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)
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”

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

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