Bone and Joint Infections

Question 1

Types of bone and joint infections

Answer 1

Bone

• haematogenous osteomyelitis
• contiguous osteomyelitis (with or without vascular insufficiency) – direct spread from adjacent tissues
• chronic osteomyelitis

Joint
- septic arthritis

Question 2

Haematogenous osteomyelitis: route, epidemiology, pathogenesis, clinical presentation, XR

Answer 2

Haematogenous = bloodstream spread

• mainly children (<16), male predominance
• in adult patients with malignancies, IVDA (vertebrae most commonly affected)
• at long bones near metaphysis (leg, arm pain) in children

Pathogenesis:
- Haversian canals containing blood vessels travel from medulla to growth plate and tapers into small plexuses –> bacteria can get stuck if there is underlying bacteraemia –> infection at metaphysis

Clinical presentation:

• local – pain, erythema, swelling; pseudoparalysis; soft tissue abscess, sinus tract (infection track onto tissue and out to skin if delayed presentation)
• systemic – fever, systemic toxicity (bacteraemia)
• XR: radiolucency inside bone, raised periosteum, soft tissue swelling, Brodie abscess (intraosseous abscess that may spread and break cortex via Volkmann canal to become subperiosteal – sinus tract)

Question 3

Haematogenous osteomyelitis: organism, diagnosis, treatment

Answer 3

Organism: S. aureus (90%)

• E. coli or group B strep in neonates
• coliforms or pseudomonads in elderly/ debilitated
• TB must be considered in HK
• s. paratyphi in sickle cell anaemia as dysfunctional spleen fails to remove salmonella from blood

Diagnosis:

• CULTURE of
• • BONE tissue (gold standard but difficult routinely)
• • BLOOD (systemic infection)
• • needle aspiration (pus discharge from sinus)
• • sinus tract swab (not preferred as may yield skin flora)
• Imaging
• Inflammatory markers (ESR, CRP, WBC) –> for monitoring treatment response since prolonged treatment needed

Treatment:

• Anti-staphylococcal agent: CLOXACILLIN (+/- other coverage based on age and culture)
• IV therapy initially (2 wks), until patient is stable
• Oral sequential therapy (2 wks) – outpatient
• poor bone penetration and low bioavailability due to poor vascularisation ==> 4-6 WEEKS DURATION

(pain relief, drainage if subperiosteal abscess present, debridement, physiotherapy )

Question 4

Contiguous focus osteomyelitis without vascular insufficiency: route, organism, treatment

Answer 4

= spread from nearby structures

• direct inoculation of bacteria from env. or skin e.g. trauma, surgical procedure

Organism: POLYMICROBIAL (s. aureus, staph epidermidis, GN bacilli, anaerobes)

Treatment:
- broad coverage – Augmentin

Question 5

Contiguous focus osteomyelitis with vascular insufficiency: risk factors, organism, treatment

Answer 5

Vascular insufficiency due to DM, atherosclerosis, vasculitis

Affect extremities with poor blood supply
e.g. infected diabetic food ulcer

Organism: POLYMICROBIAL

Treatment: Augmentin

Question 6

Chronic osteomyelitis: pathogenesis, specific features, course, treatment, prevention

Answer 6

progress from haematogenous or contiguous osteomyelitis

• indolent course with repeated flares (mths to yrs)
• 25% open fractures, 1% post-operative

Improper treatment of previous osteomyelitis –> chronic nidus of infection formed
=> dead bone (sequestrum) formation –> further acts as persistent nidus of infection (severe prolonged periosteal infection)
=> reactive new bone (involucrum) formation
=> sinus tract formation

Treatment:

• difficult to cure without surgical removal of sequestrum (radical debridement)
• AT LEAST 6 WEEKS antibiotics after last debridement (cloxacillin)
• rest and pain control/ correct underlying risk conditions

Prevention:

• prophylactic antibiotics
• open fracture (decontamination, remove necrosed tissue, external fixator)

Question 7

Septic arthritis: pathogenesis, routes of infection, risk factors, clinical presentations

Answer 7

Invasion of synovial membrane by micro-organisms usually with extension into the joint –> close space infection (very painful!)
- damages articular cartilage (fibrosis, ankylosis)

Routes of infection:

• haematogenous
• direct inoculation
• contiguous e.g. osteomyelitis very close to joint

Risk factors:

• immunocompromised
• children (none, sometimes adjacent osteomyelitis)
• adults (bacteraemia, IVDA, co-existing joint disease)

Clinical presentations:

• MONOarticular (DDx: gout)
• Knee/ hip joints commonly involved
• local: erythema, swelling, hotness, pain; decrease ROM
• systemic: fever, systemic toxicity

Question 8

Septic arthritis: organisms, diagnosis, treatment

Answer 8

Organism: s. aureus (60-90%)

• neonates - E. coli, grp B strep
• pre-school children - grp A strep
• adults - N. gonorrhoea (disseminate from urethral or endocervial mucosa)
• elderly - pneumococci, GN bacilli

Diagnosis:

• JOINT FLUID ANALYSIS – gram’s stain, culture, rate crystal birefringence (rule out gout), inspection (turbid)
• BLOOD culture
• Imaging
• WBC, ESR, Rheumatoid factor

Treatment:

• Anti-staphylococcal agent - IV CLOXACILLIN, 2-4 weeks (shorter than bone) – adjust according to culture
• disseminated gonococcal arthritis (1 wk)
• SURGICAL DRAINAGE/ LAVAGE of joint (indicated once there is +ve gram stain results – improve treatment results as antibiotics don’t penetrate 100%)

(physiotherapy)