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Septic Arthritis

  • Septic arthritis is an infection of the joint.
    • In infants, the capillaries penetrating the physeal plate into the epiphysis persist until age 18 months, so spread of infection may occur from the metaphysis indirectly to the epiphysis and then to the joint.
    • Possible irreparable damage to growth plate occurs.
  • Classification: Polyarticular septic arthritis is seen in ~5% of all patients with septic arthritis .
General Prevention
  • Treatment of systemic infections and prevention of gonorrhea may decrease the risk of septic arthritis.
  • Most important to recognize and treat the condition early, to avoid complications
  • It can affect any joint, at any age.
  • No gender preference in monarticular septic arthritis
  • Gonococcal septic arthritis is 4 times more common in females than in males.
  • Occurs in <0.5% of infants
  • Variable in children and adults
Risk Factors
  • Neonates with multiple potential sources of infection
  • Concurrent rheumatologic disease, joint prostheses, HIV infection, diabetes mellitus, hemophilia, sickle cell anemia (Staphylococcus aureus or Salmonella), or intravenous drug abuse (Gram-negative organisms)
  • S. aureus causes 80% of cases of septic arthritis in the first 6 months of life.
  • Neonatal septic arthritis also is caused by group B streptococci, Candida, and Gram-negative enteric bacteria.
  • In children <2 years old, Haemophilus influenzae is a cause. (Since 1989, vaccination against H. influenzae has become nearly universal and is protective against this source.)
  • In children, Gram-negative bacilli, Streptococcus, or Neisseria meningitidis is the most common cause.
  • Young adults:
    • Neisseria gonorrhoeae is the most common cause.
    • S. aureus is the next most common cause.
    • Other causes include Gram-negative bacilli, Pseudomonas, and Streptococcus.
  • In patients with sickle cell anemia, Salmonella is the cause in 50% of infections.
  • Lyme disease is not a cause of septic arthritis; it is a reactive arthritis.
Associated Conditions
Signs and Symptoms
  • Children generally are febrile, irritable, and apprehensive; they may be lethargic and have decreased appetite.
  • However, some children may appear healthy with fever of unknown origin and findings localized to a given extremity.
  • In the neonate, 75% of patients may not be acutely sick, but symptoms may include failure to eat or to gain weight, and 25% may have signs of sepsis.
  • Tenderness to palpation or joint motion is the earliest physical sign in children and adults.
  • Swelling, warmth, muscular spasm, and decreased ROM may appear later.
  • Joint effusion usually is present.
  • Erythema usually is not seen with septic arthritis because the inflammation is contained within the joint capsule.
Physical Exam
  • Tenderness with movement is the earliest physical sign.
  • Other signs include fevers, irritability, swelling, warmth, muscle spasm, limited ROM, and joint effusion.
  • Gram stain is positive in only 30-40% of patients.
  • Cell count and differential
    • A white blood cell count in the aspirate of >50,000 cells/mL in an immunocompetent patient suggests the presence of infection.
    • >90% of the cells are polymorphonuclear.
  • Culture of the synovial fluid aspirate; ESR
    • Useful when it is elevated to 50-100 mm per hour unless the patient has had previous antibiotic therapy
    • May be helpful for assessing patient’s response to treatment
    • Unreliable in neonates, in children with sickle cell disease, and in patients taking steroids
  • C-reactive protein becomes elevated early in the disease process and returns to normal quickly.
  • White blood cell count:
    • A high systemic white blood cell count with left shift is nonspecific.
    • 40-75% of patients with septic arthritis have a normal white blood cell count at the time of initial diagnosis.
  • Urate crystal determination
  • Culture and sensitivity:
    • Blood culture always should be obtained before treatment is started because, in 40% of cases, the organism can be identified with blood cultures.
    • Fewer cultures are positive after antibiotics.
    • Joint fluid cultures are negative in up to 25% of patients with bacterial septic arthritis, for unknown reasons.
  • Radiographs may show periarticular soft-tissue swelling and distention of the joint capsule. In neonates; a lateral shift of the femoral neck with respect to the acetabulum is evidence of septic arthritis of the hip.
  • Neither MRI nor CT is used in diagnosis of joint infection within the first 24-36 hours.
  • Bone scintigraphy can detect alterations in bone much earlier than plain radiographs, but these scans usually are unnecessary because of greater reliability of aspiration.
    • Bone scanning is recommended only when poor localization of clinical findings is present.
Pathological Findings
  • Characterized by purulent synovial fluid, often with >90% polymorphonuclear cells
  • The synovium becomes thickened.
  • If infection persists for more than a few days without treatment, destruction of joint cartilage may begin.
Differential Diagnosis
  • Osteomyelitis
  • Rheumatologic disease
  • Inflammatory arthropathy
  • Transient synovitis of the hip:
    • Suggested by inability to bear weight on the limb, temperature <101°, normal white blood count, and normal sedimentation rate.
General Measures
  • Consider septic arthritis an orthopaedic emergency; initial treatment should include hospitalization.
  • Principles of treatment include adequate administration of bactericidal antibiotics, drainage, and early immobilization.
    • Antibiotics/aspiration:
      • Begin intravenous antibiotics immediately after obtaining samples for culture.
      • 3-6 weeks of antibiotic treatment are needed.
      • Intravenous antibiotic treatment is indicated until clinical improvement is seen.
      • Oral antibiotics may be used if: Patient shows a clinical response to intravenous antibiotics; organism causing infection is known; organism is susceptible to orally administered antibiotics; patient tolerates oral antibiotics.
      • Aspiration and intravenous antibiotics may be sufficient for treating some organisms in small joints.
      • When septic arthritis is diagnosed early in a superficial joint (e.g., ankle, elbow), it is reasonable to aspirate the joint, begin appropriate antibiotics, and carefully monitor the patient for 24-48 hours.
      • Aspiration may be repeated as needed.
    • Drainage:
      • Surgical drainage is necessary for all infections that do not respond to aspiration or antibiotics within 72 hours, have loculated synovial fluid, or involve the hip.
      • Arthroscopic drainage may be a good treatment option for certain joints such as the knee, elbow, ankle, and shoulder.

