SM 242a - Bone and Joint Infections

Question 1

Which bones are likely to be infected with osteomyelitis due to hematogenous spread?

Which organism is a likely culprit?

Answer 1

Long bones, vertebrae

S. aureus

Question 2

How is osteomyelitis treated?

Answer 2

Get diagnostic tests before starting an antibiotic

• You want to choose the right antibiotic
• Less urgent than septic arthritis
  
  • However, if the patient is septic treat empirically immediately

Question 3

Describe the clinical presentation of a disseminated gonococcal infection (DGI)

Answer 3

• One of two major presentations
  
  • Tenosynovitis, dermatitis, and polyarthralgia
  • Purulent monoarticular arthritis
• More common in women than men

Question 4

Which organisms is the most common cause of osteomyelitis?

Answer 4

Staphylococcus aureus

Question 5

Describe the clinical manifestation of osteomyelitis

Answer 5

Nonspecific presentation

• Pain around the involved site
• Fever, chills, local swelling, erythema in the proximity of the involved bone is infrequent
• Occasionally can see a draining sinus tract over the involved bone
  
  • This is pathognomonic for osteomyelitis

Question 6

Which bacteria are likely to cause septic arthritis after a cat or dog bite?

Answer 6

Pasteurella multocida, Capnocytophaga spp.

Question 7

A 65 year-old male presents with several weeks of progressive back pain and several hours of left lower extremity weakness. MRI shows L4-L5 diskitis, osteomyelitis, and epidural fluid collection with posterior displacement of the spinal cord. Should treatment be delayed until deep tissue specimens can be obtained for culture?

Answer 7

No!

Neurologic signs (left lower extremity weakness) = an emergency. Need to treat immediately to avoid permanent injury and paraplegia

Treat immediately with broad spectrum antibiotic while the patient waits for emergent surgery to decompress the spinal cord (via surgery or percutaneous drainage)

Question 8

A 25 year-old woman presents with several days of right knee pain, swelling and low grade fever. Arthrocentesis shows 70,000 white blood cells with 95% neutrophils. A gram stain of the joint fluid shows no microorganisms. Blood and synovial fluid cultures are negative.

Is any further evaluation necessary?

Answer 8

Yes!

• >50,000 WBCs and >90% neutrophils indicates a joint infection
• Synovial fluid and blood cultures can be negative, especially since the bacteria may exist in biofilms
• Fever indicates septic arthritis

Most likely culprits are S. aureus and N. gonorrhoeae. Futher testing for N. gonorrhoeae is indicated. Treat empirically with vancomycin for S. aureus and ceftrioxone for N. gonorrhoeae

Question 9

What are the clinical manifestations of septic arthritis?

Answer 9

• Monoarticular in 80% of cases
  
  • Usually a knee in adults or a hip in children
• Pain and loss of function
• Swelling and redness, increased warmth
• Fever and malaise
• In peripheral joints…
  
  • Focal tenderness, inflammation, effusion
  • Limited ROM
• Axial joints
  
  • Focal tenderness
  • Distance source of infection in ~50% of patients

Question 10

In which populations is Pseudomonas aeruginosa a likely culprit for joint infection?

Answer 10

• IV drug users

Note: often involves fibrocartilaginous joints (pubic symphysis, sternoclavicular and SI joints)

Question 11

When are prosthetic joint infections usually contracted?

Answer 11

During placement of the new joint

Usually due to contamination of the prosthesis by skin microorganisms during surgery

Question 12

What is the key diagnostic test and result for septic arthritis?

Answer 12

Arthrocentesis with >50,000 WBCs, >90% neutrophils

Culture positive in 80-90% of patients

Question 13

Eikenella corrodens might cause joint infection after which exposure?

Answer 13

Human bite

Question 14

What is the most common culprit in septic arthritis?

Answer 14

Staphyloccous aureus

Question 15

Why is Nesseria gonorrhoeae infection difficult to treat?

Answer 15

Surface glycoproteins on the bacteria undergo phase and antigenic variation; this allows them to evade the immune system

• The longer an infection persists untreated, the greater the opportunity for invasive, serum-resistant strains to emerge
• Infection is often asymptomatic, and therefore persists untreated
  
  • More commonly asymptomatic in women than in men

Question 16

What factors promote bacterial attachment to synovial joints?

