MSK Infections Flashcards
What is osteomyelitis?
Inflammation of the bone and medullary cavity usually located in long bones. Can be acute or chronic and spreads by many mechanisms.
Who commonly gets osteomyelitis?
Often children by haematogenous spread.
Also PWID
Elderly if lots of central lines or dialysis
Organisms that may be involved in osteomyelitis?
Literally any
Staph Aureus= go to answer
PWID may get strep or weird infections
Dialysis and children likely Staph A
Describe the pathology of osteomyelitis?
Organism from the blood settles in the bone, infection spreads rapidly with acute inflammation and pus formation. There will be penetration through the cortex and the periosteum becomes raised and there is spread to the epiphysis. Penetration through soft tissue and new bone begins to be laid down but at the same time there is excessive necrosis. Involucrum of new irregularly formed bone. The presence of necrotic areas ensures the inflammation continues.
Presentation of osteomyelitis?
Red, hot, swollen, painful and loss of function at the site. May have a fever.
Gold standard for diagnosis of osteomyelitis?
Bone biopsy
Describe diagnosis of osteomyelitis?
History
Exam: Probe to bone test, if bone is visible and infection you automatically have osteomyelitis
Tests: Blood cultures are not always diagnostic. Gold standard is bone biopsy.
Name 3 complications of osteomyelitis?
Chronic osteomyelitis, disturbance of bone growth and amyloid disease.
Management of osteomyelitis?
Best to wait on microbiology. Don’t give empirical antibiotics unless patient is systemically unwell or septic
Surgery must remove infected tissue, drain and debride as no antibiotic will work on the necrotic centre.
6 weeks antibiotics. Depends on the organism. Staph A= flucloxacillin. Staph epidermidis= vancomycin. Strep pyogenes= doxycycline. Gram negatives= clindamycin. Anaerobes= metronidazole.
In blood tests for chronic disease what is important?
Anaemia of chronic disease
Describe the toxin PVL and what it will cause?
It is produced by some strains of Staph A and can cause necrotising disease
Strep are gram positive cocci in ___1____ and Staph are gram positive cocci in ___2_____
1) chains
2) clusters
Gram positive cocci in clusters that is coagulase positive is?
GOLDEN APPEARANCE
Staph Aureus
Gram positive cocci in clusters that is coagulase negative is?
WHITE APPEARANCE
Staph Epidermis
Describe alpha haemolytic strep
GREENISH COLOUR ON BLOOD AGAR
Strep pneumonia most common cause of pneumonia.
Strep viridians can be a commensal or cause endocarditis if spreads from mouth after dental procedure
Describe beta haemolytic strep
Group A: strep progenies (throat infections)
Group B: neonatal meningitis
Group C G etc
Describe non-haemolytic strep
Enterococci- usually gut commensals, can cause UTIs.
Open fractures are usually _______
polymicrobial
Diabetic ulcers are usually _______
polymicrobial
Describe gram positive cover of pathogens?
Flucloxacillin IV for Staph (and Strep)
(Vancomycin instead of flucloxacillin of penicillin allergic)
Oral switch for gram positives is doxycycline ( bone penetration excellent. Oral Flucloxacillin has poor bone penetration)
People with Sickle cell anaemia may get osteomyelitis from what organism?
Salmonella
can still get Staph A though
What disease has low prevalence in developed world but higher elsewhere?
Skeletal TB. Usually due to haematogenous spread from focus in lungs or GI tract.
What happens in skeletal TB?
The spine is commonly involved (Pott’s disease) with damage to the bodies of two neighbouring vertebrae leading to acute vertebral collapse and angulation of the spine (gibbous). Later an abscess from, pus can track along tissue planes and discharge at a point far from the affected vertebra.
Presentation of Skeletal TB?
Kyphosis, local pain, swelling, malaise, fever and night sweats
Treatment of Skeletal TB?
Same as pulmonary TB but extended to 9 months with initial immobilisation.
Sources of prosthetic joint infection?
From direct inoculation at time of surgery, manipulation of joint at time of surgery or seeding of joint at a later time.
Risk factors for prosthetic joint infection?
Rheumatoid arthritis, diabetes, malnutrition and obesity
Why is diagnosis of prosthetic joint infection difficult?
Often caused by organisms that are common contaminants. So need to take samples from multiple sites as this increases significance.
Treatment of prosthetic joint infection?
Ideally need to remove prosthesis and cement. Therapy for at least 6 weeks (type will depend on the bug)
Rifampicin is added to treatment of prosthetic joints as in theory it helps get through biofilms
Re-implantation of joint after aggressive antimicrobial therapy.
Why is rifampicin given in prosthetic joint infections?
Helps get through biofilms
Sources of Septic arthritis?
Can be caused by direct invasion, blood stream infection.
Less commonly from an infectious focus from cellulitis abscess or spread from osteomyelitis.
Pathogens involved in septic arthritis?
Usually Bacterial
Staph A (sometimes PVL- not common but look out for in a disproportionately sick person)
Streptococci
Only Staph Epi if related to a prosthetic joint
Neisseria gonorrhoea if sexually active
Presentation of septic arthritis?
Medical emergency: young people- joint will be red, hot, swollen and agonisingly painful. It is immobile. In elderly may have less obvious symptoms.
Investigations for septic arthritis?
Aspirate joint (purulent fluid), send fluid to micro, blood cultures, swabs, must check for crystals as presents similar to gout.
