Bone and joint infections Notes

NOTES NOTES BONE & JOINT INFECTIONS GENERALLY, WHAT ARE THEY? PATHOLOGY & CAUSES ▪ Bacterial invasion and destruction of bone and joint cartilage ▪ Caused by bacteria ▫ E.g. Staphylococcus aureus (S. aureus), Mycobacterium tuberculosis (M. tuberculosis), Pseudomonas aeruginosa (P. aeruginosa) RISK FACTORS ▪ Trauma/open fractures, diabetes/ atherosclerosis, orthopedic implants, existing infection etc. COMPLICATIONS ▪ ▪ ▪ ▪ Chronic infections Bone fractures Loss of mobility Dissemination of infection SIGNS & SYMPTOMS DIAGNOSIS DIAGNOSTIC IMAGING MRI ▪ Detect bone infections CT scan, X-ray ▪ Detect fractures LAB RESULTS ▪ Blood tests ▪ Needle aspiration: pathogen detection TREATMENT MEDICATIONS ▪ Before identifying pathogen → general antibiotics ▪ Known pathogen → specific antibiotics SURGERY ▪ Surgical cleaning ▪ Pain → individual avoids using infected joint Systemic ▪ Fever, chills, weakness, headache Local ▪ Swollen, painful, warm OSMOSIS.ORG 587

OSTEOMYELITIS osms.it/osteomyelitis PATHOLOGY & CAUSES ▪ Cortical loss ▪ Contrast enhancement of abscess rim ▪ Bacterial infection (S. aureus, M. tuberculosis most common) → bone, bone marrow inflammation ▪ Bacteria → bone via bloodstream, nearby infection, open fractures/orthopedic implants ▪ First week: bacterial reproduction → inflammation → bone necrosis (e.g. sequestrum); if periosteum bursts → abscess ▪ Later: cytokines induce bone resorption → replacement with fibrous tissue → new bone formation around necrotic one (e.g. involucrum) Nuclear medicine scans ▪ If MRI not attainable: higher radiotracer uptake CT scan, X-ray ▪ not sensitive for 1–2 weeks ▫ Osteopenia (decreased bone density) ▫ Periosteal reaction (thickening of periosteum) ▫ Aggressive infection → Codman’s triangle (lifted periosteum with triangleshaped, ossified edge) RISK FACTORS ▪ Diabetes, fractures, splenectomy, orthopedic procedures/hardware COMPLICATIONS ▪ If M. tuberculosis disseminates from joint to vertebra → Pott disease ▪ Inadequate treatment → chronic infection → bone fractures, sepsis SIGNS & SYMPTOMS Local ▪ Redness, swelling, painful site, sinus connecting to abscess Systemic ▪ Weakness, fever, headache, shivering DIAGNOSIS DIAGNOSTIC IMAGING MRI ▪ Edema → signal changes 588 OSMOSIS.ORG Figure 106.1 An X-ray image of the tibia demonstrating a radiolucency with a sclerotic border consistent with a Brodie abscess.

Chapter 106 Bone & Joint Infections ▫ Endosteal scalloping (focal resorption of endosteum) ▫ Advanced osteomyelitis → cortical bone breakage ▫ Peripheral sclerosis (increased density at periphery, lower density centrally) OTHER DIAGNOSTICS Needle aspiration guided with ultrasound ▪ Specific antibiotic therapy TREATMENT MEDICATIONS ▪ Long-term intravenous antibiotics SURGERY Figure 106.2 A plain radiograph of the right lower leg of an individual with postoperative osteomyelitis. The surgical wound started discharging pus two weeks post open reduction. There is medial cortical destruction and loss of trabeculations with lateral cortical thickening. ▪ Surgical removal of dead bone ▪ Severe cases → amputation SEPTIC ARTHRITIS osms.it/septic-arthritis PATHOLOGY & CAUSES ▪ Joint structures: infected, damaged ▪ Pathogen enters the joint via bloodstream, from nearby infection/directly (e.g. open fracture) ▪ Infection of joint → endotoxin production → cytokine release → neutrophil attraction → inflammation, damage of joint structures CAUSES ▪ Most commonly S. aureus (any age group), Neisseria gonorrhoeae (N. gonorrhoeae; sexual transmission → adults) RISK FACTORS ▪ ▪ ▪ ▪ ▪ ▪ ▪ Diabetes Joint trauma Artificial joint, surgical procedure Osteomyelitis Chronic arthritis (e.g. rheumatoid arthritis) Immunocompromised HIV SIGNS & SYMPTOMS ▪ Most commonly affects knee; less commonly ankle, hip, shoulder OSMOSIS.ORG 589

Local ▪ Restricted range of motion; painful, warm, swollen joint Systemic ▪ Fever, weakness DIAGNOSIS DIAGNOSTIC IMAGING X-ray, CT scan ▪ Normal in early stages ▪ ↑ fluid in synovial part of joint ▪ Narrowing of joint space due to destruction of cartilage ▪ Destruction of bone adjacent to cartilage MRI ▪ Edema around synovium ▪ Assess spread of infection outside the joint Ultrasound ▪ ↑ fluid ▪ Guiding needle for aspiration Figure 106.3 A red, hot, swollen left knee in an individual with septic arthritis. TREATMENT MEDICATIONS Blood test ▪ ↑ white blood cells count (WBC); ↑ sedimentation rate (ESR) ▪ General antibiotics depending on Gram stain of joint fluid ▪ Switch to specific antibiotics once bacteria identified ▪ Pain medications (e.g. NSAIDs, acetaminophen) Aspiration of joint fluid ▪ → bacterial culture → specific antibiotics SURGERY LAB RESULTS 590 OSMOSIS.ORG ▪ Surgically drain, cleanse joint fluid