Bone and joint infections Flashcards
What main pathogen causes septic arthritis (SA)?
Staphylococcus aureus
How might septic arthritis present?
- Usually occurs in the really young (infants) or elderly (after a joint replacement)
- 60-80% of cases are mild
- 1/3 will have a fever (>39 degrees)
- limitation of joint movement
- swelling
- synovial effusion
Which joint is most commonly affected by septic arthritis?
knee
What are the 5 potential routes of infection in SA?
- Haematogenous (most common route in children)
- From adjacent osteomyelitis
- From local soft tissue infections (cellulitis)
- Penetrating trauma (open fractures)
- Iatrogenic
Which gram positive and gram negative organisms are associated with SA?
Gram +ve cocci:
- staphylococcus aureus
- streptococci –> pyogenes, pneumoniae + group B
Gram +ve bacilli:
- clostridium sp
Gram -ve cocci:
- Neisseria gonorrhea
Gram -ve bacilli:
- escherichia coli
- pseudomonas aeruginoa
- eikenella corrodens
- haemophilus influenza
List some pre-disposing factors for S.
pre-existing arthritis trauma other disease other infection previous damage to joint untreated systemic infection conditions that affect blood supply
How can SA be diagnosed (apart from clinical presentation)?
Lab findings:
- elevated ESR or CRP
- neutrophilia (usually see immature neutrophils without segmented nuclei)
- SF examination
1. turbid or purulent
2. leukocytes, predominantly neutrophils
3. gram stain positive
4. <25 mg/dL of glucose - blood culture will be positive in 1/3-2/3 of pts
Radiology:
- soft tissue swelling
- joint capsule distension
- destructive changes seen after at least 2 weeks
- mycobacterial infection (joint space narrowing, effusions, erosions, cyst formation)
How is SA managed?
First, DDX: acute RA, gout, chondrocalcinosis
- drainage
- antibiotics (depends on gram stain etc)
- -> given as IV for 3-4 weeks (start with broad spectrum)
What is reactive arthritis? What is the biggest pre-disposing factor?
Sterile inflammatory process also called Reiter’s arthritis
Most common in people where HLA-B27 is present
What is reactive arthritis usually preceded by? How does it present?
Preceded by enteric infection (salmonella, campylobacter etc) or genitourinary infection (Chlamydia trachomatis) Usually presents with extra-articular symptoms: - eye inflammation - lower back pain - diarrhoea - scaly skin patches on genitalia - swelling in knee, heel or ball of foot - flaky skin patches on sole - sausage toes
How is the spread of osteomyelitis different in children and adults?
Children: haematogenous spread
- more at risk than adults as epiphyseal growth plates are open and blood supply is tortuous and sluggish
Adults: contiguous spread from an infected focus, or direct trauma, or spinal osteomyelitis (if >45)
What are the consequences of osteomyelitis?
microabscess forms in vascular loop
cortex undergoes necrosis = sequestra
- osteoblasts are then activated
- reactive woven bone covers the sequestra = involucrum
List some predisposing factors for osteomyelitis.
- impairment of immune surveillance
- malnutrition
- extremes of age - impairment of local vascular supply
- DM
- venous stasis
- radiation fibrosis
- sickle cell disease
What are the clinical features of osteomyelitis?
- haematogenous long bone
- haematogenous vertebral + chronic
- general
- haematogenous long bone
- abrupt onset of high fever
- decreased limb movement + adjacent joint effusion - Haematogenous vertebral + chronic
- insidious onset, vague complaints over 1-3 months - General
- local, non-specific pain
- elevated neutrophil count
- elevated ESR
*also brodies abscess - where bone has eroded away; lytic lesions surrounded by thick dense reactive sclerosis that fades into surrounding tissue
What is the result of chronic osteomyelitis? What are some complications that can arise?
Result: local bone loss and persistent drainage through sinus
Complications: squamous cell carcinoma and amyloidosis (rare)
