Overview
Osteomyelitis is an infection of bone characterised by progressive inflammatory destruction and apposition of new bone. Infection commonly occurs after an open fracture or from haematological seeding in the setting of acute bacteremia. It is common in the Paediatric population in Africa due to significant transient bacteremia (e.g. following strep throat) and slow blood flow in the venous sinusoids beneath the growth plate (femur and tibia – long bones are commonly involved). It is often chronic in these patients. The principles of operative treatment include infection control, dead space management, bone and soft tissue reconstruction and antibiotics. Metaphyseal infections generally heal better than mid-diaphyseal infections.
The greatest burden of chronic osteomyelitis is in resource-limited settings. The incidence is 15 – 20 times higher in low-income than high-income countries. For sub-Saharan Africa, chronic osteomyelitis commonly involves the tibia and femur, and the highest incidence is in males age 10 – 20 years.
Age group and common organism
| Age group | Organisms |
|---|---|
| < 4 months | S. aureus, GAS, GBS, Enterobacter, GN enteric bacteria, Candida |
| 4 months – 5 years | S. aureus, Kingella kingae, Streptococcus pneumoniae, Neisseria meningitidis, H. influenzae |
| > 5 years | S. aureus (80%), GAS, GBS |
Risk factor and associated causative organism
| Risk factor | Organism |
|---|---|
| Immunocompromised patient with penetrating trauma | Pseudomonas aeruginosa |
| Immunocompromised and IV drug use | Candida (fungus) |
| Long-term IV medication and parenteral nutrition | Fungus |
| Severe malnutrition | Fungus |
| Sickle cell disease | Salmonella (though Staph aureus is still the most common cause) |
| Sexually active | Neisseria gonorrhoea |
| Prosthetics | Staphylococcus epidermidis |
| Tuberculosis (Pott disease) | Mycobacterium tuberculosis |
| Dog or cat bite | Pasteurella multocida |
Risk factor and location of osteomyelitis
| Risk factor | Location |
|---|---|
| Dialysis | Spine and ribs |
| Intravenous drug use | Medial or lateral clavicle |
| Diabetes | Feet and decubitus ulcers |
| Children | Tibia or femur |
Mechanisms of spread
| Mechanism | Description |
|---|---|
| Hematogenous spread | Infection originates from blood. This is the most common etiology in children. In adults the vertebrae is the most common site for hematogenous spread. S. aureus is the most common organism. |
| Contiguous spread | Infection spreads from an area of previous surgery, trauma or wound infection. It is more likely in the setting of poor perfusion since the body cannot clear the infection. Can be caused by bacteria, myocabcteria or fungi. |
| Direct inoculation | Occurs due to penetrating injuries, open fractures and surgical contamination |
Classification of osteomyelitis based on timing (roughly)
| Classification | Duration |
|---|---|
| Acute osteomyelitits | Infection within 2 weeks |
| Subacute osteomyelitis | Within one to several months |
| Chronic osteomyelitis | Persists after several months (defined as persisting for at least 6 weeks with radiographic evidence) |
- Risk factors for osteomyelitis
- Trauma or surgery
- Scar tissue
- Venous stasis
- Peripheral vascular disease
- Chronic bone and joint disease
- Foreign bodies including implants
- Intravenous drug use
- Malnutrition
- Diabetes
- Rheumatoid arthritis
- Corticosteroids and other immunosuppressants
- Immunodeficiency
- Common causative organisms
- Staphylococcus aureus (most common cause)
- Streptococcus pneumonia
- Streptococcus pyogens
- MRSA (if community acquired MRSA)
- Haemophilus influenzae type B
- Pathophysiology
- Osteomyelitis has 3 mechanisms of spread: hematogenous spread, contiguous spread and direct inoculation
- Slow blood flow in the vascular loops at the metaphysis encourage the deposition of pathogens
- Organisms colonize and proliferate in the bone
- Inflammation: release of TNF-1 and IL-1 by macrophages promotes neutrophil transmigration. Neutrophils release proteolytic enzymes which lyse the bone, surrounding tissue and microbes producing pus
- Pus causes increased intramedullar pressure. This inflammatory exudate can rupture through the cortex and into the periosteum. The periosteum becomes disrupted leading to bone ischemia and necrosis.
