Bone Infection Flashcards
Learning outcomes
- Describe the presentation of osteomyelitis and septic arthritis and suggests suitable treatment
- Present and recognise the characteristics of a susceptible host for bone infection
- Identify when a patient needs referral to surgery for debridement.
- Describe the mode of action and spectrum of activity for 2 commonly prescribed antimicrobials: ceftriaxone and doxycycline
- Define Outpatient Parenteral Antibiotic Therapy and list characteristics of patients suitable for this treatment method
Osteomyelitis
Haematogenous spread: Bone infection secondary to primary infection elsewhere (metastasising)
- skin via blood to bone- most likely Staph. A
- Urethra via blood to bone
Neisseria gonorrhoea causing a urethral infection; Mycobacterium tuberculosis (TB) causing a lung infection.
Contiguous focus
- Superficial infection penetrating
Trauma or chronic skin breaking (ulceration, potentially through peripheral vascular disease or diabetes)
Acute- of recent onset
Chronic- associated with poorly oxygenated, neuropathic tissues ( limb neuropathy or ischaemia)
OM presentation and diagnosis
Cardinal signs of inflammation- red, hot, swollen, painful, decreased mobility
Less so in chronic infection
Certain organisms with tropism for bones and joints- e.g Staph. A, Neisseria gonorrhoeae, Mycobacterium tuberculosis, Salmonella (and other coliforms) in children
Gold standard in diagnosis is bone biopsy which is difficult, and cannot be done through site of contiguous infection
Infection can be introduced through this procedure
Septic arthritis pathophysiology
- Often co-existing with OM, particularly vertebral bodies and intervertebral discs
Septic arthitis distinct from reactive arthritis, where there are no organisms in joint fluid
- Immunologically mediated (autoimmune)
- Bacteria (GI and GU infections)
- Viruses ( Rubella, Mumps b19)
Native and prosthetic joint infections (PJI)- type of septic arthitis
Joint prostheses increasingly common, especially in cases of arthitis e.g osteo, with large joints like hips and knees most commonly replaced
- Life- long risk of infection with lost of function of joint
- Less virulent staphylococci and other gram positives often involved
- Biofilm formed on the prostheses, and often at the bone/ cement junction- very difficult to remove using antibiotics alone, may need removal
Treatment principles for bone infection
- Remove de-vitalised tissue (sequestrum, or dead bone)
- Aspirate infected fluid collections (particularly in joints)
- Remove foreign bodies
- High doses to penetrate tissues and into joint spaces to be therapeutically active (mainly IV over oral)
- Long courses as bone is slow to turn over
Characteristics of a susceptible host for bone infection
- Dead or damaged bone susceptible to bone infection > tissue colonised, leads to infection and inflammatory response, which can occur in:
Trauma
Osteoporosis
Diabetics with peripheral vascular disease, risk factors include
- nutritional deficiency
- Glycosalisation of tendons in foot> Charcot foot, loss of pressure in foot when walking which can lead to ulceration
- ischaemia- poor oxygenation of tissues ( V.D)
- neuropathy- skin/ tissue breakdown, predisposition to infection
- loss of skin overlying bone (diabetic foot ulceration)
- colonisation of ulcers with potential pathogens
Epiphyseal growth plates of growing bone also susceptible to haemotogenous spread in children
- Debridement or surgery
- Debride where possible
- Sometimes surgery needed to biopsy- samples for cultures
- Vascular surgery also potentially useful as part of treatment, which enhance blood supply to the limb
OM in diabetic lower limb is LIMB- THREATENING infection
Sequential amputation possible
- OM- curative treatment with antibiotics
Sometimes in combination with surgery, time to cure reduced with surgery
- High doses of IV antibiotics: “6 weeks IV: 6 weeks PO”
Long courses- peripherally inserted central catheter (PICC) into
- secure venous access
- cumulative risk of adverse events
- OM- suppresive treatment
Is the cure worse than the disease? Long IV therapy, invasive surgery- risks of invasive treatments and secondary infections?
Aggressive treatment to cure in some with chronic OM or multiple comorbities not suitable
-Chronic OM in neuropathic limbs may be painless
- Patient may never be expected to mobilise again
- Therapeutic goal set to limit spread, and prevent sepsis
Septic arthitis treated with drainage/ device removal
- Joint space relatively avascular, antibiotics will fail to get into infected joint effusions (biofilm formation)
- PJI represents a deep surgical site infection with foreign body
-2 stage revisions
joint prostheses removed, then antibiotic
containing granules inserted into the space left for perhaps six weeks.
-During that period the patient will also be given IV antibiotics. - new joint would be placed once the antibiotic granules are remove
- Long term treatment with device retention
Ceftriaxone
- Cephalosporin antibiotic family: family of beta lactams
(beta lactam ring binds to transpeptidase enzyme on bacterial cell wall, stops cross linking in walls> death) - 3rd generation
- well tolerated antibiotic, can be given to children, pregnant women etc.
- Can cause C. diff
Ceftriaxone spectrum
Sensitive- Staph A, Strep. Pneumo, Neisseria meningitidis, haemophilus influenzae ( last 3 are 3 commonest causes of bacterial meningitis)
- IV Only
First line for suspected bacterial meningitis (anti-inflammatory on meninges)
Outpatient parenteral antibiotic therapy
- Soft tissue infection, bone and joint infection
Doxycycline
Class tetracyclines
- Inhibits bacterial protein synthesis by binding to the bacterial ribosomes, inhibiting protein synthesis -Bacterostatic drugs, but do not actively kill vegetative bacterial cells, kill them more slowly
- Only administered orally ( P.O = Per Os, by mouth)
- Binds to Ca2+ and Mg2+ ions, so bind to bone- good in bone and joint infection, but stains growing teeth ( not used in children and pregnant women).
Spectrum
Sensitive- Staph A., Strep. pneumo, legionella pneumophila, chlamydia trachomatis, mycoplasma pneumoniae ( last 3 atypical pneumonia)
PO treatment for MRSA
- Respiratory infection
- OM, as PO “step down” after 6 weeks IV treatment
- long term/ life long suppresion in chronic OM
Side effects are teeth staining ^
Photosensitivity
- sun exposed skin
