Soft tissue, bone and joint infections

Question 1

What is the aim of the skin and what are its 3 main layers?

Answer 1

physical barrier against microorganisms
3 layers:
1) epidermis: outer layer and waterproof
2) dermis: tough connective tissue, hair follicles and sweat glands
3) subcutaneous layer: fat and connective tissue

Question 2

What are the non-specific defences of skin?

Answer 2

exfoliation: sloughing of the stratum corneum dislodges many adherent bacteria
dryness: bacterial counts much higher in moist areas
acidic: pH 5.5
low temperature
sweat glands: saltiness - inhibits bacteria
normal bacterial flora - complete for colonisation sites, compete for nutrients

Question 3

What is the normal flora of the skin?

Answer 3

microorganisms are always present on the skin

• s epidermidis
• s aureus
• micrococci
• diphtheroids

some microorganisms are transient flora and are prevented from colonising due to:

• mechanical barrier
• sebum
• cleaning and washing

Question 4

What type of organism is staphylococcus aureus?

Answer 4

gram +ve cocci and coagulase positive 
golden colonies - yellowy/cream colour 
30-40% of population are colonised 
acquired resistance to beta-lactam antibiotics - methicillin 
causes haemolysis of red cells

Question 5

What type of organism is streptococcus pyogenes?

Answer 5

group A streptococci
gram +ve cocci
beta haemolytic - get partial haemolysis of alpha chains
colonises the pharynx

Question 6

What syndromes do you get within the epidermidis and dermis?

Answer 6

impetigo 
folliculitis
furunculosis 
carbunculosis 
erysipelas
\+ cellulitis

Question 7

What syndromes do you get within the superficial fascia, subcutaneous fat, nerves, arteries, veins and deep fascia ?

Answer 7

necrotising fascitis

Question 8

What syndrome do you get in the muscle?

Answer 8

myonecrosis

Question 9

What conditions predispose to skin invasion?

Answer 9

excessive moisture - induces breakdown of the stratum corneum - occlusive dressings, obesity (infections seen in intertriginous folds)
minor abrasions
surgery
crush injuries - RTAs
burns - infections primary cause of death in burns patients
percutaneous e.g. intravenous catheters
bed sores- cutaneous lesions due to pressure lead to skin necrosis and secondary infections
conditions that compromise the blood supply- diabetes

Question 10

What is impetigo?

Answer 10

superficial skin infection 
friable golden crusts over erythematous skin 
more common in children 
very contagious
usually due to strep A

Question 11

What is folliculitis?

Answer 11

infection of the hair follicles
common sites are groin and scalp
causative organism= s aureus
tx= flucloxacillin

Question 12

What are some pyogenic skin infections?

Answer 12

furunculosis = deep inflammatory lesion progressing from a folliculitis
carbuncle = multiple fistulas = extend into the subcutaneous layer, multiple abscesses develop, separated by connective tissue
acute paronchia = skin infection arising from nail - remove nail and pus pores out

tx= oral flucloxacillin

Question 13

What is cellulitis?

Answer 13

acute, spreading inflammation of the lower dermis and associated with subcutaneous layer of skin
diffuse inflammation without necrosis or localisation of pus
often seen as red halo around wound
skin is hot, red and painful

Question 14

What is the causative agent of cellulitis commonly ?

Answer 14

s. aureus

less common- s pyogenes, c perfringens

Question 15

How is cellulitis diagnosed?

Answer 15

most commonly affects lower extremities
acute, tender, erythematous and swollen area of skin - could be a DVT
fever and malaise
WCC and CRP usually raised
blood cultures only useful if pt is septic

Question 16

What is the treatment for cellulitis?

Answer 16

rest and elevation
mark area of cellulitis
oral penicillin V and flucloxacillin
if severe may need IV abx

Question 17

What is erysipelas?

Answer 17

infection involving the upper dermis and extends into the superficial cutaneous lymphatics
distinguished clinically by lesions raised above surrounding skin, clear line of demarcation of involved and not involved tissue
Group streptococci A most common cause
most common on legs or face
diagnosis: clinical appearance
treatment: penicillin

Question 18

What is staphylococcal scalded skin syndrome?

Answer 18

seen in infants, young children and immunocompromised
clinical:
- starts with erythema, then fever, followed by large fluid filled bullae (large blister containing serous fluid), rupture and causes widespread exfoliation

toxins released into blood from localised S aureus infection - can die from this

Treatment: flucloxacillin

Question 19

What do you worry that cellulitis might progress to?

Answer 19

necrotising fasciitis

Question 20

What is necrotising fasciitis?

Answer 20

can be caused by one organism on its own (group A strept) or combination of bacteria
enter fascial plane following trauma, surgery or occult bacteraemia
inflammatory response - affects neurovascular bundles
thrombosis of vessels compromises blood supply and nerves to the skin

Question 21

What are the 3 stages of symptoms in necrotising fasciitis?

Answer 21

1) early (<24 hours)
- presence of skin trauma but pain seems disproportionate to injury
- flu like symptoms and thirst
2) advanced symptoms
- swelling of painful area
- large dark blotches (violet)
- mottled flaky appearance at trauma site
3) critical symptoms
- severe fall in BP
- toxic shock from poisons released by bacteria
- unconsciousness

TX= IV abx and surgery

Question 22

What is gas gangrene?

