osteomyelitis

Question 1

definition of osteomyelitis

Answer 1

infection of the bone

either:

• acute haematogenous, secondary to contiguous local infection (with or w/o vascular disease)
• direct inoculation from trauma or surgery

both can progress to chronic

Question 2

aetiology of osteomyelitis

Answer 2

infection may spread from boils, abscesses, pneumonia, or genitourinary instrumentation - often no primary site is found

common organisms

• staphylococcus aureus
• pseudomonas
• E coli
• streptococci

other organisms

• salmonella - esp with sickle cell disease
• mycobacterior
• fungi

always look for osteomyelitis in diabetic feet and deep pressure sore

Question 3

pattern of infection in osteomyelitis

Answer 3

cancellous bone often affected in adults - vertebrae (IV drug use) and feet (diabetics)

in children - vascular bone eg long bone metaphyses especially distal femur, upper tibia

infection -> cortex erosion with holes (cloacae)

exudation of pus lifts up the periosteum interrupting blood supply to underlying bone and necrotic fragments of bone may form (sequestrum) - typical of chronic infection

new bone formation created by elevated periosteum forms an involucrum

pus may discharge into joint spaces or via sinuses to the skin

Question 4

signs and symptoms of osteomyelitis

Answer 4

pain of increasing onset and unwillingness to move over the coarse of a few days

locally:

• tenderness
• warmth
• erythema
• slight effusion in neighbouring joints

signs of systemic infection

all signs less marked in adults

Question 5

RF for osteomyelitis

Answer 5

dm

vascularf disease

impaired immunity

sickle cell disease

surgical prostheses

open fractures

impaired immunity

Question 6

epidemiology of osteomyelitis

Answer 6

incidence decreasing as living standards increase

Question 7

investigations for osteomyelitis

Answer 7

high ESR/CRP

high WCC

blood culture - +ve in 60% - mosty useful in haematogenous spread

bone biopsy gold standard for pathogen identification and dx - rarely needed

swabs from discharging sinuses or needle aspiration of material near bone - may give misleading results

XR not apparent for 10-14days, then haziness +- loss of density of affected bone, then subperiosteal rn then sequestrum and involucrum (infected cancellous bone shows less change)

MRI

isotope scans

Question 8

summarise chronic osteomyelitis

Answer 8

poor treatment = pain, fever and sequestra (infected dead bone) and sinus suppuration (presence of a sinus tract is pathogenomic) with long remissions

suspect in vascular insufficiency with non-healing tissue ulceration, overlying bony prominences

diabetic ulcers have a righ risk of osteomyelitis even before bone exposed - if bone felt on probing ulcer = chronic osteomyelitis

XR - thick irregular bone

Question 9

summarise bone TB

Answer 9

eg vertebral body = Potts disease

1-3% of all TB

incidence rising, rare in UK

spread is haematogenous/from near nodes