Answer 16

• Bacterial adhesins (**S. aureus)
• Host inflammatory factors
• Extracellular proteins promote bacterial attachment

Question 17

Which bones are likely to be infected with osteomyelitis due to contiguous spread?

Which organism is a likely culprit?

Answer 17

Foot, sacrum

Polymicrobial

Question 18

Which organism is likely to cause osteomyelitis in immunocompromised patients?

Answer 18

Aspergilllus

Mycobacterium avium complex

Candida albicans

Question 19

Describe the clinical presentation of lyme disease

Answer 19

Early infection

• Erythema migrans
  
  • Expanding, annular erythematous skin lesion
• Disseminated infection
  
  • Fever, chills, secondary annular skin lesions
  • Meningitis
  • Cranial neuritis -> Facial palsy, carditis, migratory arthrits

Late infection

• ​Arthritis
• Chrnoic encephalopathy

Question 20

What pathologies could result in an arthrocentesis with >100,000 WBCs?

Answer 20

• Septic arthritis
• RA flare
• Leukemia
• Gout
• Reaction to intraarticular injection

Question 21

What imaging studies are useful in the evaluation of septic arthritis?

Answer 21

CT and MRI

Both are sensitive for early septic arthritis. Will show fluid as well as surrounding bone involvement

Question 22

Which imaging modalities are choice for the diagnosis of osteomyelitis?

Answer 22

CT and MRI

Question 23

Why is S**taphylococcus aureus a common culprit of joint infections?

Answer 23

S**taphylococcus aureus produces adhesins that permit adherence of the bacteria to cartilage

Question 24

The high relapse rate with osteomyelitis is secondary to…

A. Underlying immunosuppression

B. Inadequate treatment

C. Biofilm formation on devascularized bone

D. Delayed diagnosis

Answer 24

C. Biofilm formation on devascularized bone

Question 25

How are prosthetic joint infections treated?

Answer 25

Several options, but two-stage exchange is the gold standard * Debridement with retention of prosthesis and abx * One- or **two-stage exchange + abx** * Long-term antimicrobial suppression (palliative) * Implant removal without replacement + abx * Amputation may be needed

Question 26

Why are prosthetic joint infections difficult to treat?

Answer 26

Biofilms tend to form on the surface of prosthetic material This dampens the immune response and limits antibiotic penetration

Question 27

Describe the pathogenesis of osteomyelitis

Answer 27

Bacteria escapes host defences through * **Adherence to damaged bone** * **Persistence within osteoblasts** * Can lay dormant for years * **Formation of biofilm** over bacteria and underlying bone surfaces * Forms on areas of de-vascularized bone * Prevents eradication of the bacteria

Question 28

Which organism is associated with osteomyelitis caused by animal or human bites?

Answer 28

* *Pasteurella moltocida* from animal bites * *Eikenella corrodens* from human bites

Question 29

What is Pott’s disease? Describe the clinical presentation

Answer 29

Tuberculous spondylitis = vertebral osteomyelitis due to *M**ycobacterium tuberculosis* * Systemic symptoms are often absent * Back pain or stiffness is commonly the only symptom * Delayed diagnosis is common * Abnormal chest x-ray in \<50% of patients

Question 30

Which organism is associated with osteomyelitis in patients with sickle cell disease?

Answer 30

Salmonella ## Footnote *Streptococcus pneumoniae*

Question 31

Which virus is associated with “persistent, symmetric polyarthritis”?

Answer 31

Human Parvovirus B19

Question 32

*Pasteurella multocida* or *Capnocytophaga* spp. may cause joint infection after which exposure?

Answer 32

Dog or cat bite

Question 33

What is the treatment for diabetic foot infection?

Answer 33

* Revascularization when indicated * Surgical debridement of infected bone and soft tissue * Broad-spectrum antibiotic therapy targeting aerobic and anaerobic bacteria

Question 34

Why are joints particularly susceptible to infection during bacteremia?

Answer 34

The vascular synovial membrane lacks a limiting basememnt membrane; this makes them susceptible to bacterial deposition

Question 35

Which viruses are most commonly associated with viral arthritis?

