SM 249: Bone and Joint Infections

Question 1

What is septic arthritis?

Answer 1

Infection in a joint

Question 2

What are the two ways septic arthritis can be acquired?

Answer 2

Septic Arthritis may be acquired via:

Hematogenous = bacteremia

Direct inoculation = surgery/trauma

Question 3

Describe the hematogenous spread of septic arthritis?

Answer 3

Hematogenous spread occurs during bacteremia because the vascular synovial membrane lacks a basement membrane to prevent infiltration of bacteria

Question 4

Describe the acquisition of septic arthritis via direct inoculation?

Answer 4

Surgery, trauma, and spread from adjacent infected tissue can directly introduce bacteria into a joint and cause septic arthritis

Question 5

What are the risk factors for septic arthritis?

Answer 5

Pre-existing abnormal joint

Immunosuppression

Diabetes

IV Drug use

Malignancy

Question 6

How can bacteria cause septic arthritis?

Answer 6

JSE

Joint disease/injury facilitates bacterial adherence

S. aureus adhesins can bind cartilage

Endotoxins break down cartilage

Question 7

What are MSCRAMMs?

Answer 7

Microbial Surface Components Recognizing Adhesive Matrix Molecules

= S. aureus adhesins

Question 8

How can the host inflammatory response contribute to septic arthritis?

Answer 8

Host-derived ECM proteins promote attachment

Leukocyte proteases and cytokines cause destruction of cartilage and subchondral bone

Inflammation raises intra-articular pressure, reducing capillary blood flow and promoting ischemia/necrosis

Question 9

How rapidly can intra-articular cartilage be destroyed?

Answer 9

Very rapidly, seen < 3 days

Question 10

Why is septic arthritis treated as an emergency?

Answer 10

Irreversible destruction of the joint cartilage occurs within 3 days, and most people don’t present until after a few days

Question 11

What Gram positive and Gram negative bacteria commonly cause septic arthritis?

Answer 11

Gram Positive = S. aureus

Gram Negative = E. coli, P. aeruginosa, K. kingae

Question 12

What host characteristics make someone susceptible to septic arthritis due to E. coli?

Answer 12

Immunocompromised Hosts

Neonates/elderly

IV drug users

Question 13

What group does P. aeruginosa typically infect to cause septic arthritis?

Answer 13

IV Drug users

Question 14

Which bacteria tends to cause septic arthritis in fibrocartilagenous joints?

Answer 14

P. aeruginosa

Question 15

Who does Kingella kingae tend to cause septic arthritis in?

Answer 15

Children

Question 16

What bacteria causes septic arthritis from a dog or cat bite?

Answer 16

Pasteurella multocida

Question 17

What bacteria causes septic arthritis fro a human bite?

Answer 17

Eikenella corrodens

Question 18

How does septic arthritis present?

Answer 18

Pain + loss of function

Swelling, redness, warmth, fever

Single joint (knee or hip)

Question 19

What are the physical exam findings of septic arthritis?

Answer 19

For peripheral joints: focal joint tenderness, inflammation, and effusion with limited ROM

For axial joints: focal tenderness over the area with a distant source of infection

Question 20

How do ESR and CRP change in Septic Arthritis and what bacteria do they suggest?

Answer 20

CRP and ESR are elevated

Non-specific markers = don’t suggest a specific bacteria

Question 21

What will arthrocentesis produce in septic arthritis?

Answer 21

Inflammatory findings:

50,000+ WBC and 90%+ PMNs

Question 22

What is the best test to identify a cause of septic arthritis?

Answer 22

Synovial fluid culture

Could also use blood culture for difficult to aspirate joints, but less sensitive

Question 23

What can ultrasound reveal in septic arthritis?

Answer 23

Extremely sensitive for the presence of effusion and guides needle aspiration

Question 24

What is the preferred imaging modality in septic arthritis?

Answer 24

CT and MRI, not Xray

Shows bone erosion, joint effusion, and periarticuar soft tissue infection

Question 25

What should be considered in a differential diagnosis of fever and polyarthritis?

Answer 25

Infectious arthritis Gout/Pseudogout ``` Reactive Arthritis (Post-infectious like RF) Rheumatoid Arthritis ``` Lupus

Question 26

Can a person have gout and an infection in a joint?

Answer 26

Yup

Question 27

How should septic arthritis be treated?

Answer 27

Joint drainage Antibiotics (empiric or specific, based on blood culture)

Question 28

Which antibiotics should be used in septic arthritis?

Answer 28

If no synovial culture: use empric treatment against S. aureus and N. gonnorrhae = Vanco + Ceftriaxone If there is a synovial culture: use specific treatment based on culture results

Question 29

What is Gonoccocal Arthritis and how does it present?

Answer 29

Gonococcal Arthritis = bacteremia secondary to mucosal infection of urethra, cervix, or rectum Presents with tenosynovitis and polyarthralgia

Question 30

Which group is at increased risk for Gonococcal Arthritis and why?

Answer 30

Women are at increased risk, due to potential for asymptomatic mucosal infection

Question 31

What bacteria frequently causes Gonococcal Arthritis, and why?

Answer 31

Neisseria Gonorrhoeae Surface Glycoproteins undergo Phase and Antigenic variation = invasive, persistent infection with lots of resistances

Question 32

What causes Lyme disease and what is it's vector?

