Paediatrics: Infections: septic arthritis

Infections: septic arthritis

An infectious arthritis of a synovial joint. The frequency is highest in young children with half of all cases presenting in the first 2yrs. Males > female (2:1).

Pathogenesis

Septic arthritis can develop from osteomyelitis especially in neonates where infection spreads from the metaphysis via transepiphyseal vessels. It may also arise due to haematogenous spread of infection or by direct inoculation.

Aetiology

•   Age <12mths old: Staphylococcus aureus, Group B streptococcus, Gram –ve bacilli, Candida albicans.

•   Age 1–5yrs: Staph. aureus, Haemophilus influenza (rarely in immunized children), Group A streptococcus (pyogenes), Streptococcus pneumonia, Kingella kingae, Neisseria gonorrheae (child abuse).

•   Age 5–12yrs: Staph. aureus, Group A streptococcus.

•   Age 12–18yrs: Staph. aureus, Neisseria gonorrhoeae (sexually active).

•   Community acquired MRSA (CA-MRSA) is increasing worldwide.

Common joints affected 

Most (75%) are in lower limb. Knee > hip > ankle. Other 25% are in upper limbs.

Differential diagnosis

This depends on age and joint involved:

•   Hip: transient synovitis, Perthes, slipped capital femoral epiphysis, psoas abscess, proximal femoral or vertebral osteomyelitis, discitis.

•   Knee: distal femoral or proximal tibial osteomyelitis. Pain often referred from the hip.

•   General: cellulitis, pyomyositis, other infectious arthritis (viral, mycoplasmal, mycobacterial, fungal, Lyme disease), sickle cell, haemophilia, trauma, collagen vascular disease, Henoch–Schönlein purpura, reactive arthritis from GI infections or GU infections, streptococcal pharyngitis, viral hepatitis, salmonella, or post-viral (HIV, CMV).

•   >1 joint involved: pauciarticular arthritis, rheumatic fever, serum sickness, HSP, collagen vascular disease, sickle cell disease, chronic recurrent multifocal osteomyelitis (CRMO).

•   Haemophilia: increased risk of septic arthritis due to haemarthrosis

(predisposes to infection: pneumococci).

Symptoms and signs

Infants characteristically do not appear ill. 50% do not have fever. In the older child—acute onset; decreased range of movements or pseudopa-ralysis; pain on passive motion; hot, warm, swollen joint; inability to weight bear; systemic symptoms of infection. In <10% of cases more than one joint affected (except gonococcal infections). The clinical picture may be less acute if the child has received antibiotics.

Investigations

·Blood: FBC, ESR, CRP, blood cultures; Lyme titres if exposure.

• X-ray of joint: usually normal initially (widened joint space suggests an effusion). Subluxation/dislocation, joint space narrowing and erosive changes are later signs.

• Joint aspiration: most useful diagnostic investigation. Send aspirate for microscopy and culture. PCR may be useful if already on antibiotics.

• US: to detect effusion and guide aspiration.

• MRI: if diagnosis in doubt to exclude osteomyelitis, (do not delay treatment while waiting for MRI).

• CT: to imaging sternocalvicular and sacroiliac joints. Psoas abscess.

• Bone scan: if multiple sites and child too unwell to localize pain.

• Lumbar puncture: if a septic joint with Haemophilus influenzae (increased incidence of meningitis).

Treatment

• Medical: IV antibiotics, after aspirate taken, for up to 3wks (until inflammatory markers normalize), followed by oral antibiotics for a total of 4–6wks. Outcome of treatment is time dependent.

• Surgical: early referral to orthopaedic team as there is a low threshold for irrigation and debridement of the affected joint (+ drainage of any associated osteomyelitis).

• Splintage: In the acute setting a brief period of splintage improves pain and allows inflammation to settle. Splint in position of function.

• Physiotherapy: to avoid joint stiffness.

Prognosis

Usually good unless the diagnosis is delayed. Recurrence of disease and development of chronic infection occur in <10%. Long-term follow-up is needed as growth-related sequelae may not become apparent for months or years. Hip joint infection has the worst prognosis for anatomical and functional impairment.

Complications

Chondrolysis, ongoing infection and bone destruction, joint incongruity/ stiffness, and growth disturbance. Avascular necrosis of the femoral head can occur.