Bone and Joint Infection - Osteomyelitis, Septic Arthritis, and Reactive Arthritis

Question 1

What are the general characteristics of osteomyelitis?

Answer 1

Bacterial infection in bone, causing inflammatory bone destruction, necrosis, and ectopic overgrowth of bone

Question 2

What bones / joints are typically affected in osteomyelitis?

Answer 2

Typically affects long weight-bearing bones

Joint involvement is usually monoarticular

Question 3

What are the two general types of osteomyelitis?

Answer 3

1. Acute

2. Chronic (recurring)

Question 4

What is the most common cause of osteomyelitis? What is one surgical exception?

Answer 4

S. aureus, less commonly gram negatives, mycobacteria, or fungi

Surgically: coagulase negative Staphs can infect in joint replacement

Question 5

What is the biggest contributor to the pathogenesis of osteomyelitis? What is most serious in children?

Answer 5

Toxin or proteolytic enzyme-mediated degradiation of cartilage, especially around the epiphyseal plate / metaphysis (common origin of infection) which can stunt growth / lead to longbone asymmetry

Question 6

What is typically done to identify the affected bone and determine antibiotic course?

Answer 6

X-ray or NMR to visualize the bone prior to invasive sampling prior to anti-microbial susceptibility testing

Blood culture is frequently positive for infected organism as well

Question 7

What condition can result from an infecting organism spreading from bone to adjacent joint?

Answer 7

Septic arthritis

Question 8

What is a sequestrum?

Answer 8

An area of necrosis and separation of dead bone fragments due to poor blood supply and infection

Question 9

What is an involucrum?

Answer 9

An ectopic bone formation, especially around necrotic areas (periosteal thickening)

Question 10

What joint sites most often affect infants and adults?

Answer 10

Infants - pain around knee

Adults - pain in back (thoracolumbar spine)

Question 11

What types of adults get osteomyelitis commonly?

Answer 11

History of recent UTI, immunocompromised

Question 12

What are three main causes of osteomyelitis?

Answer 12

Recent trauma (hematologic spread) - common in young people
Surgery (local spread)
Diabetes - poor vasculature / insufficiency / necrosis

Question 13

What are the treatments for acute osteomyelitis?

Answer 13

1. IV / oral antibiotics

2. Surgery to debride dead bone

Question 14

What time scale defines chronic osteomyelitis, and what is the main difference from acute?

Answer 14

> 3 months duration, often following acute OM

Main difference: chronic can be polymicrobial (acute is usually monomicrobial)

Question 15

Why is chronic OM so difficult to treat? How is it treated?

Answer 15

Loss of vascularity to necrotic bone can make antibiotics ineffective

Treatment: need longterm antibiotics after debridement surgery + bone grafting

Question 16

What is septic arthritis and what usually causes it?

Answer 16

Active and overt infection of joint, usually caused by direct inoculation due to trauma, or by movement from bone nearby

Question 17

What are the most common joints affected by septic arthritis?

Answer 17

Knee and ankle joints (usually mono-articular disease)

Question 18

What are the major risk factors for septic arthritis?

Answer 18

Poor health indicators (low SES, diabetes, IDU)
rheumatoid arthritis
joint prostheses / history of steroid injections to joints

Question 19

What is the usual causative agent of septic arthritis? Neonates and young adults?

Answer 19

S. aureus,

Neonates: used to be alot by H. influenzae but not anymore due to vaccine

Young adults: N. gonorrhoeae

Question 20

What causes joint damage in septic arthritis?

Answer 20

Toxins and proteolytic enzymes secreted by bacteria growing in synovial fluid, degrading cartilage

Also the host’s inflammatory response to the infection

Question 21

In what cases can mycobacteria, parasites and fungi cause septic arthritis?

Answer 21

Immunosuppressed patients / very aged population

Question 22

How is septic arthritis detected?

Answer 22

Usually via MRI / X-rays to visualize the joint + Abx susceptibility testing, but blood cultures are usually positive for S. aureus

Question 23

What is one additional treatment of joint needed in septic arthritis?

Answer 23

Drainage of pus from the joint

Question 24

What is reactive arthritis (ReA) and its two forms?

Answer 24

Inflammation of a joint frequently accompanied by one or more extra-articular manifestations following GI or UG infections

1. Acute: within 2-4 weeks of GI or UG infection
2. Chronic: Can cycle between active arthritis and quiescent (half of patients)

Question 25

How many joints are affected in reactive arthritis and where are they?

Answer 25

Four or fewer typically, asymmetrically affected

Joints of lower limbs and back are most common

Question 26

What are some extra-articular manifestions of reactive arthritis?

Answer 26

Anterior uveitis, conjunctivitis, keratoderm blennorrhagicum (psoriasis-like, often on feet)

I.e. Juvenile idiopathic arthritis

Question 27

What are common urogenital infections triggering reactive arthritis?

Answer 27

Chlamydia trachomatis, N. gonorrhoeae

Question 28

What are common GI infections triggering reactive arthritis?

Answer 28

Often Salmonella, Shigella, Campylobacter, Yersinia, Klebsiella

Question 29

How can a respiratory pathogen be involved with ReA?

Answer 29

Chlamydia pneumonia is implicated

Question 30

How does Chlamydia differ in its pathogenesis of ReA vs other organisms?

Answer 30

All are carried by mononuclear cells

Chylamydia is believed to be alive and viable once they reach the joint, causing massive inflammatory response, but cannot be cultured

Salmonella and other GI pathogens are assumed to be dead, and the immune system is reacting to dead pathogen in a sterile site (joint)

Question 31

Why is it difficult to detect the causative agent of ReA? How is it usually done?

Answer 31

Cannot be cultured because it is dead, antibody titers are usually very low to causative organisms

For Chlamydia, PCR of synovial tissue must be used as direct fluorescence assay is often negative

For Salmonella / GI, PCR with Salmonella is insufficient, DFA must be used

Question 32

Why are antibiotics a questionable treatment for ReA?

Answer 32

Salmonella-related - bacteria are probably dead already

Chlamydia - may be alive in tissues but just unculturable. Antibiotics might not penetrate into joints

Question 33

What is the standard treatment for ReA?

Answer 33

Use of NSAIDS, corticosteroids, and TNF blockers

Question 34

What is one thing to always remember when ruling out ReA?

Answer 34

Chlamydia is often asymptomatic, so the patient simply saying they haven’t had urethritis doesn’t rule it out