Tissue and bone infection: Osteomyelitis

Question 1

What is osteomyelitis?

Answer 1

Bone infection

Question 2

In adults, which other diseases tend to be associated with Acute osteomyelitis?

Answer 2

DM
Rheumatoid arthritis
Immunocompromised
Long-term steroid use

Question 3

How does infection get into the bone/spread? (3)

Answer 3

Haematogenous spread – children and elderly

Local spread from nearby site of infection – associated with trauma (open fracture), bone surgery (ORIF), joint replacement

Secondary to vascular insufficiency i.e. PVD, breakdown of skin over toes etc

Question 4

Source of infection in infants, children and adults

Answer 4

Key thing is that formation of biofilms results in persistent infections i.e

Infants: infected umbilical cord

Children: boils, tonsillitis, skin abrasions

Adults: UTI, arterial line

Question 5

What is the most common infecting organism in Acute Osteomyelitis?

Answer 5

Staph aureus

Question 6

What organisms cause diabetic foot and pressure sores?

Answer 6

Mixed infection including anaerobes

Question 7

Where do we see osteomyelitis?

Answer 7

At the ends of long bones i.e. femur, tibia (between the knee) or humerus

In joints with intra-articular metaphysis - it can stay in the bone or rupture into the joint which results in associated septic arthritis of the joint i.e hip or elbow

Question 8

Pathology of acute osteomyelitis?

Answer 8

Some sort of trauma at the metaphysis causes bruising or stasis of blood flow and that may lead to venous congestion and arterial thrombosis. This then causes acute inflammation which increases pressure in the area.

Organism establishes an area to breed - suppuration (pus filled boil)

Soon the pressure is released and the infection either goes into the medulla, sub-periosteal area or into the joint.

Necrosis of the bone occurs within the bone (sequestrum)

Some organisms like Staph A cause new bone to form (involucrum)

If it doesn’t resolve - chronic osteomyelitis

Question 9

Clinical features of osteomyelitis in infants

Answer 9

may be minimal signs, or may be very ill

failure to thrive

poss. drowsy or irritable

metaphyseal tenderness + swelling. May not see the swelling due to chubby legs/arms

Use the limb less

Positional change of limb- flexed

Question 10

Clinical features of osteomyelitis in children

Answer 10

Severe pain

Reluctant to move the joints (neighbouring joints held flexed for comfort); not weight bearing

May be tender

Fever (swinging pyrexia) + tachycardia due to infection

Malaise (fatigue, nausea, vomiting

Toxaemia

Question 11

Clinical features of osteomyelitis in adults

Answer 11

Primary OM seen commonly in thoracolumbar spine so patients often present with backache

They may have a history of UTI or urological procedure

Tends to be Elderly, diabetic, immunocompromised patients

Secondary OM is much more common - often after open fracture, surgery

Question 12

Which initial investigations are carried out in suspected osteomyelitis?

Answer 12

History and examination - pulse and temp for infection

FBC and diff WBC - neutrophil leucocytosis seen in response to infection

ESR and CRP will be elevated (may not be much change to them in early stages of infection however)

Blood cultures x3 - to detect organism

U+E’s - patient is very ill, dehydrated

Question 13

Imaging / diagnostic procedures for acute osteomyelitis? (6)

Answer 13

X-ray - will be normal in first 10-14 days as early on, any organisms breeding in the bone won’t show until there is some sort of change/ reaction/ death in the bone.

USS - detects subperiosteal puss if it exists

Aspiration of pus

Isotope bone scan - Tc-99 - inject into blood and it’s taken up by bone. More uptake in areas with increased bone turnover i.e. areas of infection

Labelled white cell scan - Take the patient’s WC and label them. Then reinject them and they will migrate to areas of infection

MRI

Question 14

Differential diagnosis for suspected infection

Answer 14

Acute septic arthritis
Acute inflammatory arthritis
Trauma (fracture, dislocation, etc.)
Transient synovitis (“irritable hip”)

Rare: sickle cell crisis, Rheumatic fever or haemophilia

Soft tissue infections:

Cellulitis 
Ersipelas
Necrotising fasciitis
Gas gangrene
Toxic shock

Question 15

What ways can a doctor obtain a microbiological diagnosis in order to plan treatment? (4)

Answer 15

Blood cultures in haematogenous osteomyelitis and septic arthritis

Bone biopsy

Tissue or swabs from up to 5 sites around implant at debridement in prosthetic infections

Sinus tract and superficial swab results may be misleading (skin contaminants)

Question 16

Why might Sinus tract and superficial swab results be misleading?

Answer 16

If you get OM and it ruptures out into the periosteum the pus will always find a way out and tunnel it’s way out through the skin resulting in discharge (common in chronic OM).

Superficial sinus tracts often get colonised by other organisms so if you take a swab you get a whole range of organisms and not the primary organism infecting the bone

Question 17

How do you treat Acute osteomyelitis?

Answer 17

These patients are unwell and septic so supportive treatment is important - pain management, fluids for dehydration, analgesia

Rest and splintage

Infection - antibiotics
Start with IV then give oral

Question 18

Which antibiotics are given for suspected osteomyelitis while waiting for a diagnosis?

Answer 18

Flucloxicillin + BenzylPenicillin as it is likely to be staph A or strep

Question 19

Why is timing important when it comes to treatment?

Answer 19

In early stages before pus forms you may be able to treat with simple antibiotics

But as soon as pus starts to form (24-48 hours) surgery is required. Operate, drain and wash it out.

Question 20

What must be done if a patient has a pus filled cavity/abscess?

Answer 20

It must be drained as antibiotics can’t reach these

Multiple drill holes in the metaphysis area to allow pus to drain out and release pressure and then close the wound to prevent sinus tract

Question 21

What are the complications of acute osteomyelitis?

Answer 21

Not treated - chronic OM

Ongoing metastatic infection i.e infection can seed to somewhere else in the skeleton or larger abscesses form around the body

Pathological fracture - infection weakens bone so if you then put weight on it, it can fracture. If this occurs through an area of chronic OM, it will never heal

If infection/pus spreads into joint space - septic arthritis

Septicemia, death

Altered bone growth - if infection is near growth plate it can be damaged – bone can become bent or short

Growth disturbance + deformities – if there is chronic infection near the growth plate (in children)

Squamous cell carcinoma (0.07%) – recurrent discharging sinuses – skin overlying can change to squamous cell

Question 22

How does chronic osteomyelitis come about?

Answer 22

may follow acute osteomyelitis

may start de novo
following operation, open fracture (poss. many years earlier) or in the immunosuppressed, diabetics, elderly, drug abusers, etc.

Repeated breakdown of “healed” wounds. Where someone has had surgery wounds or ulcers that have healed over, there is little resistance to pus escaping in these areas. This results in repetitive pus formation in this area of infected bone which then discharges out

Question 23

Most common organism in chronic osteomyelitis?

Answer 23

Often mixed infection but usually the same group of organisms each flare up because they are sitting in bone (often areas of dead bone) waiting for the opportunity to breed.

mostly Staph. Aureus, E. Coli, Strep. pyogenes, Proteus

Question 24

Treatment of chronic osteomyelitis

Answer 24

Try to suppress it - long-term antibiotics? either local or systemic

Eradicate bone infection - surgically (multiple operations)

Treat soft tissue problems
deformity correction? – squint bone

massive reconstruction? – remove large amount of bone and replace with graft etc

May need amputation

Question 25

What is bone ‘cement’?

Answer 25

Sometimes cavities are filled by an antibiotic releasing substance that is like cement

Question 26

What are lytic areas?

Answer 26

Areas of bone destruction leaving a hole in the bone