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Chronic Osteomyelitis

Definition

  • Osteomyelitis following
    • Inadequately treated acute osteomyelitis
    • Post-traumatic
    • Post-surgical treatment
  • Chronic haematogenous form - 30% of all chronic osteomyelitis

Histological definition

  • Infection of bone corresponding with development of necrotic bone

Chronological definition

  • Osteomyelitis persisting after 6 months (variable time used in literature)

    • OR

  • Osteomyelitis with radiologic evidence of sequestra, involucrum, radiolucency, & clinical evidence of sinus or fistula

Aetiology

  • Often improperly treated conditions
  • Pertinent factors predisposing to it include
    • Degree of bone necrosis
    • Nutritional status of involved tissues
    • Nature of infecting organisms
  • Risk factors
    • Old
    • Debilitated
    • IV drug users
  • Organisms involved are most commonly
    • S Aureus & Gram neg rods
    • May see
      • Pseudomonas
      • Enterobacter
      • E coli
      • Polymicobial in > 30%
    • Pure Staph ~ 25%
    • Note increasing incidence of G- rods over past 20 years

Pathogenesis

  • Initial metaphyseal abscess or direct innoculation
  • Resolves with appropriate treatment
  • Contained by host defences & persists as subacute or chronic localised infection
  • Spreads to involve adjacent structures
  • Medullary canal fills with pus & pressure forces infection through Haversian canals to the periosteum to form subperiosteal abscess
  • The hole in the cortex is the cloaca
  • Periosteum lifts & may form new bone resulting in an involucrum
  • Vascular obstruction with thrombosis may result from many factors
    • Pressure
    • Leucocytic enzymes & acidic pH
    • Periosteal stripping
  • Results in segment of dead bone called the sequestrum
  • In the adult the periosteum is adherent to the cortex so pus tends to break through to form multiple soft tissue abscesses
  • overlying skin is affected in chronic conditions
    • Indurated, puckered & adherent to bone
    • Sinus often connects the skin with bony lesion
  • histological picture is one of chronic inflammatory cell infiltrate around areas of acellular bone or microscopic sequestra

Classification

Anatomic “MSLD”

Four Anatomic Stages of Chronic Osteomyelitis
Stage Description
1
  • Medullary Infection nidus is endosteal
2
  • Superficial Breakdown in soft tissue overlying the bone with involvement of periosteum & cortex
3
  • Localized Localised involvement of medulla & cortex of segment of bone with or without soft tissue involvement
  • There may be fistulous tract & cloacae
  • Entire lesion can be excised without causing instability
4
  • Diffuse Permeative infection involving entire segment bone
  • Unstable pre or post debridement

Host

  • A Healthy
    • WCC > 1,500/mm3
    • Albumin > 3.5g/dL
    • Protein > 6g/dL
    • Ferritin 10-200 ng/mL
    • Transferrin < 200mg/dL (20-40% saturated)
  • B Local &/or systemic compromise
  • C Severe compromise
    • Not a surgical candidate

"Clinical" Staging

Clinical Staging of Chronic Osteomyelitis
Stage Description
1 Simple deadspace & simple closure
2 No deadspace & complex closure
3 Simple stabilization with complex deadspace & closure
4 Complex stabilization/ closure/ deadspace

Complications

  • Pathological fracture
  • Constant sinus
  • Eczematous skin reaction
  • Neoplastic change in sinus
  • Epidermoid carcinoma in 0.5%
  • Malignant bone transformation to sarcoma
  • Amyloidosis

Clinical Features

  • Recurring bouts of pain, redness, pyrexia & tenderness
  • Discharging sinus common
  • May have underlying non-union of bone particularly if post-traumatic

Investigations

Laboratory

  • WCC, ESR, CRP, blood cultures
  • WCC & ESR/CRP may be variably elevated during the flares
  • Bacterial cultures need to be repeated regularly to ensure changing sensitivity identified ?

