osteomyelitis

Acute haematogenous osteomyelitis

definition

· inflammation of bone caused by blood-borne bacteria

epidemiology

· uncommon disease

· most common in children

· peak age 10 yrs

· true haematogenous infection rare in adults

· usually involves spine rather than long bones

· boys more common (2:1)

· most commonly affects femur and tibia

· affects metaphysis initially

pathogenesis

· 3 patterns depending on age of patient (Trueta)

· differences due to changing blood supply of bone

Children

Blood supply

· nutrient artery supplies majority of metaphysis

· peripheral metaphysis and epiphysis have separate blood supplies

· branches of nutrient artery

· reach growth plate at right angles

· turn down in acute loops

· enter system of large venous lakes

· area of relative stasis near growth plate

· now thought that hairpin loops do not exist

· large metaphyseal sinusoids between bony columns

Infection

· blood flow slows down and provides excellent medium for bacteria

· infection causes inflammation between forming bony columns

· leads to thrombosis in venous lakes and secondary thrombosis of nutrient artery

· oedema forces fluid and organisms through haversian and Volkmann’s canals

· causes

· lifting of periosteum

· disruption of vascular connection between metaphyseal cortex and periosteum

· periosteum lays down new layer of bone called involucrum

· deprivation of blood to entire cortex occurs

· to inner half by thrombosis of nutrient artery

· to outer half by lifting of periosteum

· leads to cortical death and sequestrum formation

· epiphyseal involvement and joint infection rare

· growth disturbance rare

· increased blood flow to metaphysis may cause generalised growth stimulation

Infants

Blood supply

· vessels from metaphysis penetrate growth plate

· at end, vessels expand into large venous lakes close to surface of epiphysis

· transphyseal vessels persist to about age 1 year

· after that, growth plate becomes effective vascular barrier

Infection

· infection frequently occurs at epiphysis and in joint

· consequence is

· joint damage

· interference with growth

· profuse involucrum formation often occurs

· usually resolves completely due to richness of periosteal blood supply

Adults

Blood supply

· after fusion of growth plates, vascular connections formed between metaphyseal and epiphyseal vessels

· blood in nutrient artery reaches surface of epiphysis

Infection

· infection may occur in subarticular region and involve joint

· periosteal fibrosis and adhesion to cortex makes detachment by pus more difficult

· prevents formation of subperiosteal abscess and preserves blood supply of outer cortex

· thus large sequestra not formed

· leads to spread of infection along shaft of bone

· causes resorption of bone

· lack of reparative capacity commonly leads to chronic infection

Summary

Children

· extensive cortical damage with involucrum formation

· no joint infection

· no epiphyseal damage

Infants

· severe epiphyseal damage

· joint infection

· large involucrum but only transient damage to shaft and metaphysis

Adults

· frequent joint infection

· cortex absorbed instead of becoming sequestrum

· whole of bone invaded

· chronic infection common

aetiology

Portal

· due to bacteraemia or septicaemia

· history of recent infection in 25%

· respiratory

· ear

· skin

· site of entry of organism not identified in 75%

· umbilical cord is potential portal of entry in infants

Bacteriology

· organism identified in 50-60%

· Staph aureus most common

· Pseudomonas seen in puncture wounds to foot

· Salmonella associated with sickle cell disease

Children

· Staph aureus

· Haemophilus (18 mths to 3 yrs)

Neonates

· coliforms

· Strep pyogenes

· Staph aureus

Adults

· Staph aureus

· gram-negatives

pathology

Metaphysis

· infection commences in metaphysis

· may lead to bone death

· sufficient blood supply leads to

· apposition of new bone

· osteoclastic resorption of necrotic bone

· persistence of necrotic bone seeded with bacteria leads to chronic osteomyelitis

