Osteomyelitis; Septic arthritis

Question 1

[] is the most common causative pathogen in osteomyelitis.

Answer 1

Staph aureus is the most common causative pathogen in osteomyelitis.

Question 2

What are the two types of osteomyelitis? [2]

State common causes for each

Answer 2

There are two types of osteomyelitis as defined by their source: haematogenous and nonhaematogenous.

Haematogenous:
* Indwelling intravascular catheter (e.g. Hickman line)
* Haemodialysis
* Endocarditis
* IV drug use

Non-haematogenous:
* Skin ulcers
* Trauma
* Surgery (especially when foreign material is placed)
* Animal / insect bites

Question 3

Which bones are more commonly affected by haematogenous vs non-haematogenous osteomyelitis?

Answer 3

Haematogenous:
- axial skeleton, primarily the vertebral bones
- sternum and pelvis

Non-Haematogenous:
- ares of trauma / surgery

Question 4

Clinical features of acute and chronic osteomyelitis?

Answer 4

Acute osteomyelitis:
- Pain is the most common symptom
- Warm and erythema
- Systemic symptoms

Chronic osteomyelitis:
- Tends to present only with local symptoms such as swelling, erythema and pain
- Systemic symptoms such as fever are often ABSENT
- Often secondary to DM vascular injury - diabetics with ulcers >2cm2 are very likely to have osteomyelitis, even if no bone is visible
- A draining sinus tract may be seen - this is pathognomonic of osteomyelitis

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Question 5

In patients with a history of intravenous drug use, what organism is the most common cause for osteomyelitis?

Salmonella spp.

S. aureus

P. aeruginosa

E. coli

Answer 5

In patients with a history of intravenous drug use, what organism is the most common cause for osteomyelitis?

Salmonella spp.

S. aureus

P. aeruginosa

E. coli

Question 6

Investigations for osteomyeltis? [+]

Answer 6

Serology:
- Acute = raised WCC / CRP
- Chronic = often has normal WCC
- Blood cultures are positive in around half of cases

X-ray:
- Acute = first two weeks of infection may show normal
- Soft tissue swelling, osteopaenia (bone thinning), bone destruction, periosteal reaction (changes to the surface of the bone), endosteal scalloping and new bone apposition

MRI:
- Best imaging for dx
- Sequestrum: Refers to a dead piece of devitalised bone that has been separated (i.e. sequestered) due to necrosis from the surrounding bone.
- Involucrum: New growth of periosteal bone around a sequestrum.
- Cloaca: An opening in an involuvcrum that allows the internal necrotic bone and pus to discharge out.

Question 7

Label A-C

Answer 7

Sequestrum: Refers to a dead piece of devitalised bone that has been separated (i.e. sequestered) due to necrosis from the surrounding bone.

Involucrum: New growth of periosteal bone around a sequestrum.

Cloaca: An opening in an involuvcrum that allows the internal necrotic bone and pus to discharge out.

Question 9

What is A? [1]

Answer 9

Sequestrum

Question 10

What is shown in this image? [1]

Answer 10

draining sinus tract

Question 12

What is the arrow pointing to? [1]

Answer 12

involucrum: formation of new bone around an area of bony necrosis

Question 13

What is the arrow pointing to? [1]

Answer 13

sequestrum: devitalized bone that serves as a nidus for infection

Question 14

Describe the treatment for osteomyelitis [3]

Answer 14

Antibiotics +/- surgical debridement forms the mainstay of management.

Abx:
- Should be held until bone cultures are completed
- Guided by microbiology
- BNF: flucloxacillin for 6 weeks; possibly with rifampicin or fusidic acid added for the first 2 weeks
- Chronic osteomyelitis usually requires 3 months or more of antibiotics.
- Clindamycin in penicillin allergy
- Vancomycin or teicoplanin when treating MRSA

Surgery:
- More common in non-haem. spread
- infected necrotic bone must be removed

Question 15

What are the indications for surgery in osteomyelitis? [3]

Answer 15

• Failure to respond to antibiotic therapy
• Formation of discrete abscess
• Neurological deficit (vertebral osteomyelitis)

Question 16

Answer 16

S. aureus

Question 17

Answer 17

Salmonella

Question 18

Septic arthritis can be caused by direct inoculation of the joint or by haematogenous spread of bacteria from another site. The most common causative organism in adults is [].

Answer 18

Septic arthritis can be caused by direct inoculation of the joint or by haematogenous spread of bacteria from another site. The most common causative organism in adults is Staphylococcus aureus.

Question 19

Describt the different causes of septic arthritis

Answer 19

When septic arthritis is caused by haematogenous spread it may be a result of:
Bacterial migration from a distant site
* Abscesses and wounds
* Septicaemia

Disseminated infection
* Gonorrhoea

OR

When septic arthritis is caused by direct inoculation it may be a result of:
Iatrogenic procedures
* Joint injections (e.g. steroid injections)
* Joint arthrocentesis
* Athroscopy

Traumatic injuries
* Infected wounds around the joint
* Penetrating injuries from foreign objects

Question 20

Describe investigations for septic arthritis?

Answer 20

Joint aspiration is key and should be obtained prior to antibiotics (whenever possible):
- Also decompresses joint space
- synovial fluid appearance: often yellow/green and turbid on aspiration compared to uninfected fluid which is clear and usually colourless.
- Cultures of synovial fluid in cases of gonococcal septic arthritis yield positive results in only 25% of cases.
- Synovial fluid WCC: is often raised with neutrophil predominance.

Question 21

The Kocher criteria for the diagnosis of septic arthritis is [4]

Answer 21

The Kocher criteria for the diagnosis of septic arthritis:
* fever >38.5 degrees C
* non-weight bearing
* raised ESR
* raised WCC

Question 22

Describe the management plan for septic arthritis

Answer 22

First: rule out sepsis

Empirical IV antibiotics should be given until the sensitivities are known. Often following are given:
* Flucloxacillin (often first-line)
* Clindamycin (penicillin allergy)
* Vancomycin (if MRSA is suspected)
* Ceftriaxone if gonorrhoea

Antibiotics are typically continued IV for 2 weeks before switching to PO if the patient is improving.