2.6.5. Infections of Joints and Bones

Question 1

How common are healthy individuals to get osteomyelitis?

Answer 1

Not common because in healthy individuals bone is resistant to infection

Question 2

How can infection get into bone?

Answer 2

o Spread from a contiguous focus of infectin
o Direct inoculation (trauma, surgery)
o Hematogenously

Question 3

How does hematogenous infection occur?

Answer 3

Infection enters through nutrient artery and into the metaphysis. Bone destruction and absess formation at metaphysis

Question 4

Why may children be more susceptible to epiphysis infection instead of the metaphysis?

Answer 4

Transphyseal vessel closes by 18 months, so epiphysis and joint relatively protected in all but young children

Question 5

Why do infections even happen at the metaphysis more than anywhere else on the bone?

Answer 5

Metaphyseal loops are areas of slow blood flow, and classically considered the site where infection begins

Question 6

What happens with hematogenous infection over time in bone?

Answer 6

In all patients, over time the infection extends within the bone and then out through compact bone where it raises the periosteum from the cortex, and over time results in new bone formation (involucrum)

Question 7

Describe the structural process that causes the body to necrotize its own bone in response to a hematogenous infection

Answer 7

Inflammatory responses increase pressure within the bone, resulting in thrombosis of branches of the nutrient artery and compression of capillaries within the Haversian canals, resulting in necrosed bone within bone (sequestrum)

Basically, you get necrosis bc blood vessels within the area of the bone and that area within bone does not have a lot of space for inflammation to occur

Question 8

Why is Staph Aureus the number one cause of osteomyelitis?

Answer 8

• It’s all over the skin
• S. aureus has Collagen Adhesin which enables binding to collagen
• Makes a biofilm – clumps of bacteria within an Extracellular polymeric substance made up of polysaccharides, proteins and DNA. This biofilm inhibits clearence by the immune system and penetration of antibiotics.

Question 9

For osteomyelitis, how do we make a definitive diagnosis?

Answer 9

BONE BIOPSY and CULTURE in the operating room

Question 10

For osteomyelitis, why might it be important to also do histology?

Answer 10

Histology helps rule out concomitant squamous cell carcinoma

Question 11

What do we see in Acute hematogenous bone infection? What do we do about it?

Answer 11

NO BONE NECROSIS, no abscess

→ abx alone usually sufficient (especially for early hematogenous disease)

Question 12

What do we do when we start getting abscesses during hematogenous infection?

Answer 12

→ abx alone, plus improvement of blood flow, often sufficient

Question 13

What do we do in bad cases of hemtogenous infection of bone?

Answer 13

→ generally require combined surgical debridement + Abx

Question 14

For joint infections, what lab findings do we find?

Answer 14

Lab Findings
• Leukocytosis common
• ESR and CRP usually elevated

Question 15

What joint is infected the most?

Answer 15

Knee (50%)

Question 16

How do we get Brucella infection? What does it cause?

Answer 16

unpasteurized milk

Causes sacroillitis

Question 17

How can we get Pseudomonas?

Answer 17

IV drugs

Question 18

What bacteria are we worried about with a human bite?

Answer 18

eikenella, oral anaerobes

Question 19

What bacteria are we worried about with an animal bite?

Answer 19

pasteurella

Question 20

How do we get the bacteria Pantoea agglomerans?

Answer 20

Plant thorns

Question 21

What bacteria are we worried about with a rat bite?

Answer 21

Strephtobacillis moniliformis

Question 22

What are we worried about with some who has an erythema migrans rash?

Answer 22

Lyme

Question 23

How do we diagnose septic arthritis?

Answer 23

Synovial fluid analysis

Question 24

Lab results for septic arthritis

Answer 24

1. WBC count (>50,000 cells/ml common with septic joint, but also for gout and pseudogout!)
2. Synovial fluid glucose at least 50% below blood glucose
3. Blood culture

Question 25

How do we diagnose for Lyme?

Answer 25

PCR of synovial fluid

Question 26

How do we diagnose Gonococcus?

Answer 26

For gonococcus: can be cultured on chocolate agar, but often negative and make diagnosis by isolation from cultures elsewhere in body (cervix, urethra, rectum, oropharynx). Synovial PCR for GC is good (80% sensitivity reported).

Question 27

Treatment for infected joints

Answer 27

Antibiotics AND joint drainage

Question 28

For osteomyelitis how long do changes take to occur?

Answer 28

10 days: periosteal rxn occurs

lytic changes appear ~2-6 weeks (once 50-75% bone density lost)

Irregular erosions of adjacent vertebral bodies suggest infection (bone tumors do not usually extend to adjacent vertebrae)

Question 29

Diagnosis for osteomyelitis should be done with what imaging?

Answer 29

MRI

best modality for detecting early bony changes & epidural abscesses (later complication of osteomyelitis)

should be performed in all suspected cases

Question 30

How do we treat osteomyelitis in kids?

Answer 30

Children (acute hematogenous infx)

5-10 days IV antibiotics

follow with oral antibiotics

Question 31

How do we treat osteomyelitis in adults?

Answer 31

Adults (acute and vertebral infx)

4-6 WEEKS IV antibiotics

Question 32

How do we treat chronic osteomyelitis?

Answer 32

surgical debridement

long-term antibiotic therapy

Risk limb amputation