Bone and Joint Infections

Question 1

What is the most common etiology of septic arthritis in adults?

Answer 1

Staph aureus

Question 2

What are the three most common etiologies of septic arthritis inadults?

Answer 2

Staph aureus, strep pyogenes, and beta-hemolytic strep

Question 3

What is the most common cause of septic arthritis in adults with diabetes, cancer, and genitourinary tract abnormalities?

Answer 3

Group B streptococci

Question 4

What are the most common causes of septic arthritis in neonates, the elderly, IV drug users, and the immunocompromised?

Answer 4

E coli and other gram-negative bacilli

Question 5

Which populations are most susceptible to pseudomonas aeruginosa septic arthritis?

Answer 5

IV drug users

Question 6

Which joints are most likely to be affected by p. aeruginosa septic arthritis?

Answer 6

Fibrocartilaginous joints (ex. pubic symphysis or sternoclavicular joints)

Question 7

What are the most common etiologies of septic arthritis in children?

Answer 7

Formerly H influenzae (not anymore bc of vaccine), also kingella kingae

Question 8

What is the main route of infection of bacterial arthritis?

Answer 8

Hematogenous spread

Question 9

Why are joints susceptible to septic arthritis during bacteremia?

Answer 9

The synovial membrane lacks a basement membrane that can block bacteria deposition

Question 10

What are alternative routes of septic arthritis bacterial deposition?

Answer 10

Surgery, trauma, contiguous spread from infected bone/tissue

Question 11

What are predisposing host factors for septic arthritis?

Answer 11

immunosuppression, diabetes mellitus, malignancy, chronic renal failure, IV drug abuse

Question 12

What is responsible for the most joint injury in septic arthritis?

Answer 12

Host inflammatory response (bacteria/toxins only cause some of the damage)

Question 13

What is the effect of leukocyte-derived proteases and inflammatory cytokines in septic arthritis?

Answer 13

They directly and indirectly cause cartilage destruction, inhibition of cartilage synthesis, and subchondral bone loss

Question 14

What added complication do prosthetic joints pose in the context of septic arthritis?

Answer 14

Skin microorganisms can colonize and form a biofilm that resists antibiotic penetration and the host immune response

Question 15

What are the symptoms of septic arthritis?

Answer 15

Pain, loss of joint function, swelling, redness, warmth, fever, malaise

Question 16

What is the typical distribution of bacterial arthritis?

Answer 16

Single joint (80-90% of the time) and knee is most common in adults (hip in children) or in any prosthetic joint

Question 17

What lab tests are used for evaluation of bacterial arthritis?

Answer 17

Erythrocyte sedimentation rate and C-reactive protein (both are nonspecific)

Question 18

What are the arthrocentesis findings of bacterial arthritis?

Answer 18

Purulent synovial fluid with elevated PMN count

Question 19

What are the x-ray findings of bacterial arthritis?

Answer 19

Early infection: soft tissue swelling, normal bone

Advanced infection: joint space loss, periosteal reaction, subchondral bone destruction

Question 20

What is the most sensitive and specific type of imaging for suspected joint infection?

Answer 20

MRI (followed by CT)

Question 21

What condition can often mimic septic arthritis?

Answer 21

Gout or pseudogout

Question 22

What is the treatment of acute bacterial arthritis?

Answer 22

Drainage and antimicrobial therapy, removal of prosthetic joint when applicable

Question 23

What is the most common sexually transmitted type of bacterial arthritis?

Answer 23

Disseminated gonococcal infection

Question 24

What are the classic findings of disseminated gonococcal infection?

Answer 24

Dermatitis, tenosynovitis, migratory polyarthralgia/polyarthritis

Question 25

What are the symptoms of borrelia burgdorferi infection?

Answer 25

Expanding annular erythematous skin lesion followed by fever, chills, meningitis, carditis, and migratory arthritis with long-term persistent arthritis

Question 26

What is the most common cause of viral arthritis?

Answer 26

Human parvovirus B19

Question 27

What is the typical presentation of viral arthritis?

Answer 27

Acute, symmetric polyarthritis or PIP and MCP joints associated with morning stiffness

Question 28

What are the most common fungal pathogens that cause arthritis in immunocompetent hosts?

Answer 28

Blastomyces and coccidioides in their endemic regions

Question 29

What are the most common fungal pathogens that cause arthritis in immunocompromised hosts?

Answer 29

Candida, cryptococcus, and aspergillus

Question 30

What is the treatment for prosthetic joint infection?

Answer 30

Since it is a biofilm, it often requires surgical debridement with or without removal/replacement and antibiotic therapy

Question 31

What are possible spread routes leading to osteomyelitis?

Answer 31

From adjacent soft tissues, hematogenous seeding, or direct inoculation

Question 32

How does bacteria escape host defenses in osteomyelitis?

Answer 32

Adhering tightly to damaged bone, entering and persisting within osteoblasts, and coating surfaces with biofilms

Pus can also spread and impair blood flow

Question 33

What are the symptoms of osteomyelitis?

Answer 33

Nonspecific pain, vague systemic symptoms (fever, chills, swelling, etc)

Question 34

What is the treatment for osteomyelitis?

Answer 34

Surgical therapy and prolonged antimicrobial treatment

Question 35

What is vertebral osteomyelitis?

Answer 35

Infection of intervertebral disks and/or adjacement vertebrae (if both = spondylodiskitis) that causes localized insidious pain

Question 36

What is Pott’s disease?

Answer 36

Vertebral osteomyelitis due to mycobacterium tuberculosis

Question 37

Where are bone infections common in diabetic patients?

Answer 37

Feet - due to peripheral neuropathy and foot ulcers with reduced vascular supply

Question 38

A 25 y.o. woman presents with several days of right knee pain, swelling, and a 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 38

Yes - synovial fluid is consistent with septic arthritis. Important to rule out neisseria gonorrhoeae via cervical, rectal, and oral swabs for PCR

Question 39

A 65 y.o. male presents with several weeks of progressive back pain and several hours of left lower extremity weakness. MRI shows L4-5 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 39

No. Lower extremity weakness suggests spinal cord impingement, which can cause permanent injury and paraplegia. Broad spectrum antibiotics are indicated after emergent decompression of spinal cord via surgery or drainage.

Question 40

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 40

c) biofilm formation on devascularized bone

Question 41

Drainage of infected synovial fluid in cases of septic arthritis is necessary because

a) inflammatory synovial fluid destroys cartilage
b) antibiotics will not penetrate into synovial fluid
c) undrained fluid will ultimately drain into the skin via disfiguring sinus tracts

Answer 41

a) inflammatory synovial fluid destroys cartilage