Xray

  • Classic picture
    • bone resorption with surrounding sclerosis & thickening
  • May have periosteal reaction/ involucrum & very dense sequestrum
  • Deformity common
  • Features may mimic tumour

Bone Scan

  • Increased activity in both the blood pool & bone phases
  • More sensitive with WCC-labelled indium scan or gallium scan

CT/MRI

  • Show extent of bone destruction & hidden abscesses/sequestra
  • Helpful for pre-op planning

Aspiration/Biopsy

  • 1. Sinus tract cultures
    • Specificity 86%, Sensitivity 76%
    • Isolation of Staph bears little resemblance to organism in bone
    • Isolation of G- bacteria bears no relation to bone
    • Pseudomonas from sinus in bone only 30%
    • Should not be used as guide for AB usage
  • 2. Biopsy
    • Preferred diagnostic procedure
    • Increased incidence of multiple organisms
    • Treatment

Treatment

Five parts

  • Appropriate Antibiotics
    • Obtain MCS at time of debridement
    • Commence AB after debridement
  • Adequate Debridement
    • Remove necrotic bone
    • Obliterate dead space
  • Skeletal Stabilisation
    • External or internal fixation
  • Adequate Soft Tissue Cover
    • Introduce healthy vascularised tissue
  • Consider Delayed Bone Grafting

Antibiotic Therapy

  • Seldom eradicated by antibiotics alone
  • Important to
    • Stop spread of infection to healthy bone
    • Control acute flares
  • Generally combination of Beta-lactam antibiotic & Aminoglycoside recommended due to synergistic nature & may prevent resistance
  • The total period of therapy may be up to 3 months

Local Treatment

  • Temporary measures prior to surgical treatment
  • Dressings of sinuses
  • Drainage of acute abscess

Surgical treatment

  • 1. Debridement
    • Remove all dead & infected material
    • May need to be radical
    • Saucerization of cortex & curettage of medullary contents to bleeding bone
    • Irrigation of area
    • Stabilization if unstable may be required
    • Often external fixator required
  • 2. Soft Tissue & Bony Reconstruction
    • Includes (all considered as closure of dead space)
      • Local muscle flaps
      • Free cancellous bone grafting
      • Free myocutaneous & osteomyocutaneous flaps
      • Vascularised bone graft
      • Bypass grafts
      • Distraction osteogenesis
      • Amputation
    • Local Flaps
      • Not used much due to inability to provide good blood supply & durable soft tissue
    • Open Cancellous Bone Grafting (Papineau technique)
      • First described by Rhinelander in 1975 & then Papineau in 1979
      • For small defects (< 4cm) in a well patient (type A)
      • Defect in bone filled in with cancellous bone chips & dressing applied
      • Changed every few days with debridement of any necrotic bone
      • Process continued until bone graft covered with healthy granulation tissue
      • Then cover by secondary intention, graft or flap
      • Contraindicated in segmental defects > 4cm
    • Free Myocutaneous Flaps
      • 79-100% success
      • Good blood supply
      • Must not transfer to tissue that still infected
        • doomed to fail
      • Requires good stable underlying bony bed
    • Vascularized Bone Graft
      • Indicated when bony defect > 6cm
      • Best if minimal soft tissue loss but can take with muscle or skin if significant loss
      • Fibula & Iliac crest commonest sites
    • Complications include
      • Loss of graft vascularity
      • Recurrence of infection
      • Delayed/ nonunion of segment
    • Bypass Grafts
      • Cross union established usually between Tibia & Fibula
      • Proximal & distal to defect
      • Allows protection of grafted defect
    • Distraction osteogenesis
      • Ring external fixator (Ilizarov, TSF)
      • May be the only option in large defects
    • Amputation
      • If cannot manage limb with bony defect, instability & persistent infection
      • Maybe indicated early in treatment plan
      • Type C host

