242. Bone/Joint Infections

Question 1

Two main mechanisms of Septic Arthritis Pathogenesis

Answer 1

1. Hematogenous spread from blood to synovium

2. Direct Inoculation: surgery, trauma, contiguous spread from adjacent soft tissue

Question 2

Risk factors for septic arthritis

Answer 2

Abnormal joint
Previous joint injection
IV drug use
immunosuppression, DM, malignancy
Chronic renal failure

Question 3

Bacterial Factors in Septic Arthritis

Answer 3

Joint Disease/Injury improves bacterial adherence (why bacteria target damaged joints)

S.aureus (MSCRAMMs adhesins stick to cartilage)
Endotoxins promote cartilage breakdown

Question 4

Etiology of Septic Arthritis

Answer 4

1. S. Aureus (MOST COMMON)
2. S. Pyogenes/Agalactiae
3. G- bacilli (E. coli, pseudomonas, kindella kingae)
4. P. multocida/eikenella corrodens, borrelia burgdorferi, tropheryma whipplei

Question 5

Clinical manifestations of septic arthritis

Answer 5

Pain/loss of fx
Swelling, redness, warmth
fever, malaise
80% monoarticular (50% adults knee, kids hip)

Question 6

Septic arthritis Lab/Imaging

Answer 6

High ESR/CRP
Arthrocentesis: >50k WBC with 90+% neutrophils
Synovial Fluid and Blood Cultures +
Xray: swelling, if severe, destruction of subchondral bone
CT/MRI: good at early dx - erosive bone changes, joint effusions, periarticular soft tissue infection extension

Question 7

Treatment of Septic Arthritis

Answer 7

1. Joint drainage (decompression) via arthrocentesis or arthroscopic lavage
2. ABx: empiric against staph and N. gonorrhoeae, specific based on cultures

Question 8

Viral Arthritis (Types)

Answer 8

Chikungunya Virus: Aedes mosquito vector, acute onset viremia, rash, arthralgia, arthritis

Hep B/C

Human Parvovirus B19: fifth disease/erythema infectiosum (slapped cheeks), symmetric polyarthritis of PIP/MCP with morning stiffness

Question 9

Etiology of chronic infectious arthritis

Answer 9

Healthy: Blasto and Cocci Fungi

Immunocompromised: Candida, Cryptococcus, Aspergillus

TB: 10% extrapulmonary tb involves bone and joints

Question 10

Prosthetic Joint Infections (what is unique about it, dx, tx,)

Answer 10

Biofilm formation is strong (hard to detect, hard for immune system to catch, hard for ABx to penetrate)
Dx: Imaging: development of SINUS TRACT (pathognomic), high esr/crp
Tx: Debridement with ABx, long-term antimicrobials, amputation if severe

Question 11

Osteomyelitis (Pathogenesis, Bacterial Pathophys, Etiology)

Answer 11

1 S. aureus, then coag-negative staph, enterobacteriaceae, psudomonas, strep, p. multocida, Eikenella corrodens

Hematogenous vs. Contiguous

Bacteria form biofilms, persist within osteoblasts, adhere to damaged bone, MSCRAMMs bind collagen/fibronectin on bone - survive in dormant state

Question 12

Clinical Manifestations of OM + Labs

Answer 12

Nonspecific pain near site
Infrequent fever, chills, sweating, erythema
Occasional draining of sinus tract

High WBC, ESR, CRP
CT/MRI standard of care
Needle aspiration for etiology dx - SEND FOR EVERYTHING

Question 13

Pott’s Disease and Diabetic Foot Infection

Answer 13

Pott’s: Vertebral OM due to TB

DFI: DM pts, due to neuropathic skin ulcer - contiguous OM “Probe-to-bone” high sensitivity for OM