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Flashcards in Bone and joint infections Deck (14):

Septic infectious arthritis

-Infection involving the joint space, higher incidence in pts w/ RA
-High morbidity, any joint can be affected but most commonly the knee and then hip (monoarticular)
-Organisms can enter joint thru blood, spread form contiguous (adjacent) site of infection (abscess), or by direct inoculation (trauma)


Course of infection for infectious arthritis

-Organisms enter joint space and adhere to articular cartilage
-Some bacteria have tropism for joints due to adherence characteristics: S aureus, N gonorrhea, strep
-PMNs enter joint space/synovial membrane and damaged is caused in 48 hrs via increased pressure, bacterial toxins, inflammation
-Destruction of cartilage leads to joint space narrowing, erosion of cartilage, and possible extension to bone/soft tissue


Organisms causing infectious arthritis

-Usually S aureus (cat +), then strep sp (cat -, if pyogenes is beta-hemolytic)
-Other bacterial causes in adults: borrelia burgdorferi (ECM), E coli, N gonorrhea
-IV drug users: staph aureus and pseudomonas
-Infants: group B strep, GN bacilli, S aureus (also are causes of meningitis in infants)
-Human bite: eikenella corrodens
-Cat bite: pasteurella multocida
-Fungal: coccidiodes immitis
-Viral: parvovirus B19, rubella, HIV, HTLV1


Dx of infectious arthritis

-Hx: fever, chills, painful/swollen/red joint, joint effusion, limited motion
-Imaging: X-rays for swelling (early) and joint narrowing (late), MRI for determining bone involvement and abscesses
-Labs: elevated CRP, ESR, WBC count, blood cultures
-Synovial fluid analysis: consitency/color (thick and cloudy), WBC count (>50,000, mostly PMNs), gram stain not always +, culture of fluid


Complications of septic infectious arthritis

-Cartilage destruction
-Pain and LOF
-Degenerative arthritis
-Avascular necrosis of femoral head
-Subluxation and dislocation
-Recurrent infections



-Infection of the bone, can be due to hematogenous spread, direct inoculation, or adjacent spread
-4 types: type I is medullary (hematogenous)
-Type II is superficial (ulcer w/ exposed bone), soft tissue
-Type III is localized (cortex/medullary canal involved, bone stable), infected sequestrum
-Type IV is diffuse (all parts of bone affected), diffuse infected sequestrum


Host classification in osteomyelitis

-Host A: normal
-Host B: compromised
-Host C: no surgery indicated due to medical problems
-Pediatric osteomyelitis: hematogenous (medullary type I) is most common


Pathophysiology of osteomyelitis

-Bacterial predilection for metaphysis due to slowing of blood in sinusoids and reduced phagocytosis
-There is acute inflammation w/ increased vascularity, edema, and PMNs
-There is often thrombosis and infarction of bone leading to necrosis
-The pus can also embolize to other parts of the bone/joint and thus spread the infection
-Chronic suppurative osteomyelitis can lead to sinuses forming to skin leading to squamous cell CA, secondary amyloidosis


Dx for osteomyelitis

-WBC, ESR, CRP elevated
-Blood cultures
-Bone aspiration and biopsy
-Xrays for soft tissue swelling (early) and cortical/marrow destruction (late)
-MRIs and bone scans


Post-traumatic/post-surgical osteomyelitis

-Principles of infected ununited fractures: infection control, fracture stabilization, soft tissue coverage, bone grafting
-Infection control: debridement (most important), culture and then Rx (local antibiotic beads), antibios usually 4-6 wks
-Fracture stabilization: external fixation mostly
-Soft tissue coverage: improve vascularity to promote fracture healing
-Bone grafting: provides scaffold for new bone formation
-Osteomyelitis is never cured only controlled


Vertebral osteomyelitis

-Most common site of hematogenous osteomyelitis
-Bacteria can be from any site, but particularly GU in men (chronic prostatitis)
-Also can be from IV drug use
-Sx: non-specific back pain, low-grade fever, month-long illness
-Dx: radiographs showing erosions of end plates of adjacent vertebral bodies and narrowing of intervening disk space, biopsy to confirm
-Microbiology: S aureus most common, then E coli/enterics, TB, pseudomonas if IV drug user


Infections of SI joint

-Mostly due to S aureus, risk factors: indwelling intravascular catheters, IV drugs, endocarditis
-Usually associated w/ osteomyelitis of adjacent bones
-Have fever, acute and very severe sacral and pelvic pain
-Dx: blood culture, aspiration of SI joint, radiography/MRI


Brodie's abscess

-Chronic, localized bone abscess
-Most commonly in distal tibia w/ single lesion
-75% of pts are <25 yo
-Can be acute, subacute (fever and pain) or chronic (afibrile, chronic dull pain)


Osteomyelitis in sickle cell disease

-Sickle cell disease creates an increased risk for osteoarticular infections
-Must be differentiated from bone infarcts
-Common organisms: S aureus, salmonella (classic test question will be looking for salmonella)