum Dis Clin North Am. May 1998;24(2):287-304. [Medline].

Article Last Updated: Dec 5, 2007