Osteomyelitis

Question 1

What are the types of osteomyelitis?

Answer 1

Acute
Chronic
Specific e.g. TB
Non-specific - most common

Question 2

Who is most likely affected by acute osteomyelitis?

Answer 2

• Mostly children (different ages)
• Boys > girls
• History of trauma (minor)
• In adults - history other disease e.g diabetes, rheum arthritis, immune compromise, long-term steroid treatment, sickle cell

Question 3

What are the sources of infection in acute osteomyelitis?

Answer 3

• Haematogenous spread - occurs in children and the elderly
• Local spread from contiguous site of infection - trauma (open fracture), bone surgery (ORIF), joint replacement
• Secondary to vascular insufficiency

Question 4

What are sources of infection in acute osteomyelitis specific to infants, children and adults?

Answer 4

• Infants - infected umbilical cord
• Children - boil, tonsillitis, skin abrasions
• Adults - UTI, arterial line

Question 5

What are the causative organisms of acute osteomyelitis in infants (<1 year)?

Answer 5

• Staph aureus - most common
• Group B streptococci
• E. coli

Question 6

What are the causative organisms of acute osteomyelitis in older children?

Answer 6

• Staph aureus
• Strep pyogenes
• Haemophilus influenzae

Question 7

What are the causative organisms of acute osteomyelitis in adults?

Answer 7

• Staph aureus
• Pseudomonas aeroginosa (esp. secondary to penetrating foot injuries, IVDAs) - particularly in immunosuppressed adults, trainer foot
• Coagulase negative staphylococci (prostheses) •Propionibacterium spp (prostheses) - shoulder replacement
• Mycobacterium tuberculosis - uncommon in UK but in the increase

Question 8

What are the causative organisms in AO associated with diabetic foot and pressure sores?

Answer 8

Mixed infection including anaerobes

Question 9

What is the causative organism in AO associated with sickle cell disease?

Answer 9

Salmonella spp. (species)

Question 10

What are the causative organisms in AO associated with fishermen and filleters?

Answer 10

Mycobacterium marinum

Question 11

What are the causative organisms in AO associated with debilitating illness, HIV & AIDS, long-term antibiotic therapy, extensive GI surgery and malignancy?

Answer 11

Candida

Question 12

What are the causative organisms acute vertebral osteomyelitis?

Answer 12

• Staph aureus

* TB (uncommon and slower onset)

Question 13

What are the causative organisms in AO associated with butchers?

Answer 13

Brucella

Question 14

When can proteus mirabilis be a cause of AO ?

Answer 14

Joint replacement

Question 15

Where does acute osteomyelitis tend to be found in long bones?

Answer 15

• At the end of long bones - metaphysis (where the growth plate is):
• Distal femur
• Proximal tibia
• Proximal humerus

n.b. adults do also have a metaphysis region of long bones

Question 16

What is the feature of the joints affected by AO?

Answer 16

They are joints with intra-articular metaphysis

e.g. hip and elbow (radial head)

Question 17

Describe the pathological sequence of acute osteomyelitis

Answer 17

1. Starts at metaphysis - role of trauma? metaphysial injuries are not uncommon in children - lead to stasis
2. Vascular stasis - leads to venous congestion and arterial thrombosis - organism can inhabit area
3. Acute inflammation follows - causes increase of pressure
4. Suppuration (pus production)
5. Release of pressure - ruptures into medullary cavity, beneath the periosteum or into the joint (if nearby)
6. Necrosis of bone (sequestrum)
7. New bone formation (involucrum - shell of new bone that form - common in staph a infection)
8. Resolution (if not - chronic osteomyelitis)

Question 18

What are the clinical features of AO in an infant?

Answer 18

• May be minimal signs, or may be very ill
• Failure to thrive
• Possibly drowsy or irritable
• Metaphyseal tenderness + swelling - chubby legs prevent this and and by the time this occurs, pus is rupturing into the periosteal area
• Decrease ROM - range of motion
• Positional change
• Commonest around the knee
• Often have multiple sites

Question 19

What are the clinical features of AO in a child?

Answer 19

• Severe pain - able to communicate
• Reluctant to move - neighbouring joints held flexed, not weight bearing, may be tender
• Fever (swinging pyrexia) •Tachycardia
• Malaise (fatigue, nausea, vomiting, fretful)
• Toxaemia

Question 20

What are the clinical features of AO in an adult?

Answer 20

• Primary OM seen commonly in thoracolumbar spine
• Backache
• History of UTI or urological procedure
• Elderly, diabetic, immunocompromised
• Secondary OM much more common
• Often after open fracture, surgery (esp. ORIF) - so in younger age group
• Mixture of organisms

Question 21

What tests should you perform for diagnosis of suspected acute osteomyelitis?

Answer 21

• History and clinical examination (pulse + temp.)
• FBC + diff WBC (patients usually have a neutrophil leucocytosis in response to infection)
• ESR (may not be raised very early infections), CRP
• Blood cultures x3 (at peak of temperature - 60% +ve)
• U&Es – ill, dehydrated

Question 22

What tests should you perform for diagnosis of suspected acute osteomyelitis cont.?

Answer 22

• X-ray (normal in the first 10-14 days)
• Ultrasound - demonstrates sub-periosteal pus if it exists
• Aspiration (of pus)
• Isotope Bone Scan (Tc-99, Gallium-67) - taken up by bone as an alternative to calcium, increased turnover due to infection will light up
• Labelled white cell scan (Indium-111) - white cells labelled and re-injected and go to area of infection
• MRI

Question 23

What will you find on radiographs/x-rays of AO?

