Septic arthritis

Question 1

Summarise septic arthritis.

Answer 1

· Infection of 1 or more joints caused by pathogenic inoculation of microbes.
· Occurs either by direct inoculation or via haematogenous spread.

Question 2

What is the pathophysiology of SA?

Answer 2

Bacterial virulence factors as well as the immunological host response determines disease development.

Question 3

What 3 factors are associated with a poorer prognosis?

Answer 3

1. Older age.
2. Pre-existing joint disease.
3. Presence of joint prosthesis.

Question 4

What is the aetiology of SA?

Answer 4

· Predominant causative organisms of SA are staph or strep - 91% of cases.
· Most commonly staphylococcus aureus.

Question 5

List the most common risk factors.

Answer 5

· Underlying joint disease:

• RA.
• OA.

· Joint prostheses. 
· IV drug abuse. 
· Alcohol use disorder. 
· Diabetes.
· Previous intra-articular corticosteroid injection. 
· Cutaneous ulcers.

Question 6

What are the most common signs and symptoms of SA?

Answer 6

· Hot, swollen, tender, restricted joint.

· Fever.

Question 7

What investigations would you request if you suspected SA in a patient? What would the results show?

Answer 7

· Synovial fluid Gram stain and culture. 
· Synovial fluid WCC.
· Blood culture - before abx therapy. 
· WCC - elevated.
· CRP and ESR - elevated.

Question 8

Suggest some differentials.

Answer 8

· OA - synovial fluid will not reveal micro-organisms.
· RA/Psoriatic arthritis - synovial fluid will not reveal micro-organisms.
· Gout/Pseudogout.
· Haemarthrosis.
· Trauma.
· Bursitis - swelling is external to the joint and it’ll move freely and painlessly.
· Cellulitis - will be an unrestricted joint.

Question 9

What are the treatment options for SA?

Answer 9

· Joint aspiration.

· IV Abx (dependent on what’s grown in fluid sample).

Question 10

What complications may arise?

Answer 10

· Abx-associated allergic reaction.
· Osteomyelitis - if infection isn’t controlled, it can spread into surrounding bone.
· Joint destruction.

Question 11

What antibiotics would you give to a SA patient who had a gram-positive stain?

Answer 11

· 1ST LINE: vancomycin plus joint aspiration IV

· 2ND LINE: clindamycin or cephalosporin plus joint aspiration IV

Question 12

What antibiotics would you give to a SA patient who had a gram-negative stain?

Answer 12

· 1ST LINE: 3rd gen cephalosporin e.g. ceftriaxone IV.

· 2nd LINE: IV ciprofloxacin plus joint aspiration e.g. ciprofloxacin IV.