Basics
Description
Microbiologic infection and inflammation of the usually sterile joint space
Epidemiology
- Most common age: toddler and school age (2 " 6 years)
- Predominant sex: male (2:1 female)
- Most common location: lower extremities (hip, knee, and ankle) and large joints (hip, shoulder, elbow)
Pathophysiology
- Entry of bacteria into joint space
- Hematogenous spread (seeding during transient bacteremia) most common
- Direct inoculation (penetrating trauma or during surgery)
- Extension from bone infection (mainly in children <1 year old when vessels cross from metaphysis to epiphysis)
- In response to cytokines, influx of inflammatory cells, and release of proteolytic enzymes
- Leads to destruction of synovium and cartilaginous structures
Etiology
- Most common causes by age:
- Neonates: group B Streptococcus, Staphylococcus aureus, Escherichia coli, and Candida albicans
- Older children: Staphylococcus aureus, group A Streptococcus, Kingella kingae in toddlers, Haemophilus influenzae
- Also consider
- Salmonella: in patients with sickle cell
- Neisseria gonorrhoeae: in sexually active teens and neonates
- Neisseria meningitidis
- Mycobacterium tuberculosis
- Rubella
- Parvovirus
- Hepatitis B or C
- Mumps
- Herpesviruses (Epstein-Barr virus, cytomegalovirus, herpes simplex virus, varicella-zoster virus)
- Fungal etiologies (e.g., coccidioidomycosis)
Commonly Associated Conditions
- Sickle cell disease: Salmonella
- Immunocompromised patients: Mycoplasma, Ureaplasma, Klebsiella, or Aspergillus infection
Diagnosis
History
- Systemic symptoms:
- Fever (occurs within the first few days of illness in 75% of patients)
- Malaise
- Poor appetite
- Joint symptoms:
- Pain: worsening, does not wax and wane
- Limp
- Inability to bear weight, refusal to move joint, positional preferences
- Typically monoarticular
- Consider hip involvement when the patient complains of knee or thigh pain.
Physical Exam
- Ill appearing
- Joint
- Warm, swollen, erythematous
- Held in "position of comfort " maximizing intracapsular joint volume (e.g., hip held flexed, abducted, externally rotated)
- "Pseudoparalysis " : refusal to move the affected extremity
- Pain throughout entire range of motion (even passive motion)
- Presentation may be delayed and without external findings in deep joints (hip and shoulder).
- In the frightened or uncooperative child, it is possible to have the parent perform an examination for tenderness and range of motion while observing from a distance.
Diagnostic Tests & Interpretation
Lab
- Synovial fluid analysis is critical for diagnosis:
- WBC count: >50 " 100,000/mm3 with >75% neutrophils
- Glucose: <50% that of the serum
- Gram stain: reveals organism in ’ Ό50% of cases
- Culture: reveals organism in ’ Ό75% of cases (except for gonorrhea)
- Emerging polymerase chain reaction (PCR) technology may allow higher yield and faster identification of causative organisms.
- Inoculation of joint fluid into blood culture bottle facilitates recovery of K. kingae.
- Real-time PCR for K. kingae toxin from joint fluid provides higher yield than routine Gram stain or culture alone.
- Other supportive blood tests:
- WBC count: neither sensitive nor specific
- Erythrocyte sedimentation rate (ESR): elevated (>30 mm/h) in 95% of cases
- C-reactive protein (CRP): increased (>1.0 mg/dL). In one study, a CRP <1.0 mg/dL had a negative predictive value of 87%.
- Blood cultures: positive in ’ Ό40% of cases, sometimes yield pathogen when joint cultures are negative
- Serology for Borrelia burgdorferi or PCR of joint fluid may be helpful in differentiating between bacterial arthritis and Lyme disease.
Imaging
- Radiography
- May show widening of joint space and/or displacement of normal fat pads
- Ultrasound
- Delineates amount of fluid within joint capsule
- Increased blood flow with color Doppler is associated with infection. Bilateral effusions suggest transient synovitis.
- Useful in guiding needle aspiration (especially of deep joints such as the hip)
- MRI and bone scan
- Should not delay aspiration or antibiotic management
- MRI: early detection of joint fluid; also will reveal adjacent bone abnormalities to suggest osteomyelitis
- Bone scan: reveals increased uptake in the perimeter of the joint during the "blood pool " phase of the study
- Such imaging should be considered to identify concomitant osteomyelitis in patients <4 years of age, involvement of the shoulder, or symptoms >6 days.
