Infections of MSK System Flashcards
What is osteomyelitis?
Infection of the bone and bone marrow
Osteomyelitis can be acute or chronic; discuss the difference
- Chronic osteomyelitis: deep seated, slow growing infection with slowly developing symptoms
- Acute osteomyelitis: develops more rapidly (typically occurs in children)
Osteomyelitis can spread in two different ways; describe each
- Haematogenous: spread via blood from distant site
- Direct: contact between bone and infective agent e.g. in trauma or perioperatively
Discuss the pathphysiology of osteomyelitis
- First you get periosteal elevation and thickening
- Followed by inflammation & necrosis of bone producing a sequestrum (dead bone). Sequestrum is nidus (place where bacteria multiply) for infection. *Inflammation causes inflammatory exudate which can increase intramedullary pressure and cause vascular thrombosis leading to avascular necrosis
- Involucrum (new bone) then begins to form and undergoes remodelling
What is the most common causative organisms of osteomyelitis?
Staphylococcus aureus
What is the most common causative organisms of osteomyelitis in sickle cell disease?
Salmonella typhi
State some risk factors for osteomyelitis
- Open bone fracture
- Orthopaedic surgery
- Immunocompromised
- Sickle cell anaemia
- Tuberculosis
- Distal or local infections
- Rheumatoid arthritis
- IVDU
State the signs & symptoms of osteomyelitis
- Fever (but may also be afebrile)
- Localised pain
- Immobility/inability to weight bear
- Erythema of affected region
- Swelling of affected region
- Tenderness in affected region
Discuss what investigations you would do if you suspect osteomyelitis, include:
- Bedside
- Bloods
- Imaging
Bedside
- Swab of draining sinus tracts: find causative organism- NOT RELIABLE
Bloods
- Blood cultures: check for organism being carried in blood
- FBC: signs of infection- leucocytosis
- CRP: sign on infection/inflammation
- ESR: sign of infection/inflammation
Imaging
- Plain x-ray of affected area: show osteomyelitis
- MRI: show osteomyelitis
- ?bone marrow aspiration or bone biopsy with histology & culture
Discuss whether taking swabs of draining sinus tracts is reliable way of isolating causative organism of osteomyelitis
Not reliable as they may be contaminated
Describe what you may see on x-ray of someone with osteomyelitis
- Osteopenia: shown as radiolucencies on x-ray
- Involucra: layer of new bone growth outside existing bone (new bone develops around dead bone)
- Sequestrum: piece of dead bone that has become separated from normal healthy bone during process of necrosis
- Cloaca: opening in involucrum which allows drainage of purulent and necrotic material out of dead bone
- Joint effusion in local joints
Discuss what the best mode of imaging for diagnosing osteomyelitis is
X-rays are often the initial investigation but MRI is the best imaging investigation for establishing a diagnosis (x-ray may be normal in osteomyelitis)
*NOTE: for x-ray make sure you ask for the x-ray to include the joint above and below to rule out alternative causes e.g. SCFE
Discuss the management of osteomyelitis
Give antibiotics & supportive therapy e.g. analgesia, immbolisation of limb if requried.
- Acute infections: IV antibiotics fro 4-6 weeks
- Chronic infections: IV antibiotics and surgical drainage & debridement
Discuss what antibiotics you might use in osteomyelitis
- Flucloxacillin (as Staphylococcus aureus is most common causative organism)
- Vancomycin (if MRSA risk is high)
- Piperacillin/tazobactam: if you suspect pseudomonas may be causative organism
State some potential complications of ostemomyelitis
- Sepsis
- Amputation required
- Growth disturbance in children & adolescents (can cause premature physeal closure)
- Increased risk of fracture in the affected bone
In what bones does osteomyelitis typically occur in?
Metaphysis of long bones
What is necrotising fasciitis?
Necrotising fasciitis is a life-threatening subcutaneous soft-tissue infection that may extend to the deep fascia, but not into the underlying muscle.
Sometimes called ‘flesh eating disease’
We can classify necrotising fasciitis as type I or type II; describe each
- Type I: polymicrobial bacterial infection
- Type II: monomicrobial bacterial infection- classically a Group A Streptococcal infection
When should you suspect necrotising fasciitis?
Necrotising fasciitis should be suspected in any patient with a soft-tissue infection accompanied by prominent pain and/or anaesthesia over the infected area, or signs and symptoms of systemic toxicity. Also consider if pt has risk factors
State some risk factors for necrotising fasciitis
- IVDU
- Non-traumatic skin lesions e.g. eczema, psoriasis
- Cutaneous injury
- Varicella zoster infection
- Immunosupression
State some signs & symptoms of necrotising fasciitis
- Fever
- Features of cellulitis (e.g. erythema, swelling, hot to touch) AND ADDED FEATURES:
- Severe pain over area
- Anaesthesia over area
-
Systemic signs of infection e.g.:
- Tachycardia
- Hypotension
- Tachypnoea
- Light-headedness
- Nausea & vomitting
Discuss what investigations you would if you suspet necrotising fasciitis, include:
- Bedside
- Bloods
- Imaging
Bedside
- ABG: if signs of respiratory compromise. Also give you lactate- sign of systemic infection/?potential sepsis
- Tissue sample and culture if possible
Bloods
- FBC: show signs of infection e.g. leucocytosis
- U&Es: urea & creatinine may be raised in systemic infection
- Creatine kinase: may be elevated in systemic infection
- CRP: sign of inflammation/infection
- Blood cultures: check for causative organism
Imaging
- Plain radiography, utlrasound or CT/MRI: may show oedema along fascial planes and/or soft tissue gas
Discuss the management of necrotising fasciitis
Surgical emergency requiring:
- Empirical broad spectrum IV antibiotics
- Surgical deridement
Discuss potential complications of necrotising fasciitis
- Death
- Skin loss and scarrring (caused by extensive surgical debridement; may require reconstructive surgery)
