Osteomyelitis Flashcards
What organisms are most common in osteomyelitis?
All age groups:
–> staph aureus, enterobacter
<18:
-Strep A (newborns also strep B)
Sickle cell patients:
-SAUR most common, salmonella is pathognomonic
What osteomyelitis classification systems are there?
Osteomyelitis can be classified on basis of:
-Patient age (adult/paediatric)
-Causative organism
-Pathogenesis (contiguous spread, traumatic, haematogenous)
-Anatomic location
-Duration of symptoms (acute, subacute, chronic)
No universally accepted classification system. Cierny-Mader is most common:
-Describes anatomic involvement, host, treatment, prognosis
Cierny classification of osteomyelitis
Describes anatomic involvement, host, treatment, prognosis
What are the two modes of infection in osteomyelitis?
Exogenous
Haematogenous
Describe exogenous osteomylelitis
Most common osteomyelitis in adults
–> acute osteomyelitis from open fracture or bone exposed at surgery
–> Chronic osteomyelitis from neglected wounds: diabetic feet, decubitus ulcers
Describe haematogenous osteomyelitis. Describe mechanism and location
Most common osteomylelitis in children
–> Bloodborne organisms of sepsis
Paediatric: immature immune system
–> metaphysis or epiphysis of long bones
–> lower extremety more often than upper
–> boys more often than girls
Adults: immunocompromised: vertebrae most commmon adult haematogenous site
–> dialysis patient: rib and spine osteomyeltiis
–> IV drug user: clavicle osteomyelitis
–> elderly, IV drug user, transplant patients
Describe mechanism of brodie abacess formation
Either:
-Residual acute osteomyelitis
-Haematogenous seeding of growth plate trauma (mild trauma makes seeding more likely)
Describe the invasion and inflammation stage of osteomyelitis
–> terminal branches of metaphyseal arteries form loops at growth plate and enter irregular afferent venous sinusoids
–> Blood flow is slowed and turbulent, predisposing to bacterial seeding
–> in addition, lining cells have little phagocytic activity
–> area is catch basin for bacteria, and abscess may form
Describe suppuration stage of osteomyelitis
-Abscess, limited by growth plate, spreads transversely along volkmann canals and elevates periosteum; extends subperiosteally and may invade shaft
-In infants <1, some metaphyseal arterial branches pass through growth plate, and infection may invade epiphysis and joint
Describe necrosis (sequestration) and new bone formation stage
-As abscess spreads, segment of devitalised bone (sequestrum) remains within
-Elevated periosteum may lay down bone to form encasing shell (involucrum)
-Occasionally abscess is walled off by fibrosis and bone sclerosis to form Brodie’s abscess
Describe resolution stage
-Infectious process may erode periosteum and form sinus through soft tissues and skin to drain externally
-Process influenced by virulence of organism, resistance of host, administration of antibiotics and fibrotic and sclerotic responses
Describe the stages of pathogenesis of osteomyelitis
- Invasion and inflammation
- Suppuration
- Necrosis (sequestration)
- New bone formation (involucrum)
- Resolution (sinus and drainage)
What is an abcess?
-Localised collection of pus surrounded by granulation tissue, usually caused by infection with a pyogenic organism
What is pus?
Thick yellowish liquid formed as part of an inflammatory response, usually associated with an infection and composed of exudate chiefly containing dead WBCs, tissue debris and pathogenic micro-organisms
What is the pathogenesis of pus formation?
Microbial invasions –> acute inflammation with vascular congestion and exudation of fluids with infiltration of PMN cells
What is the fate of an abscess?
-Resolution
-Rupture
-Spread-sepsis
-Chronic abscess formation
What is the definition of sequestrum?
-Dead bone that has become separated during the process of necrosis from normal/sound bone. It is a complication (sequela) of osteomyelitis
Definition of involucrum
-Reactive woven/lamellar bone depositions forming a shell of living tissue around sequestrum
-Or thick sheath of periosteal new bone surrounding sequestrum
Why pus may burst through the bone?
-Due to increased intraosseous pressure due to increased osmolarity which occurs due to tissue breakdown
-Due to formation of a large rounded cloacal opening in the involucrum
-Pus will therefore escape through involucrum and the surrounding soft tissue to the skin surface within a sinus tract
Why should metalwork be removed in osteomyelitis?>
-Has become septic focus
-Formation of biofilm: less sensitive to antibiotics
-Implant might be loose
Why could an SCC develop in sinus tract from osteomyelitis?
Chronic inflammation
In chronic osteomyelitis what is the sequence of events by which the draining sinus can develop SCC?
Chronic inflammation –> hyperplasia –> dysplasia –> carcinoma
What protein is deposited in chronic osteomyelitis?
Amyloid AA
How is osteomyelitis treated?
Antibiotics
–> blood cultures taken, IV antibiotics active against SAUR, Streptococci and gram-ve rods (e.g. e.coli) are given
–> cephalosporins, co-amoxiclav/combination of fluclox and gent can be given
Supportive treatment for pain and dehydration
Splintage of limb
Surgical drainage: if no response to abx for 2/7.
Differential diagnosis of swollen knee
-OA
-Septic arthritis
-Gout
-Pseudogout
-Haemarthrosis
-Trauma (ligamentous injury, fracture, patellar dislocation)
-Polyarthritis (RA, reiters)
What single bedside test could you do to differentiate diagnoses of hot swollen knee?
Aspiration
What tests would you do on the aspirate?
-Urgent gram stain
-M, C and S
-Cytology, chemical analsysis, crystals
Gout vs pseudogout
