day 2 - Bone and joint infection Flashcards
what is OSTEOMYELITIS
Osteomyelitis is infection of bone. It can arise by haematogenous spread, by extension from an infected joint, by direct invasion as a result of trauma, or by iatrogenic infection following surgery or instrumentation.
osteomyelitis pathology
Pressure within the infected bone can compromise blood flow, resulting in avascular necrosis. A part of bone can become totally separated from its blood supply, forming a sequestum, which cannot heal, leading to a smouldering chronic infection with draining sinuses and loss of functional integrity. Growth may be severely impaired, particularly if the epiphysis is involved.
Seeding of organisms into the bloodstream may result in sepsis and metastatic infection.
osteomyelitis investigations
Blood cultures: only useful if taken when patient is bacteraemic
Aspiration of pus or bone biopsy (histology and microbiology)
X-rays - appear normal in early stages
MRI (Gold Standard for diagnosis of osteomyelitis), radionuclide scanning
Radiography:
- Changes usually lag at least 2 weeks behind the infection’s evolution
- Earliest changes seen are soft-tissue swelling, periosteal thickening, and focal osteopenia
Radionuclide scans:
- A negative technetium diphosphonate test can rule out the diagnosis of osteomyelitis
FDG-PET scans are more sensitive
MRI – 90-100% specificity
CT – better for sequestra/fragments if surgery planned, or if metal present
osteomyelitis management
Dependent on aetiology and patient response. Surgical drainage essential if collections or sequestra present.
Antimicrobial agents with good bone penetration must be chosen (e.g. flucloxacillin/fucidin or clindamycin for S.aureus; ciprofloxacin for Gram negative bacilli). Duration is usually six weeks in adults for acute OM, but should be reviewed in light of response of fever and acute phase reactants.
Acute OM: usually medical treatment alone
Empirical antibiotics
Targeted antibiotics
Chronic OM: surgical and medical treatment
Debridement, removal of sequestra
Removal or replacement of metalware, if present
Soft tissue coverage
clinical features of septic arthritis
Abrupt onset - pain, fever, swelling
diagnosis of septic arthritis
Arthrocentesis/synovial biopsy - septic bacterial fluid contains a neutrophil pleocytosis. Organisms will be detected microscopically in >50%. A mononuclear pleocytosis is found in tuberculous and partially treated bacterial arthritis
Synovial biopsy is more reliable, and allows histological studies
Blood cultures - limitations as for osteomyelitis, CRP, WBC and ESR raised
Radiology is of little use - may show soft tissue swelling
Cultures of other sites of potential infection/colonisation (e.g. urethra, cervix, rectum, pharynx if N. gonorrhoea is suspected)
Serology - Lyme disease, Brucella, syphilis
management of septic arthritis
Surgical drainage if joint distended by pus.
Antibiotics guided by aetiology and patient setting. High intra-articular levels of antimicrobial agent need to be achieved. Duration of treatment is usually 2-4 weeks, depending on response.
Implant associated infections: if chronic removal of metalwork is essential for optimum results. In acute infections, metalware that is well fixed may be retained.
def and management of impetigo
- A pyogenic infection of the epidermis, usually caused by S. aureus (occ. S. pyogenes)
- Treated with oral antistaphylococcal agents (flucloxacillin)
def and management of Furunculosis
- Infection of sebaceous glands or sweat glands, usually caused by S. aureus
- Antistaphylococcal agents, with surgical drainage of abscesses
def and management of Scalded skin syndrome
Caused by exfoliative toxins produced by S. aureus
• Treated with systemic antistaphylococcal agents
def and management of Erysipelas
- Intradermal infection caused by S. pyogenes
- Indurated, hot, tender erythematous lesion clearly demarcated from normal skin
- Spreads rapidly via lymphatics; blood cultures usually negative
- Regional lymphadenopathy
- Treated with IV benzylpenicillin, amoxicillin or erythromycin
def and management of Cellulitis
• Infection of loose subcutaneous tissue
• Often results from penetrating injury or local lesion which allows ingress of pathogenic
bacteria, usually S. pyogenes or S. aureus
• Usually treated with intravenous flucloxacillin
def and management of Gas gangrene
• A clostridial infection of subcutaneous infection and muscle tissue
• Most cases follow inoculation of C. perfringens into a wound; other clostridia may also be
involved
• Usually complicates war/field sports wounds
• Rapidly advancing swelling and discolouration with blisters and crepitus + severe pain
• Radiological evidence of gas in tissues
• Clostridia seen and isolated from wound/fluid
• Treatment comprises surgical debridement and intravenous antibiotics (benzylpenicillin/metronidazole)
• May be prevented by prophylactic antibiotics for high risk surgery (high amputations) and after contamination of traumatic or military wounds. Adequate cleaning, removal of debris and devitalised tissue and avoiding primary closure of severely contaminated wounds all decrease the risk of anaerobic infection
def and management of Necrotising fasciitis
• A rapidly spreading infection that causes necrotic liquefaction of subcutaneous fat
• Usually polymicrobial, involving skin flora (including S. pyogenes) and bowel flora
• Treatment comprises extensive debridement together with broad spectrum antibiotics
(clindamycin/benzylpenicillin/ciprofloxacin)
def and management of Intertrigo
a fungal infection. Candida isolated from swabs; treated with oral/topical azoles
