Infection

Question 1

What are the RFs for infective arthritis?

Answer 1

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

Question 2

What are the common organisms involved in infective arthritis?

Answer 2

staphylococcal aureus (70%)
streptococci/haemophilus (children)
gonococcus (sexual active adults)

Question 3

What are the common sites of infective arthritis?

Answer 3

knee
hip

almost always a single joint only

Question 4

What are the RFs for developing osteomyelitis?

Answer 4

most commonly in children 
immunosuppression/malnutrition 
diabetes 
damaged muscles 
presence of foreign material

Question 5

What are the common organisms involved in osteomyelitis?

Answer 5

staphylococcus aureus 
strep pyogenes/pneumonia
haemophilus influenza 
E.coli 
salmonella 
TB

Question 6

What are the target sites in osteomyelitis?

Answer 6

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

Question 7

What are the clinical features of septic arthritis?

Answer 7

single joint
pain, rapid onset and constant
swelling
warmth
loss of movement - joint rigid with pain
fever - from 48 hours of onset of symptoms

Question 8

In which patients might the picture of septic arthritis be less dramatic?

Answer 8

elderly
immunosuppressed
those with RA

Question 9

What are the differential diagnoses to consider in septic arthritis?

Answer 9

• 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

Question 10

What is the clinical presentation of acute osteomyelitis?

Answer 10

• 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

Question 11

What are the clinical features in subacute osteomyelitis?

Answer 11

• usually in children and adolescents

- pain near to a large joint for several weeks

Question 12

What are the clinical features of chronic osteomyelitis?

Answer 12

• follows an acute infection
• recurrent bouts of pain, redness and tenderness at the site
• chronic seropurulent discharge from a sinus which intermittently heals

Question 13

What are the three most common causes of osteomyelitis?

Answer 13

post-trauma osteomyelitis
post-surgery osteomyelitis
acute haematogenous spread

Question 14

What will the blood results show in septic arthritis?

Answer 14

raised WCC, CRP, ESR

also test for uric acid, clotting and rheumatoid immunology

Question 15

What investigations should be carried out in septic arthritis?

Answer 15

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

Question 16

What will be seen on joint aspiration in septic arthritis?

Answer 16

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

Question 17

How is septic arthritis managed?

Answer 17

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

Question 18

What is the antibiotic regimen for septic arthritis?

Answer 18

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

Question 19

Describe the pathology of septic arthritis

Long

Answer 19

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

Question 20

What is seen in a xray in septic arthritis?

Answer 20

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

Question 21

What are the 5 pathological stages of osteomyelitis?

Answer 21

inflammation 
suppuration 
necrosis 
new bone formation 
resolution

Question 22

Describe the pathology of osteomyelitis?

Answer 22

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

Question 23

What radiological changes are seen in osteomyelitis?

Answer 23

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

Question 24

What is viral arthropathy?

Answer 24

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

Question 25

What are the clinical features of viral arthropathy?

Answer 25

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

Question 26

What investigations can be carried out when suspecting viral arthropathy?

Answer 26

depends on infection
viral titres 
viral antigens 
antibody levels 
rheumatoid factor