Physis

· physis may be damaged in infants

· growth disturbance occurs if germinal cells damaged by ischaemia or chondrolysis

clinical features

Child

Symptoms

· presentation usually delayed

· usually starts with pain in limb

· often ascribed to trauma

· become febrile and unwell

Signs

· fever

· tenderness over metaphysis of long bone affected

· active movement resisted

· careful passive movement possible

· redness and swelling with extraosseous extension

Neonate

· mildly febrile and unwell

· refusal to move limb

· redness and swelling common

investigations

Laboratory

· ESR usually raised

· CRP raised

· WCC may be raised but nonspecific

Plain x-ray

· initially show soft tissue swelling

· bony changes do not occur until 10 days

· first feature is periosteal new bone formation

· later features are

· bony destruction with metaphyseal lucency

· sequestrum formation with cortical sclerosis

Bone scan

· increased blood pool and bone uptake suggest osteomyelitis

· may see cold spots early

· sensitivity and specificity 90%

· false negatives may occur, esp. early in course

· false positives may be due to

· tumour

· trauma

Ultrasound

· useful investigation

· fluid near bone highly suggestive of pus

treatment

Principles

1. antibiotic most effective before pus formed

· do not delay administration

2. antibiotics cannot sterilise avascular tissues and pus

· these should be removed

3. once avascular tissues and pus removed, antibiotics can prevent their further formation

· thus primary suture of skin is safe

4. bone is damaged by ischaemia

· surgery should not cause ischaemia

5. antibiotic therapy should be continued after surgery

Antibiotics

Timing

· start immediately once diagnosis suspected

· take blood for cultures first

Type

· initial

· flucloxacillin 25 mg/kg/dose q6h

· penicillin sensitivity

· cephalothin 40 mg/kg/dose q6h

· severe penicillin sensitivity, cephalosporin sensitivity or nosocomial infection

· vancomycin

· subsequent

· alter according to bacteriology

Route and duration

· IV route until child well, afebrile and local signs settled

· usually 72 hrs

· then convert to oral

· review with x-ray and ESR at 3 weeks

· discontinue antibiotics if

· no limb tenderness or pain on movement

· ESR declining

· no cavities or new bone formation on x-ray

· otherwise continue antibiotics for another 3 weeks

Immobilisation

· bed rest

· immobilisation of limb on pillow or in skin traction

Surgery

Indications

1. presence of abscess clinically

2. severely ill patient

3. inadequate clinical response to antibiotics

Procedure

· tourniquet

· incision over maximal tenderness

· release of pus in soft tissues and under periosteum

· drill-hole in cortex if no subperiosteal pus found

· skin closed

complications

Death

· rare

Recurrence

· risk is 20%

Chronic osteomyelitis

· more common in adults

Growth disturbance

· more common in infants

· depends on

· volume of physis affected (severity)

· part of physis affected (angular deformity)

Septic arthritis

· more common in

· neonates (transphyseal vessels)

· shoulder and hip (metaphysis intracapsular)

Pathological fracture

· more common in adults with bone resorption

Prognosis

· 80% will settle with antibiotics

Subacute osteomyelitis

epidemiology

· increasing incidence

· commonly affects children and young adults

· most commonly affects

· distal femur

· proximal and distal tibia

aetiology

· mildness due to

· infection with low-virulence organism

· resistance of host

· usually due to coagulase-positive Staphylococcus

· haematogenous spread

· no septicaemia

pathogenesis

· two types of lesion

With abscess formation

· usually osteolytic lesion in metaphysis

· little surrounding reaction

· may be surrounding sclerosis and periosteal reaction

· usually occurs in diaphysis

· called Brodies abscess

Without abscess formation

· patchy necrosis

· no sequestration or abscess formation

· usually occurs in diaphysis

· called Garre’s osteomyelitis

pathology

· usually well-defined cavity in cancellous bone

· filled with seropurulent fluid

· cavity lined by granulation tissue

· thickened surrounding trabeculae

clinical features

· insidious onset

· intermitent pain in affected region

· local swelling and tenderness

· constitutional symptoms rare

investigations

Laboratory

· ESR usually normal

· blood culture sterile

Radiology

Brodie’s abscess

· most common in tibial metaphysis

· also seen in

· os calcis

· proximal humerus

· distal radius

· osteolytic lesion

· surrounded by dense sclerosis

· variable periosteal reaction

Garre’s osteomyelitis

· sclerosis and thickening of cortical bone

· partial obliteration of medullary cavity

differential diagnosis

· tuberculosis

· osteoid osteoma

· primary malignant bone tumour

· Ewing’s sarcoma

· osteosarcoma

· fibrous dysplasia

treatment

Antibiotics

· as for acute osteomyelitis

· 6 week course

Drainage

· indications

· abscess cavity

· failure to respond

· diagnosis in doubt