Bone and Joint Infection - Osteomyelitis, Septic Arthritis, and Reactive Arthritis Flashcards
What are the general characteristics of osteomyelitis?
Bacterial infection in bone, causing inflammatory bone destruction, necrosis, and ectopic overgrowth of bone
What bones / joints are typically affected in osteomyelitis?
Typically affects long weight-bearing bones
Joint involvement is usually monoarticular
What are the two general types of osteomyelitis?
- Acute
2. Chronic (recurring)
What is the most common cause of osteomyelitis? What is one surgical exception?
S. aureus, less commonly gram negatives, mycobacteria, or fungi
Surgically: coagulase negative Staphs can infect in joint replacement
What is the biggest contributor to the pathogenesis of osteomyelitis? What is most serious in children?
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
What is typically done to identify the affected bone and determine antibiotic course?
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
What condition can result from an infecting organism spreading from bone to adjacent joint?
Septic arthritis
What is a sequestrum?
An area of necrosis and separation of dead bone fragments due to poor blood supply and infection
What is an involucrum?
An ectopic bone formation, especially around necrotic areas (periosteal thickening)
What joint sites most often affect infants and adults?
Infants - pain around knee
Adults - pain in back (thoracolumbar spine)
What types of adults get osteomyelitis commonly?
History of recent UTI, immunocompromised
What are three main causes of osteomyelitis?
Recent trauma (hematologic spread) - common in young people
Surgery (local spread)
Diabetes - poor vasculature / insufficiency / necrosis
What are the treatments for acute osteomyelitis?
- IV / oral antibiotics
2. Surgery to debride dead bone
What time scale defines chronic osteomyelitis, and what is the main difference from acute?
> 3 months duration, often following acute OM
Main difference: chronic can be polymicrobial (acute is usually monomicrobial)
Why is chronic OM so difficult to treat? How is it treated?
Loss of vascularity to necrotic bone can make antibiotics ineffective
Treatment: need longterm antibiotics after debridement surgery + bone grafting
What is septic arthritis and what usually causes it?
Active and overt infection of joint, usually caused by direct inoculation due to trauma, or by movement from bone nearby
What are the most common joints affected by septic arthritis?
Knee and ankle joints (usually mono-articular disease)
What are the major risk factors for septic arthritis?
Poor health indicators (low SES, diabetes, IDU)
rheumatoid arthritis
joint prostheses / history of steroid injections to joints
What is the usual causative agent of septic arthritis? Neonates and young adults?
S. aureus,
Neonates: used to be alot by H. influenzae but not anymore due to vaccine
Young adults: N. gonorrhoeae
What causes joint damage in septic arthritis?
Toxins and proteolytic enzymes secreted by bacteria growing in synovial fluid, degrading cartilage
Also the host’s inflammatory response to the infection
In what cases can mycobacteria, parasites and fungi cause septic arthritis?
Immunosuppressed patients / very aged population
How is septic arthritis detected?
Usually via MRI / X-rays to visualize the joint + Abx susceptibility testing, but blood cultures are usually positive for S. aureus
What is one additional treatment of joint needed in septic arthritis?
Drainage of pus from the joint
What is reactive arthritis (ReA) and its two forms?
Inflammation of a joint frequently accompanied by one or more extra-articular manifestations following GI or UG infections
- Acute: within 2-4 weeks of GI or UG infection
- Chronic: Can cycle between active arthritis and quiescent (half of patients)
How many joints are affected in reactive arthritis and where are they?
Four or fewer typically, asymmetrically affected
Joints of lower limbs and back are most common
What are some extra-articular manifestions of reactive arthritis?
Anterior uveitis, conjunctivitis, keratoderm blennorrhagicum (psoriasis-like, often on feet)
I.e. Juvenile idiopathic arthritis
What are common urogenital infections triggering reactive arthritis?
Chlamydia trachomatis, N. gonorrhoeae
What are common GI infections triggering reactive arthritis?
Often Salmonella, Shigella, Campylobacter, Yersinia, Klebsiella
How can a respiratory pathogen be involved with ReA?
Chlamydia pneumonia is implicated
How does Chlamydia differ in its pathogenesis of ReA vs other organisms?
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)
Why is it difficult to detect the causative agent of ReA? How is it usually done?
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
Why are antibiotics a questionable treatment for ReA?
Salmonella-related - bacteria are probably dead already
Chlamydia - may be alive in tissues but just unculturable. Antibiotics might not penetrate into joints
What is the standard treatment for ReA?
Use of NSAIDS, corticosteroids, and TNF blockers
What is one thing to always remember when ruling out ReA?
Chlamydia is often asymptomatic, so the patient simply saying they haven’t had urethritis doesn’t rule it out
