Tissue Expanders and Alloplastic Material

Tissue Expansion 

• To understand tissue expansion, one should understand its physiology, consequences, tools, techniques, and surgical principles.
• It is characterized as the creation of extra skin and soft tissue for the reconstruction of locoregional defects when there is less possibility of raising a flap or a graft. In brief, the method is as follows:
  • A tissue expander is placed under the skin and inflated with saline solution at regular intervals.
  • The constant application of mechanical force leads to mechanical and biological creep, which is responsible for tissue expansion.
  • Creep refers to the ability of the tissue to lengthen or stretch under constant mechanical force or tension.
  • When the expander is placed initially, it will cause mechanical creep, which will lead to 70% tissue expansion, disruption of mechanical fibers, and displacement of interstitial fluid. This displacement leads to viscoelastic changes in collagen and, hence, stretching.
  • The continuation of mechanical creep leads to biological creep, which is responsible for 30% of tissue expansion. Here,
    • Cell proliferation
    • There is an increase in fibroblasts and collagen synthesis with realignment of collagen fibers.
    • Increased angiogenesis/ neovascularization leads to increased vascularity within the expanded skin flap.
• All these biological processes contribute to tissue expansion. Furthermore, the expander acts as a foreign body and generates a biological response in the form of a fibrous capsule around the tissue expander. This capture is better seen with textured tissue expanders.

Changes in Skin

The following crucial changes occur with tissue expanders:

• Dermal thinning.
• Epidermal thickening.
• Realignment of collagen fibers.
• Subcutaneous tissue atrophy: The thickness of the fat layer will decrease due to pressure atrophy.
• Thinning of muscles, however, the function stays intact. 
• Angiogenesis: Blood vessels will increase in size and caliber.
• Increased vascular endothelial growth factor (VEGF) expression.
• Skin appendages and nerves are unaffected.

Advantages of Tissue Expansion

• It permits the creation of large flaps with similar physical and mechanical properties to the skin.
• It allows for matching color and texture to the tissue being reconstructed.
• It allows the transfer of sensitive skin with intact appendages.
• The flap's vascularity is augmented due to angiogenesis.
• There is minimal donor side effect(deformity).

Indications

• It is an ideal method for reconstructing hair-bearing skin like the scalp.
• It is a common method for breast reconstruction after mastectomy.
• It can be used for face, neck, forehead, and trunk reconstruction.
• It can be used for auricular reconstruction.
• However, it cannot be used to reconstruct extremities. The rate of complications with tissue expanders has been found to be high.

Contraindications for Tissue Expansion

• It cannot be used in previously irradiated tissue due to lack of vascularization.
• It is not applicable in areas with prior skin grafts.
• It cannot be used in tissues with active infections.
• As mentioned earlier, it is not suitable for extremity reconstruction.
• Diabetes or connective tissue disorders have poor wound healing. The outcomes are not optimal in these patients.

Expanders Used in Tissue Expansion

Expanders can vary in shape, such as round, square, rectangular, and crescentic. Crescentic expanders are not favored in current clinical practices as they do not expand uniformly. They can also vary in size, which is calculated based on the volume of the tissue expander. The envelope can be smooth or textured. The expansion can be isotropic (uniform on all sides) or anisotropic (non-uniform). Some tissue expanders are capable of self-expansion.

The only disadvantage they have is that if they expand too much, it will cause pressure atrophy.

Surgical Principles for Tissue Expansion

• Expander placement in either the subcutaneous or subfascial plane. A subcutaneous plane is usually preferred for the face and trunk, and a subfascial plane is used for the forehead and scalp.
• An expander comes with an inflation port. This port can be integrated or buried. It can also be in a remote area, externalized away from the expander, and placed on firm, stable tissue. For instance, remote ports are utilized during post-auricular tissue expansion.
• The expander is filled with saline around 2 weeks after primary surgery. Appropriate time should be given for tissue healing.
• The expansion is done weekly until the patient experiences some degree of pain and palpable tightness. After that, it should be stopped.
• The expansion can take anywhere between 2-3 weeks to 2-3 months.
• The expander is removed once adequate gain is established, and the flap is advanced over the defect.

Alloplastic Materials/Implants/Prosthesis

These are synthetic substances implanted in living tissue to augment and reconstruct soft tissues and bony defects. The advantages are

• These are useful in patients with autologous tissue that is unavailable.
• There is an absence of donor site morbidity and scarring.
• These are non-biodegradable materials and do not undergo resorption.
• These can be manufactured to meet special needs, such as controlled-release drug delivery systems.
• Using alloplastic material can elicit tissue responses or reactions, as they are considered foreign substances by the host. These will be dependent on-
  • Chemical composition of the implant
  • Micro- and macro-structure of the synthetic material.
  • The physical form will determine the response type, whether the implant is solid or meshed, smooth or rough.
  • Two types of reactions can be observed-, that is-
    • Fibrous encapsulation (silicon implant)
    • Tissue ingrowth- Fibrous tissue penetrates the interstices. The implant can incorporate the tissue (meshed implant)

Ideal Implant

The characteristics are as follows:

• Non-toxic or non-allergenic
• Non-carcinogenic and non-immunogenic
• Mechanically reliable
• Biocompatibility: It should produce the desired outcomes without triggering adverse local and systemic tissue reactions or events
• Easy to shape
• Radiolucent, sterilizable, and infection-resistant
• Resistant to absorption and deformation
• No foreign body inflammatory reaction

Tissue Bed Characteristics

• Thickness of overlying soft tissue
• Mobility of surrounding tissues
• Vascularity of recipient site
• Adequacy of pocket dissection
• Proximity to bacterial-laden cavities
• Tension of soft tissue closure
• Exposure to mechanical loading

Implant Characteristics

• Surface texture
• Flexibility
• Hardness
• Porosity
• Ease of antibiotic absorption
• Ease of material porosity
• Implant fixation

Technical Aspects

The underlying soft tissue coverage over the implant should be as thick as possible. If the overlying tissue is thin, there is a high chance of implant extrusion or exposure.

Deeply placed implants—such as subgaleal, subperiosteal, or subfascial—have minimal chance of extrusion or exposure. A Sterile placement technique needs to be followed. Fix the implant to a stable adjacent structure to minimize implant mobility. The incision is always placed away from the implant.

Question Asked Question

Q: What is the use of tissue expanders?

Answer: Reconstruction

Q: What is an ideal implant?

Answer: The characteristics are as follows:

• Non-toxic or non-allergenic
• Non-carcinogenic and non-immunogenic
• Mechanically reliable
• Biocompatibility: It should produce the desired outcomes without triggering adverse local and systemic tissue reactions or events
• Easy to shape

Q: When is the tissue expander filled with saline post-surgery?

Answer: 2 weeks after surgery

Hope you found this blog helpful for your NEET SS Surgery Skin and Subcutaneous preparation. For more informative and interesting posts like these, keep reading PrepLadder’s blogs.