6 - Skin, scars and invisible lines of force

Question 1

3 functions of skin

Answer 1

Protection against: UV, injury, dehydration, invasion by micro-organisms
Sensation: Receptors for touch/pressure and pain/temperature
Thermoregulation: sweat glands, hair, adipose tissue

Question 2

What are dermal papillae?

Answer 2

They act like tread to give the epidermis and dermis grip so the skin doesn’t slide of and increases the surface area allowing nutrients from down below to get up to the skin

Question 3

What are some epidermal derivatives/appendages and what are they important for?

Answer 3

• hair, nail, sweat glands, sebaceous glands

- intrinsic to skin and important in healing as source of epithelial cells to migrate to wounds

Question 4

Describe the dermis

Answer 4

• thickest skin layer
• collagen for tensile strength and elastin for elasticity made by fibroblasts
• has a weave pattern not uniform in all directions

Question 5

What does it mean that skin is anisotropic?

Answer 5

• skin has different physical properties in different directions meaning it can stretch more in one direction than another

Question 6

Why is the skin anisotropic?

Answer 6

• the collagen is in a 3d weave in many directions
• a fibril of collagen is, at rest, more stretched out compared to its structure in the other direction i.e. the fibril is already drawn out/extended/there is already tension in the skin so it is limited compared to the fibre being less drawn out in direction 90 degrees to that

Question 7

4 ways the skin can be damaged?

Answer 7

• thermal injury
• abrasions
• lacerations and puncture wounds
• surgical incisions

Question 8

What does how skin is repaired depend on?

Answer 8

• depends on the degree of tissue loss and depth of the wound
• superficial wounds can heal with little or no scarring (through epidermis or partly through dermis)
• wounds of a certain depth inevitably heal with scarring and or contraction
• there is a wide range of possibilities of colour or texture change
• skin is a renewable source for skin graphs. Can harvest from same place multiple places
• usually not the same as normal skin can tell was damaged

Question 9

How long does wound healing take?

Answer 9

A long time at least 12 -24 months before activity stops

Question 10

What are the 6 steps of wound healing?

Answer 10

1. Bleeding control and clot (haematoma) formation
2. Inflammation (redness/erythema, swelling/oedema, heat and pain)
3. Matrix formation
   - fibroblast migration producing collagen and elastin
4. Neovascularisation (new BV formation)
5. Re-epithelialisation
   - epithelial cell migration/growing over of skin
6. Wound contraction and remodelling

Question 11

Describe wound healing very briefly

Answer 11

• piece of tissue missing with the area filled with RBCs platelets etc. that release signals to get help
• then get an advancing layer of squamous epithelium over the top of the wound which is covered by a scab (dried blood products) that acts as a cap/plug on top of the epithelial cells
• it is a very complicated and lengthy biological process

Question 12

What is the wound strength at 5 days, 21 days and a year?

Answer 12

5 days - 10% (wouldn’t take much to be disrupted)
21 days - 45%
1 year - 90%
Never get the area of skin back to full strength
Helps to decide when you should take sutures out

Question 13

What is a scar?

Answer 13

• it is a patch as the skin is not able to return to the same state it was before and restore complete structural integrity
• during scar formation the collagen becomes ALIGNED along the lines of stress

Question 14

Why does a hypertrophic or keloid scar occur?

Answer 14

• for some unknown reason sometimes excessive or disorganised connective tissue is produced during healing leading to these abnormal scars
• they are histologically the same as normal scars but behave differently

Question 15

What are hypertrophic scars?

Answer 15

• red, raised and itchy
• remain within the confines of the original wound
• many scars have an ELEMENT of hypertrophy but usually regresses in 2-6 months
• hypertrophic scars remain for an indefinite amount of time and then MAY regree
• they may contract

Question 16

What is a hypertrophic scar like under the microscope?

Answer 16

• in the reticular layer of the dermis of the scar is lots of disorganised collagen surrounded by collagen bands caused by tension in the skin which causes the collagen to align
• after burns patients wear tight garments to apply pressure to change the nature of the scar and improve it

Question 17

What are keloid scars?

Answer 17

• keloid scars are equivalent to benign tumours and are only found in humans
• they too are red, itchy and raised but unlike hypertrophic scars they can invade surrounding tissues
• they DO NOT contract or regress like hypertrophic scars
• they may occur months/years after initial injury and often reoccur even if cut out
• often on earlobes, shoulders, trunk, face and after cardiac surgery

Question 18

Dupuytren’s contracture?

Answer 18

Fibrous band on palm of hand meaning fingers can flex greatly into palm

Question 19

Dupuytren

Answer 19

• Noticed someone who stabbed themselves with a circular cross section awl had slit like puncture wounds.
• Discovered the distortion on puncture wounds was due to some relationship with the innate, natural tension of the skin

Question 20

How advanced Dupuytren’s ideas?

Answer 20

• Langer. Stabbed cadavers and found the slit like wounds followed a pattern

Question 21

What was causing misinterpretation on Langer’s work?

Answer 21

• he had stabbed a child’s abdomen but adults on the other side
• meant the lines were transverse on one side but oblique on the other
• Langer’s lines were misinterpreted and inaccurately reproduced in pristigous surgical textbooks
• UOA professor discovered

Question 22

McBurney’s Incision?

Answer 22

• the inaccurate reproduction of Langer’s Lines had unfortunate consequences for generations of patients undergoing surgery for appendicitis
• showed where you should cut to go along the lines of tensions

Question 23

Cox?

Answer 23

• also stabbed cadavers 20 000
• more elegant lines of skin tension
• in the abdomen the lines were pretty much transverse unlike what was used in the Mcburneys incision
• other researchers found differences especially in the head
• M. Flint at UOA did a paper on this
• today what is called Langer’s Lines is actually Cox’s work

Question 24

What did M. Flint discover?

Answer 24

• that the lines of skin tension could be visualised by using a rubber circular flint stamp on the patient in the flexed fetal position
• when they then straighten into the anatomical position the circles deform into ellipses
• the long axis of the ellipses align with the skin tension lines (Langer’s Lines)

Question 25

How are the skin tension lines used clinically?

Answer 25

• if you make a cut INLINE with the skin tension lines there is a natural tendency for the wound to stay together (like pulling 2 pieces of string next to each other tight and the 2 middle pieces come together UNDER THE TENSION)
• if you make an incision at right angles to the skin tension lines the tension tends to bring the wound apart, not heal nicely, and more likely to lead to a hypertrophic scar

Question 26

What is another clinical relevance of the skin tension lines?

Answer 26

• given the nature of the lines you can often find redundant skin to use and this enables you to cut something large out and sew it together without a skin graft