Osteomyelitis

Question 1

What is osteomyelitis?

Answer 1

Bone marrow infection.

Question 2

How do pathogens get into bone?

Answer 2

1. Trauma -> direct inoculation
2. Contiguous spread from adjacent tissues (older adults, DM, ulcers)
3. Haematogenous seeding secondary to bacteraemia (most common)

Question 3

Why is haematogenous OM more likely in the vertebrae of adults and long bones of children?

Answer 3

As the long bones are still developing, they have high blood flow, but with age, the vertebrae become more vascular, making bacterial seeding of the vertebral endplate more likely.

Question 4

Describe the age distribution of OM.

Answer 4

Bimodal age distribution - most common in young and old.
Children - acute haematogenous OM
Young adults - contiguous OM, often direct trauma
Elderly - DM/PVD/arthroplasty.

Question 5

Give 3 risk factors for OM.

Answer 5

Behavioural eg risk of trauma
Vascular supply eg sickle-cell disease
Pre-existing bone/joint problem eg RA
Immune deficiency

Question 6

Give 3 risk factors for haematogenous OM.

Answer 6

IVDUs
Caused by bacteraemia so:
Dialysis, sickle cell disease, UTI
Endocarditis

Question 7

Give 3 common causative organisms for OM.

Answer 7

Staph aureus
Salmonella in sickle-cell
P. aeruginosa in IDVU.
Aerobic gram -ve bacilli.

Question 8

Give 3 acute changes seen on histology in OM.

Answer 8

Inflammatory cells, oedema, vascular congestion, small vessel thrombosis.

Question 9

Give 3 chronic changes seen on histology in OM.

Answer 9

Necrotic bone ‘sequestra’
New bone formation ‘involucrum’
neutrophil exudates
lymphocytes, histiocytes

Question 10

Describe the presentation of acute OM

Answer 10

Onset over several days
Dull pain at site of OM
May be aggravated by movement
Fevers, rigors, sweats, malaise
Local tenderness, warmth, erythema and swelling

Question 11

Give 3 signs of chronic OM

Answer 11

Similar to acute but also with:
Draining sinus tract (abnormal channel to the outside of the body)
Deep ulcer that resist treatment (eg DM –> OM)
Non-healing fractures

Question 12

What happens if the infection spreads from the bone to a joint?

Answer 12

It is septic arthritis by definition.

Question 13

If the WCC and inflammatory markers are normal, what may this mean?

Answer 13

Chronic low-grade OM, especially of the small joints.

Question 14

How is OM diagnosed?

Answer 14

1. Bloods - Raised ESR/CRP and WCC in acute OM
2. Blood cultures. If common OM pathogen found, don’t need biopsy. If not:
3. Bone biopsy - microbiology and histology.
4. Imaging - X ray and MRI

Question 15

Give 3 X-ray changes seen in chronic OM. How long after onset would they appear?

Answer 15

Up to a month.
Cortical erosion
Periosteal reaction
Sclerosis

Question 16

What changes would be seen on MRI and how long after onset would they appear?

Answer 16

Marrow oedema from 3-5 days

Delineates cortical, bone marrow and soft tissue inflammation.

Question 17

What could cause symptoms of OM eg osteonecrosis other than OM?

Answer 17

Avascular necrosis due to steroids/radiation/bisphosphonates
Malignancy
Gout

Question 18

Describe the management of OM.

Answer 18

1. Debridement, hardware replacement or removal
2. Antibiotics - empirical then targeted depending on culture results. May need multiple abx for multiple pathogens. sensitivities - MRSA?

Question 19

What could have a slower onset and mild symptoms?

Answer 19

TB osteomyelitis

Question 20

What type of OM could present with chronic low-grade back pain?

Answer 20

Spinal TB.

Question 21

Give 3 virulence factors of staph aureus,

Answer 21

Surface proteins that promote colonization of host tissues
Invasins eg kinases that promote bacterial spread in tissues
Phagocytosis-resistance capsule.