Infection Flashcards
What are the RFs for infective arthritis?
being a child/young adult
penetrating injury
open fractures
insertion of surgical prosthesis (at knee and hip)
non-sterile intra-articular injection of steroids
IV drug use
What are the common organisms involved in infective arthritis?
staphylococcal aureus (70%)
streptococci/haemophilus (children)
gonococcus (sexual active adults)
What are the common sites of infective arthritis?
knee
hip
almost always a single joint only
What are the RFs for developing osteomyelitis?
most commonly in children immunosuppression/malnutrition diabetes damaged muscles presence of foreign material
What are the common organisms involved in osteomyelitis?
staphylococcus aureus strep pyogenes/pneumonia haemophilus influenza E.coli salmonella TB
What are the target sites in osteomyelitis?
Acute haematogenous infection = metaphysis of the growing end of the long bone in children and spine is most common adults
subacute haematogenous infection = distal femur and prox/distal tibia in subacute haematogenous infection
chronic infection = open fracture or operative procedure
What are the clinical features of septic arthritis?
single joint
pain, rapid onset and constant
swelling
warmth
loss of movement - joint rigid with pain
fever - from 48 hours of onset of symptoms
In which patients might the picture of septic arthritis be less dramatic?
elderly
immunosuppressed
those with RA
What are the differential diagnoses to consider in septic arthritis?
- irritable hip (reactive arthritis)
- perthes disease
trauma causing haemarthrosis or effusion - crystal deposition (gout/pseudogout/ acute calcific tendonitis in the shoulder)
- Monoarticular presentation of RA/seronegative arthritis/SLE
What is the clinical presentation of acute osteomyelitis?
- usually in a child
- sometimes with a history of preceding skin lesion, injury or sore throat
- pain: continuous, throbbing, often worse at night
- fever
- general malaise
- acute ‘finger tip’ tenderness near one of the large joints
- local redness, swelling, warmth and oedema are late signs and signify pus
- failure to thrive with drowsiness and being irritable in the newborn
- backache and mild fever in adults
What are the clinical features in subacute osteomyelitis?
- usually in children and adolescents
- pain near to a large joint for several weeks
What are the clinical features of chronic osteomyelitis?
- follows an acute infection
- recurrent bouts of pain, redness and tenderness at the site
- chronic seropurulent discharge from a sinus which intermittently heals
What are the three most common causes of osteomyelitis?
post-trauma osteomyelitis
post-surgery osteomyelitis
acute haematogenous spread
What will the blood results show in septic arthritis?
raised WCC, CRP, ESR
also test for uric acid, clotting and rheumatoid immunology
What investigations should be carried out in septic arthritis?
bloods
joint aspiration (synovial fluid analysis)
blood cultures
leucocytosis
skin wound swabs, sputum and throat swabs or urine (may be positive and indicate source of infection)
X-rays of NO VALUE
What will be seen on joint aspiration in septic arthritis?
do a microscopy for crystals, cells and organisms
fluid for urgent gram staining, culture and sensitivities
fluid is frankly purulent, but indicates inflammatory cells and not necessarily infection
How is septic arthritis managed?
Early washout - open or arthroscopic, take multiple specimens and repeat washout for reaccumalation as required
Antibiotics
Rest the joint and ensure mobilisation of joints around it
What is the antibiotic regimen for septic arthritis?
initial IV therapy after specimen taken, agents tailored to culture and sensitivity
flucloxacillin for gram positives, cephalosporin if gram negative cover is needed
2 weeks of IV abx followed by 4 weeks oral
Describe the pathology of septic arthritis
Long
joint is invaded through a penetrating wound, by eruption of the bone abscess or by haematological spread from a distal site
infection spreads through joint and cartilage is destroyed
pus bursts out of the joint and cartilage is destroyed
with healing the raw articular surfaces may adhere to produce fibrosis or bony ankylosis
What is seen in a xray in septic arthritis?
not useful for diagnosis
x ray in the first 2 weeks shows soft tissue swelling, widening of joint space due to effusion ad periarticular osteoporosis
later x-rays show joint space becomes narrowed and there are signs of bone destruction is advanced
What are the 5 pathological stages of osteomyelitis?
inflammation suppuration necrosis new bone formation resolution
Describe the pathology of osteomyelitis?
acute inflammation reaction leads to intense pain and obstruction of blood flow –> suppuration - pus appears in the medulla and can extend along the shaft and into soft tissues –> necrosis - blood supply increasingly compromised and necrosis occurs at day 7 –> new bone formation (if infection persists - chronic osteomyelitis) –> resolution
What radiological changes are seen in osteomyelitis?
Normally no abnormality on x-ray for 10 days, radio-isotope scan shows increasing activity. By two weeks there may be a reduction in bone density and new bone formation. Bone becomes ragged if remains untreated –> sclerosis and thickening of the cortex with healing. MRI may distinguish between bone and soft tissue infection
What is viral arthropathy?
arthritis caused by acute infection of the joint by a virus or an arthritis reactive to viral infection at a distant site
typically self limiting and requires no specific intervention
What are the clinical features of viral arthropathy?
vary depending on causative virus
occur during the viral prodrome with characteristic rash
tend to be symmetrical with small joint involvement
- Non-destructive
- Doesn’t lead to chronic disease
What investigations can be carried out when suspecting viral arthropathy?
depends on infection viral titres viral antigens antibody levels rheumatoid factor
