Bone and joint infections

Question 1

Septic infectious arthritis

Answer 1

• 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)

Question 2

Course of infection for infectious arthritis

Answer 2

• 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

Question 3

Organisms causing infectious arthritis

Answer 3

• 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

Question 4

Dx of infectious arthritis

Answer 4

• 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

Question 5

Complications of septic infectious arthritis

Answer 5

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

Question 6

Osteomyelitis

Answer 6

• 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

Question 7

Host classification in osteomyelitis

Answer 7

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

Question 8

Pathophysiology of osteomyelitis

Answer 8

• 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

Question 9

Dx for osteomyelitis

Answer 9

• 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

Question 10

Post-traumatic/post-surgical osteomyelitis

Answer 10

• 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

Question 11

Vertebral osteomyelitis

Answer 11

• 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

Question 12

Infections of SI joint

Answer 12

• 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

Question 13

Brodie’s abscess

Answer 13

• 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)

Question 14

Osteomyelitis in sickle cell disease

Answer 14

• 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)