Chronic Osteomyelitis

Chronic osteomyelitis is persistent bone infection characterised by devascularised infected bone, biofilm, impaired local perfusion and recurrent inflammation.

The defining pathological structures are:

Sequestrum

A fragment of necrotic devascularised bone separated from viable bone.

Systemic antibiotics penetrate it poorly because it has no functioning blood supply.

Involucrum

Reactive new bone formed around the infected sequestrum.

Cloaca

An opening through involucrum allowing pus to drain externally.

Sinus tract

A chronic tract communicating infected bone with the skin.

Longstanding sinus tracts rarely undergo malignant transformation into squamous cell carcinoma, termed a Marjolin ulcer.

Cierny Mader classification

This classification combines anatomical disease extent with host physiology.

Anatomical type

Type I: Medullary

Infection is confined predominantly to the medullary canal.

Examples include infected intramedullary devices and selected haematogenous infections.

Type II: Superficial

Infection involves the cortical surface without full thickness cortical involvement.

Often associated with a soft tissue wound.

Type III: Localised

Full thickness cortical infection with a localised cavity, but the remaining bone is mechanically stable after adequate debridement.

Type IV: Diffuse

Circumferential or extensive bone involvement producing or threatening structural instability.

Frequently requires major reconstruction.

Physiological host

A host

Normal systemic and local healing capacity.

B host

Healing is compromised.

BL

Local compromise, for example:

• Severe scarring
• Poor soft tissue envelope
• Venous stasis
• Radiation fibrosis
• Local vascular insufficiency

BS

Systemic compromise, for example:

• Malnutrition
• Diabetes
• Renal disease
• Smoking
• Immunosuppression

BLS

Both local and systemic compromise.

C host

The morbidity of attempted curative treatment is greater than the burden of the disease itself.

In such patients, suppressive treatment, palliation or occasionally amputation can be preferable to complex salvage.

Presentation can be indolent.

Typical findings include:

• Chronic bone pain
• Recurrent swelling
• Intermittent purulent discharge
• Sinus tract
• Previous open fracture
• Previous fixation
• Recurrent infection after previous debridement
• Nonunion
• Implant loosening

Systemic fever may be absent.

An infected nonunion should be suspected when there is:

• Persistent fracture pain
• Implant loosening or breakage
• Failure of progressive union
• Drainage
• Raised inflammatory markers
• Repeated unexplained wound inflammation

Obtain full length radiographs of the affected bone.

Look for:

• Sequestrum
• Involucrum
• Cloaca
• Cortical thickening
• Lucency around implants
• Nonunion
• Bone loss

CT: defines sequestra and cortical architecture.

MRI: maps marrow and soft tissue disease but metal implants can reduce image quality.

Cultures

The diagnostic gold standard is multiple deep tissue and bone cultures obtained during surgery.

Take several separate deep samples using separate clean instruments.

Do not base treatment on a superficial sinus swab.

In a stable patient, obtain deep cultures before initiating a new antibiotic course whenever feasible.

Histology is particularly useful when:

• Cultures are negative
• Tuberculosis or fungal infection is possible
• Malignancy is a concern

Chronic osteomyelitis usually cannot be cured by antibiotics alone.

Successful management requires five principles:

• Remove necrotic and infected tissue
• Obtain microbiological diagnosis
• Manage dead space
• Restore skeletal stability
• Achieve durable vascularised soft tissue coverage

Debridement

Excise:

• Sequestra
• Necrotic cortex
• Infected granulation tissue
• Chronic sinus tracts where appropriate
• Nonviable soft tissue
• Infected scar tissue that prevents healthy closure

Debride bone until viable punctate bleeding bone is encountered, traditionally described as the paprika sign, while recognising that gross appearance alone is imperfect.

Inadequate debridement is one of the commonest reasons chronic osteomyelitis recurs.

Implant management

If a fracture has united and the implant is infected:

Remove the implant whenever safe.

If the fracture has not united, the problem is an infected nonunion and both infection and mechanical stability must be addressed.

Options include:

• Exchange internal fixation
• External fixation
• Circular frame
• Staged reconstruction

A grossly unstable infected fracture should not simply have all fixation removed and be left mechanically unstable.

Dead space management

Debridement can leave a substantial cavity.

Options include:

• Antibiotic loaded PMMA cement
• Antibiotic loaded calcium sulphate
• Bone graft after infection control
• Muscle flap to obliterate dead space

Vancomycin and aminoglycosides are commonly incorporated into local antibiotic carriers because they tolerate cement polymerisation and provide high local concentrations.

Local antibiotics complement rather than replace systemic treatment and debridement.

Bone defects

Small defects can be treated with:

• Cancellous bone grafting
• Acute shortening in selected long bones

Larger segmental defects can require:

Masquelet induced membrane technique

Stage 1:

• Radical debridement
• Stabilisation
• Antibiotic cement spacer

Stage 2:

• Remove spacer after soft tissue recovery and infection control
• Preserve induced membrane
• Fill with autologous cancellous bone graft

Distraction osteogenesis or bone transport

Particularly valuable for large tibial defects.

Vascularised bone graft

Useful in selected extensive defects.

Soft tissue reconstruction

Exposed bone or implants require vascularised soft tissue.

Options include:

• Local muscle flap
• Rotational flap
• Free tissue transfer

Do not repeatedly skin graft directly over exposed infected bone or hardware.

Systemic antibiotics

After adequate deep cultures and debridement, use culture directed therapy.

Approximately 6 weeks of systemic antimicrobial therapy remains a common reference duration after definitive debridement, although the appropriate duration depends on residual bone, implants, reconstruction strategy and organism.

C host and suppression

If definitive eradication would require disproportionate surgery in a medically fragile patient, chronic suppressive oral antibiotics may be reasonable.

This is suppression, not cure.

Use an oral agent active against the identified organism with acceptable long term toxicity.

Amputation

Consider when:

• Limb is functionally unsalvageable
• Infection repeatedly threatens life
• Vascular supply is inadequate for reconstruction
• Severe neuropathy and soft tissue loss prevent durable salvage
• Multiple failed reconstructions have produced a painful nonfunctional limb

Amputation should be viewed as a reconstructive option when it provides better overall function and lower morbidity than repeated unsuccessful limb salvage.