SM 242a - Bone and Joint Infections Flashcards
Which bones are likely to be infected with osteomyelitis due to hematogenous spread?
Which organism is a likely culprit?
Long bones, vertebrae
S. aureus
How is osteomyelitis treated?
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
Describe the clinical presentation of a disseminated gonococcal infection (DGI)
- One of two major presentations
- Tenosynovitis, dermatitis, and polyarthralgia
- Purulent monoarticular arthritis
- More common in women than men
Which organisms is the most common cause of osteomyelitis?
Staphylococcus aureus
Describe the clinical manifestation of osteomyelitis
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
Which bacteria are likely to cause septic arthritis after a cat or dog bite?
Pasteurella multocida, Capnocytophaga spp.
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?
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)
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?
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
What are the clinical manifestations of septic arthritis?
- 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
In which populations is Pseudomonas aeruginosa a likely culprit for joint infection?
- IV drug users
Note: often involves fibrocartilaginous joints (pubic symphysis, sternoclavicular and SI joints)
When are prosthetic joint infections usually contracted?
During placement of the new joint
Usually due to contamination of the prosthesis by skin microorganisms during surgery
What is the key diagnostic test and result for septic arthritis?
Arthrocentesis with >50,000 WBCs, >90% neutrophils
Culture positive in 80-90% of patients
Eikenella corrodens might cause joint infection after which exposure?
Human bite
What is the most common culprit in septic arthritis?
Staphyloccous aureus
Why is Nesseria gonorrhoeae infection difficult to treat?
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
What factors promote bacterial attachment to synovial joints?
- Bacterial adhesins (**S. aureus)
- Host inflammatory factors
- Extracellular proteins promote bacterial attachment
Which bones are likely to be infected with osteomyelitis due to contiguous spread?
Which organism is a likely culprit?
Foot, sacrum
Polymicrobial
Which organism is likely to cause osteomyelitis in immunocompromised patients?
Aspergilllus
Mycobacterium avium complex
Candida albicans
Describe the clinical presentation of lyme disease
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
What pathologies could result in an arthrocentesis with >100,000 WBCs?
- Septic arthritis
- RA flare
- Leukemia
- Gout
- Reaction to intraarticular injection
What imaging studies are useful in the evaluation of septic arthritis?
CT and MRI
Both are sensitive for early septic arthritis. Will show fluid as well as surrounding bone involvement
Which imaging modalities are choice for the diagnosis of osteomyelitis?
CT and MRI
Why is S**taphylococcus aureus a common culprit of joint infections?
S**taphylococcus aureus produces adhesins that permit adherence of the bacteria to cartilage
The high relapse rate with osteomyelitis is secondary to…
A. Underlying immunosuppression
B. Inadequate treatment
C. Biofilm formation on devascularized bone
D. Delayed diagnosis
C. Biofilm formation on devascularized bone
How are prosthetic joint infections treated?
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
Why are prosthetic joint infections difficult to treat?
Biofilms tend to form on the surface of prosthetic material
This dampens the immune response and limits antibiotic penetration
Describe the pathogenesis of osteomyelitis
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
Which organism is associated with osteomyelitis caused by animal or human bites?
- Pasteurella moltocida from animal bites
- Eikenella corrodens from human bites
What is Pott’s disease?
Describe the clinical presentation
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
Which organism is associated with osteomyelitis in patients with sickle cell disease?
Salmonella
Streptococcus pneumoniae
Which virus is associated with “persistent, symmetric polyarthritis”?
Human Parvovirus B19
Pasteurella multocida or Capnocytophaga spp. may cause joint infection after which exposure?
Dog or cat bite
What is the treatment for diabetic foot infection?
- Revascularization when indicated
- Surgical debridement of infected bone and soft tissue
- Broad-spectrum antibiotic therapy targeting aerobic and anaerobic bacteria
Why are joints particularly susceptible to infection during bacteremia?
The vascular synovial membrane lacks a limiting basememnt membrane; this makes them susceptible to bacterial deposition
Which viruses are most commonly associated with viral arthritis?
- Chikungunya virus
- Hepatitis B virus
- Hepatitis C virus
- Human parvovirus B19
- Persistent, symmetric polyarthritis
Which bacteria are likely to cause septic arthritis after a human bite?
Eikenella corroens
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?
- Healthy hosts
- Blastomyces dermatitidis
- Coccidioides spp.
- Immunocompromised hosts
- Candida spp.
- Cryptococcus
- Aspergillus
What samples are best for the diagnosis of osteomyelitis?
Tissue samples or a syringe of pus
These will yield more accurate results than a swab
Describe the presentation of viral arthritis casued by human parvovirus B19
Persistent, symmetric polyarthritis
Drainage of infected synovial fluid in cases of septic arthritis is necessary because…
- Inflammatory synovial fluid destroys cartilage
- Antibiotics will not penetrate into synovial fluid
- Undrained fluid will ultimately drain to the skin via disfiguring sinus tracts
a. Inflammatory synovial fluid destroys cartilage
Describe the typical clinical presentation of a contiguous osteomyelitis infection
- Affects sacrum, pelvis, or foot
- May be adjacent to neuropathic ulcers
- More common in adults than children
- Usually polymicrobial
Describe the typical clinical presentation of hematogenous osteomyelitis
- Usually affects the long bones, vertebrae, or sternoclavicular joint
- More common in children than adults
- Usually monobacterial
What is the treatment for septic arthritis?
- 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
- Empiric: Direct against S. aureus and N. gonorrhoeae
Which bacteria is associated with Lyme disease?
How is it transmitted?
Borrelia burgdorferi
Tick bite (Ixodes tick)
How do biofilms contribute to the pathogenesis of osteomyelitis and septic arthritis?
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
Which organism is associated with osteomyelitis due to a foreign body?
Coagulase-negative staphylococci
Describe the clinical presentation of vertebral osteomyelitis
- 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!!
Which organism is associated wtih nosocomial osteomyelitis?
Enterobacteriaceae
In which populations is Kingella kingae a likely culprit for joint infection?
- Children
What are the risk factors for septic arthritis?
- Abnormal joint
- Previous intraarticular steroid injection
- Immunosuppression
- Diabetes melitus
- Malignancy
- Chronic renal failure
- Intravenous drug abuse
Why do synovial cultures of prosthetic joints have poor sensitivity for infection?
- 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
Which organism is associated with osteomyelitis caused by nail puncture wounds to the foot?
Pseudomonas aeruginosa
Usually from the sweat in sneakers/gym shoes
In which populations is E. coli a likely culprit for joint infection?
- Neonates
- Elderly
- IV drug users
- Immunocompromised hosts
