MSK: Septic Arthritis Flashcards
What is septic arthritis?
Infection within a joint space
It is most common in children less than what age?
2 years old
Most cases are caused by what bacteria?
Staphylococcus aureus
Group A Streptococcus
Less than 3 months also: E. coli and other gram negative bacteria, Candida albicans, neisseria gonorrhoea
3 months to 5 years: also streptococcus pneumonia, HiB
More than 5 years: also neisseria gonorrhoea
What causes it?
Usually results from haematogenous spread Puncture wound Infected skin lesions e.g chickenpox Spread from adjacent osteomyelitis Cellulitis - especially if overlying a prosthetic joint Immunodeficiency Sickle cell disease Previous joint damage /joint surgery
Usually one joint is affected. True or false?
True
What joint is of particular concern if it is infected in infants and young children?
Hip joint
How does it typically present?
Erythematous, warm, acutely tender joint
Reduced range of movement
Initially may be a limp/ unable to weight bearing
Acutely unwell child
Fever
Infants often hold limb still and cry if it is moved
Describe the onset
Acute
What is found on examination of the joint?
Joint very tender to move
Erythematous
Effusion may be detected in peripheral joints
Why can diagnosis of septic arthritis in the hip be difficult?
The joint is well covered by subcutaneous fat
What is the characteristic posture of the hip in infants with septic arthritis?
Leg held flexed,abducted, externally rotated
No spontaneous movements - pseudoparalysis
Held in this way to reduce intracapsular pressure
What investigations should be done?
FBC and CRP - WCC and CRP raised
Blood culture
USS of deep joints e.g hip to identify effusion
X rays to exclude trauma
MRI or radioisotope bone scan
Aspiration of joint space for organism and culture, under US guidance = definitive investigation
What does x ray show?
Often normal initially
May show joint space widening and soft tissue swelling
How is it managed?
IV antibiotics (ideally after blood cultures and joint aspiration unless septic and acutely unwell) - start empirically before culture results known
- typically does 2-3 weeks before switching to oral
- typical regime may include: flucloxacillin 2g IV QID
Washing out of joint or surgical drainage may be required if resolution doesn’t not occur rapidly or joint deep seated e.g hip
Joint initially immobilised via splinting for first few days, but subsequently mobilised to prevent permanent deformity
Why is early treatment essential?
Prevent destruction of articulate cartilage and bone
The CRP and WCC are usually over…
CRP over 20
WCC over 12
Is osteomyelitis or septic arthritis more common?
OM
What situations/risk groups have been associated with bone joint infection?
Preceding trauma
Presence of prosthetic material
Sickle cell disease (salmonella species)
Immunodeficiency
Are joints of upper or lower limbs usually involved?
Lower limbs
If there is hip pain/restriction of movement associated with a CRP > 20, what should be done?
Early MRI
Which joints are most commonly affected?
Knee Hip Ankle Elbow Shoulder
What is the IV antibiotic choice in less than 3 months and over 3 months?
Less than 3 months : IV cefotaxime or ceftriaxone
Over : IV flucloxacillin
Hat should be the length of total antibiotic therapy?
2-4 weeks
Before stopping treatment…
Patient asymptomatic and CRP normal
Should an orthopaedic referral be done immediately?
Yes - joint drainage and irrigation at earliest opportunity
What are the indications to switch from IV to oral antibiotics?
Afebrile or clear temp decrease Improvement of symptoms, with decreased inflammation and pain Decrease in CRP 30-50% from max value No complication signs e.g DVT Neg blood culture if initially positive