Answer 32

Lyme disease is caused by Borrelia burgdoferi Transmitted by Ixodes tick

Question 33

Can Lyme disease cause arthritis?

Answer 33

Yes, after it disseminates and causes bullseye skin lesions

Question 34

What are causes of viral arthritis?

Answer 34

Human Parvovirus B19 (persistent) Chikungunya virus (persistent) Hep B/C

Question 35

What chronic infections can cause infectious arthritis?

Answer 35

Healthy hosts: Blasto + Cocci Immunocompromised: Candida, Cryptococcus, Aspergillus Also consider TB

Question 36

What types of bacteria cause prosthetic joint infection and how?

Answer 36

Skin microorganisms that contaminate a surgery and establish a biofilm on a prothetic joint

Question 37

What is pathnognomonic for infectious etiology?

Answer 37

Sinus tract = pus under pressure that is trying to escape a joint

Question 38

How many synovial cultures are needed to diagnose a joint infection?

Answer 38

Need at least 3-4 because the bacteria may be growing in an area of the implant that was not sampled

Question 39

Why are synovial cultures sonicated?

Answer 39

Destroy biofilms and improve yield/diagnosis

Question 40

What should be seen on histology in prosthetic joint infection?

Answer 40

10+ neutrophils in 5 high power fields

Question 41

What is the gold standard treatment of Prosthetic Joint Infection?

Answer 41

Two stage exchange + antibiotics: Remove infected joint Add spacer impregnated with antibiotics Replace joint

Question 42

What is the antibtiotic therapy for prosthetic joint infection?

Answer 42

Pathogen specific IV antibiotics (Ciprofloxacin) + Rifampin to increase penetrance of biofilms Consider chronic oral antimicrobial suppression and debridement

Question 43

What are the two broad categories of osteomyelitis and who gets them?

Answer 43

Hematogenous osteomyelitis = kids Contiguous osteomyletis = adults

Question 44

Where does hematogenous osteomyelitis effect and with how many bacteria?

Answer 44

Hematogenous osteomyelitis effects long bones and vertebrae, usually monobacterial

Question 45

Where does contiguous infection leading into osteomyelitis infect and with how many bacteria?

Answer 45

Sacrum and foot adjacent to ulcers Usually polymicrobial

Question 46

How are the bacteria that cause Osteomyelitis able to escape host defenses?

Answer 46

Adhere to damaged bone Persist in osteoblasts (S. aureus) Biofilms

Question 47

How does S. aureus cause osteomyelitis?

Answer 47

S. aureus uses it's MSCRAMMs to bind bone surface S. aureus can also survive in a dormant state within Osteoblasts allowing for antibiotic resistance and high relapse rate

Question 48

What is a biofilm and what do they facilitate?

Answer 48

Biofilms are organized groups of microorganisms ``` They facilitate: Gene transfer (virulece and resistance factors) Evade host response (change antigen expression) ``` Antibiotic resistance (slow defusion of drugs)

Question 49

What are the two states of bacteria in a biofilm?

Answer 49

Planktonic = free floating, high metabolism Sessile = within biofilm, low metabolism

Question 50

What are common causes of osteomyelitis?

Answer 50

S. aureus Enterobacteriacae (nocosomial infection) P. aeruginosa (nocosomial, foot wound)

Question 51

How doess Ostoemyelitis present?

Answer 51

Nonspeciifc pain Fever, chills, swelling, erythema Draining sinus tract Subacute to chronic presentation

Question 52

Why are Xrays not used to diagnose bone infections?

Answer 52

Takes 10 - 14 days for an abnormality to show up on Xray, too slow

Question 53

What is the current gold standard for diagnosing Osteomyelitis via imagng?

Answer 53

CT and MRI

Question 54

What use do ESR and CRP have in Osteomyelitis?

Answer 54

Nonspecific so can't diagnose with them, but can trend them for response to treatment

Question 55

What is the ideal way to diagnose Osteomyelitis, with or without sepsis?

Answer 55

Without spesis = wait until adequate tissue samples are obtaiend With sepsis = treat empirically and try to diagnose speciifc cause with tissue sample

Question 56

What is vertebral osteomyelitis and how does it present?

Answer 56

Vertebral osteomyelitis is an infection involving the intervertebral disk or adjacent vertebrae that occurs after bacteria reaches the disk via spinal arteries Presents with pain and tenderness in spine as well as motor and sensor deficits = surgical emergency

Question 57

What is Potts disease?

Answer 57

Vertebral ostoemyeltis due to Mycobacterium Tuberculosis, which often presents with only back pain and no systematic symptoms

Question 58

What is a diabetic foot infection and how does it develop?

Answer 58

Osteomyeltis in patients with diabetus that develops in the foot due to neuropathy, vascular insufficiency, and hyperglycemia

Question 59

Why do diabetic foot infections progress to seious stages without action by the patient?

Answer 59

Neuropathy from the diabetes prevents patient from feeling pain, so the foot gets bad

Question 60

How is diabetic foot infeciton manged?

Answer 60

Revascularization if needed Surgial debridement of infected bone and tissue Broad spectrum antibiotics b/c the infection is polymicrobial

Question 61

Is diabetic foot infection monomicrobial or polymicrobial?

Answer 61

Polymicrobial, since diabetes predisposes a variety of infections and damaged feet can obtain bacteria from the environment

Question 62

Why does osteomyelitis have a high relapse rate?

Answer 62

Biofilms and bacteria hiding in the osteoblasts