Answer 22

very rare - common cause of death in the past military conflicts - arising in devitalised wounds contaminated with soil
clostridium perfringens - most common cause - produces toxin which causes cell death
can occur in synergistic soft tissue infections e.g. wound contaminated with coliforms - use up oxygen making it amenable for anaerobes to grow
Tx= urgent surgery to remove dead tissue

Question 23

Which patients is gas gangrene more common in ?

Answer 23

underlying blood vessel disease, diabetes or colon cancer

Question 24

What are surgical site infections?

Answer 24

infections that affect the surgical wound or deeper tissues handled during the procedure resulting in local signs and clinical symptoms

up to 20% of all healthcare associated (nosocomial) infections - >5% of patients who undergo surgery develop an SSI

associated with morbidity, extended hospital stay and financial burden to patients and healthcare system
majority are preventable

Question 25

What is the actual definition of SSI?

Answer 25

incisional (superficial or deep) organ/space infection - has to occur within 30 days or 1 year if an implant was inserted
Criteria
1) assessment of the surgical site (purulent drainage)
2) microbiology culture/s from sterile sites
3) signs of infection (fever, pain, tenderness, redness, heat)

Question 26

What patient factors impact risk of SSI?

Answer 26

extremes of ages
poor nutritional state 
obesity 
immunosuppression, diabetes, steroids
smoking 
infections at other body sites

Question 27

What microbial factors impact risk of SSI?

Answer 27

level of contamination (with prophylaxis)
clean wound 5%
clean contaminated 10%
contaminated 20%

Question 28

What procedural factors impact risk of SSI?

Answer 28

length of surgical scrub 
skin anti-sepsis 
pre-op shaving 
pre-op skin prep
length of op
operating theatre ventilation 
inadequate instrument sterilisation 
foreign material at surgical site

Question 29

What pre-op measures can be in place to prevent SSI?

Answer 29

patient preparation (showering)
hair removal (clippers)
antibiotic prophylaxis
staff preparation

Question 30

What intra-op measures can be in place to prevent SSI?

Answer 30

operating team preparation
patient skin preparation
maintaining patient homeostasis
wound dressings

Question 31

What post-op measures can be in place to prevent SSI?

Answer 31

dressing and cleaning wound
antibiotic treatment
debridement
specialist wound care services

Question 32

What are the typical features of SSI?

Answer 32

Increased exudate
increased swelling 
increased erythema 
increased pain 
increased local temperature 
peri-wound cellulitis - invasive infection, change in appearance of granulation tissue (discolouration, prone to bleed, highly friable)

Question 33

What are the 2 major types of bone infections?

Answer 33

septic arthritis - infection of joint spaces, s. aureus, streptococci, gram negatives

osteomyelitis - infection of bone - s.aureus, h. influenzae, e.coli, p.aeruginosa, proteus mirabilis

Question 34

What are the different routes by which bacteria can enter a joint in septic arthritis?

Answer 34

haematogenous route= most important
direct inoculation via trauma
arthritis with associated tendonitis

more common in a joint affected by rheumatoid disease or history of trauma
bacteria in an occult bacteraemia enter joint space=>inflammatory response= invasion of neutrophils into the joint

Question 35

What is acute osteomyelitis?

Answer 35

bone may become infected following direct introduction into the tissue by trauma/surgery or by haematogenous route
chronic or acute infection

Question 36

What are the clinical features of acute osteomyelitis in adults ?

Answer 36

severe pain 
reluctant to move 
fever, malaise 
backache
history of UTI or urological procedure 
old, diabetic, immunocompromised

Question 37

What are the clinical features of acute osteomyelitis in infants?

Answer 37

failure to thrive, drowsy, irritable
metaphyseal tenderness
decrease ROM
commonest around knee

Question 38

How do you diagnose osteomyelitis?

Answer 38

Hx and clinical exam 
FBC, ESR, CRP, Blood cultures 
XR 
US 
Bone scan 
MRI 
Aspiration

Question 39

What is the treatment for osteomyelitis?

Answer 39

flucloxacillin
- or clindamycin if penicillin allergic
- or vancomycin if MRSA (+ fusidic acid or rifampicin if prothesis present or life-threatening condition)
treat acute infection for 4-6 weeks
treat chronic infection for at least 12 weeks

Question 40

What do diabetic foot ulcers progress from?

Answer 40

cellulitis> deep soft tissue infection> osteomyelitis

Question 41

What are the risk factors for diabetic foot infections?

Answer 41

vascular disease
peripheral neuropathy
poor foot care

Question 42

What organisms usually cause diabetic foot infections?

Answer 42

s. aureus, beta-haemolyic streptococci, diphtheroids
gram-ve bacilli (e.coli, k. pneumoniae, pseudomonas sp)
anaerobes

Question 43

What viruses can cause skin reactions?

Answer 43

herpes and vzv (chickenpox)- can persist in dorsal root ganglia and have potential to reactivate
other viruses: rubella, parvovirus, measles, HSV6
HSV limited to genital and oral regions -

Question 44

What are dermatophyte infections?

Answer 44

fungi invade dead tissues of the skin or its appendages (nails and hair)
most common = trichophyton, epidermophyton and microsporum
difficult to distinguish clinically
spread from person to person or animal to person

Question 45

How do you diagnose dermatophyte infections?

Answer 45

based on site
tinea corporis = ringworm
tinea pedia = athlete’s foot
tinea barbae = barber’s itch

Question 46

What is the treatment for dermatophyte infections?

Answer 46

topical imidazoles or other anti-fungal preparations e.g. nystatin, canestan, clotrimazole
drug resistant strains or those with invasive life-threatening infections require triazole therapy (fluconazole)