- Necrotic bone is known as the sequestrum.
- The periosteum can rupture leading to a soft-tissue abscess that can channel to the skin creating a draining sinus. Bone fragments from the sequestrum can pass through the sinus tract.
- Once infection is established, it persists due to formation of biofilm (makes antibiotics less effective due to difficulty penetrating the biofilm and the low metabolic rate of the bacteria)
- If infection persists (past the first week), macrophages release TGF-B and FGF which stimulates osteoclast resortpion of bone, fibrous tissue deposition and deposition of bone at the periphery.
- This newly deposited bone surrounds the sequestrum and is known as the involucrum.
- Investigations
- X-ray (orthogonal views): osteolytic changes take two weeks to be visible on X-ray. Bone loss must be 50% before it is evident on X-ray
- Periosteal thickening or reaction (earliest sign of osteomyelitis)
- Secondary signs of bone infection e.g. soft tissue swelling
- Decreased bone density
- Sclerotic rim
- Sequestrum (radiodense devitalized bone)
- Involucrum (formation of new bone around an area of bony necrosis)
- MRI: best test for diagnosis early osteomyelitis and localizing the infection. Bone marrow edema can be seen as early as 1 – 2 days. Can also aid surgical planning
- Bone and soft-tissue edema (on T2 weighted)
- Penumbra sign (on T1 weighted): a dark central abscess with a bright internal wall, and a dark external sclerotic rim
- Contrast enhanced CT-scan: to assist in diagnosis and plan for surgery by identifying margins of necrotic bone.
- Ultrasound: useful in low-resource settings to assess long bones. Can detect osteomyelitis as early as 1 – 3 days. Cannot assess the bone marrow.
- Soft tissue edema along the bony cortex
- Periosteal thickening
- Subperiosteal fluid or abscess
- Technetium (Tc-99) bone scan and gallium scan: demonstrates areas of inflammation and necrosis
- Complete blood count: leukocytosis (in 1/3 of patients)
- ESR or CRP: CRP is more sensitive and decreases faster than ESR in successfully treated patients
- Blood culture: to guide treatment in hematogenous osteomyelitis. May be negative.
- Culture of bone: gold standard for guiding antibiotic therapy. Obtained during surgery.
- Sinus tract culture: not reliable for guiding antibiotic therapy. Obtained during surgery.
- Biopsy and histology:
- Acute osteomyelitis: live osteocytes with numerous neutrophils
- Chronic osteomyeltitis: no osteocyts with fibrosis of marrow and chronic inflammatory cells
- X-ray (orthogonal views): osteolytic changes take two weeks to be visible on X-ray. Bone loss must be 50% before it is evident on X-ray
Complications of osteomyelitis
| Timeline | Complication |
|---|---|
| Acute | Bacteremia, septicaemia, septic shock, septic arthritis |
| Chronic | Persistent infection, recurrence (30% at 12 months), sepsis, amputation, pathological fractures, endocarditis, malignant transformation of a chronic sinus tract (Marjolin’s ulcer, 1%) |
Acute Osteomyelitis
Acute osteomyelitis commonly affects children, following hematogenous spread from infection at a distant site. Acute osteomyelitis and septic arthritis usually present together during infancy since infection spreads from the metaphysis to the adjacent epiphysis and cartilage. There is also a marked periosteal reaction
- Patient History
- History of birth difficulty, umbilical artery catheterization or puncture wound in infants
- History of febrile infection in children e.g. strep throat, otitis media (bacteremia might be a cause)
- History of trauma
- History of surgery
- Sexual history if age appropriate (≥ 12-13 years)
- Vaccination status (especially HiB vaccination status)
- Signs and symptoms of acute osteomyelitis in infants (< 12 months old)
- Irritablity
- Refusal to feed
- Failure to thrive
- Fever
- Signs and symptoms of acute osteomyelitis in children
- Pain
- Fever
- Refusal to bear weight or move the limb (pseudoparalysis)
- Swollen and erythematous limb (late sign)
- Joint tenderness and impaired range of motion (concurrent septic arthritis)
- Signs and symptoms of acute osteomyelitis in adults
- Pain
- Limp and/or pain inhibition with weight-bearing or motion
- Difficulty in movement
- Fever and tachycardia (sepsis) + hypotension (septic shock)
- Differential diagnosis
- Cellulitis
- Septic arthritis
- Necrotizing soft tissue infection
- Acute rheumatic fever
- Sickle-cell crisis
- Gaucher disease
- Treatment of acute osteomyelitis
- Antibiotics: initial broad-spectrum empirical antibiotics then organism specific antibiotics as guided by culture for at least 4 – 6 weeks. Transition to oral antibiotics once symptoms resolve
- Incision and drainage of abscess +/- bone drilling (for intramedullary abscess)
- Splinting and immobilization of the affected part
- Supportive treatment for pain and dehydration
- Complications of acute osteomyelitis
- Sepsis and septic shock
- Epiphyseal damage and growth arrest
- Suppurative arthritis (especially in the hip joint where the metaphysis is intracapsular)
- Metastatic abscess of the lungs, brain, serous cavitis etc.