Antibiotic Bead Pouch Technique

  • Henry & Seligson pioneered technique
  • Addition to debridement process
  • Reduce bony ablation
  • Maintain germ free wound site
  • Diaphyseal spacer for later application of bone grafts
  • Bead chains used
  • Deliver higher concentrations to site but avoid systemic complications
  • Can use Gentamicin or Vancomycin
  • Involves placing the beads in defect & placing a Non-permeable adhesive dressing over the area & drains without suction in place
  • Changed every 48-72 hours in operating theatre

Hyperbaric O2

  • Increases O2 tension in tissue beds
  • Intramedullary bone O2 tension normally 32-45mmHg; in osteomyelitis 17-23mmHg
  • Increased O2 tension
  • Toxic to anaerobic bacteria
  • Aids neutrophil intracellular bacteriocidal mechanism
  • Aids tissue genesis
  • Augments bacteriocidal action of aminoglycosides
  • Indications not clear at present
  • No clear benefit shown

Brodies Abscess

  • Localised form of chronic OM occurring most often in long bones of LL in young adults
    • Reflects incomplete healing
    • Caused by organism of low virulence
    • Staph 50%
  • Location
    • Metaphyseal in skeletally immature
    • Metaphyseal-epiphyseal in adult
    • May occur rarely in diaphysis
  • Clinical
    • Intermittent pain & local tenderness
  • Investigations
    • Easily mistaken for tumour on XR
      • Osteoid osteoma
      • Chondroblastoma
      • Enchondroma
      • Eosinophilic granuloma
      • Intraosseous ganglion
      • Giant cell tumour
    • May need Bx
  • Treatment
    • Local curettage ± bone graft
    • AB

Chronic Recurrent Multifocal Osteomyelitis

  • “CRMO”
  • Children & young adults
  • Mainly affects
    • Metaphyses of clavicle (most often – 60% at presentation)
    • Tubular bones
    • Can be symmetrical
  • Pathology
    • Histologically chronic osteomyelitis with predominance of plasma cells
  • Clinical
    • Insidious onset of low grade fever, local swelling & pain in affected bones
    • Symptoms wax & wane over months/ years
    • Intermittent periods of exacerbation & remission over several years
    • Some patients have recurrent skin lesions
    • Palmoplantar pustulosis
  • Investigations
    • Cultures negative
    • XR changes suggest OM
    • Bone scan shows multiple areas of involvement
  • Treatment
    • Symptomatic
    • Long term prognosis good

Sclerosing Osteomyelitis of Garre

  • Garre 1893
  • Mainly children & young adults
  • Average age 16 years
  • Aetiology
    • Unclear aetiology
    • Unusual organisms
      • Proprionibacterium acnes (low grade, anaerobic)
  • Pathology
    • No necrosis or purulent exudate
    • Little granulation tissue
    • Intense proliferation of the periosteum leading to bony deposition
    • Histologically see non-specific chronic inflammation with new bone formation & areas of necrosis
  • Clinical
    • Insidious onset & local pain & tenderness
    • Most common area is
    • Shaft of long bones
    • Other area is Mandible
  • Investigations
    • Moderate ↑ in ESR
    • Cultures usually negative
    • See pronounced sclerosis with cystic areas on XR
  • May be difficult to distinguish from
    • Ewings
    • Osteosarcoma
    • Osteoid osteoma
    • Osteoblastoma
    • Pagets
  • Course
    • Recurrence of symptoms at intervals with eventual subsidence
  • Treatment
    • No treatment protocol predictably helpful
    • Fenestration & Curettage provides temporary relief
    • Prolonged antibiotic therapy does not affect natural history

Caffey’s Disease

  • Infantile cortical hyperostosis
  • Periostitis affecting infants < 6 months of age
  • Malaise / fever & swelling of long bones, mandible & scapula
  • XR show marked periosteal new bone formation
  • Always spontaneously resolves
  • Distinguish from scurvy & osteomyelitis & syphilis
  • May require antibiotic therapy
    • Penicillin
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