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Introduction
  • Epidemiology 
    • incidence
      • 1 in 5000 children younger than 13 years old
    • demographics
      • mean age 6.6 years
      • 2.5 times more common in boys
      • more common in the first decade of life due to the rich metaphyseal blood supply and immature immune system
      • not uncommon in healthy children
    • location
      • typically metaphyseal via hematogenous seeding
    • risk factors
      • diabetes mellitus
      • hemoglobinopathy
      • rheumatoid arthritis
      • chronic renal disease
      • immune compromise
      • varicella infection
  • Pathophysiology
    • mechanism
      • local trauma and bacteremia lead to increased susceptibility to bacterial seeding
    • microbiology
      • Staph aureus
        • is the most common organism in all children
        • strains of community-acquired (CA) MRSA have genes encoding for Panton-Valentine leukocidin (PVL) cytotoxin
        • PVL-positive strains are more associated with complex infections, multifocal infections, prolonged fever, abscess, DVT, and sepsis
        • MRSA is associated with increased risk of DVT and septic emboli
      • Group B Strep
        • is most common organism in neonates
      • Kingella kingae
        • becoming more common in younger age groups
      • Pseudomonas
        • is associated with direct puncture wounds to the foot 
      • H. influenza
        • has become much less common with the advent of the Haemophilus influenza vaccine
      • Mycobacteria tuberculosis 
        • children are more likely to have extrapulmonary involvement
        • biopsy with stains and culture for acid-fast bacilli is diagnostic
      • Salmonella
        • more common in sickle cell patients
    • pathoanatomy
      • acute osteomyelitis
        • most cases are hematogenous
        • initial bacteremia may occur from a skin lesion, infection, or even trauma from tooth brushing
        • microscopic activity
          • sluggish blood flow in metaphyseal capillaries due to sharp turns results in venous sinusoids which give bacteria time to lodge in this region
          • the low pH and low oxygen tension around the growth plate assist in the bacterial growth
          • infection occurs after the local bone defenses have been overwhelmed by bacteria
          • spread through bone occurs via Haversian and Volkmann canal systems
          • purulence develops in conjunction with osteoblast necrosis, osteoclast activation, the release of inflammatory mediators, and blood vessel thrombosis
        • macroscopic activity
          • a subperiosteal abscess develops when the purulence breaks through the metaphyseal cortex
          • septic arthritis develops when the purulence breaks through an intra-articular metaphyseal cortex (hip, shoulder, elbow, and ankle) 
        • Infants <1 year of age can have infection spread across the growth plate via capillaries causing osteomyelitis in the epiphysis and septic arthritis
      • chronic osteomyelitis
        • periosteal elevation deprives the underlying cortical bone of blood supply leading to necrotic bone (sequestrum)
        • an outer layer of new bone is formed by the periosteum (involucrum)
        • chronic abscesses may become surrounded by sclerotic bone and fibrous tissue leading to a Brodie's abscess 
    • definitions
      • involucrum 
        • a layer of new bone growth outside existing bone seen in osteomyelitis 
      • sequestrum
        • the necrotic bone which has become walled off from its blood supply and can present as a nidus for chronic osteomyelitis 
  • Prognosis
    • mortality has decreased from 50% to <1% due to new antibiotic treatment
Classification
  • Acute osteomyelitis
    • see pathoanatomy above
  • Subacute osteomyelitis
    • uncommon infection with bone pain and radiographic changes without systemic symptoms  
    • increased host resistance, decreased organism virulence, and/or prior antibiotic exposure
    • radiographic classification
      • types IA and IB show lucency
      • type II is a metaphyseal lesion with cortical bone loss
      • type III is a diaphyseal lesion
      • type IV shows onion skinning
      • type V is an epiphyseal lesion
      • type VI is a spinal lesion
  • Chronic osteomyelitis
    • see pathoanatomy above
Presentation
  • History
    • limb pain
    • recent local infection or trauma
    • obtain immunization history regarding H. influenza
    • ask about prior antibiotic use, as it may mask symptoms
  • Symptoms
    • limp or refusal to bear weight
    • generally not toxic appearing
    • +/- fever
  • Physical exam
    • inspection & palpation
      • edematous, warm, swollen, tender limb
      • evaluate for point tenderness in pelvis, spine, or limbs
    • range of motion
      • restricted motion due to pain
Imaging
  • Radiographs  
    • recommended views
      • obtain AP and lateral of the suspected area
    • findings
      • early films may be normal or show loss of soft tissue planes and soft tissue edema  
      • new periosteal bone formation (5-7 days)
      • osteolysis (10-14 days)  