- Pathological fracture
- Chronic osteomyelitis
Subacute Osteomyelitis
Subacute osteomyelitis is a mild form of osteomyelitis that is caused by less virulent organisms. The infection (seropurulent fluid) is well-contained by granulation tissue in cancellous bone Brodie’s abscess – but may erode the cortex. It commonly affects the distal femur, or proximal/distal tibia.
- Signs and symptoms of subacute osteomyelitis
- Limb and/or joint pain for several weeks
- Difficulty bearing weight
- Tenderness and swelling of the limb
- Treatment of subacute osteomyelitis
- Antibiotics for at least 4 – 6 weeks. May extend up to 12 months
- Bone curretage and biopsy if infection does not resolve followed by antibiotics
Chronic Osteomyelitis
Chronic osteomyelitis usually occurs after an open fracture or surgery. It is characterized by chronic bone infection with acute flares and periods of quiescence. The bone is destroyed with the formation of the necrotic sequestra and formation of a distinct bony involucrum which surrounds the sequestra. There may also be a sinus tract. The staging of chronic osteomyelitis (Cierny-Mader) helps to determine treatment and predict outcome by taking into account the bone involvement and the state of the patient.
- Signs and symptoms
- Pain
- Fever
- Redness and tenderness
- Discharging sinus tract
- Deformity and non-union in post-traumatic osteomyelitis
Cierny-Mader classification of chronic osteomyelitis based on anatomic location
| Classification | Description |
|---|---|
| Type I (Medullary) | Limited to bone marrow |
| Type II (Superficial) | Limited to the cortical bone |
| Type III (Localized) | Clearly defined edges and stability of the bone is preserved |
| Type IV (Diffuse) | Spread throughout the bone circumferentially with bone instability either before or after debridement i.e. an intractable diffuse infection + non-union |
Cierny-Mader classification of chronic osteomyelitis based on host type
| Classification | Description |
|---|---|
| Type A | Competent immune system, no comorbidities |
| Type B | Compromised |
| BL | Local compromise (smoking, lymphedema or local scarring) |
| BS | Systemic comprmise (diabetes, malnutrition, AIDS, renal or hepatic failure) |
| BLS | Combined local and systemic compromise |
| Type C | Severe underlying disease such that surgical treatment is worse for the patient than the disease |
- Treatment of chronic osteomyelitis
- Irrigation and debridement followed by organism-specific antibiotics for 4 – 6 weeks: bone should be debrided until punctate bleeding is seen – “paprika sign”). Debridement may be done in stages with delayed soft tissue coverage.
- Chronic suppressive antibiotics for 6 – 9 months: in immunocompromised patients or patients who cannot undergo operative treatment.
- Lifelong suppressive antibiotics may be required if there is recurrence after discontinuation of the antibiotics.
- Hyperbaric oxygen: as an adjunct to antibiotics
- Dead-space management with antibiotic-impregnanted beads or rods, cancellous bone grafts, flaps, or bone-transport (Llizarov technique)
- Soft-tissue cover with grafts or flaps
- External fixation for bony stability
- Amputation: offered as definitive treatment for chronic infection with a pervasive wound and bone damage that cannot be salvaged.
- Complications of chronic osteomyelitis
- Recurrency (30% at 12 months)
- Amputation
- Pathological fracture
- Endocarditis
- Malignant transformation of a chronic sinus tract (Marjolin’s ulcer, 1%)
