Osteoarticular Infections Flashcards
What is the incidence of osteomyelitis
1-13 / 100 000
2.38/1000 admissions
What are the definitions of acute OM and chronic OM
OM: inflammation of bone and bone marrow due to infection
Acute - symptoms up to 4weeks
Chronic - symptoms >4wks with a vascular bone (sequestrum) or surrounded by new bone (involucrum) is present (Brodies’ abscess)
What are the common organisms for OM
S. Aureus
Kingella kingae - 12% in infants, 6 in older children
S. Pneumonia
S. Pyogenes
Where does OM typically occur?
Metaphysis of any long tubular bone because of presence of nutrient artery end emptying into venous sinusoids
Why is SA found more commonly with OM in younger children?
Because of trnasphyseal vessels prior to growth plate closure, and the joint capsule extends beyond epiphyseal plate allowing easier spread from metaphysis
What are clinical manifestations of OM or SA
Pseudoparalysis in affected area, limping
Pain
Swelling, erythema or fluctuance if abscess present = may look like overlying cellulitis
What are features of SA alone
Specific swelling of joint
Joint effusion
Pain on movement of isolated joint
What is included in the differential diagnosis of OM/SA and what are differentiating features?
AO/SA - pseudoparalysis/limp, history of fevers, tenders at site, decreased ROM, swelling/erythema
Transient synovitis of hip - age 4-10y, hip pain, limp, low-grade fever, preceding URTI, CRP<20
Fracture/trauma - acute onset with activity, hematoma, swelling, no fever
Lyme arthritis - endemic area, mono arthritis, no constitutional symptoms, less painful, CRP<40, may have Baker’s cyst
Cellulitis - rapid development of swelling, redness, pain, erythema before pain, more extensive than one focal area, +/- lymphangitis
CRMO - insidious onset, low-grade fever and malaise and wt loss in 1/3, worse at night, unusual sites, intense sclerosis with healing, may have dermatological conditions (psoriasis, palmoplantar pustulosis)
Heme malignancy: systemic complaints, arthralia, myalgia, metaphyseal licences or periosteal reactions, no localized pain, may have mild synovitis or joint swelling
Bone neoplastic lesion - diaphysis or flat bones, gradual onset, pain at night, refusal to weight bear, may have palpable mass
JIA - gradual onset, >6wk, may have extraarticular symptoms, less severe symptoms
SLE - constitutional symptoms, cutaneous symptoms, usually milder arthritis, heme or urine abN
Reactive arthritis - usually large joints, 2-3 weeks after an infection (GI or GU), may have ocular and urinary sx
PSRA - usually polyarticular non-migratory, persistent or recurrent, 3-14d after strep infection, may have other post-strep manifestations (GN, vasculitis, ARF)
What lab findings are suggestive of OM
WBC - may be elevated
CRP - elevated (t1/2 8h)
Blood culture
Imaging: X-ray, U/S for effusions, MRI with gadolinium and bone marrow edema, bone scans
Why is CRP better than ESR in OM
T1/2 - 8h - more sensitive (95%), decreases faster with therapy, normalizes by 10+/-0.5 days
When can you see x-ray changes with OM/SA? What are classic changes?
7-21d after onset of infection
- lyric lesions
- localized periosteal lifting
What is the earliest finding of OM on imaging
Bone marrow oedema
Is an MRI needed if there is supporting lab parameters and a positive clinical response to empiric therapy for OM
No
What is the sensitivity of bone scans?
What are FN and FP causes
80%
May be false negative if early in course, or if bone infarction
May be false positive with fractures, tumours f
How can SA be diagnosed ?
Optimal: joint aspiration
Other: U/S of joint, MRI
How common is it for blood, bone and joint fluid cultures to test negative
30-90%
What is the dominant pathogen in children <4yo presenting with SA +/- OM
K. Kingae
What other causes of OM/SA need to be considered in neonates, immunocompromised, or unique environmental exposures?
Entereobacteriaceae, fungi,
SCD - Salmonella
If blood cultures are positive - when should they be repeated?
In 48h to ensure clearance
When should surgery be considered in OM
If fails empiric antibiotics
If joint fluid collections
If soft tissue, periosteal abscess
What is the empiric antibiotic choice for OM/SA
1st gen cephalosporin - cefazolin - covers MSSA and K kingae
- does: 100-150mg/kg/d q6-8h IV
What is K Kingae resistant to?
Clindamycin
Vancomycin
Cloxacillin
When should H influenza be considered as a pathogen? What antibiotic coverage should be used?
If unimmunised, or living in areas with invasive H. Flu is more common than usual
Cefuroxim 150mg/kg/d divide q8H IV
If the isolate is MSSA what antibiotic can therapy be narrowed to?
Cloxacillin 150-200mg/kg/d IV divided q6h
How long does OM/SA need to be treated? When can step down to oral therapy occur?
SA - 3-4 weeks (if hip involved 4-6 weeks total)
OM - 3-4 weeks total
Step down when clinically improved - including able to weight bear , decreased CRP (50% by day 4, or down to at least 20-30)
(usually 3-7d)
Why can we step down so early to PO in OM/SA if we require 6 weeks of therapy?
Because failure rates between IV and PO are the same (5-6% versus 4-5%)
Fewer complications than with prolonged IV courses
What are contraindications to oral therapy?
Poor medication compliance or follow up
Malabsorption
Slow clinical resolution
What are oral options for OM/SA due to MRSA
Clindamycin
Sentra
Linezolid
What follow up is required for OM/SA
A normal CRP
X-ray if growth plate was involved or if there was a large lyric lesion initially (look for sclerosis and healing)
Usually ortho follow up needed