      • late films (1-2 weeks) show metaphyseal rarefaction (reduction in metaphyseal bone density) or possible abscess
  • CT
    • indication
      • more helpful later in the disease course to demonstrate bone changes or abscesses
  • MRI  
    • detects abscesses and early marrow and soft tissue edema
    • indications
      • can assist with decision making when a poor clinical response to antibiotics or surgical drainage considered  
    • views
      • T1 signal decreased
      • T1 with gadolinium signal increased
      • T2 signal increased
    • 88% to 100% sensitivity, sensitivity increased by Gadolinium contrast
  • Bone scan
    • indications
      • nondiagnostic x-ray 
      • localize pathology in infant or toddler with non-focal exam
      • technetium-99m can localize the focus of infection and show a multifocal infection
      • 92% sensitivity
      • a cold bone scan may be associated with more aggressive infections
Studies
  • Serum labs
    • WBC count
      • elevated in 25% of patients and correlates poorly with treatment response 
    • C-reactive protein
      • elevated in 98% of patients with acute hematogenous osteomyelitis
      • becomes elevated within 6 hours
      • most sensitive to monitor therapeutic response
      • declines rapidly as the clinical picture improves 
      • CRP is the best indicator of early treatment success and normalizes within a week 
        • failure of the C-reactive protein to decline after 48 to 72 hours of treatment should indicate that treatment may need to be altered 
    • ESR
      • elevated in 90% of patients with osteomyelitis
      • rises rapidly and peaks in three to five days, but declines too slowly to guide treatment
      • less reliable in neonates and sickle cell patients
    • plasma procalcitonin
      • new serologic test that rises rapidly with a bacterial infection, but remains low in viral infections and other inflammatory situations
      • elevated in 58% of pediatric osteomyelitis cases  
    • bone aspiration  
      • helps establish a definitive diagnosis
      • 50% to 85% of affected patients have positive cultures
    • blood culture
      • is positive only 30% to 50% of the time and will likely be negative soon after antibiotics are administered, even if treatment is not progressing satisfactorily
  • Aspiration
    • assists in diagnosis and management
      • helps guide antibiotic selection when organism identified (50% of the time)
      • proceed with surgical drainage if pus is aspirated 
    • technique
      • large bore needle utilized to aspirate the subperiosteal and intraosseous spaces under fluoroscopic or CT-guidance
      • start antibiotics after aspiration
  • Biopsy and culture
    • consider when diagnosis not clear (i.e. subacute osteomyelitis) and need to rule out malignancy 
Treatment
  • Nonoperative treatment
    • antibiotic therapy alone
      • indications
        • early disease, no abscess
        • surgery is not indicated if clinical improvement obtained within 48 hours
      • antibiotics
        • begin with empiric therapy
          • generally, nafcillin or oxacillin, unless high local prevalence of  MRSA (then use clindamycin or vancomycin)
          • mechanism of action for vancomycin involves binding to the D-Ala D-Ala moiety in bacterial cell walls
          • if gram stain shows gram-negative bacilli - add a third generation cephalosporin
        • convert to organism-specific antibiotics if organism identified
          • mycobacterium tuberculosis
          • treatment for initial 1 year is multiagent antibiotics and rarely surgical debridement due to risk of chronic sinus formation
        • duration
          • typically treat with IV antibiotics for four to six weeks
            • controversial duration
  • Operative treatment
    • surgical drainage, debridement, and antibiotic therapy
      • indications
        • deep or subperiosteal abscess   
        • failure to respond to antibiotics   
        • chronic infection
        • contraindications
          • hemodynamic instability, as patients should be stabilized first - however sometimes operative treatment of the underlying infection helps stabilize the patient
        • example of institution algorithm treatment pathway 
      • technique
        • evacuate all purulence, debride devitalized tissue, and drill as needed into intraosseous collections
        • remove the sequestrum in chronic cases
        • send tissue for culture and pathology to rule out neoplasm
        • close wound over drains or pack and return to OR in two to three days
        • follow with IV antibiotics and consider changing to PO antibiotics when ESR or CRP has returned to normal
Complications
  • DVT
    • is an infrequent complication in children    
      • risk factors
        • CRP > 6
        • surgical treatment
        • age > 8-years-old
        • MRSA 
  • Meningitis
  • Chronic osteomyelitis
  • Septic arthritis
    • bones with intra-articular metaphysis are at risk
    • hip, shoulder, elbow, ankle
  • Growth disturbances and limb-length discrepancies from growth plate involvement 
    • may result in gait abnormalities
  • Pathologic fractures
 

