What are the risks of placing tissue expanders superficial to the pectoralis major muscle?

Risks of Placing Tissue Expanders Superficial to the Pectoralis Major Muscle

Placing tissue expanders superficial to the pectoralis major muscle significantly increases the risk of complications including infection, implant exposure, capsular contracture, and implant loss compared to submuscular placement.

Anatomical Considerations and Placement Options

Tissue expanders for breast reconstruction are traditionally placed in one of two positions:

1. Submuscular placement (standard approach):

   • Expander placed beneath the pectoralis major muscle
   • Inferior and lateral coverage provided by serratus anterior muscle/fascia
   • Creates multiple layers of tissue between the skin and implant

2. Prepectoral/subcutaneous placement (superficial to pectoralis):

   • Expander placed directly beneath the mastectomy skin flaps
   • No muscle coverage
   • Relies solely on skin flap thickness for protection

Major Risks of Superficial Placement

1. Increased Infection Risk

• Lack of well-vascularized muscle coverage increases infection susceptibility
• Higher bacterial colonization potential due to fewer tissue barriers
• Infection can lead to implant removal and reconstruction failure 1

2. Implant Exposure

• Without muscle coverage, thin mastectomy flaps are more likely to break down
• Skin necrosis directly exposes the implant when placed superficially
• Studies show muscle coverage under the incision prevents implant exposure even when marginal skin necrosis occurs 2

3. Poor Cosmetic Outcome

• Higher rates of visible implant edges and rippling
• Less natural breast contour without the muscle layer
• Increased risk of animation deformity and implant malposition 3

4. Capsular Contracture

• Higher rates of capsular contracture with superficial placement
• Particularly problematic if radiation therapy is needed 1

5. Implant Loss

• The combined risks above lead to higher rates of complete reconstruction failure
• Salvage procedures are more complex after superficial placement complications

Evidence-Based Recommendations

The NCCN guidelines emphasize that reconstruction selection should be based on assessment of cancer treatment needs, patient factors, and surgical expertise 1. While not explicitly prohibiting superficial placement, the guidelines consistently describe the standard approach as submuscular placement with:

1. Elevation of the pectoralis major muscle
2. Release at its inferior attachment
3. Creation of a pocket beneath the muscle
4. Additional coverage using serratus anterior fascia 4

Risk Factors That Compound Superficial Placement Risks

The following factors make superficial placement particularly risky:

• Smoking: Significantly increases wound healing complications and tissue necrosis 1
• Obesity: Associated with higher rates of wound complications and implant failure 1
• Radiation therapy: Causes tissue changes that make superficial placement more prone to complications 1
• Thin mastectomy flaps: Provide inadequate coverage for superficial implants 2

Alternative Approaches

If complete submuscular coverage is challenging, consider these safer alternatives:

1. Partial muscle coverage with acellular dermal matrix (ADM) to complete the pocket 5
2. Complete coverage using musculofascial flaps combining pectoralis major with serratus anterior fascia 6
3. Delayed reconstruction if skin flaps are compromised or radiation is planned

Clinical Decision Algorithm

1. Assess patient risk factors:

   • High-risk patients (smokers, obese, planned radiation): Avoid superficial placement
   • Low-risk patients: Consider standard submuscular approach

2. Evaluate mastectomy flap quality:

   • Thin flaps: Submuscular placement mandatory
   • Well-vascularized, thick flaps: Submuscular still preferred

3. Consider surgical expertise:

   • Superficial placement should only be attempted by highly experienced reconstructive teams
   • Even then, risks should be thoroughly discussed with patients

Conclusion

While superficial placement of tissue expanders may seem appealing for reducing post-operative pain and animation deformity, the significantly increased risks of complications make submuscular placement the standard of care for most patients undergoing breast reconstruction.