  • Immobilization:
    • Splint in a position of comfort until clinical signs show a decrease in swelling and tenderness, and the patient has a comfortable ROM.
    • Begin muscle strengthening and ROM exercises (see Physical Therapy).
Special Therapy
Physical Therapy
  • Once clinical improvement is noted, deformity should be prevented and function should be re-established gradually.
  • Muscle-strengthening exercises with isometric regimens should be instituted in adults, and active ROM exercises are started.
  • Some studies have shown that continuous passive motion may inhibit the formation of adhesions and pannus, and promote better nutrition of the cartilage during the healing phase.
  • Antibiotics, which must be started immediately after aspiration and obtaining blood cultures, may be divided into initial and definitive categories.
    • Initial diagnosis:
      • A combination of agents administered parenterally until the identity and susceptibility of the bacteria are known.
      • Initial antibiotic choices are based on broad coverage and knowledge of common causative organisms.
    • Definitive diagnosis:
      • Specific antibiotics given to which the organism is sensitive
First Line
  • Except in children <4 years old, the most common causative organism is Staphylococcus.
  • Because most infections are caused by penicillin-resistant strains, a β-lactamase-resistant cephalosporin, such as ceftriaxone or cefazolin, is usually a 1st-line drug.
  • After local signs of infection have subsided, an oral antibiotic, such as amoxicillin with clavulanic acid, may be substituted.
  • Open irrigation and debridement is the most dependable way to sterilize the joint and remove all inflamed cells, enzymes, and debris; leave an opening in the joint capsule to allow drainage.
  • Consider arthroscopic irrigation and debridement in the knee, shoulder, elbow, and ankle.
  • Exception: Gonococcal arthritis usually does not need surgical drainage.
  • With prompt diagnosis and appropriate treatment, the prognosis usually is good for complete recovery.
  • Prognosis is worse in immunocompromised or premature patients.
  • Delay in diagnosis in patients with a generalized septic condition is associated with a poor prognosis, and aggressive surgical debridement and antibiotic therapy are critical.
  • Delay in diagnosis and treatment >5 days from the onset of symptoms plays an important role in the incidence of complications.
  • Pathologic dislocation associated with septic arthritis of the hip occurs in children who are treated late; it is seen rarely in adults.
  • Destruction of articular cartilage can lead to restricted joint motion or ankylosis of the joint.
    • Damage to the cartilaginous epiphysis and growth plate in children leads to joint deformity and leg-length discrepancy.
    • Septic necrosis of the femoral head, in hip infections, can cause growth disturbance and later degenerative joint disease.
  • Patients with prostheses in joints other than the site of principal infection may experience seeding to the prosthetic joints hematogenously.
Patient Monitoring
  • The patient should be monitored in a hospital setting initially until the following occur:
    • The patient is clinically stable.
    • Appropriate antibiotics are instituted.
    • Patient response is noted (patient afebrile in 48-72 hours, decreased swelling and tenderness, return of white blood cell count to normal, and decreasing ESR).
  • Then the patient may be discharged home; improvement may be monitored by physical examination, ESR, and possibly C-reactive protein and radiographs.
  • Worsening clinical status may indicate a need for repeat aspiration.
711.00 Septic arthritis
Patient Teaching
  • Patients must understand the need for compliance with antibiotics and the necessity of preventing deformity and re-establishing function through physical therapy.
  • If the organism is gonococcal, patient education and treatment of sexual partners is key to preventing recurrence.
Q: What is the role of aspiration alone in septic arthritis?
A: It is an option for accessible small- to moderate-sized joints in mature patients who show no signs of sepsis. It is not indicated for a septic hip.

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