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Questions (27)
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(OBQ06.167) A 7-year-old boy presents with right elbow and left wrist swelling for the past 3 months. Clinical photos of the elbow and wrist are shown in Figures A and B, and radiographs in Figures C and D. His parents report that he has had night sweats and a loss of appetite, and physical examination is notable for bilateral axillary lymphadenopathy. Leukocyte count is normal but the ESR is elevated. The child undergoes a diagnostic biopsy shown in Figure E. What is the most likely diagnosis? Review Topic

QID: 353
FIGURES:
1

Multicentric giant cell tumor

7%

(81/1126)

2

Letterer-Siwe disease

6%

(65/1126)

3

Polyostotic mycobacterial infection

73%

(827/1126)

4

Hand-Schuller-Christian disease

11%

(120/1126)

5

Metastatic rhabdomyosarcoma

2%

(27/1126)

Select Answer to see Preferred Response

PREFERRED RESPONSE 3

(OBQ08.50) Sequestrum is defined as which of the following? Review Topic

QID: 436
1

reactive bone in acute osteomyelitis

2%

(32/1982)

2

reactive bone in chronic osteomyelitis

8%

(161/1982)

3

necrotic bone providing a nidus for infection in chronic osteomyelitis

88%

(1749/1982)

4

healthy bone adjacent to chronic osteomyelitis

1%

(28/1982)

5

healthy bone adjacent to acute osteomyelitis

0%

(7/1982)

Select Answer to see Preferred Response

PREFERRED RESPONSE 3
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(OBQ05.149) An 8-year-old boy twists his right leg while playing soccer 6 days ago. Initial radiographs on the day of injury were negative, and the patient was placed into a knee immobilizer by his pediatrician. Despite being non-weightbearing on crutches, his pain has continued to worsen, and he presented to the ER with a low grade fever and irratibility. A current bone scan and MRI is shown in Figure A and B. Examination shows no knee effusion but there is tenderness to palpation over the proximal tibia. Current WBC and ESR is normal and CRP is elevated. What is the next most appropriate initial step in management? Review Topic

QID: 1035
FIGURES:
1

Long leg cast and continued non-weightbearing to the extremity

8%

(51/637)

2

Chest CT scan and referral to an orthopaedic oncologist

21%

(131/637)

3

Neoadjuvant chemotherapy followed by surgical resection

1%

(9/637)

4

Percutaneous biopsy with culture and antibiotics

67%

(427/637)

5

Percutaneous pinning of the physeal fracture and long leg cast placement

3%

(16/637)

Select Answer to see Preferred Response

PREFERRED RESPONSE 4

(OBQ08.97) A pediatric patient has just been diagnosed with osteomyelitis of the femur. All of the following are risk factors for the development of deep venous thrombosis EXCEPT? Review Topic

QID: 483
1

Surgical treatment of osteomyelitis

10%

(128/1266)

2

CRP > 6

9%

(114/1266)

3

Methicillin-resistant staphylococcus aureus

18%

(225/1266)

