Infective Arthritis: Osteomyelitis

Question 1

Definition

Answer 1

Inflammatory condition affecting any bone in the skeleton, usually as a result of bacterial infection.
Most cases are acute + bacterial in origin, however some cases can be chronic + rarely even fungal.
- In adults are the vertebrae are the most commonly affected bones
- In children, long bones are more commonly affected

Question 2

Epidemiology

Answer 2

Children = haematogenous spread mc,
Adults = infection secondary to direct trauma
Men

Question 3

Risk factors

Answer 3

Penetrating injury
Intravenous drug use: S. aureus, Pseudomonas
Diabetes mellitus
HIV infection
Recent surgery
Distal or local infection: haematogenous spread
Sickle cell disease: salmonella infection
Rheumatoid arthritis
Chronic kidney disease
Immunodeficiency: e.g. SCID, IgA deficiency
Respiratory tract or varicella infection: in children

Question 4

Aetiology

Answer 4

Staphylococcus aureus: most common causative organism
Coagulase-negative staphylococcus
Streptococcus pneumonia: more common in children
Haemophilus influenzae: more common in unvaccinated children
Pseudomonas aeruginosa: increased risk with intravenous drug use
Salmonella species: most common cause in sickle-cell disease patients

Question 5

Pathophysiology

Answer 5

Bacteria enter the bone tissue, they express adhesions to bind to the host tissue proteins and produce a polysaccharide extracellular matrix. Through this, the pathogens are able to propagate, spread and seed further in the tissue.
In chronic cases, the infection can lead to devascularisation of the affected bone, resulting in subsequent necrosis forming and the resorption of the surrounding bone.
This leads to a floating piece of dead bone, termed a sequestrum which acts as a reservoir for infection (and is not penetrated by antibiotics as it is avascular)
An involucrum can also form, following the sequestrum formation = whereby the region becomes encased in a thick sheath of periosteal new bone

Question 6

Signs

Answer 6

Acutely : DULL BONY PAIN + HOT SWOLLEN
- Puncture wound
- Limp/ reluctance to weight-bear
- Local inflammation
- Local erythema
Chronically: + DEEP ULCERS (SEQUESTRAE)

Question 7

Symptoms

Answer 7

Fatigue: particularly with chronic osteomyelitis
Pain: at infection site
Fever: low-grade in chronic osteomyelitis
Reduced range of movement

Question 8

Diagnosis

Answer 8

ESR/CRP: Can be normal
Blood cultures: to identify systemic bacteraemia

X-ray of affected area:
Osteopenia
Bone destruction
Periosteal reaction
Cortical breaches

MRI: most definitive imaging modality

Question 9

Treatment

Answer 9

Acute: Immobilise +
FIRST LINE = IV FLUCOLOXACILLIN
MRSA = VANCOMYCIN, TEICOPLANIN, or LINEZOLID
Pseudomonas = Piperacillin/tazobactam
SECOND LINE = Surgical debridement

Question 10

DDx

Answer 10

CHARCOT JOINT: Damage to sensory nerve due to diabetic neuropathy
- causes progressive degeneration of weight bearing joint + bony destruction.
Often affect foot, presents with “diabetic feet”.

Question 11

RULE OUT TB

Answer 11

BM biopsy = caseating granuloma +ve