Septic Arthritis

Question 1

Define Septic Arthritis

Answer 1

Join inflammation resulting from intra-articular infectoin

Question 2

Aetiology of Septic Arthritis

Answer 2

Direct inoculation or haematogenous spread

Predominant dause: staphylococci or streptococci (91%)
Sexually active: gonococcal arthritis can be suspected
< 4 years old: strep. pneumoniae
Immunocompromised: gram -ve, TB

Question 3

Risk factors for Septic Arthritis

Answer 3

Pre-existing joint disease e.g. RA, osteoarthritis 
Joint prostheses 
Immunosuppression
IV drug misuse
Sexual activity 
Exposure to ticks 
HIV infection 
Alcohol use disorder
Diabetes 
Previous intra-articular injection
Recent joint surgery

Question 4

Symptoms of Septic Arthritis

Answer 4

Excruciating joint pain and swelling + redness
Fever
Loss of joint function
Usually affects a single large joint

Question 5

Signs of Septic Arthritis on examination

Answer 5

Painful, hot, swollen and immobile joint
Overlying erythema
Severe pain that presents passive movement
Pyrexia
Signs of aetiology e.g. small pustules near joint (N. gonorrhoea)

Question 6

Investigations for Septic Arthritis

Answer 6

Joint aspiration: aspirate is grossly purulent | polarising microscopy negative | cytology shows micro-organism presence

FBC: raised WCC, neutrophilia
CRP/ESR: raised
LFTs: assess for spesis and end-organ damage

Plain joint radiograph: affected joint normal initially -> degenerative changes or chondrocalcinosis
MRI: (exclude osteomyelitis)
USS: for guided aspiration