Septic Arthritis Flashcards
What is the epidemiology of septic arthritis?
More common in the elderly with multimorbidities and in the immunosuppressed
Incidence in prosthetic joints:
- 1.5-2.5% in primary interventions
- Up to 20% for revision procedures
What is the aetiology of septic arthritis?
S.aureus = the most frequent pathogen in any age group; most of these are methicillin-sensitive; also:
- Strep. pyogenes
- Strep. pneumoniae
- H. influenzae
N. gonoccal arthritis is increasing - more common in the elderly and immunosuppressed
Salmonella t. - common in sickle cell patients (but S.aureus still most common in this group)
Lyme disease and TB are also possible causes
Haematogenous spread, direct invasion through penetrating wound, from osteomyelitic bone, from cellulitic abscess
Risk factors:
- Paediatrics and older age
- DM
- Prior joint damage e.g. RA, gout
- Joint surgery, hip/knee prosthesis +/- skin infection
- Immunodeficiency
How does septic arthritis present?
Single swollen erythematous joint
- Polyarticular is very rare (check for immunosuppression)
- Possibly in prosthetic joints
Pain on active +/- passive movement
- Pain + its radiation will depend on joint affected
- Knee = most common (1/2) then hip, shoulder, ankle and wrists
Fevers + rigors are very common
Bacteraemia, manifesting in vomiting and hypotension is also common
How does the presentation of septic arthritis differ in certain groups?
Fewer signs/less localisation in:
- Children (esp preschool infants + toddlers)
- Elderly
- Immunocompromised
- Drug users
- Infections involving the spine, hip and shoulder joints
- In those with prostheses
Will often present with fever, some joint pain or unwillingness to move affected joint including a limp
What clinical sign might indicate a Gonoccal septic arthritis?
The presence of multiple skin lesions = dermatitis-arthritis syndrome
How do you investigate septic arthritis?
Bloods:
- FBC - leukocytosis, raised inflammatory markers
- Cultures - at least 2 to exclude bacteraemia
Synovial fluid:
- Leukocyte count + MC+S + polarising light microscopy
Possible:
- Swabs (rectal, cervical, urethral, pharyngeal) + cultures for Gonorrhoea
- Lyme tests
- Serology for other rheum or vasculitic disorders as appropriate
What imaging is indicated in septic arthritis?
XR: (2 view)
- May be normal within the first few days of infection - DONT RELY ON XR
- Fat pad displacement, swelling of capsule + soft tissue; possible joint space increase due to local effusion
- May show underlying osteomyelitis
- Later, joint destruction might be present
USS:
- Not as sensitive as CT/MRI but cheaper and less invasive
- Good for early effusions, guiding joint aspiration and draining
CT/MRI:
- Most sensitive at detecting abscess, effusion and osteomyelitis
- Usually reserved for when Dx is uncertain
How do you manage septic arthritis?
Antibiotics:
- Empirical before cultures are known; half the time gram stains do not find bugs and so age + sexual activity will help determine likelihood of gonococcal infection
- Should cover S.aureus + other Strep species
- IV, high dose for 2-3wks before PO switch (often for further 2-4wks)
- 1s choice: Flucoxacillin 4-6wks + Co-amox; clindamycin if allergy
- MRSA: Vancomycin or teicoplanin
- Gonoccal or G-ve: Cefotaxime
Surgical drainage of joint:
- Repeated percutaenous aspiration may be required if infection unresponsive to Abx
- May need USS guidance (e.g. hip, shoulder, SI joints)
- Surgical drainage may be required = especially true for prosthetic joints (DO NOT aspirate in A+E - needs surgical washout +/- revision)
Splinting of joint:
- Splinted in position of function e.g. knees in extension, elbow at 90 degrees etc
- Once infection is under control, joint immobilisation will promote healing
Prosthesis involved - seek specialist advice
What is Kocher’s criteria?
Tool useful for the differentiation of septic arthritis from septic arthritis in the child with a painful hip
1) Non-weight bearing on affected side +1
2) ESR +40
3) Fever >38.5 +1
4) WCC >12 +1
Score of 3-4 = 90-99% likelihood of septic arthritis
