Bone And Joints Infections

Question 1

Definition of Bone 🦴 and joint infection

Aetiology/ causes

Risk Factors

Answer 1

Definition—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.

SIGNS & SYMPTOMS
▪ Pain → individual avoids using infected joint
Systemic
▪ Fever, chills, weakness, headache
Local
▪ Swollen, painful, warm

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

COMPLICATIONS
▪ Chronic infections
▪ Bone fractures
▪ Loss of mobility
▪ Dissemination of infection

Question 2

OSTEOMYELITIS

Answer 2

PATHOLOGY & CAUSES
▪ 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)
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

▪ Cortical loss
▪ Contrast enhancement of abscess rim
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 triangle- shaped, ossified edge)

▫ 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
▪ Surgical removal of dead bone ▪ Severe cases → amputation

Question 3

SEPTIC ARTHRITIS

Answer 3

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

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
LAB RESULTS
Blood test
▪ ↑ white blood cells count (WBC); ↑ sedimentation rate (ESR)
Aspiration of joint fluid
▪ → bacterial culture → specific antibiotics

TREATMENT
MEDICATIONS
▪ General antibiotics depending on Gram stain of joint fluid
▪ Switch to specific antibiotics once bacteria identified
▪ Pain medications (e.g. NSAIDs, acetaminophen)
SURGERY
▪ Surgically drain, cleanse joint fluid