Osteomyelitis Flashcards
what is the definition of OM?
Osteomyelitis is an inflammatory condition of bone caused by an infecting organism, most commonly Staphylococcus aureus. It usually involves a single bone but may rarely affect multiple sites. It may occur in the peripheral or axial skeleton.
what is the epidemiology of OM?
Higher in men
Increases with age and children
Common hospital admission
Increasing the prevalence of diabetes
what is the aetiology of OM?
Osteomyelitis may be caused by haematogenous spread of infection, from direct inoculation of microorganisms into bone, or from a contiguous focus of infection. A trivial skin infection may cause bacteraemia, or it may result from more serious infections such as acute or subacute bacterial endocarditis. Intravenous drug misuse has been linked to haematogenous osteomyelitis involving the long bones or vertebrae
Common organisms implicated in acute osteomyelitis are Staphylococcus aureus, streptococci, Enterobacteriaceae, and anaerobic bacteria. Native vertebral osteomyelitis is commonly monomicrobial and most frequently due to S aureus
what are the risk factors for OM?
Previous infection Penetrating injury IV drug Diabetes HIV infection Recent surgery Infections Sickle cell anaemia Rheumatoid arthritis CKD Immunocompromising conditions URT or varicella infection in children
what is the pathophysiology of OM?
Direct inoculation - After trauma, direct inoculation of bone, polymicrobial or monomicrobial
Contiguous spread - from adjacent soft tissue infection, polymicrobial or monomicrobial, (DM)
Haematogenous spread - bacteria in bloodstream, children (Long Bones), adults (vertebrae), monomicrobial
Bacteria that enter the bloodstream exist in a free-floating planktonic state. Most osteomyelitis is caused by biofilm-forming bacteria. These bacteria express surface components called adhesins that bind to proteins found in host tissues. Once attached, the bacteria produce a polysaccharide extracellular matrix, forming a biofilm. Once sufficient numbers of organisms are present in the biofilm, a complex system of cell-to-cell signalling develops, known as quorum sensing. This controls further development of the mature biofilm. It may also propagate the spread of infection by controlling separation of fragments of this biofilm which seeds to local sites. Some of the organisms in biofilm are able to enter a dormant state with minimal cellular division. In this state, antibiotics that act on cell division are ineffective. Similarly the organisms are also partially protected from the host immune system within the glycocalyx. The sensitivity of a culture in the laboratory on an agar plate (in vitro) may bear no relationship to the ability of the same antibiotic to kill bacteria in a biofilm in dead tissue or in an implant (in vivo). In vitro biofilm models may be more representative. Staphylococcus aureus has been shown to express a number of virulence factors, and can invade living cells and survive inside osteoblasts.
what are the key presentations of OM?
Risk factors Limp Non-specific pain Malaise and fatigue Local back pain Paravertebral muscle tenderness and spasm Local inflammation Fever Spinal cord compression Non healing fractures
what are the signs of OM?
Wound drainage
Risk factors
Spinal cord compression
Warmth and erythema
what are the symptoms of OM?
Scars Reduced range of motion Reduced sensation in diabetics Limp Non-specific pain Malaise and fatigue Local back pain Paravertebral muscle tenderness and spasm Local inflammation Fever UTI symptoms, torticollis (twisting of neck), tenderness
what are the differential diagnoses of OM?
Septic arthritis, JIA, transient synovitis
how is OM managed?
Initial:
Follow sepsis protocol
Acute:
Suspected peripheral - antibiotic therapy (adults - flucloxacillin or vancomycin, children - cefazolin or clindamycin), pseudomonas antibiotic cover, supportive care, surgery
Suspected vertebral - infectious diseases and spine surgeon referral, supportive care, antibiotics, surgery
Suspected diabetic foot - MDT foot care, antibiotics,
how is OM monitored?
Monitor the patient for recurrence of infection and side effects from antimicrobial and other medications
what are the complications of OM?
Drug reactions, flap failure, amputation
what is the prognosis of OM?
Most patients with acute osteomyelitis recover with no long-term complications if osteomyelitis is diagnosed promptly and treated adequately.
what are the first line and gold standard investigations for OM?
FBC - WBC may be raised
ESR - usually raised
CRP - usually raised
Blood culture - may be positive for bacteria (in about 50% of blood cultures)
Plain x-rays - (acute) osteopenia appearing after 6-7 days, (discitis) lateral spine radiographs show late changes at 2–3 weeks, (vertebral) initially shows localised rarefication (‘thinning’) of a single vertebral body, and then later, anterior bone destruction, (chronic disease) intramedullary scalloping, cavities, and cloacae may be seen, with a ‘fallen leaf’ sign noted when a piece of endosteal sequestrum has detached and fallen into the medullary canal
MRI (if x-ray negative) - may show high signal on T2 images or fat suppression sequences, may show changes in children within 3-5 days of onset, may show vertebral bone changes
Bone biopsy - may be positive, indicating the infecting organism and microbial sensitivities, may show other pathology such as tumour or granulomatous disease, do no bias PCR if nothing
