Osteoarticular Infections

Question 1

What is the incidence of osteomyelitis

Answer 1

1-13 / 100 000

2.38/1000 admissions

Question 2

What are the definitions of acute OM and chronic OM

Answer 2

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)

Question 3

What are the common organisms for OM

Answer 3

S. Aureus
Kingella kingae - 12% in infants, 6 in older children
S. Pneumonia
S. Pyogenes

Question 4

Where does OM typically occur?

Answer 4

Metaphysis of any long tubular bone because of presence of nutrient artery end emptying into venous sinusoids

Question 5

Why is SA found more commonly with OM in younger children?

Answer 5

Because of trnasphyseal vessels prior to growth plate closure, and the joint capsule extends beyond epiphyseal plate allowing easier spread from metaphysis

Question 6

What are clinical manifestations of OM or SA

Answer 6

Pseudoparalysis in affected area, limping
Pain
Swelling, erythema or fluctuance if abscess present = may look like overlying cellulitis

Question 7

What are features of SA alone

Answer 7

Specific swelling of joint
Joint effusion
Pain on movement of isolated joint

Question 8

What is included in the differential diagnosis of OM/SA and what are differentiating features?

Answer 8

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)

Question 9

What lab findings are suggestive of OM

Answer 9

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

Question 10

Why is CRP better than ESR in OM

Answer 10

T1/2 - 8h - more sensitive (95%), decreases faster with therapy, normalizes by 10+/-0.5 days

Question 11

When can you see x-ray changes with OM/SA? What are classic changes?

Answer 11

7-21d after onset of infection

• lyric lesions
• localized periosteal lifting

Question 12

What is the earliest finding of OM on imaging

Answer 12

Bone marrow oedema

Question 13

Is an MRI needed if there is supporting lab parameters and a positive clinical response to empiric therapy for OM

Answer 13

No

Question 14

What is the sensitivity of bone scans?

What are FN and FP causes

Answer 14

80%

May be false negative if early in course, or if bone infarction

May be false positive with fractures, tumours f

Question 15

How can SA be diagnosed ?

Answer 15

Optimal: joint aspiration
Other: U/S of joint, MRI

Question 16

How common is it for blood, bone and joint fluid cultures to test negative

Answer 16

30-90%

Question 17

What is the dominant pathogen in children <4yo presenting with SA +/- OM

Answer 17

K. Kingae

Question 18

What other causes of OM/SA need to be considered in neonates, immunocompromised, or unique environmental exposures?

Answer 18

Entereobacteriaceae, fungi,

SCD - Salmonella

Question 19

If blood cultures are positive - when should they be repeated?

Answer 19

In 48h to ensure clearance

Question 20

When should surgery be considered in OM

Answer 20

If fails empiric antibiotics
If joint fluid collections
If soft tissue, periosteal abscess

Question 21

What is the empiric antibiotic choice for OM/SA

Answer 21

1st gen cephalosporin - cefazolin - covers MSSA and K kingae
- does: 100-150mg/kg/d q6-8h IV

Question 22

What is K Kingae resistant to?

Answer 22

Clindamycin
Vancomycin
Cloxacillin

Question 23

When should H influenza be considered as a pathogen? What antibiotic coverage should be used?

Answer 23

If unimmunised, or living in areas with invasive H. Flu is more common than usual

Cefuroxim 150mg/kg/d divide q8H IV

Question 24

If the isolate is MSSA what antibiotic can therapy be narrowed to?

Answer 24

Cloxacillin 150-200mg/kg/d IV divided q6h

Question 25

How long does OM/SA need to be treated? When can step down to oral therapy occur?

Answer 25

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)

Question 26

Why can we step down so early to PO in OM/SA if we require 6 weeks of therapy?

Answer 26

Because failure rates between IV and PO are the same (5-6% versus 4-5%)

Fewer complications than with prolonged IV courses

Question 27

What are contraindications to oral therapy?

Answer 27

Poor medication compliance or follow up
Malabsorption
Slow clinical resolution

Question 28

What are oral options for OM/SA due to MRSA

Answer 28

Clindamycin
Sentra
Linezolid

Question 29

What follow up is required for OM/SA

Answer 29

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