MSK Infections

Question 1

What is osteomyelitis?

Answer 1

Inflammation of the bone and medullary cavity usually located in long bones. Can be acute or chronic and spreads by many mechanisms.

Question 2

Who commonly gets osteomyelitis?

Answer 2

Often children by haematogenous spread.
Also PWID
Elderly if lots of central lines or dialysis

Question 3

Organisms that may be involved in osteomyelitis?

Answer 3

Literally any
Staph Aureus= go to answer
PWID may get strep or weird infections
Dialysis and children likely Staph A

Question 4

Describe the pathology of osteomyelitis?

Answer 4

Organism from the blood settles in the bone, infection spreads rapidly with acute inflammation and pus formation. There will be penetration through the cortex and the periosteum becomes raised and there is spread to the epiphysis. Penetration through soft tissue and new bone begins to be laid down but at the same time there is excessive necrosis. Involucrum of new irregularly formed bone. The presence of necrotic areas ensures the inflammation continues.

Question 5

Presentation of osteomyelitis?

Answer 5

Red, hot, swollen, painful and loss of function at the site. May have a fever.

Question 6

Gold standard for diagnosis of osteomyelitis?

Answer 6

Bone biopsy

Question 7

Describe diagnosis of osteomyelitis?

Answer 7

History
Exam: Probe to bone test, if bone is visible and infection you automatically have osteomyelitis
Tests: Blood cultures are not always diagnostic. Gold standard is bone biopsy.

Question 8

Name 3 complications of osteomyelitis?

Answer 8

Chronic osteomyelitis, disturbance of bone growth and amyloid disease.

Question 9

Management of osteomyelitis?

Answer 9

Best to wait on microbiology. Don’t give empirical antibiotics unless patient is systemically unwell or septic
Surgery must remove infected tissue, drain and debride as no antibiotic will work on the necrotic centre.
6 weeks antibiotics. Depends on the organism. Staph A= flucloxacillin. Staph epidermidis= vancomycin. Strep pyogenes= doxycycline. Gram negatives= clindamycin. Anaerobes= metronidazole.

Question 10

In blood tests for chronic disease what is important?

Answer 10

Anaemia of chronic disease

Question 11

Describe the toxin PVL and what it will cause?

Answer 11

It is produced by some strains of Staph A and can cause necrotising disease

Question 12

Strep are gram positive cocci in ___1____ and Staph are gram positive cocci in ___2_____

Answer 12

1) chains

2) clusters

Question 13

Gram positive cocci in clusters that is coagulase positive is?

Answer 13

GOLDEN APPEARANCE

Staph Aureus

Question 14

Gram positive cocci in clusters that is coagulase negative is?

Answer 14

WHITE APPEARANCE

Staph Epidermis

Question 15

Describe alpha haemolytic strep

Answer 15

GREENISH COLOUR ON BLOOD AGAR
Strep pneumonia most common cause of pneumonia.
Strep viridians can be a commensal or cause endocarditis if spreads from mouth after dental procedure

Question 16

Describe beta haemolytic strep

Answer 16

Group A: strep progenies (throat infections)
Group B: neonatal meningitis
Group C G etc

Question 17

Describe non-haemolytic strep

Answer 17

Enterococci- usually gut commensals, can cause UTIs.

Question 18

Open fractures are usually _______

Answer 18

polymicrobial

Question 19

Diabetic ulcers are usually _______

Answer 19

polymicrobial

Question 20

Describe gram positive cover of pathogens?

Answer 20

Flucloxacillin IV for Staph (and Strep)
(Vancomycin instead of flucloxacillin of penicillin allergic)
Oral switch for gram positives is doxycycline ( bone penetration excellent. Oral Flucloxacillin has poor bone penetration)

Question 21

People with Sickle cell anaemia may get osteomyelitis from what organism?

Answer 21

Salmonella

can still get Staph A though

Question 22

What disease has low prevalence in developed world but higher elsewhere?

Answer 22

Skeletal TB. Usually due to haematogenous spread from focus in lungs or GI tract.

Question 23

What happens in skeletal TB?

Answer 23

The spine is commonly involved (Pott’s disease) with damage to the bodies of two neighbouring vertebrae leading to acute vertebral collapse and angulation of the spine (gibbous). Later an abscess from, pus can track along tissue planes and discharge at a point far from the affected vertebra.

Question 24

Presentation of Skeletal TB?

Answer 24

Kyphosis, local pain, swelling, malaise, fever and night sweats

Question 25

Treatment of Skeletal TB?

Answer 25

Same as pulmonary TB but extended to 9 months with initial immobilisation.

Question 26

Sources of prosthetic joint infection?

Answer 26

From direct inoculation at time of surgery, manipulation of joint at time of surgery or seeding of joint at a later time.

Question 27

Risk factors for prosthetic joint infection?

Answer 27

Rheumatoid arthritis, diabetes, malnutrition and obesity

Question 28

Why is diagnosis of prosthetic joint infection difficult?

Answer 28

Often caused by organisms that are common contaminants. So need to take samples from multiple sites as this increases significance.

Question 29

Treatment of prosthetic joint infection?

Answer 29

Ideally need to remove prosthesis and cement. Therapy for at least 6 weeks (type will depend on the bug)
Rifampicin is added to treatment of prosthetic joints as in theory it helps get through biofilms
Re-implantation of joint after aggressive antimicrobial therapy.

Question 30

Why is rifampicin given in prosthetic joint infections?

Answer 30

Helps get through biofilms

Question 31

Sources of Septic arthritis?

Answer 31

Can be caused by direct invasion, blood stream infection.

Less commonly from an infectious focus from cellulitis abscess or spread from osteomyelitis.

Question 32

Pathogens involved in septic arthritis?

Answer 32

Usually Bacterial
Staph A (sometimes PVL- not common but look out for in a disproportionately sick person)
Streptococci
Only Staph Epi if related to a prosthetic joint
Neisseria gonorrhoea if sexually active

Question 33

Presentation of septic arthritis?

Answer 33

Medical emergency: young people- joint will be red, hot, swollen and agonisingly painful. It is immobile. In elderly may have less obvious symptoms.

Question 34

Investigations for septic arthritis?

Answer 34

Aspirate joint (purulent fluid), send fluid to micro, blood cultures, swabs, must check for crystals as presents similar to gout.