Flashcards in Orthopaedics - Emergencies Deck (31)
What is osteomyelitis?
Osteomyelitis is inflammation of the bone caused by an infective organism. Bone is normally resistant to bacterial colonization but trauma, surgery, foreign bodies and prosthesis can lead to bone infection. Osteomyelitis can also result from haematogenous spread caused by a bacteraemia.
Why is osteomyelitis associated with prosthesis difficult to treat?
When bacteria grow on a prosthesis they usually form a biofilm. This protects them from antibiotic treatment. Osteomyelitis associated with prothesis usually requires treatment with rifampicin and other antibiotics depending on the strain.
Which parts of the skeleton are affected in osteomyelitis?
The adult skeleton is divided into 2 components - the axial skeleton and the appendicular skeleton.
Haematogenous osteomyelitis (bone infection spreading via the bloodstream) typically involves the vertebrae but infection may also involve the metaphysis of the clavicle, pelvis and long bones. It is usually 2 adjacent vertebrae and the IVD that are affected with the lumbar spine being most common.
Post traumatic osteomyelitis begins outside the bony cortex and works its way towards the medullary canal, typically found in the tibia.
Contiguous focus osteomyelitis often occurs in the bones of the feet and in patients with diabetes.
In which group of patients is acute haematogenous osteomyelitis most common?
Haematogenous osteomyelitis can occur in adults, and when it does the vertebrae are usually involved. But acute haematogenous osteomyelitis is more common in children and usually occurs in the long bone metaphysis.
What is the most common organism causing acute osteomyelitis?
S.aureus is the most common cause, followed by S.pyogenes or S.pneumoniae. In young children H. influenza is not uncommon.
What osteomyelitis are patients with sickle cell aneamia most susceptible to?
How is the infection introduced in acute osteomyelitis?
Bacteria infect the bloodstream from a skin abrasion or boil, or infected umbilical cord in the newborn. In adults the source of the infection may be an indwelling device such as an arterial line.
Organisms settle on the metaphysis at the growing end of long bones. This may be due to the hairpin arrangement of capillaries which slows down the rate of blood flow.
What is the progression of acute haematogenous osteomyelitis?
An infective focus at the metaphysis spreads towards the surface of the bone to a form a subperiosteal abscess (this is because pus spreads along the Volkmann canals). Bone may die and become encased in perisoteal new bone as a sequestrum. New bone forms and thickens to form an involcrum which encloses the infected tissue. If infection is controlled bone will heal but may remain thickened.
What are the clinical features of acute osteomyelitis? How do (i) infants and (ii) adults present?
Osteomyelitis often presents with non specific symptoms such as pyrexia, lethargy and irritability. The classic signs of local pain, swelling and redness may appear but can disappear within 5-7 days and often signify late disease, making them unreliable.
In infants the symptoms may be mild, the baby can fail to thrive and be drowsy or irritable. They may have reduced limb movement and pain in the affected limb. Suspicion should be raised by a history of birth complications or umbilical artery catheterization.
In adults, the commonest site of haematogenous infection is the spine. Suspicious features are backache and mild fever.
Why do negative radiographs not exclude the diagnosis of osteomyelitis?
For the first 5-7 days in children and 10-14 days in adults, x-rays show no abnormalities. When findings are present they are usually late on in the infection. They can include cortical thickening, sclerosis and irregularity. New bone formation can also be present.
What other imaging modalities are useful in osteomyelitis?
CT is useful for guiding needle biopsies and preoperative planning.
MRI may help distinguish between bone and soft tissue infection.
What investigations should be performed in acute osteomyelitis?
FBC is useful and often shows a leucocytosis and anaemia. Leucocytosis is common in acute osteomyelitis, and ESR and CRP are also usually raised.
Blood cultures are positive in only 50% of case. Fine needle aspiration or open bone biopsy is the most accurate way to confirm osteomyelitis. Even if no pus is found a smear of the aspirate can be examed for MC&S.
Name some complications of osteomyelitis
1) Spread - infection may spread to the joint (septic arthritis) or to other bones (metastatic osteomyelitis)
2) Growth disturbance - this is more common in children especially if the physis are damaged leading to deformity or shortening
3) Persistent infection - this may still develop in 5-10% of patients treated appropriately
Is there a classification system for osteomyelitis?
There are in fact several classification systems used for osteomyelitis. The most widely used one is the Cierny-Mader system which is split into 2 parts. Part 1 looks at the extent of the disease and has 4 sub groups, part 2 looks at the physiology, immunology and metabolism of the patient.
