Acute

Definition

 

Infection of bone 2° blood-borne bacteria

 

Epidemiology

 

Most common children

- peak 10 years

 

True haematogenous OM rare in adults

- usually involves spine

 

M: F 2:1

 

Site

 

Most common femur & tibia

- initially affects metaphysis 

- distal femur

- proximal and distal tibia

 

Pathogenesis

 

1.  Infants

 

Blood Supply

- metaphyseal blood vessels penetrate physis

- blood vessels expand into large venous lakes at epiphysis surface 

- transphyseal blood vessels persist to 1 year

- then physis becomes a barrier

 

Infection

- infection frequently occurs at epiphysis & in joint

- i.e. hip joint

- joint damage / growth disturbance

- profuse involucrum common

- usually resolves completely due to rich periosteal BS

 

2.  Children

 

Blood Supply

 

Nutrient artery supplies majority of metaphysis

- branch of nutrient artery reaches physis at right angle

- turn down in acute loops

- enter large venous lakes

 

Peripheral metaphysis / epiphysis have separate blood supply

 

Aetiology

 

A.  Area of relative stasis near physis

- low oxygen tension

B.  High amount of blood flow near physis

C.  Trauma

- haematoma and oedema

 

Infection

 

Secondary thrombosis of nutrient artery

- periosteum lifts / cortex devascularised

 

A.  Periosteum lays down involucrum

- periosteal new bone

- forms over cortex surrounding infected area

 

B.  Cortical death / sequestrum

- entire cortex avascular

- inner 1/2 because of nutrient artery thrombosis

- outer 1/2 because of periosteal lifting  

 

Epiphyseal involvement & joint infection rare

- growth disturbance rare

- increased blood flow to metaphysis may cause growth stimulation

 

3.  Adults

 

Blood supply

 

After physeal closure, blood vessels again connect metaphysis and epiphysis

 

Infection

 

May occur in subarticular region & involve joint

 

Periosteal fibrosis / adhesion makes detachment by pus difficult

- prevents formation of subperiosteal abscess & preserves BS outer cortex

- thus large sequestra not formed

- hence infection spreads along shaft of bone

 

Aetiology

 

Secondary to bacteraemia 

- history recent infection in 25%

 

Neonates

- E Coli

- Strep pyogenes 

- Group B Strep

- S aureus

 

Children

- S aureus

- Hemophilus 18/12 - 3 years (unless immunised)

 

Adults

- S aureus

- G neg

 

Consider

- Gonnococcus (young adults)

- Salmonella (sickle cell)

- Pseudomonas (foot puncture)

- Fungal

 

Clinical Features

 

Child

- usually delayed presentation

- history of trauma

- complaining of limb pain

- become febrile / unwell

- tender metaphysis

- may be red / swollen

 

Neonate

- mildly febrile / unwell

- refusal to move limb

- red / swollen limb common

 

Bloods

 

ESR / CRP raised

WCC may be increased

 

Early blood culture before antibiotics

 

X-ray 

 

Bony changes at 10 days

 

1.  First feature is periosteal new bone 

- later involucrum

 

2.  Brodies abscess

- osteolytic metaphyseal lesion

- well defined cavity in cancellous bone

 

3.  Garre's osteomyelitis

- sclerosis and thickening of cortical bone

- partial obliteration of medullary cavity

- often diaphyseal

- consider anaerobe Propionibacterium acnes

 

Proximal Femur Osteomyelitis

 

Bone Scan

 

Positive all 3 phases in 24 - 72 hours

- sensitivity & specificity 90%

 

US

 

Identify fluid in joint space which may be septic arthritis

 

CT

 

Sequestrum

 

MRI

 

Increased signal on TI

 

Abscess

- high signal rim with low signal in middle

- rim / ring enhancement with gadolinium

 

Proximal Femur Osteomyelitis MRIProximal Femur Osteomyelitis MRi 2

 

Aspiration / Biopsy

 

Subperiosteal / intra-osseous

- positive culture in 60 - 90%

 

Management

 

Principles

 

1. Antibiotics most effective before pus forms

- don't delay administration

- low threshold

- i.e. child with leg pain and likely early OM

 

2.  Antibiotics can't sterilise avascular tissues or pus 

- these should be removed surgically

 

Antibiotics

 

80% will settle with antibiotics

 

Options

 

Flucloxacillin 25 - 50 mg/kg/dose q6h

Cephalothin 25 - 50 mg/kg/dose q6h

 

May be better to use broad spectrum

 

Route & Duration

 

Intravenous until child well, afebrile & non tender

- minimum 72 hours

- then convert to oral

- 24 weeks

- cease when CRP normal and child clinically well

 

Results

 

Peltola et al Pediatrics 1997

- 50 cases with change to oral at 4 days

- average duration 23 days

- effective treatment in all cases

 

Peltola et al Pediatr Infective Disease Journal 2010

- repeated same study

- same findings

 

Surgery

 

Indications

1.  Abscess

2.  Sequestrum

3.  Severely ill patient

4.  Poor response to antibiotics ~24hrs

5.  Diagnosis in doubt

 

Procedure

- tourniquet

- incision over maximum tenderness

- release of pus in ST & under periosteum

- drill-holes in cortex if no subperiosteal pus found

- close skin over drain

 

Complications

 

Septic arthritis

- < 12/12 old (blood vessels cross physis)

- intra-articular metaphysis i.e. hip

 

Septicaemia

 

Premature physeal arrest

 

Pathological fracture

 

Chronic OM

 

Prognosis

 

Recurrence 4%