56 - Bone and joint infections

Question 1

Osteomyelitis is…

Answer 1

Infection of bone

Heterogenous disease
Difficult to diagnose and treat

Question 2

Pathogenesis of osteomyelitis

Answer 2

Haematogenous - bacteria in blood go to bone e.g. endocarditis

Contiguous-focus - spread from adjacent area of infection

Direct inoculation - trauma or surgery

Question 3

Classification of osteomyelitis

Answer 3

Stage 1 Medullary (necrosis of medullary contents - haematogenous)

Stage 2 superficial - necrosis localised to exposed surface

Stage 3 localised - full thickness cortical sequestation

Stage 4 diffuse - extensive, unstable bone

Question 4

Osteomyelitis - clinical presentation

Answer 4

Pain
Soft tissue swelling
Erythema
Warmth
Localised tenderness
Reduced movement of affected limb
Systemic upset

Question 5

Osteomyelitis - causative organisms

Answer 5

Staph. aureus (most common 60%)
Steptococci - A or B
Enterococci
Gram -ve bacilli e.g. salmonella
Anaerobes
Mycobacterium tuberculosis

Question 6

Osteomyelitis - investigations

Answer 6

gold standard - culture and histology of bone biopsy / needle aspirates

Blood cultures 50% positive

Superificial swabs are of limited value

Leukocytosis - not diagnostic

CRP - usually raised

Question 7

Osteomyelitis - therapy

Answer 7

Antimicrobials +/- surgery

Avoid empirical antimicrobial therapy

Give targeted ATX therapy

IV ATX initially given to ensure compliance and optimal bone levels as penetration to bone is low

Question 8

Osteomyelitis - drug therapy

Answer 8

Clindamycin
Ciprofloxacin
Vancomycin
B-lactams
Gentamicin

Flucloxacillin IV - agent of choice for S.aureus

Question 9

Septic arthritis - definition

Answer 9

Inflammatory rxn in joint space caused by infection resulting from direct invasion of a joint

Question 10

Septic arthritis - classification system

Answer 10

Native joint infection vs prosthetic joint infection

Question 11

Septic arthritis - pathogenesis

Answer 11

Organisms enter via haematogenous or trauma

Synovial tissue is highly vascular and lacks basement membrane allowing seeding

Cartilage erodes narrowing joint space

Question 12

Septic arthritis - predisposing factors

Answer 12

Rheumatoid arthritis
Trauma
IV drug use
Immunosuppressive disease

Question 13

Septic arthritis - prosthetic joint infection

Answer 13

Organisms enter a joint via the blood

Joint prosthesis and cement provide a surface for bacterial attachment

Polymorph infiltration results in tissue damage instability of the prosthesis

Question 14

Septic arthritis - clinical presentation

Answer 14

Joint - pain, swelling, tenderness, redness and limited movement

Systemic upset - fever, chills, night sweats

Question 15

Septic arthritis - causative organisms

Answer 15

Bacteria
Fungi
Parvovirus B19, rubella, mumps

Question 16

Septic arthritis - more causative organisms

Answer 16

Native joint - staph aureus, strep A,B,C,G, haemophilus influenzae, neisseria gonorrhoeae, neisseria meningitidis, anaerobes, mycobacteria

Prosthetic - staph aureus, strep A,B,C,G; anaerobes, enterococci, gram –ve bacilli

Question 17

Septic arthritis - investigations

Answer 17

WBC count
Differential WCC
Gram stain
Crystal exam (gout can mimic infection

Culture
PCR

Question 18

Septic arthritis - therapy for native joint

Answer 18

Removal of purulent material (drainage + washout)

Empirical IV therapy then directed

Duration of 2-4 weeks

Question 19

Septic arthritis - therapy for prosthetic joint

Answer 19

Removal of implant or some elements and wash out

Empirical IV then directed

Duration for 6 weeks then oral switch