Differential Diagnosis
- Infectious
- Osteomyelitis with or without contiguous spread to proximal joint
- Infectious and postinfectious reactive arthritides: N. meningitidis, group A Streptococcus, Salmonella, Mycoplasma, Campylobacter, Shigella, Yersinia, Chlamydia
- Cellulitis causing decreased range of motion of joint secondary to inflammation
- Psoas abscess or retroperitoneal abscess
- Tuberculous arthritis
- Lyme arthritis (B. burgdorferi)
- Septic bursitis
- Tumors
- Osteogenic sarcoma (long bone pain spreading to joint space)
- Leukemia/lymphoma
- Trauma
- Occult fracture in proximity to growth plate
- Ligamentous injury (sprain)
- Foreign body synovitis
- Traumatic knee effusion/hemarthrosis
- Immunologic/rheumatic
- Toxic (transient) synovitis: most common mimic; must examine joint aspirate to differentiate from septic arthritis
- Acute rheumatic fever
- Systemic lupus erythematosus
- Juvenile rheumatoid arthritis
- Henoch-Sch Άnlein purpura
- Reactive arthritis syndrome (after GI or chlamydial infection): arthritis, uveitis, urethritis
- Beh §et syndrome (iridocyclitis, genital, and oral ulcerations)
- Serum sickness
- Inflammatory bowel disease
- Musculoskeletal
- Knee: apophysitis (e.g., Osgood-Schlatter disease), patellofemoral pain syndrome, osteochondritis dissecans
- Hip: slipped capital femoral epiphysis
- Algorithm to differentiate septic arthritis and transient synovitis of the hip: Absence of all 4 factors is strongly associated with absence of septic arthritis.
- Fever
- ESR >20 mm/h
- CRP >1.0 mg/dL
- WBC >11,000 cells/mL
- Joint space fluid apparent on plain radiograph
Alert
- Clinical examination in conjunction with a history of acute onset should raise suspicion for septic arthritis, even in the face of "negative " laboratory screening tests. Analysis of the synovial fluid is necessary for diagnosis.
- Some children, especially neonates and young infants, will not manifest signs of systemic disease early in the course of the illness.
Treatment
Medication
- Should be initiated immediately after blood and fluid cultures obtained
- Target empiric antibiotic therapy toward common organisms in age group; may be aided by Gram stain results
- Typical 1st line: antistaphylococcal penicillin or 1st-generation cephalosporin
- In areas of methicillin-resistant Staphylococcus aureus (MRSA) high prevalence (>15%), consider vancomycin or clindamycin as 1st-line treatment.
- Consider addition of 3rd-generation cephalosporin:
- In neonates (alternatively could add gentamicin)
- If gram-negative organism on Gram stain
- If no organisms on Gram stain
- High suspicion for K. kingae
- In sexually active adolescents for coverage of N. gonorrhea
- In patients with sickle cell for coverage of Salmonella
- Narrow coverage once organism is identified and susceptibilities known
- Duration of therapy depends on organism:
- Staphylococcus aureus: 3 weeks
- Streptococcus pneumoniae, K. kingae, and N. meningitidis: 2 " 3 weeks
- Longer courses may be necessary for unusual organisms and in complicated courses.
- May be able to transition to oral antibiotics after short course of intravenous therapy if improving exam and labs
- Pain management with analgesics
- Intra-articular injection of antibiotics is not recommended.
Inpatient Considerations
Initial Stabilization
- Orthopedic emergency: Drainage of infection should occur as soon as possible.
- Antibiotic administration immediately after joint aspiration is performed
- Indications for open surgical drainage and/or irrigation
- Hip involvement
- Shoulder involvement (controversial)
- Thick, purulent, loculated, or fibrinous exudate unable to pass through 18-gauge needle
- Lack of improvement within 3 days
- Immobilization of extremity
- Pain management
Ongoing Care
Follow-up Recommendations
Patient Monitoring
- Follow-up with orthopedic surgery.
- Physical therapy may be useful.
- When to expect improvement:
- Symptoms typically improve with 2 days of appropriate antibacterial therapy.
- CRP typically peaks on day 2 of therapy and quickly normalizes within 7 " 10 days.
- Concerning signs:
- Continued pain, fever, or lack of improvement of range of motion after 3 " 4 days of appropriate antibiotic treatment
- Rising ESR or CRP in the face of antibiotic treatment
- Severe cases of septic arthritis may require serial drainage and debridement.
