Osteomyelitis

Question 1

Define osteomyelitis.

Answer 1

Inflammatory condition of bone caused by an infecting organism (commonly Staph aureus). Usually involves a single bone but may rarely affect multiple sites.

Question 2

What is the aetiology of osteomyelitis?

Answer 2

Infection is either:

• haematogenous - originating from bacteraemia e.g. from skin infection, acute/subactue endocarditis, IV drug use
• contiguous focus - originating from a focus of infection adjacent to the area of osteomyelitis

Micro organisms in haematogenous osteomelitis: (most common is Staph aureus). Different groups of patients are susceptible to different organisms

Question 3

Which organisms most commonly cause haematogenous osteomyelitis in infants and young children?

Answer 3

Infants:

• S aureus
• Group B streptococci
• Aerobic garm -ve bacilli

Children <4:

• S aureus
• Strep pyogenes
• H. influenzae (if not immunised)
• Kingella kingae

Question 4

Which organisms cause haematogeous osteomyelitis in older children and older adults?

Answer 4

Older children and adults

Staph aureus

Older adults

Gram -ve bacilli

Question 5

What is the pathophysiology of osetomyelitis?

Answer 5

• Bacteria enter bloodstream
• Most of these are biofilm forming bacteria
• Infecetion spreads once bacteria adhere to surface
• Antibiotics that act on cell division are ineffective because these bacteria have minimal cellular invasion
• Usually affects metaphysis of long bones in children or vertebral bodies in adults
• Usually spares joint - but septic arthritis of adjacent joint may be indication of acute osteomyelitis esp in children

Question 6

What are the four anatomical subtypes of osteomyelitis?

Answer 6

• I - medullary and endosteal bone (haem)
• II - suuperficial osteomyelitis (contiguous)
• III - medullary and cortical involvement, but only part of circumference of bone affected
• IV - diffuse involvement of entire circumference of bone

Question 7

How common is osteomyelitis?

Answer 7

• 21.8/100,000 incidence
• Higher in men
• Recently incidence triples in patients with diabetes-related illnesses

Question 8

What are the risk factors for osteomyelitis?

Answer 8

• penetrating injuries
• surgical contamination
• IV drug use - S aureus and Pseudomonas aeruginosa
• diabetes mellitus - usually following minor trauma
• periodonitis - periodontal abscesses occur in osteomyelitis of the mandible

Question 9

What are the symptoms of osteomyelitis?

Answer 9

• Fever (typically low-grade)
• Non-specific pain at the site of infection
• Decreased sensation in cases of diabetic foot
• Malaise and fatigue
• Redness
• Swelling
• Sinus or wound drainage.

Question 10

What are the signs of osteomyelitis on examination?

Answer 10

• Local inflammation and erythema/swelling
• Acute/old healed sinuses, scars from previous surgery, fracture fixture
• Previous operations, scars/flap designs
• Decreased range of motion above and below the infected segment
• Deformitu of limd - esp in childhood osteomyelitis that may resulted in premature fusion of the physeal plate, resulting in limb shortening or angular deformity
• Tenderness to percussion over subcutaenous border of affected bones in chronic osteomyelitis
• Cervical vertebral osteomyelitis in those with torticollis secondary to seft-tissue infection of the neck
• Lumbar vertebral osteomyelitis will present with low back pain and may be associated with recen urosepsis, possibly due to anatomy of Batson’s plexus

Question 11

What investigations would you do for osteomyelitis?

Answer 11

Bloods:

• FBC - raised WCC/normal in chronic
• ESR/CRP - raised/normal in chronic. Good indicator of treatment efficacy.
• Culture of aspirate/biopsy/blood - deep samples should be taken after stopping antibiotics for 2 weeks.
• Histology - gram stainng of aspirate gives good indication of organism present

Imaging:

• Plain radiographs - look for fractures, tumours, osteopenia (6-7 days after infection onset). In chronic infection “fallen leaf” sign is when piece of endosteal sequestrum detaches and falls into medullary canal.
• US - associated collections, subperiosteal abscesses, joint effusions (=septic arthritis), guiding biopsy
• MRI /CT - most hepful T2.

Question 12

What may be seen in acute and chronic osteomyelitis on plain radiograph imaging?

Answer 12

acute disease:

• osteopenia appears 6-7 days after infection onset,
• and evidence of bone destruction,
• cortical breaches,
• and periosteal reaction follow quickly;
• involucrum and sequestra* can sometimes be seen, with further diffuse osteopenia developing later secondary to disuse of the affected limb;

chronic disease:

• intramedullary scalloping, cavities, and cloacae may be seen,
• with a ‘fallen leaf’ sign noted when a piece of endosteal sequestrum has detached and fallen into the medullary canal

Question 13

What are involucrum and sequestra in osteomyelitis?

Answer 13

The sequestrum is a piece of dead bone that has become separated during the process of necrosis from normal or sound bone.

When the sequestrum becomes encased in a thick sheath of periosteal new bone, known as an involucrum.