Bone Infections

Question 1

Routes of entry into bone:

Answer 1

1) hematogenous

2) contiguous focus

Question 2

Sequestra:

Answer 2

Large, de-vascularized fragments of bone

Question 3

Contiguous focus osteomyelitis risk factors:

Answer 3

Surgical interventions (i.e., orthopaedic surgery)
Diabetes or peripheral vascular disease
Trauma, including open fractures

Question 4

Hematogenous osteomyelitis:

Answer 4

Usually involves a single bone (tibia, femur, humerus).

Source of bacteremia is often not apparent, but there is frequently a history of blunt trauma.

Question 5

Hematogenous osteomyelitis causes:

Answer 5

95% caused by single pathogen

50% caused by S. aureus

Question 6

Hematogenous osteomyelitis signs/symptoms:

Answer 6

Fever, chills, malaise, irritability.
Restriction of movement.
Difficulty weight bearing or walking.
Local pain, tenderness, edema, erythema.

Question 7

Vertebral osteomyelitis:

Answer 7

Organisms reach vertebrae via spinal arteries.

Most often involves lumbar or thoracic spine.

Question 8

Vertebral osteomyelitis causes:

Answer 8

95% caused by a single pathogen
50% caused by S. aureus
Others: Viridans strep, enterococci, E. coli

Question 9

Vertebral osteomyelitis risk factors:

Answer 9

Age >50
Sickle cell disease
Diabetes mellitus
Hemodialysis
Endocarditis
Injection drug use
Nosocomial bacteremia
Long-term vascular access
Urinary tract infections 
Minor trauma or fall

Question 10

Vertebral osteomyelitis signs and symptoms:

Answer 10

Usually insidious in onset, and then subacute or chronic.
Fevers and rigors may present weeks before back pain.
Back or neck pain with percussion tenderness.

Question 11

Vertebral osteomyelitis diagnosis:

Answer 11

Positive blood culture in 20-50%
Plain films show irregular erosions in end plates of adjacent vertebral bodies and narrowing of intervening disk space (virtually diagnostic)
CT or MRI may show epidural, paraspinal, retropharyngeal, mediastinal, retroperitoneal, or psoas abscess originating in the spine.

Question 12

Contiguous focus osteomyelitis without vascular insufficiency:

Answer 12

Related to penetrating injuries or surgery, or by direct extension from adjacent soft tissues.

Question 13

Contiguous focus osteomyelitis with vascular insufficiency:

Answer 13

Usually involves the small bones of the foot. Poor tissue perfusion impairs wound healing and inflammatory responses.

Question 14

Contiguous focus osteomyelitis:

Answer 14

S. aureus is the predominant pathogen.
30% to 50% are polymicrobial.
May be caused by aerobic gram-negatives, anaerobes (bites, deep punctures), Pseudomonas.

Question 15

Osteomyelitis lab findings:

Answer 15

Blood cultures are useful in acute osteomyelitis.
ESR, CRP are elevated in most cases of active infection.
CRP can be measured to assess treatment efficacy.

Question 16

Osteomyelitis diagnosis:

Answer 16

Samples for culture should be obtained BEFORE INITIATION OF ANTIMICROBIAL THERAPY.

Question 17

Osteomyelitis radiography:

Answer 17

Lytic changes are detected only after 2 to 6 weeks, once 50-75% of the bone density has been lost.
Sensitivity 60%, specificity 70%.

Question 18

Osteomyelitis radionuclide scans:

Answer 18

Three phase bone scan.
Osteomyelitis shows increased uptake in all 3 phases.
Soft tissue infections show increased uptake in only 2 phases.

Question 19

Osteomyelitis CT:

Answer 19

Limited role in acute osteomyelitis.
CT superior to MRI for detection of sequestra, cortical destruction, soft tissue abscesses, and periosteal new bone formation.

Question 20

Osteomyelitis MRI:

Answer 20

MRI is the most sensitive and specific test for osteomyelitis.
It can detect a bone marrow signal change, cortical bone interruption, and soft tissue edema surrounding involved bone.
Sensitivity 96%, specificity 87%.

Question 21

Osteomyelitis treatment principles:

Answer 21

Obtain cultures before starting treatment
Use bactericidal agents
Start with PARENTERAL therapy
Use high dose antibiotics
Empiric coverage for S. aureus is advisable
Treatment duration usually 4-6 weeks

Question 22

Streptococcal osteomyelitis treatment:

Answer 22

Penicillin G

Question 23

Staphylococcal osteomyelitis treatment:

Answer 23

Nafcillin or oxacillin

Question 24

MRSA osteomyelitis treatment:

Answer 24

Vancomycin (or linezolid, daptomycin)

Question 25

Gram-negative osteomyelitis treatment:

Answer 25

Ampicillin, cefazolin, ceftriaxone or a quinolone.

Question 26

P. aeruginosa osteomyelitis treatment:

Answer 26

Aminoglycoside plus a beta-lactam or quinolone.

Question 27

Vertebral osteomyelitis surgery indications:

Answer 27

Spinal instability
New or progressive neurologic deficits
Large soft tissue abscesses
Failure of medical therapy

Question 28

Treatment of chronic osteomyelitis:

Answer 28

Combined surgical (debridement) and medical approach. After surgery, 4-6 weeks of parenteral therapy.

Question 29

Treatment of contiguous osteomyelitis with vascular insufficiency:

Answer 29

Revascularization of limb before debridement.

Prognosis is poor without removal of all infected bone.

Question 30

Skeletal tuberculosis:

Answer 30

Usually thoracic spine.
Usually accompanied by abnormal chest x-ray.
Histopathology shows necrotizing granulomas, but the infection is paucibacillary (so stains may be negative).