Prognosis
- Depends on duration of illness prior to institution of appropriate therapy
- If antibiotic therapy not instituted within first 4 days of illness, increased incidence of residual joint dysfunction
Complications
- Permanent limitation of range of motion due to tissue destruction and scarring
- Growth disturbance if the epiphysis is involved (leg length discrepancy)
- Avascular necrosis of femoral head (due to increased pressure within joint interrupting blood flow)
Additional Reading
- 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. 2006;88(6):1251 " 1257. [View Abstract]
- Ceroni D, Cherkaoui A, Ferey S, et al. Kingella kingae osteoarticular infections in young children: clinical features and contribution of a new specific real-time PCR assay to the diagnosis. J Pediatr Orthop. 2010;30(3):301 " 314. [View Abstract]
- Kocher MS, Mandiga R, Murphy JM, et al. A clinical practice guideline for treatment of septic arthritis in children: efficacy in improving process of care and effect on outcome of septic arthritis of the hip. J Bone Joint Surg Am. 2003;85-A(6):994 " 999. [View Abstract]
- Liu C, Bayer A, Cosgrove SE, et al. Clinical practice guidelines by the Infectious Diseases Society of America for the treatment of methicillin-resistant Staphylococcus aureus infections in adults and children. Clin Infect Dis. 2011;52(3):e18 " e55. [View Abstract]
- Montgomery CO, Siegel E, Blasier RD, et al. Concurrent septic arthritis and osteomyelitis in children. J Pediatr Orthop. 2013;33(4):464 " 467. [View Abstract]
- P € €kk Άnen M, Kallio MJ, Kallio PE, et al. Sensitivity of erythrocyte sedimentation rate and C-reactive protein in childhood bone and joint infections. Clin Orthop Relat Res. 2010;468(3):861 " 866. [View Abstract]
- P € €kk Άnen M, Peltola H. Bone and joint infections. Pediatr Clin North Am. 2013;60(2):425 " 436. [View Abstract]
- Sultan J, Hughes PJ. Septic arthritis or transient synovitis of the hip in children: the value of clinical prediction algorithms. J Bone Joint Surg Br. 2010;92(9):1289 " 1293. [View Abstract]
Codes
ICD09
- 711.00 Pyogenic arthritis, site unspecified
- 711.05 Pyogenic arthritis, pelvic region and thigh
- 711.06 Pyogenic arthritis, lower leg
- 711.07 Pyogenic arthritis, ankle and foot
- 041.00 Streptococcus infection in conditions classified elsewhere and of unspecified site, streptococcus, unspecified
- 711.01 Pyogenic arthritis, shoulder region
- 041.9 Bacterial infection, unspecified, in conditions classified elsewhere and of unspecified site
- 711.02 Pyogenic arthritis, upper arm
- 041.10 Staphylococcus infection in conditions classified elsewhere and of unspecified site, staphylococcus, unspecified
ICD10
- M00.9 Pyogenic arthritis, unspecified
- M00.859 Arthritis due to other bacteria, unspecified hip
- M00.861 Arthritis due to other bacteria, right knee
- M00.879 Arthritis due to other bacteria, unspecified ankle and foot
- M00.019 Staphylococcal arthritis, unspecified shoulder
- M00.069 Staphylococcal arthritis, unspecified knee
- M00.269 Other streptococcal arthritis, unspecified knee
- M00.00 Staphylococcal arthritis, unspecified joint
- M00.819 Arthritis due to other bacteria, unspecified shoulder
- M00.219 Other streptococcal arthritis, unspecified shoulder
- M00.20 Other streptococcal arthritis, unspecified joint
- M00.829 Arthritis due to other bacteria, unspecified elbow
- M00.869 Arthritis due to other bacteria, unspecified knee
- M00.80 Arthritis due to other bacteria, unspecified joint
- M00.079 Staphylococcal arthritis, unspecified ankle and foot
- M00.229 Other streptococcal arthritis, unspecified elbow
- M00.029 Staphylococcal arthritis, unspecified elbow
- M00.279 Other streptococcal arthritis, unspecified ankle and foot
- M00.259 Other streptococcal arthritis, unspecified hip
- M00.059 Staphylococcal arthritis, unspecified hip
SNOMED
- 372939007 Suppurative arthritis (disorder)
- 372941008 Pyogenic arthritis of hip
- 239777004 Knee pyogenic arthritis
- 267882003 Pyogenic arthritis of the ankle and/or foot (disorder)
- 239779001 elbow pyogenic arthritis (disorder)
- 36678001 Pyogenic arthritis of shoulder region
- 111820003 Staphylococcal arthritis (disorder)
- 48245008 Bacterial arthritis (disorder)
- 51646002 Streptococcal arthritis (disorder)
FAQ
- Q: What is the optimal management of the child with suspected septic arthritis of the hip?
- A: Aspiration of the hip joint is indicated. If purulent fluid is found or analysis of the fluid is suspicious for infection, open drainage of the joint is indicated and must be performed to prevent long-term joint damage. This is a surgical emergency.