Osteomyelitis Flashcards by Kathleen McKenzie

Osteomyelitis

- Define

Inflammation of bone that is almost always due to infection
MC bacterial but can be viral or fungal as well

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Three ways to classify osteomyelitis

timing
mechanism of injury
type of host response

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Osteomyelitis classification

- timing

Acute <2 weeks
Subacute 2-6 weeks
Chronic > 6 weeks

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Osteomyelitis classification

- Mech. of injury

Exogenous: originates from outside the body

- Hematogenous: originates from body itself

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Osteomyelitis classification

- host response

Pyogenic: produces pus from infecting org

- Non-pyogenic: no abscess or pus production

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Keys to clinical success

Early dx

- Appropriate surgical and antimicrobial treatment (may require multidisciplinary approach: ortho, ID, plastics)

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Three types of osteomyelitis studied

acute hematogenous
subacute hematogenous
chronic

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What is MC type of osteomyelitis

Acute Hematogenous

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Acute Hematogenous Osteomyelitis

- ages affected

MC <2 and 8-12
MC in males
can occur in adults

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Acute Hematogenous Osteomyelitis

- areas of bone effected

children: long bone metaphysis d/t bacteremia MC

- adults: vertebrae MC, also long bones, pelvis, clavicle

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Acute Hematogenous Osteomyelitis

- was is bacterial seeding associated with?

localized trauma
chronic illness
malnutrition
inadequate immune system

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Acute Hematogenous Osteomyelitis

- overview of patho in children

Metaphysis is rapidly growing and has a lot of vasculature
Bacterial seeding → inflammatory rxn, causing localized ischemic necrosis of bone and subsequent bone abscess formation
Abscess enlarges, causing intramedullary pressure, cortical ischemia and destruction.
The purulent infectious material can escape the cortex and enter the subperiosteal space → subperiosteal abscess

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Acute Hematogenous Osteomyelitis

- what happens if untreated?

extensive sequestra formation and chronic osteomyelitis

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Acute Hematogenous Osteomyelitis

- two major complications

Involcrum: thick sheath of periosteal new bone surrounding a sequestrum
Sequestrum:
- Devascularization of a portion of bone with necrosis and resorption of surrounding bone leaving a “floating” piece
- Acts as a reservoir for infection
- Avascular = not penetrated by abx, usually requires excision

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Acute Hematogenous Osteomyelitis

- pathophys for children <2 yo

Blood vessels cross the physis, allowing epiphysis involvement
Can result in limb shortening or angular deformities
Contiguous joint involvement can occur, more likely if involves intra-articular physis: MC is hip, also proximal humerus, radial neck, distal fibula. Can results in septic arthritis
Metaphysis has relatively fewer phagocytic cells than physis or diaphysis = more infection potential

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Acute Hematogenous Osteomyelitis

- pathophys children >2 yo

Physis acts like a barrier to spread from metaphyseal abscess
o Once physis is closed, acute hematogenous osteomyelitis is much less common
o Once physis is closed, infection can extend directly from metaphysis into epiphysis and involve the joint (why septic arthritis from acute hematogenous osteomyelitis is seen only in infants and adults)
The metaphyseal cortex is thicker so diaphysis is at more risk

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Acute Hematogenous Osteomyelitis

- microbiology

Older children and adults: Staphylococcus aureus
Infants: S. aureus. Also Group B Streptococcusand gram negative coliforms
Premature neonates: S. aureus and gram neg orgs
Incidence of Hemophilus influenza decrease d/t immunizations, MC in children 6 months – 4 years
Adult vertebral infection: gram negative bacteria
IV drug users: Pseudomonas
Sickle cell: Salmonella, tends to be diaphyseal
Chronically ill, long term IV therapy: fungal infections

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Acute Hematogenous Osteomyelitis

- Hx and PE

Fever, malaise
Pain, localized tenderness
Swelling
Compartment syndrome in children

Acute Hematogenous Osteomyelitis

- Labs for dx

CBC: often have NL WBC
CRP: usu elevated. Repeat 2-3 days after abx
ESR no longer used, replaced by CRP
Abscess or bone aspiration for C&S

Acute Hematogenous Osteomyelitis

- Imaging for dx

Plain films: usu not visible for 10-12 days
Technetium 99m bone scan: can confirm dx 24-48 hours after onset in 90-95% of cases
MRI: early inflammatory changes in bone marrow or soft tissue involvement