Answer 35

* Chikungunya virus * Hepatitis B virus * Hepatitis C virus * Human parvovirus B19 * Persistent, symmetric polyarthritis

Question 36

Which bacteria are likely to cause septic arthritis after a human bite?

Answer 36

*Eikenella corroens*

Question 37

If a patient presents with persistent joint pain that is difficult to diagnose (negative cultures, no improvement), fungal cultures should be sent. Which fungal organisms are likely to be culprits in healthy hosts? In immunocompromised hosts?

Answer 37

* Healthy hosts * *Blastomyces dermatitidis* * *Coccidioides* spp. * Immunocompromised hosts * *Candida* spp. * *Cryptococcus* * *Aspergillus*

Question 38

What samples are best for the diagnosis of osteomyelitis?

Answer 38

Tissue samples or a syringe of pus These will yield more accurate results than a swab

Question 39

Describe the presentation of viral arthritis casued by human parvovirus B19

Answer 39

Persistent, symmetric polyarthritis

Question 40

Drainage of infected synovial fluid in cases of septic arthritis is necessary because... 1. Inflammatory synovial fluid destroys cartilage 2. Antibiotics will not penetrate into synovial fluid 3. Undrained fluid will ultimately drain to the skin via disfiguring sinus tracts

Answer 40

a. Inflammatory synovial fluid destroys cartilage

Question 41

Describe the typical clinical presentation of a contiguous osteomyelitis infection

Answer 41

* Affects sacrum, pelvis, or foot * May be adjacent to neuropathic ulcers * More common in adults than children * Usually polymicrobial

Question 42

Describe the typical clinical presentation of hematogenous osteomyelitis

Answer 42

* Usually affects the long bones, vertebrae, or sternoclavicular joint * More common in children than adults * Usually monobacterial

Question 44

What is the treatment for septic arthritis?

Answer 44

* Joint drainage * Either repeated arthrocentesis or arthroscopic lavage * Antibiotic therapy * Empiric: Direct against *S. aureus* and *N. gonorrhoeae* * *​*Vancomycin + Ceftriaxone * Otherwise, base on blood or synovial fluid culture

Question 45

Which bacteria is associated with Lyme disease? How is it transmitted?

Answer 45

*Borrelia burgdorferi* Tick bite (Ixodes tick)

Question 46

How do biofilms contribute to the pathogenesis of osteomyelitis and septic arthritis?

Answer 46

Biofilms consist of an organized group of microorganisms in an extracellular polymeric matrix * Facilitates gene transfer * Microorganisms can pass on virulence factors and abx resistance * Evades host immune response * Rapid changes in antigen expression * Reduces antibiotic efficacy * Slows diffusion * Prevents mechanism from working effectively

Question 47

Which organism is associated with osteomyelitis due to a foreign body?

Answer 47

Coagulase-negative staphylococci

Question 48

Describe the clinical presentation of vertebral osteomyelitis

Answer 48

* Invection involves... * Vertebral disks, adjacent vertebrae, or both * +/- epidural or psoas abscesses * Localized insidious pain and tenderness in the spine * Fever in 50% of patients * Motor and ensory deficits in 15% * Spinal cord or nerve root compression * This is an emergency!! Surgery + abx!!

Question 49

Which organism is associated wtih nosocomial osteomyelitis?

Answer 49

Enterobacteriaceae

Question 50

In which populations is *Kingella kingae* a likely culprit for joint infection?

Answer 50

* Children

Question 51

What are the risk factors for septic arthritis?

Answer 51

* Abnormal joint * Previous intraarticular steroid injection * Immunosuppression * Diabetes melitus * Malignancy * Chronic renal failure * Intravenous drug abuse

Question 52

Why do synovial cultures of prosthetic joints have poor sensitivity for infection?

Answer 52

* Prosthetic joints have a lot of surface area * The infected part might hide from biopsy * Bacteria tend to form biofilms on prosthetic joints * The bacteria may not be floating freely in the synovial fluid

Question 53

Which organism is associated with osteomyelitis caused by nail puncture wounds to the foot?

Answer 53

*Pseudomonas aeruginosa* Usually from the sweat in sneakers/gym shoes

Question 54

In which populations is *E. coli* a likely culprit for joint infection?

Answer 54

* Neonates * Elderly * IV drug users * Immunocompromised hosts