Hernia mesh considerations

Question 1

List seven considerations to take into account when selecting mesh for hernia repair

Answer 1

1. Tensile strength
2. Pore size
3. Weight
4. Reactivity/biocompatibility
5. Elasticity
6. Constitution
7. Shrinkage

Question 2

What is the main determinant of tissue reaction?

Answer 2

Pore size

Question 3

How is tension on the abdominal wall calculated?

Answer 3

The law of La Place: tension = (diameterxpressure)/(4x wall thickness)

Question 4

What is the maximum pressure in the abdomen?

Answer 4

170mmHg - coughing, jumping. Most mesh can withstand this.

Question 5

What minimum size of pore is required for hernia mesh repair? Why?

Answer 5

A minimum pore size of >75um to allow infiltration by macrophages, fibroblasts, blood vessels, and collagen.

Question 6

Why is mesh with larger pores more flexible after it is incorporated into the body?

Answer 6

Larger pores allow more soft tissue ingrowth and are more flexible because of avoidance of granuloma bridging.

Question 7

What is granuloma bridging? what does this result in?

Answer 7

Bridging describes the process where individual granulomas become confluent with each other and encapsulate the entire mesh.

This leads to a stiff scar plate.

Question 8

What size pore is associated with formation of a stiff scare plate?

Answer 8

Meshes with a small pore of <800um

Question 9

What are the determinants of mesh weight?

Answer 9

Polymer weight and pore size

Question 10

What are the three determinants of mesh reactivity/biocompatibility?

Answer 10

Foreign body reaction is uniform in all mesh. However teh amoiunt of material present does influence this.

Pore size is again important - smaller pores -> stiff scare plate

Collagen composition. Mesh can alter this. During normal scar healing, initial/immature collagen type 3 is rapidly replaced by stronger type 1 collagen. Mesh delays this process.

Question 11

what subtypes of fibre can be used in mesh? What disadvantages are associated with one of these?

Answer 11

Monofilaments, multifilaments (braided) and patches (PTFE).
Multifilaments have a higher risk of infection.

Question 12

Why does mesh shrinkage occur? How much does scar tissue shrink?

Answer 12

Mesh shrinks due to scar tissue contraction around mesh.
Scar tissue shrinks around 60%

Question 13

How much do each of the following meshes shrink?
Prolene
PTFE
Ultrapro

Answer 13

Prolene 75%
PTFE 50%
Ultrapro <5%

Question 14

What is polyglecaprone-25 mesh and why is it so good for hernia repair?

Answer 14

Ultrapro mesh
This is made of approximately equal parts of absorbable poliglecaprone-25 monofilament fiber and nonabsorbable polypropylene monofilament fiber

After absorption of the poliglecaprone-25 component, only the polypropylene mesh remains.

It shrinks less than 5% cf 50-75%

Question 15

What mesh characteristics (filament type and porosity) is required to be able to consider treatment of mesh infection with antibiotics rather than explant?

Answer 15

monofilament, 75um mimimum pore size

Question 16

What causes temporary adhesions?

Answer 16

Fibrin exudates, with form after any sort of trauma. The adhesions resolve as the fibrin is absorbed by the fibrinolytic system.

Question 17

What causes permanent adhesions?

Answer 17

Anything that delays the normal fibrinolytic system from absorbing fibrin

Question 18

What can delay fibrinolysis?

Answer 18

Ischaemia
Inflammation
Foreign body

Question 19

What are the determinants of mesh adhesion?

Answer 19

Pore size
Filament structure
Surface area

Question 20

What sort of mesh induces an intense fibrotic reaction, ensuring strong adherence to the abdominal wall but also causes dense adhesion?

Answer 20

heavy weight mesh

Question 21

What kind of mesh does not allow tissue ingrowth, has a very low risk of adhesion formation, but is unable to adhere strongly to the abdominal wall?

Answer 21

Microporous PTFE

Question 22

Microporous PTFE and heavyweight mesh both have clinical drawbacks. What type of mesh is designed adhere to the abdominal wall but not the bowel?

Answer 22

Composite mesh

Question 23

What are the features of composite mesh?

Answer 23

There are two surfaces - one that sticks to the abdominal wall and one that will not form adhesions to bowel

Question 24

How does the non-stick side of composite mesh work?

Answer 24

It takes approximately 7 days for mesothelial cells to form a layer over the non stick side. Once this layer has formed, bowel will not adhere.

Question 25

What is a drawback of composite mesh?

Answer 25

There is some evidence that there deterrance of bowel adhesion formation is only temporary and that their effect is diminished after 30 days.

Question 26

By how much does mesh reduce the rate of recurrence in incisional hernia?

Answer 26

From a rate of 17-60% to 1-32%

Question 27

Where to hernia recurrences occur in relation to the mesh? Why?

Answer 27

At the edge of the mesh. Either due to inadequate mesh fixation or underestimation of mesh shrinkage

Question 28

Is mesh repair or primary suture repair of inguinal hernias associated with a higher rate of chronic pain? Why?

Answer 28

Primary suture repair has a higher rate of chronic pain. This is thought to be related to the tension-free nature of mesh repair rather than due to the mesh itself.

Question 29

How does the type of mesh used affect recurrence rates?

Answer 29

It doesnt

Question 30

List 5 factors that contribute to hernia recurrence.

Answer 30

Not using mesh Using too small a mesh Infection Seroma Haematoma

Question 31

Explain the aetiology of early and then later development of chronic pain after mesh repair of inguinal hernias

Answer 31

1. Early - nerve damage at the time of the operation - immediately post op 2. Late - Histo pathology of explanted mesh shows ingrowth of nerve fibres/fascicles within the fereign body granloumata within the mesh

Question 32

What are the pros and cons of PTFE mesh?

Answer 32

PTFE has low adhesion rates, but a higher risk of ineradicable infection.

Question 33

What are the pros and cons of prolene mesh?

Answer 33

Prolene is durable and has lower infection risk but little flexibility and high adhesion risk

Question 34

What is a generally safe mesh option and why?

Answer 34

light weight large pore Minimal surface area monofiliament =ie parietine, bard prolene mesh