septic arthritis

Question 1

what is the pathogenesis behind septic arthritis?

Answer 1

bacterial growth within a joint results in inflammation and production of proteolytic enzymes which destroy bone and cartilage and soft tissue. eventually leads to joint destruction if not treated

The source of bacteria can be:

• haematogenous from respiratory or urinary tract
• skin: cellulitis
• neighbouring bone - osteomyelitis
• or from environment in joint replacement

Question 2

what organisms are responsible for septic arthritis ?

Answer 2

S.aureus in 50%
S. epidermis (esp joint replacement)
H.influenzae (neonates, IV drug use, infants)
gram negative (diabetics and IV drug use)
gonorrhoea

Question 3

what are the symptoms of septic arthritis?

Answer 3

acute onset
Red swollen, tender and warm joint
systemic upset: fever, tachycardia, hypotensive, malaise, anorexia

mainly affects lower limb: knees in adults and children, hips in neonates.

muscle spasms can lead to immobility of the joint - pseudoparasis

Question 4

how does septic arthritis of the hip present?

Answer 4

unable to weight bear

FABER position

Question 5

how does septic arthritis caused by gonorrhoea present?

Answer 5

polyarthralgia
urogenital symptoms too
tenosynovitis
pustular rash

Question 6

How may an infected joint replacement present?

Answer 6

may have all the symptoms of septic arthritis but often just appears as loose.

Question 7

what are the risk factors for septic arthritis?

Answer 7

extremes of age
malnourished
disease: diabetes, history of crystal arthropathy and endocarditis
immunosupressants
arthroplasty or co-existing joint problems.

Question 8

how would you investigate septic arthritis?

Answer 8

bloods: FBC (raised WCC), raised ESR/CRP, U&Es (incase of sepsis)
joint aspiration
radiograph 
USS
MRI

Question 9

what would you find on joint aspirate in someone with septic arthritis ?

Answer 9

Turbid fluid
raised WCC
low viscosity
gram staining either negative or positive i.e. not sterile

Question 10

what Xray changes would you see with septic arthritis?

Answer 10

joint effusion + joint swelling
joint space widening due to breakdown

however changes only after 7-14 days so needs diagnosing before this

Question 11

whats the criteria that helps to predict likelihood of septic arthritis? Describe this criteria

Answer 11

Kochers criteria

• WCC >12
• fever >38.5
• ESR >40
• unable to weight bear

score of 1 = 3% chance, 2 = 40%, 3=93%, 4= 99%

Question 12

How do we manage septic arthritis?

Answer 12

high dose IV penicillin + IV flucoxacillin for 2-3 weeks followed by oral flucox for another 3 weeks
Wash out: aspirate (USS) and wash out with lavage
Remove any infected implants
NSAIDs/analgesia
immobilise joint followed by gentle physio

Question 13

how do we manage septic arthritis in those with penicillin allergy?

Answer 13

clindamycin

Question 14

how do we manage septic arthritis for

a) gram negative cultures
b) MRSA

Answer 14

a) cephalosporin (cefutaxime)

b) vancomycin

Question 15

what are the complications of septic arthritis?

Answer 15

local:
- joint destruction, secondary OA, periarticular osteoporosis and ankyloses
- abscess and sinus formation
- AVN
- infection of growth plate can lead to growth delay/deformity

systemic:
- septic shock – AKI