Bone and Joint Infections

Question 1

What is the osteomyelitis?

Answer 1

Infection of the bone

Question 2

What are the 3 mechanisms by which bone infections can occur?

Answer 2

Haematogenous - bacteria in the blood seed bone

Contiguous-focus - spread from adjacent area of infection

Direct Inoculation - trauma or surgery

Question 3

How are the 4 anatomical classifications of bone infection?

Answer 3

Stage I - medullary - necrosis confined to the medulla

Stage 2 - superficial - necrosis limited to exposed surface

Stage 3 - localised - full thickness destruction of cortical elements of bone - need surgery to get rid of infected bone and pus - antibiotics alone will not work

Stage 4 - diffuse - extensive, unstable bone

Question 4

What are the clinical features of osteomyelitis?

Answer 4

• Persistent pain (not just mechanical)
• Soft tissue swelling
• Erythema (redness)
• Warmth
• Localised tenderness
• Reduced movement of affected limb
• Systemic upset UNCOMMON (fever, chills, night sweats)

Question 5

What is the most common cause of osteomyelitis?

Answer 5

Usually single organism

• Staph Aureus = most common
• Streptococci A/B
• Enterococci
• Gram negative bacilli - e.g. pseudomonas = more common in infants/babies

Question 6

What laboratory investigations should be performed with osteomyelitis?

Answer 6

Cultures and histology of bone biopsy/needle aspirate (superficial swabs not great!)

Question 7

What are the diagnostic features of osteomyelitis?

Answer 7

C-reactive protein raised

Leukocytosis - not diagnostic

Question 8

What are the therapeutical options for osteomyelitis?

Answer 8

IV antibiotics
- CLINDAMYCIN - staph aureus
-Ciproflaxcin - gram negatives (pseudomonas)
- Vancomycin - gram positive (strep cocci, enterococci)
Gentamicin (Beta lactams)

FLUCOXACILLIN = treatment of choice for staph aureus osteomyelitis

Question 9

What is the term meaning inflammatory reaction in joint space by infection?

Answer 9

Septic arthritis

Question 10

What is the classification system for direct infection?

Answer 10

Native (natural joint infection) vs prosthetic (artificial) joint infection

Question 11

What is the pathogenesis of septic arthritis in native joint?

Answer 11

Organisms enter joint via blood or trauma

Synovial joint is highly vascular and lacks basement membrane - facilitates seeding

Cartilage erosion causes joint space narrowing/impaired function

Question 12

What is the pathogenies of septic arthritis in prosthetic joint?

Answer 12

• Organisms enter a joint via the blood during surgery/wound infection
• Joint prosthesis and cement provide a surface for bacterial attachment
• Polymorph infiltration results in tissue damage instability of the prosthesis

Question 13

What is the clinical presentation of septic arthritis?

Answer 13

Joint: pain, swelling, tenderness, redness and movement limitation

System upset: fever, chills, night sweats

Duration of symptoms is variable, dependent on site and organism

Question 14

What are the causative bacterial organisms for septic arthritis in native joint?

Answer 14

S Aureus
Strep A (pyogenes), B, C, G
H Influenzae
N Gonorrhoea*
N Meningitidis*
anaerobes

NATIVE = N species

Question 15

What are the causative bacterial organism for prosthetic joint infections

Answer 15

S Aureus
Step A, B, C, G
Coagulase negative staph (CoNS)*
Enterococci
Corynebacteria*
Proprioibacteria*
Bacillus Spp*
Anaerobes

*skin flora/in environment

Question 16

What are the diagnostic features of septic arthritis?

Answer 16

Total white cell count increased
- Polymorphs increased
- Gram stain (35-65%) positive
Crystal examination (check for gout)
Culture/PCR

Question 17

What is the therapy for native joint infection?

Answer 17

Removal of pus/purulent material (joint drainage/washout)

Empirical IV antimicrobial therapy

Direct IV antimicrobial therapy depending on causative organism

Question 18

What is the therapy for prosthetic joint?

Answer 18

If loose/late, removal of impact or replacement of elements - washout

Empirical (broad) IV antimicrobial therapy

Directed (specific) IV antimicrobial therapy depending on organism

Question 19

What viruses can cause infective arthritis?

Answer 19

Parvovirus B19
Rubella
Mumps

(usually self limiting)