Answer 23

• Early radiographs - minimal changes
• 10-20 days - periosteal changes
• Medullary changes - lytic areas
• Late - osteonecrosis (sequestrum)
• Late - periosteal new bone (involucrum)

Question 24

What scan can be used to image AO and how do early and late phases of AO manifest on them?

Answer 24

• Technetium-99m labelled diphosphonate
• Gallium 67 citrate delayed imaging
• Indium-111 labelled WBC scan
• MRI
• From early to late phases of AO, the areas “lit up” by the scan enlarge
• Growth plates are more biologically active than the surrounding bone to show up darker when using Technetium

Question 25

How can AO be diagnosed using microbiology (for treatment)?

Answer 25

* Blood cultures in haematogenous osteomyelitis and septic arthritis * Local spread acute osteomyelitis blood cultures tend to be negative but are taken anyway * Bone biopsy/aspiration -drill biopsy * Tissue or swabs from up to 5 sites around implant at debridement in prosthetic infections * Sinus tract and superficial swab (pus finding a way to the surface) results may be misleading (skin contaminants)

Question 26

Name 5 main differential diagnoses for AO

Answer 26

* Scute septic arthritis * Acute inflammatory arthritis * Trauma (fracture, dislocation, etc.) * Transient synovitis (“irritable hip”) * Soft tissue infection

Question 27

Name 4 rarer differential diagnoses for AO

Answer 27

* Sickle cell crisis * Gaucher's disease - fat build-up in organs * Rheumatic fever * Haemophilia

Question 28

Which soft tissue infections can be differential diagnoses of AO?

Answer 28

* Cellulitis - (deep) infection of subcutaneous tissues (Group A Strep) * Erysipelas - superficial infection with red, raised plaque (Group A Strep) * Necrotising fasciitis - aggressive fascial infection (Group A Strep, Clostridia) * Gas gangrene - grossly contaminated trauma (Clostridium perfringens) * Toxic shock syndrome - secondary wound colonisation (Staph aureus)

Question 29

How is AO treated?

Answer 29

* Supportive treatment for pain and dehydration – general care, analgesia * Rest & splintage * Antibiotics * Surgery

Question 30

What is the route of antibiotics used in AO?

Answer 30

•Start with IV and switch to oral (in consultation with a microbiologist) around the 7-10 day mark (up to 2 weeks)

Question 31

For what duration are antibiotics used in AO?

Answer 31

•4-6 weeks - depends on response and ESR

Question 32

Which antiobiotics are used to treat AO?

Answer 32

* Empirical use of flucloxacillin and benzyl penicillin (while waiting for microbiological results) * Infection most likely to be Staph A or Strep

Question 33

Without antibiotics, what is the prognosis of AO?

Answer 33

* Mortality - 70% | * Chronicity - 80% of survivors

Question 34

Which qualities are required of the antibiotics used in the treatment of AO?

Answer 34

* Spectrum of activity * Penetration to bone * Safety fro long term admininstration

Question 35

Why can antibiotics fail?

Answer 35

* Drug resistance – e.g. beta-lactamases (MRSA) * Bacterial persistence - ‘dormant’ bacteria in dead bone - bacteria can sit for many years * Poor host defences - IDDM, alcoholism * Poor drug absorption * Drug inactivation by host flora * Poor tissue penetration

Question 36

When is surgery indicated in treatment of AO?

Answer 36

* Treatment with simple antibiotics can only be done in the earliest stages (first 24hr) * Aspiration of pus for diagnosis and culture - antibiotics cannot reach pus-filled cavities so must aspirate * Abscess drainage - multiple drill holes and then closed to avoid sinus * Debridement of dead/infected/contaminated tissue * 24-48hr - pus is forming, treat with antibiotics but if this does not work (continued pyrexia) continue to operate * Operate, drain, lavage * Infected joint replacement * one stage revision - take out dead tissue and put joint back in again * two stage revision - take out dead tissue and fill hole with something that releases antibiotics (usually cement0 and go back at a later date and put in a joint replacement * patients too unwell for surgery - treat on long term antibiotics

Question 37

What are the complications of acute AO?

Answer 37

* Septicaemia, death * Metastatic infection * Pathological fracture * Septic arthritis - pus perforates into the joint * Altered bone growth * Chronic osteomyelitis

Question 38

When can chronic osteomyelitis occur?

Answer 38

•May follow acute osteomyelitis * May start de novo: * following an operation * following an open fracture * immunosuppressed, diabetic, elderly, drug abusers •Repeated breakdown of "healed" wounds

Question 39

What are the causative organisms of chronic osteomyelitis?

Answer 39

* Often a mixed infection * Usually same organism(s) each flare-up * Mostly: * staph aureus * e. coli * strep pyogenes * proteus

Question 40

What are the pathological features of chronic osteomyelitis?

Answer 40

* Cavities, possibly sinuses * Dead bone (retained sequestra) - bone comes out * Involucrum * Histological picture is one of chronic inflammation

Question 41

What are the complications of chronic osteomyelitis?

Answer 41

* Chronically discharging sinus + flare-ups * Ongoing (metastatic) infection (abscesses) * Pathological fracture * Growth disturbance + deformities * Squamous cell carcinoma (0.07%)

Question 42

How is chronic osteomyelitis treated?

Answer 42

* Long-term antibiotics * local (gentamicin cement/beads, collatamp) * systemic (orally/ IV/ home AB) * Eradicate bone infection - surgically (multiple operations) * Treat soft tissue problems * Deformity correction * Massive reconstruction * Amputation (how many operations/years later?)