Acute Hematogenous Osteomyelitis

- Tx overview

No abscess, abx may be sufficient: empirical coverage, if no response in 24-48 hours, then occult abscesses must be sought, surgical drainage considered
Often abx and surgery required

Acute Hematogenous Osteomyelitis

- Nade’s Principles of treatment

Abx will be appropriate before pus formation
Abx will not sterilize avascular tissue or abscesses, will require surgical debridement (refer to ortho)
If removal is effective, ax will prevent reformation so primary wound closure should be safe
Surgery should not further damage already ischemic bone and soft tissue
Abx should be considered after sx

Acute Hematogenous Osteomyelitis
Surgery
- 2 indications
- 2 objectives

Indications
• Presence of abscess that requires drainage
• Failure of pt to improve despite IV abx

Two objectives
• Drain abscess cavity
• Remove nonviable or necrotic tissue

Subacute Hematogenous Osteomyelitis

- overview

More insidious onset; lacks severity of sx compared to acute

Subacute Hematogenous Osteomyelitis | - why is dx often delayed?

Often 2+ weeks, indolent course bc: - Increased host resistance - Decreased bacterial virulence - Admin of abx before onset of sx

Subacute Hematogenous Osteomyelitis | - Hx and PE

- Minimal systemic s/sx - Mild temp elevation - Mild-mod pain

Subacute Hematogenous Osteomyelitis | - Dx

Labs - CBC: WBC general NL - ESR: elevated in only 50% of pts - Blood cultures: gen negative Plain film: generally positive

Subacute Hematogenous Osteomyelitis | - organisms

Staph aureus and Staph epidermidis

Subacute Hematogenous Osteomyelitis | - Brodie abscess describe

- Localized form of subacute osteomyelitis - S. aureus positive culture in 50% - MC in long bones of LE - MC complaint: intermittent pain of long duration and tenderness over affected area

Subacute Hematogenous Osteomyelitis | - Brodie abscess on plain film

lytic lesion with a rim of sclerotic bone

Subacute Hematogenous Osteomyelitis | - Brodie abscess dx

- Aggressive lesions require open bx with curettage | - Simple abscess in epiphysis or metaphysis: bx not recommended. Just IV abx X 48 hours + 6 weeks oral abx

Subacute Hematogenous Osteomyelitis | - Brodie abscess tx

- close wound loosely over drain (if open bx with curettage) | - abx

Subacute Hematogenous Osteomyelitis | - Brodie abscess classification

Gledhill classification

Chronic osteomyelitis | - hallmark sx

- Infected dead bone with compromised soft tissue envelope - Infected focci in bone are surrounded by sclerotic, relatively avascular bone with thickened periosteum and scarred muscle and subcutaneous tissue

Chronic osteomyelitis | - Types

- Medullary: in the medulla - Superficial: cortical surface infected d/t coverage defect - Localized: cortical sequestrum, can be excised w/o compromising stability - Diffuse: features of all other types, mechanical instability before or after debridement

Chronic osteomyelitis | - Hx and PE

- Skin/soft tissue integrity - Tenderness - Bone stability - Neurovascular status of limb - Presence of sinus track

Chronic osteomyelitis | - lab dx

- ESR and CRP - WBC elevated 35% - Bx for histological and microbiological eval: staph. aureus, anaerobes, gram-neg bacilli

Chronic osteomyelitis | - Imaging overview

- Plain film - Sinography (nuclear med) - Isotropic bone scanning (more useful in acute vs. chronic) - Gallium scan - CT - MRI

Chronic osteomyelitis | - Plain film

** takes 10-12 days to show up • Cortical destruction • Periosteal reaction • Sequestra

Chronic osteomyelitis | - Gallium scan

* Increased uptake where leukocytes and bacteria accumulate | * NL scan excludes osteomyelitis

Chronic osteomyelitis | - CT scan

* ID sequestra | * Define cortical bone and surrounding soft tissue

Chronic osteomyelitis | - MRI

• Shows bone margin and soft tissue edema • Eval reoccurrence after 1 year • Rim sign: well defined rim of high signal intensity surrounding focus of active dz Tx

Chronic osteomyelitis | - Tx

- Sx is usually needed: remove sequestra, resection of damaged tissue, debridement - Abx, duration is controversial - Amputation if arterial insufficiency, major nerve paralysis, malignant change, non-functional limb stiffness

Chronic osteomyelitis | - Sclerosing Osteomyelitis of Garre'

- Bone thickened and distended but no abscess or sequestra | - Unknown cause, possibly low-grade, anaerobic bacteria