Septic Arthritis/Osteomyelitis

Question 1

What is septic arthritis?

Answer 1

• infection of 1 or more joints
• caused by pathogenic inoculation of microbes (most commonly Staph Aureus, consider N. gonorrhoea in young adults)
• occurs either by direct inoculation or via hamatogenous spread
• similarly, osteomyelitis is infection of the bone -> can cause septic arthritis
• always consider septic arthritis in any acutely inflammed joint → can destroy a joint in under 24hr + mortality 11%
• crystal arthropathies main differential
• knee affected in >50% cases

Question 2

What are the signs and symptoms of septic arthritis?

Answer 2

• hot, swollen, tender restricted joint
• +/- pyrexia
• symptoms present <2 weeks at presentation
• risk factors elicited

O/E → swelling, warmth, tenderness + restriction of movement

Question 3

What are the risk factors for septic arthritis?

Answer 3

• underlying joint disease (RA, OA, CA)
• joint prostheses
• IV drug abuse
• diabetes mellitus
• immunosuppression
• chronic kidney disease
• presence of cutaneous ulcers
• low socioeconomic status

Question 4

What investigations can be done for septic arthritis?

Answer 4

• joint aspiration → synovial fluid MC+S is key before starting empirical abx
• blood cultures → essential; +ve in 25%
• ESR + WCC raised

Question 5

What is the management of septic arthritis?

Answer 5

• Obtain synovial fluid before starting treatment
• Flucloxacillin IV 2 weeks then 4 wks oral
• Or clindamycin if penicillin-allergic
• Suspected gonococcus → ceftriaxone
• Prosthetic joint → urgent referral to orthopaedics
• Needle aspiration to decompress joint
• Arthroscopic lavage may be required

Question 6

All forms of acute osteomyelitis may evolve and become chronic, sharing a final common pathophysiology, with a compromised soft-tissue envelope surrounding dead, infected, and reactive new bone. The commonest organis is staph aureus again.

What are predisposing conditions to osteomyelitis?

Answer 6

• diabetes mellitus
• sickle cell anaemia
• IVDU
• immunosuppression due to either medication or HIV
• alcohol XS

Question 7

What investigations can be done for osteomyelitis?

Answer 7

• Vitals → fever
• FBC/CRP/ESR → raised
• Blood culture → positive in 60%
• Plain XR → not so useful in early disease as initially normal (10-14 days), but in late disease, a sequestrum + an involucrum may become visible
• MRI → modality of choice; highly sensitive + specific

Rx is same as SA (flucloxacillin)

Question 8

What are differentials for monoarthritis?

Answer 8

• septic arthritis
• crystal arthritis (gout, CPPD)
• osteoarthritis
• trauma (haemarthrosis)

Question 9

What are differentials for oligoarthritis (<5 joints)?

Answer 9

• crystal arthritis
• psoriatic arthritis
• reactive arthritis eg. yersinia, salmonella, campylobacter
• ankylosing spondylitis
• osteoarthritis

Question 10

What are the differentials for polyarthritis (>5 joints involves)?

Answer 10

• Symmetrical → RA, OA, viruses (hep ABC, mumps), systemic
• Asymmetrical → reactive arthritis, psoriatic arthritis, systemic