T10-L3: Orthopaedic, Skin and Soft Tissue Infections

Question 1

What level of skin do viral warts infect? What is the usual cause?

Answer 1

Superficial skin - i.e. stream corneum, stream granulosum and stream spinosum.

They are most commonly caused by HPV. Treatment is topical salicylic acid, nitrate and cryosurgery.

HPV can cause cervical cancer and so prevention is through barrier protection and vaccination.

Question 2

What are Pilonidal cysts?

Answer 2

These are cysts or abscesses in the natal cleft. They are abscess of the hair follicle and are though to be caused by ingrowing hair. Certain patients are more susceptible and so they can be recurrent. They abscess tend to form sinuses. Treatment includes hot compress to alleviate pressure, analgesia, antibiotics (if a superficial infection is present) and surgical excision.

Question 3

What is the usual aetiology of impetigo?

Answer 3

Staph. aureus

Question 4

What causes Erysipelas? What features does the pathogen have that mean it can cause such an infection?

Answer 4

Streptococcus Pyogenes.

It has higher virulence factors and so can cut through tissue planes. It extends into the upper dermis and can get into the lymphatics and so can spread more rapidly. It can lead to a swollen appearance as well as a raised rash over the face. It is transmissible and can be recurrent. It is treated with oral antibiotics.

Question 5

Give causes of cellulitis.

Answer 5

It tends to be caused by Group A Strep (such as Step. Pyogenes), Staph. aureus and other Beta-haemolytic streptococci.

The infection travels down into the subcutaneous tissue and enter the lymphatics.

Question 6

What 4 features does cellulitis present with?

Answer 6

• Rubor
• Dolor (pain)
• Tumor
• Calor (heat)

There is also loss of skin creases, blistering, pus/exudate and fever.

Diagnosis is clinical (as septic cultures rarely helpful) and exclude other causes of red hot swollen leg. E.g. DVT. Treatment is elevation, rest (reduce swelling), antibiotics and source control (drainage of pus).

Question 7

What pathogens cause orbital cellulitis?

Answer 7

Cause organisms include: S. aureus, S. pyogenes but also S. pneumonia and H. influenzae (cause sinusitis).

Question 8

What is Type 1 necrotising fasciitis?

Answer 8

Type 1: Synergistic/poly-microbial, host impairment- gram negatives, Streps, anaerobes
○ RF: DM, obesity, immunosuppression, alcohol, older age group- e.g. Fournier gangrene

Type 1 is a synergistic type of process between impaired host immunity and infection. It is usually associated with ischaemic tissue e.g. ischemic bowel. This tissue can get colonised, causing the bacteria to multiple and cause further ischaemia. It is seen in diverticulitis and a condition known as Fournier (perineal infection and the scrotum and colonisation of infection.

Question 9

What is the risk factors for type 2 necrotising fasciitis?

Answer 9

Group A Strep (S. pyogenese) mediated - associated with a younger age group, associated with cut or injury.

Question 10

What is the clinical presentation of necrotising fasciitis?

Answer 10

• Swelling, erythema (non-confluent - it can suddenly emerge somewhere else unlike cellulitis where you can see where it is going), pain out of context with the surface appearance
• Crepitus (gas in the tissue form the infection)
• Sepsis/toxaemia
• Necrosis
• “dish water” exudate

Question 11

What is the difference between dry and wet gangrene?

Answer 11

Dry - without infection. Leads to auto-amputation
Wet - This is gangrene with infection and so presents with oggy, swollen “dactylitis, exudate and surveying erythema

Gas gangrene is that same as wet gander but with crepitus also.

Question 12

What is the pathogenesis of diabetic foot infection?

Answer 12

• Damage to blood vessels in diabetes can lead to Ischaemia, impaired immunity and poor wound healing
  
  • Damage to nerves in diabetes can cause neuropathy and so trauma as they cannot feel when they are getting injured
  • High blood sugars makes the patient to prone to bacterial infection

Question 13

What is the caustic agents of osteomyelitis?

Answer 13

• Haem- (children): S. aureus, Strep, Kingella, Haemophilus
• Contiguous: Skin (Staph, Streps) enteric (GNB, anaerobes)
• Penetrating: surgical- skin flora, open fracture- skin, environment (such as in traumatic patients as they can be exposed to the dirt)
• Sickle cell (as it can cause bone death): Salmonella sp.

Question 14

What is the pathogenesis of osteomyelitis?

Answer 14

○ Contiguous: e.g. Diabetic foot infection
○ Haematogenous: bugs in bloodstream
○Penetrating: peri-prosthetic, traumatic

Question 15

What are the causative agents if septic arthritis?

Answer 15

Staph. Aureus, Steps., Haemophilus, N. gonorrhoeae and E. coli

Question 16

What is prosthetic joint infection?

Answer 16

Infection of tissue and bone surrounding a prosthetic joint

Pathogenesis:
• Pathogens get onto surface of foreign body- immune system cannot reach it as it doesn’t have a blood supply - and so the bacteria establish biofilm (slime protecting them from mechanical or chemical destruction)

* Early: Infections usually implanted at time of surgery or shortly after (via wound or hematogenous seeded e.g. though a catheter)
* Late: Haematogenous but can be late presenting Early infections that has just presented delayed

Question 17

How can syphillis present with skin lesions?

Answer 17

Primary syphilis is characterised by a Chancre- this is a painless, firm, non-itchy ulcer at the point of contact. It is usually solitary and is the sight of entry of the spirochete. It lasts around 30-6 weeks and can be associated with lymphadenopathy.

Secondary syphilis at 4-10 weeks after the chancre the patient can progress to a symmetrical full body rash. It is red/pink and non-itchy. It can include the soles and palms (and mucus membranes) and so this is a good place to look when you suspect syphilis as many other infections that also cause a rash like this spaces the soles and palms. It is a maculo-papular or pustular rash. The rash contains Treponema but we use better tests that biopsy. It is associated with other systemic symptoms. 

Tertiary syphilis if they escape treatment can occur 3-15 years after initial infection. It can take 3 forms: 
- Gummatous - skin manifestation. This is large gummas (large inflammatory swellings of the skin, bone and liver)
- Neurological  Cardiovascular