There are others, such as the Kelly classification system that considers osteomyelitis in adults.
When is surgery considered for osteomyelitis?
Surgery is indicated in osteomyelitis if
- the patient fails to respond to specific antibiotic therapy
- evidence of persistent soft tissue abscess
- if there is also a joint infection present
What empiric antibiotic therapy is used for older children and previously fit adults who probably have a staph infection?
These patients are started on IV flucloxacillin (penicillinase-resistant penicillin) plus fusidic acid. Importantly, the antibiotic may be changed when the results of sensitivity tests are known. This should be continued until the patient shows signs of improvement (usually 1-2 weeks) and is then followed by oral antibiotics for another 3-6 weeks.
Clindamycin is a good antibiotic to continue oral therapy with.
What antibiotic is best used if MRSA osteomyelitis is suspected?
What antibiotic is preferred in acute haematogenous osteomyelitis in children under 4 years?
These children have a high incidence of haemophilus infection. In this group, and in cases with gram negative organisms it is best to start with a third generation cephalosporin such as ceftriaxone.
What surgical options are available to treat acute osteomyelitis? When should they be used?
The Cierny-Mader classification system plays an important role here. Patients with class 3 or 4 are suitable for surgery and respond well. Surgery involves adequate drainage (required in 30% of cases), debridement of necrotic tissue, and restoration of blood supply.
The Ilizarov method is often used for surgical treatment. It promotes bone growth through "distraction osteogenesis" via cortical osteotomy and other techniques.
What is subacute haematogenous osteomyelitis?
Osteomyelitis may present in a mild form, probably because the organism is less virulent or the patient is more resistant. The distal femur and proximal and distal tibia are the more common sites for subacute disease.
The patient is usually a child or teenager that has had pain near one of the large joints for several weeks.
What is a Brodie's abscess?
This is a small, oval cavity surrounded by sclerotic bone seen on plain film. The lesion can sometimes be more diffuse and a small abscess is easily mistaken for an osteoid osteoma. Therefore the diagnosis can only be made when the lesion is explored.
NB - Brodie's abscess is only one type of subacute osteomyelitis
When does chronic osteomyelitis occur? What is the usual clinical history?
This usually occurs following an open fracture or operation. An area of bone is destroyed by the acute infection, leaving a sequestra surrounded by dense sclerosed bone. The sequestra provokes a chronic purulent discharge which escapes through a sinus. Bacteria may remain dormant for years, giving rise to recurrent flare ups of acute infection.
What are the most common organisms causing chronic osteomyelitis?
S. aureus, E.coli, S.pyogenes, Proteus and Pseudomonas, S.epidermidis (surgical implants)
What are the clinical features of chronic osteomyelitis?
Remember that this tends to occur following acute infection. The patient returns with recurrent bouts of pain, redness and tenderness at the affected site. Classic signs are healed and discharging sinuses and x-ray features of sclerotic bone with cortical thickening.
How is chronic osteomyelitis treated?
This depends on the frequency of relapsing flare ups and if these are uncommon can be conservative.
A sinus may be painless and may only need dressing occassionally. Antibiotics are often used but commonly fail to penetrate the barrier of fibrous tissue plus bone sclerosis. Sequestrectomy should only be performed it is radiologically visible and surgically accessible.
Ilizarov technique can be used in refractory cases.
What agent causes post traumatic infection?
An open fracture may become infected; this is the usual cause of osteomyelitis in adults. Staph aureus is the most common.
The patient has a fever and pain and swelling over the fracture site. The wound is inflamed and there may be purulent discharge.
Blood tests show a leucocytosis and increased ESR.
Treatment is with antibiotics and wound debridement.
What predisposing factors increase the risk of post operative infection?
Post-op infections occur in 3-5% of hospital cases. S.aureus is the most common agent.
- chronic disease (e.g. RA)
- previous infection
- steroid therapy
- difficult/ long operations
- haematoma formation
What is septic arthritis? How is it different to reactive arthritis?
Septic arthritis is direct invasion of the joint space by microbes. Bacteria are most common, but viruses and fungi can also occur.
Reactive arthritis represents a sterile inflammatory condition that occurs following extra-articular infection.
What are some risk factors for septic arthritis?
- male sex (55% occur in men)
- over 65 years of age
- prosthesis (ranges from 2-10%)