ID: Bone and Joint Infection

Question 1

What are the three common causes (and the proportions) of osteomyelitis?

Answer 1

• Post-trauma or surgery.
  
  • ~50% of cases.
• Haematogenous.
  
  • ~20% of cases.
  • From Ben Clark: This is more likely to be seen in hospital practice.
• Contiguous with another infection (i.e. diabetic foot infection).
  
  • Reminder.

Question 2

Which two locations are most likely to be affected in cases of children experiencing osteomyelitis?

• What makes these areas special?

Where does the infection seed in children?

Answer 2

Femur and tibia.

• Rich blood supply.

In the growing metaphysis (at the end of the long bone).

Question 3

Name the two processes that must happen for haematogenous infection.

Answer 3

1. Bacteria gets under the skin, through the mucous membrane and gets into the bloodstream, and travels throughout the body.
2. Seeds somewhere in the skeleton.

Question 4

What is the most common location for haematogenous seeding of an infection that will lead to osteomyelitis in adults?

Answer 4

Verterbal column.

Question 5

Describe the pathogenesis of osteomyelitis (4 points).

Answer 5

• Invasive bacteria cause inflammatory reaction.
• Leukocytes release enzymes that lyse the bone.
• Oedema, vascular congestion, and small-vessel thrombosis.
• Impaired flow of both medullary and periosteal blood supply.

Question 6

What are the two requirements for chronic osteomyelitis to be categorised as such?

• What can’t be done in chronic osteomyelitis, but can be done in acute?

Answer 6

• Sequestra.
  
  • Necrotic bone formed within a diseased or injured bone.
• Involucrum.
  
  • Layer of new bone growth surrounding the sequestrum.

This leads to bone sclerosis (hardening) and deformity.

• Treatment with antibiotics.
  
  • Antibiotics won’t be able to get into the wound in high enough concentrations.

Question 7

Label the following diagram.

Answer 7

Upper left: involucrum (newly formed bone).

Lower right: sequestrum (necrotic bone).

Question 8

Match the following components with the arrows on the diagram.

1. Bone cortex.
2. Draining sinus tract.
3. Sequestrum.
4. Periosteum.
5. Principal site of infection.
6. Soft tissue.
7. Marrow cavity.

Answer 8

Question 9

• What is the most common cause of osteomyelitis in adults, infants and pre-schoolers?
• What are some other causative bacteria specific to:
  
  • Infants?
  • Pre-schoolers?
  • Adults?

Answer 9

• Staphylococcus aureus.

ADULTS

• ß-haemolytic Streptococcus.
• Gram negatives.

PRE-SCHOOLERS

• Kingella kingae.
• H. influenzae.

INFANTS (picked up going through the birth canal).

• S. agalactiae.
• E. coli.

Question 10

What are the two most common procedures/actions that can lead to haematogenous osteomyelitis?

Answer 10

1. Brushing teeth. (0-26%)
2. Chewing candy. (17-51%)

Question 11

Fill in the table (3 per column) of causative agents in different groups.

Answer 11

Question 12

Signs/symptoms of osteomyelitis?

Answer 12

• Classic inflammation signs.
  
  • Redness.
  • Swelling.
  • Fever.
  • Pain.

Question 13

• What is a Brodie abscess?
• What role does the host’s immune system play?
• Signs/symptoms (compare with classical OM)
• Typically found where?

Answer 13

• Subacute osteomyelitis → may persist for years before becoming frank osteomyelitis.
• Host’s immune system controls it.
  
  • Hole in the bone filled with pus and inflammatory infiltrates → contained.
• No classical features of OM → often misdiagnosed as a tumour.
• GRUMBLING PAIN FOR WEEKS.
• Leg > arm bones.
  
  • Eg tibia.

Question 14

• What are four raised inflammatory markers in Brodie abscess?
• What are three microbiological tests to run?

Answer 14

• CRP.
• White cell count.
• Procalcitonin.
• IL-6.
• Blood culture.
• Joint aspiration and culture.
• Bone biopsy.

Question 15

What is a test that is better than blood cultures for OM?

Answer 15

Sample of the pus.

Question 16

Are nuclear scans useful for osteomyelitis?

Answer 16

No

Question 17

• Empiric therapy must treat what?
• IV or oral antibiotics first?
• Add ____ in treatment for kids to cover Haemophilus and Kingella.
• Typical treatment regime (timing):
  
  • Kids
  • Adults

Answer 17

• S aureus.
• IV.
• Cephalosporin.
• Kids: 3-7 days IV, 3 weeks total.
• Adults: 2-4 weeks IV, >6 weeks total.

Question 18

• Three DDx for septic arthritis.
• Three causes.

Answer 18

• Reactive arthritis.
  
  • Body’s responds to antigens.
• Rheumatoid arthritis.
• Crystal arthropathy.
• Haematogenous. (>70%)
• Post-procedure.
• Adjacent osteomyelitis.

Question 19

Describe the pathogenesis of septic arthritis.

Answer 19

• Inflammation of the synovium due to bacterial infection (usually bacterial).
• No basement membrane → bacteria in synovial fluid.
• Synovial hyperplasia.
• Cytokine release.

Question 20

• Signs/symptoms of septic arthritis.
• Investigations.
• Treatment.

Answer 20

• Sx
  
  • Purulent inflammation.
  • Usually one joint, commonly knee.
    
    • Also wrist, ankle, hip.
  • Classic inflammation signs/symptoms.
• Ix
  
  • Blood cultures.
  • Joint aspirate and culture.
• Tx
  
  • Antibiotic therapy (identical to OM)
    
    • Inflammation and destruction of joints may continue even in those with sterile joints despite effective antimicrobial therapy.
    • Persistance of bacterial antigens within the joint.
  • Joint drainage/washout.

Septic arthritis = increased risk of osteoarthritis later in life (cel assignment taught me this lol)

Question 21

IVDU are at a higher risk of septic arthritis. What is a common presentation of this?

Answer 21

Painful collarbone.

Question 22

PROSTHETIC JOINT INFECTION

• Conservative approach?
  
  • When is it effective?
• Non-conservative approach?
  
  • Stages?
• Which is better?

Answer 22

• Conservative approach
  
  • Early on, or in acute phase.
  • DAIR = debridement, antibiotics, implant retention.
  • Antibiotics = high dose IV than oral for 3-6 months
• Non-conservative approach - prosthetic joint revision.
  
  • One-stage: Remove and replace.
  • Two-stage:
    
    • Remove prosthesis.
    • Cement spacer.
    • New joint later.
    • Minimum 6 weeks without joint.
      
      • Antibiotic treatment during this time I guess? (this was a question last year)
• Two-stage = higher chance of definitive cure.
  
  • Increased risk of anaesthesia and surgery.

Question 23

Three classes of OM by Waldvogel classification system?

Answer 23

• Haematogenous.
• Secondary to contiguous infection.
• Chronic OM.

Question 24

Four stages of Cierny-Mader classification.

Answer 24

1. Medullary osteomyelitis.
2. Superficial OM.
3. Localised OM.
4. Diffuse OM.