Osteomyelitis Flashcards
What is the epidemiology of osteomyelitis?
Bimodal age distribution:
- Acute, haematogenous osteomyelitis occurring mostly in paeds
- Contiguous osteomyelitis (often associated with direct trauma) is more commonly seen in adolescents and adults
What is the aetiology of osteomyelitis? (risk factors and pathogens)
Risk factors:
- Trauma - open fracture; orthopaedic surgery
- Prosthetic orthopaedic device
- DM - especially following foot ulcers; often goes unsuspected/underdiagnosed
- Peripheral artery disease
- Chronic joint disease
- Alcoholism
- IV drug use
- Chronic steroid use
- Immunosuppression
- TB, HIV/AIDS
- Sickle cell disease
- Presence of catheter related blood infection
Pathogens:
- S.aureus = most common; including MRSA
- H.influenzae
- Strep spp.
- E.coli
- Proteus spp.
- Pseudomnas spp.
- Coagulase-negative Staph spp.
- Mycobacteria
- Fungi
What is the pathophysiology of osteomyelitis?
An infection of the bone marrow which may spread to the bone cortex and periosteum via Haversian canals
- Inflammatory destruction of bone
- Periostium involvement leads to necrosis
- When dead bone becomes detached from healthy bone = ‘sequestrum’ - a focus for ongoing infection
Haematogenous vs. Direct/contiguous:
- Haematogenous = bacterial ‘seeding’ from remote source; more common in kids as metaphyses of growing bones are highly vascular
Contiguous = direct contact between infectious tissue and bone; signs are often more localised and with multiple organisms involved
Acute vs. chronic:
- Chronic can evolve over months or even years
At the active site of infection, bone remodelling can occur, often with associated deformity
How does long bone haematogenous osteomyelitis present?
Classically:
- Acutely febrile + bacteraemic patient
- Markedly painful immobile limb
- Swelling + extreme tenderness exaccerbated by movement +/- erythema +/- warmth
Other:
- May be mild symptoms including a mild/absence of pyrexia
- Possible Hx of blunt trauma which may have easily been forgotten e.g. a bump against a hard surface
- Non-specific systemic malaise attributed to viral illness before localising signs develop later
How does vertebral osteomyelitis present? What is Pott’s disease?
Usually insidiously:
- Following a septicaemic episode
- Localised erythema + tenderness OR
- Chronic, unremitting back pain which is worse at rest and at night
Pott’s disease:
- Vertebral osteomyelitis from haematogenous spread of TB
- Damage to the bodies of two neighbouring vertebrae leading to vertebral collapse and subsequent abscess formation
- Pus can track out into adjacent structures leading to systemic symptoms (malaise, fever, night sweats)
How does contiguous osteomyelitis present?
Patients present in the classical manner - fever + pain + erythema etc.
- Signs are often better localised
But associated Hx of accidental or surgical trauma i.e. the location of the infection should be more obvious
How do diabetic foot ulcers present with osteomyelitis?
In diabetic foot disease, neuropathy and vascular insufficiency complicate Dx:
- Pain + tenderness may be masked by neuropathy
- Local erythema, warmth and purulent drainage may be reduced due to poor blood flow
Systemic signs:
- Fever + chills are also often absent (2/3)
- Recalcitrant hyperglycaemia is often the only sign
How does chronic osteomyelitis present?
Patients may have one or more of the following:
- Previous acute osteomyelitis (possibly unresponsive to treatment or relapsing)
- Localised bone pain
- Erythema and swelling over affected area
- Decreased ROM in adjacent joints
- Chronic fatigue
- Generalised malaise
- Non-healing ulcer
- Draining sinus tracts
Sometimes chronic abscess formation may occur in the bone (Brodie’s abscess)
How do you investigate osteomyelitis?
Labs:
- FBC - raised WCC and inflammatory markers
- Blood cultures - +ve in 60% of cases
- Any expressed pus should be cultured, as should joint effusions and other potential primary sources e.g. urine
- Bone cultures are the gold standard for Dx
Imaging:
- MRI is the modality of choice
- Plain film XR may be helpful for Dx of chronic (patchy osteopaenia + bony destruction); periosteal reaction cannot be seen until c.7 days and bone necrosis after 10 days
What are the general principles of treatment in osteomyelitis?
5 Key principles:
- Local bone and soft tissue debridement
- Stabilisation of bone
- Local Abx
- Reconstruction of soft tissue
- Reconstruction of osseous defect zone
Surgical cleaning should be extensive; possible need for removal of implants
Analgesia +/- limb splinting (if long bone involved) = symptom control
Prompt identification + treatment is essential for good outcomes
What antibiotics are used in acute osteomyelitis?
Drug:
1) Flucoxacillin +/- fusidic acid or rifampicin for first 2 weeks
- Clindamycin if penicillin allergic
- Vancomycin/teicoplanin if MRSA suspected
High doses are essential to reach suitable concentrations in necrotic avascular bone
- IV used initially and to cover surgery and up to two weeks after
- PO switch once clinical condition stabilises, inflammatory markers are down and we know what bugs are growing for certain
Timescale:
- Acute: 4-6wks Abx
- Chronic: 3-6 months Abx
Seek specialist advice in chronic infection or prostheses
Increasingly complicated by rising prevalence of MRSA etc.
How does chronic osteomyelitis treatment differ?
Usually appropriate to delay treatment until MC+S are obtained, unless severe infection
Standard recommendation:
- Surgical debridement
- 6wks parentral ABx but optimal duration unknown