4

Fever of greater than 38.5 degrees Celsius

42%

(528/1266)

5

Patient age greater than 8-years-old

21%

(265/1266)

Select Answer to see Preferred Response

PREFERRED RESPONSE 4

(OBQ06.80) A 10-year-old boy complains of two days of worsening right knee pain. He has been unable to ambulate on the leg since waking up this morning. He denies any recent trauma to the leg. Physical exam is notable for focal tenderness over the distal femur without a palpable fluid collection. His ESR is 68 mm/hr (normal <15) and CRP is 14 mg/dL (normal <1). His temperature is currently 101.2 degrees F. Radiographs are provided in Figures A and B. An aspiration of the knee yielding 7 mL of straw colored fluid reveals 1700 nucleated cells per mL, and no organisms on gram stain. Which of the following is the most appropriate next step? Review Topic

QID: 191
FIGURES:
1

MRI of the knee

73%

(942/1296)

2

Observation with follow-up ESR, CRP, and repeat aspiration in 1-2 days

9%

(122/1296)

3

Oral cephalosporin and follow-up in 10 days

1%

(16/1296)

4

Surgical arthrotomy, debridement, and irrigation procedure

15%

(193/1296)

5

Chest, abdomen, and pelvis CT

1%

(9/1296)

Select Answer to see Preferred Response

PREFERRED RESPONSE 1

(OBQ07.232) An afebrile 8-year-old Ethiopian girl presented with a limp. Two years earlier, she had had mild trauma followed by a “bone infection” and had received short courses of oral antibiotics. Examination revealed a small, pus-secreting wound on the anterior aspect of her left thigh. Her blood count was normal, but her erythrocyte sedimentation rate was 48 mm. A radiograph and computed tomographic scan are shown in Figure A and B respectively. What do the blue arrowheads identify in both of these imaging studies? Review Topic

QID: 893
FIGURES:
1

Bone infarct

1%

(8/1098)

2

Sequestrum

24%

(269/1098)

3

Involucrum

74%

(810/1098)

4

Osteosarcoma

0%

(4/1098)

5

Hematoma

0%

(2/1098)

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PREFERRED RESPONSE 3

(OBQ07.151) In which of the following patients with osteomyelitis of the tibia is surgical debridement the next best step in treatment? Review Topic

QID: 812
1

A 9-year old girl with new-onset pain and fever

0%

(0/635)

2

A 7-year-old lethargic boy with a CRP of 20 mg/L that does not decline after a week of nafcillin and vancomycin

89%

(562/635)

3

A 7-year-old girl with three days of pain, fever, and a WBC of 21,000/mm3 who presents to the ER

3%

(22/635)

4

An 8-year-old boy whose pain and fever have decreased after 24 hours of ampicillin

0%

(2/635)

5

An 8-year old lethargic girl with a WBC of 21,000/mm3 and a CRP of 9 after 24 hours of gentamicin

7%

(46/635)

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PREFERRED RESPONSE 2

(OBQ11.29) A 9-year-old boy is being treated for acute hematogenous osteomyelitis of the distal tibia with appropriate IV antibiotic therapy. After three days of treatment, he fails to show any clinical improvement. Advanced imaging is obtained and reveals a 1.5x1.5cm abscess in the distal tibia. The patient subsequently undergoes formal open surgical debridement, without complications. Following surgery, serial evaluations of which of the following studies is the most expeditious method to determine the early success of treatment? Review Topic

QID: 3452
1

White blood cell count

2%

(49/2544)

2

MRI

1%

(15/2544)

3

Erythrocyte sedimentation rate

3%

(69/2544)

4

C-reactive protein

94%

(2389/2544)

5

Radiographs

0%

(12/2544)

Select Answer to see Preferred Response

PREFERRED RESPONSE 4

(OBQ06.131) A 14-year-old boy presents 6 months after spraining his right ankle. Radiographs obtained at the time of injury are shown in Figure A. He returns to clinic with persistent right ankle pain. The patient denies fevers, and has an ESR of 35 mm/h (nl 0-20). CRP and WBC are normal. Current radiographs and MRI images are shown in Figures B, C, and D. What is the next most appropriate step in management? Review Topic

