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MSK/Derm > SM 249: Bone and Joint Infections > Flashcards

SM 249: Bone and Joint Infections Flashcards

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Dermatology Board Prep flashcards
1
Q

What is septic arthritis?

A

Infection in a joint

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2
Q

What are the two ways septic arthritis can be acquired?

A

Septic Arthritis may be acquired via:

Hematogenous = bacteremia

Direct inoculation = surgery/trauma

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3
Q

Describe the hematogenous spread of septic arthritis?

A

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

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4
Q

Describe the acquisition of septic arthritis via direct inoculation?

A

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

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5
Q

What are the risk factors for septic arthritis?

A

Pre-existing abnormal joint

Immunosuppression

Diabetes

IV Drug use

Malignancy

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6
Q

How can bacteria cause septic arthritis?

A

JSE

Joint disease/injury facilitates bacterial adherence

S. aureus adhesins can bind cartilage

Endotoxins break down cartilage

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7
Q

What are MSCRAMMs?

A

Microbial Surface Components Recognizing Adhesive Matrix Molecules

= S. aureus adhesins

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8
Q

How can the host inflammatory response contribute to septic arthritis?

A

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

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9
Q

How rapidly can intra-articular cartilage be destroyed?

A

Very rapidly, seen < 3 days

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10
Q

Why is septic arthritis treated as an emergency?

A

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

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11
Q

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

A

Gram Positive = S. aureus

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

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12
Q

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

A

Immunocompromised Hosts

Neonates/elderly

IV drug users

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13
Q

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

A

IV Drug users

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14
Q

Which bacteria tends to cause septic arthritis in fibrocartilagenous joints?

A

P. aeruginosa

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15
Q

Who does Kingella kingae tend to cause septic arthritis in?

A

Children

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16
Q

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

A

Pasteurella multocida

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17
Q

What bacteria causes septic arthritis fro a human bite?

A

Eikenella corrodens

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18
Q

How does septic arthritis present?

A

Pain + loss of function

Swelling, redness, warmth, fever

Single joint (knee or hip)

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19
Q

What are the physical exam findings of septic arthritis?

A

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

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20
Q

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

A

CRP and ESR are elevated

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

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21
Q

What will arthrocentesis produce in septic arthritis?

A

Inflammatory findings:

50,000+ WBC and 90%+ PMNs

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22
Q

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

A

Synovial fluid culture

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

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23
Q

What can ultrasound reveal in septic arthritis?

A

Extremely sensitive for the presence of effusion and guides needle aspiration

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24
Q

What is the preferred imaging modality in septic arthritis?

A

CT and MRI, not Xray

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

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25
Q

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

A

Infectious arthritis

Gout/Pseudogout

Reactive Arthritis (Post-infectious like RF)
Rheumatoid Arthritis

Lupus

26
Q

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

A

Yup

27
Q

How should septic arthritis be treated?

A

Joint drainage

Antibiotics (empiric or specific, based on blood culture)

28
Q

Which antibiotics should be used in septic arthritis?

A

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

29
Q

What is Gonoccocal Arthritis and how does it present?

A

Gonococcal Arthritis = bacteremia secondary to mucosal infection of urethra, cervix, or rectum

Presents with tenosynovitis and polyarthralgia

30
Q

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

A

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

31
Q

What bacteria frequently causes Gonococcal Arthritis, and why?

A

Neisseria Gonorrhoeae

Surface Glycoproteins undergo Phase and Antigenic variation

= invasive, persistent infection with lots of resistances

32
Q

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

A

Lyme disease is caused by Borrelia burgdoferi

Transmitted by Ixodes tick

33
Q

Can Lyme disease cause arthritis?

A

Yes, after it disseminates and causes bullseye skin lesions

34
Q

What are causes of viral arthritis?

A

Human Parvovirus B19 (persistent)

Chikungunya virus (persistent)

Hep B/C

35
Q

What chronic infections can cause infectious arthritis?

A

Healthy hosts: Blasto + Cocci

Immunocompromised: Candida, Cryptococcus, Aspergillus

Also consider TB

36
Q

What types of bacteria cause prosthetic joint infection and how?

A

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

37
Q

What is pathnognomonic for infectious etiology?

A

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

38
Q

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

A

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

39
Q

Why are synovial cultures sonicated?

A

Destroy biofilms and improve yield/diagnosis

40
Q

What should be seen on histology in prosthetic joint infection?

A

10+ neutrophils in 5 high power fields

41
Q

What is the gold standard treatment of Prosthetic Joint Infection?

A

Two stage exchange + antibiotics:

Remove infected joint

Add spacer impregnated with antibiotics

Replace joint

42
Q

What is the antibtiotic therapy for prosthetic joint infection?

A

Pathogen specific IV antibiotics (Ciprofloxacin) + Rifampin to increase penetrance of biofilms

Consider chronic oral antimicrobial suppression and debridement

43
Q

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

A

Hematogenous osteomyelitis = kids

Contiguous osteomyletis = adults

44
Q

Where does hematogenous osteomyelitis effect and with how many bacteria?

A

Hematogenous osteomyelitis effects long bones and vertebrae, usually monobacterial

45
Q

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

A

Sacrum and foot adjacent to ulcers

Usually polymicrobial

46
Q

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

A

Adhere to damaged bone

Persist in osteoblasts (S. aureus)

Biofilms

47
Q

How does S. aureus cause osteomyelitis?

A

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

48
Q

What is a biofilm and what do they facilitate?

A

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)

49
Q

What are the two states of bacteria in a biofilm?

A

Planktonic = free floating, high metabolism

Sessile = within biofilm, low metabolism

50
Q

What are common causes of osteomyelitis?

A

S. aureus

Enterobacteriacae (nocosomial infection)

P. aeruginosa (nocosomial, foot wound)

51
Q

How doess Ostoemyelitis present?

A

Nonspeciifc pain

Fever, chills, swelling, erythema

Draining sinus tract

Subacute to chronic presentation

52
Q

Why are Xrays not used to diagnose bone infections?

A

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

53
Q

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

A

CT and MRI

54
Q

What use do ESR and CRP have in Osteomyelitis?

A

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

55
Q

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

A

Without spesis = wait until adequate tissue samples are obtaiend

With sepsis = treat empirically and try to diagnose speciifc cause with tissue sample

56
Q

What is vertebral osteomyelitis and how does it present?

A

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

57
Q

What is Potts disease?

A

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

58
Q

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

A

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

59
Q

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

A

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

60
Q

How is diabetic foot infeciton manged?

A

Revascularization if needed

Surgial debridement of infected bone and tissue

Broad spectrum antibiotics b/c the infection is polymicrobial

61
Q

Is diabetic foot infection monomicrobial or polymicrobial?

A

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

62
Q

Why does osteomyelitis have a high relapse rate?

A

Biofilms and bacteria hiding in the osteoblasts

MSK/Derm (46 decks)

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