Septic arthritis

Question 1

Septic arthritis - background

Answer 1

1. Definition = infectious arthritis of synovial joint
2. Frequency highest in young children; half of all cases present in first 2y. M:F = 2:1
3. Can develop from osteomyelitis, especially in neonates (where infection spreads from the metaphysis via transepiphyseeal vessels)
4. May also arise during haematogenous spread of infection or by direct inoculation
5. Most (75%) are in the lower limb. Knee>hip>ankle. Other 25% are in upper limbs

Question 2

Septic arthritis - etiology

Answer 2

1. Age

Question 3

Septic arthritis - sx

Answer 3

Infants
1. Typically do not appear ill. 50% do not have fever

Older child

2. Acute onset (c/w osteomyelitis more subacute onset) with decreased range of movements or pseudoparalysis
3. Pain and inability to weight-bear; pain on passive motion
4. Hot, warm, swollen joint
5. Systemic symptoms of infection

Note: in

Question 4

Septic arthritis - ix

Answer 4

1. Blood = FBE, ESR, CRP, blood cultures
2. Joint X-ray - usually normal initially, then subluxation/dislocation, joint space narrowing and erosive changes (note - widened joint space suggests an effusion)
3. **Joint aspiration = most useful diagnostic ix. Send aspirate for MCS. PCR may be useful if already on antibiotics
4. U/S = to detect effusion and guide aspiration
5. MRI - if dx in doubt to exclude osteomyelitis (do not delay tx while waiting for MRI). Bone scan if multiple sites and child too unwell to localise pain

Question 5

Septic arthritis - mx

Answer 5

1. Acute setting = splintage to improve pain and allow inflammation to settle. Analgesia
2. Empirical therapy = flucloxacillin 50mg/kg up to 2g IV 6-hourly. Therapy should be directed by the gram stain of a joint aspirate

Duration of therapy

3. Neonate = IV minimum 3 weeks, total duration 3 weeks (all IV)
4. Child = IV minimum 3d, total duration of therapy 3 weeks (completed with oral therapy)

Surgical mx
5. Early referral to orthopedic team bc low threshold for irrigation and debridement of affected joint (+ drainage of any associated osteomyelitis)

Question 6

Septic arthritis - prognosis (3)

Answer 6

1. Usually good unless dx delayed

2. Recurrence of disease and development of chronic infection occur in

Question 7

Septic arthritis - complications

Answer 7

1. Chondrolysis
2. Ongoing infection and bone destruction
3. Joint incongruity/stiffness
4. Growth disturbance
5. Avascular necrosis of femoral head