QID: 317
FIGURES:
1

Casting of the ankle and observation

5%

(62/1203)

2

CT of the tibia

2%

(26/1203)

3

Oral antibiotic therapy, with outpatient follow-up in 6 weeks

2%

(19/1203)

4

Biopsy and culture of the tibial lesion

89%

(1070/1203)

5

Urgent ankle arthrotomy

2%

(20/1203)

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PREFERRED RESPONSE 4

(OBQ05.177) A 13-year-old girl reported left ankle pain after falling while playing soccer 3 weeks ago. The pain initially improved, but for the past 10 days she has had increased pain. She reports a decreased appetite. Her temperature is 38.9 degrees celsius and her white blood cell count is normal. The ESR and CRP are elevated and blood cultures have been drawn and are pending. Current ankle radiographs are normal and T1 and T2 MRI images are shown in Figures A and B, respectively. What is the most appropriate next step in treatment? Review Topic

QID: 1063
FIGURES:
1

Discharge home on non-steroidal anti-inflammatory drug (NSAID) and short leg non-weightbearing cast

5%

(27/563)

2

Discharge home on oral antibiotics with serial ESR and CRP in an outpatient setting

2%

(10/563)

3

Admit to hospital for percutaneous aspiration for culture and intravenous antibiotics with serial ESR and CRP

84%

(471/563)

4

Admit to hospital for percutaneous biopsy and referral to orthopaedic oncologist

6%

(31/563)

5

Admit to hospital for percutaneous screw fixation of distal tibia fracture

4%

(22/563)

Select Answer to see Preferred Response

PREFERRED RESPONSE 3

(OBQ07.184) A 7-year-old boy complains of worsening left knee pain over the last 2 weeks. He has been unable to bear weight through the left lower extremity for the past 24 hours. The knee and lower leg are warm and tender to palpation. Current temperature is 100.9 degrees Fahrenheit, and CRP is 11 mg/dL (nml <1). A radiograph is provided in Figure A. A joint aspiration yields 2 mL's of synovial fluid demonstrating a cell count of 2,500 and no organisms on gram stain. Which of the following is the most appropriate next step in management? Review Topic

QID: 845
FIGURES:
1

Repeat aspiration of the left knee

8%

(139/1700)

2

Observation with repeat radiographs in one week

10%

(164/1700)

3

Magnetic resonance imaging (MRI)

70%

(1188/1700)

4

Begin intravenous broad-spectrum antibiotics and obtain an infectiouse disease consult

7%

(124/1700)

5

Exploratory surgical arthrotomy

5%

(81/1700)

Select Answer to see Preferred Response

PREFERRED RESPONSE 3

(OBQ06.216) Septic arthritis in pediatric patients may occur secondary to direct intra-articular spread from metaphyseal osteomyelitis. This can occur in all the following joints EXCEPT? Review Topic

QID: 227
1

Hip

8%

(118/1506)

2

Ankle

17%

(254/1506)

3

Shoulder

10%

(147/1506)

4

Elbow

15%

(229/1506)

5

Knee

50%

(750/1506)

Select Answer to see Preferred Response

PREFERRED RESPONSE 5

(OBQ09.161) A 6 year-old boy develops tenderness at the right heel and avoids putting weight on the right extremity after stepping on a nail 2 weeks ago while wearing tennis shoes. His mother notes that he has had a fever of 39.0. Calcaneal osteomyelitis caused by a puncture wound has an increased rate of which of the following compared to hematogenous osteomyelitis? Review Topic

QID: 2974
1

Presence of Group A Streptococcus infection

3%

(91/2772)

2

Presence of Coliforms infection

2%

(53/2772)

3

Presence of Haemophilus infection

1%

(15/2772)

4

Presence of Pseudomonas infection

92%

(2542/2772)

5

Presence of Group B Streptococcus infection

2%

(62/2772)

Select Answer to see Preferred Response

PREFERRED RESPONSE 4
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