AP

Principles of Wound Reconstruction – Skin Flaps (SPF and APF)

Cutaneous Circulation – Review

  • Skin is supplied by segmental arteries that originate from simple & mixed cutaneous arteries

  • These arteries run through/between muscles and arborize in 3 distinct plexuses that run parallel to the skin surface:

    • Deep (SQ) Plexus

    • Middle (Cutaneous) Plexus

    • Superficial (Subpapillary) Plexus

  • These networks provide excellent collateral flow and extensive connections between vascular elements

Subdermal Plexus Flaps (SPF)

  • SPF definition: Flaps that include skin and subcutaneous tissue (SQ) that receive blood supply from collateral connections to the SQ plexus; they are randomly supplied

  • Flap design: Full-thickness “tongues” of skin detached from surrounding skin along 3 of 4 quadrants and rotated or stretched into the adjacent defect

  • Survival relies on remaining collateral circulation from the SDP and its vascular connections to surrounding skin

  • Practical concept: rely on the subdermal plexus for perfusion rather than a defined direct vessel

  • Example reference (for design principles):

    • https://clinicalgate.com/flap-classification-and-design/

SPF – Guidelines

  • Address patient comorbidities prior to flap planning

  • Ensure adequate redundancy & vascularity of surrounding skin

  • Flap length should be at least as long as the wound; ideally, length should be about 1.5 times the wound length (L is greater than or equal to 1.5 times W, where W is wound length)

  • Flap width: base should be slightly wider than the overall width of the flap

  • Careful undermining: avoid disturbing the SDP; elevate away from SQ/muscle to reduce metabolic demand on the flap (Halsted’s Principles)

  • Closure: typically 2–3 layers; ideally buried SQ; skin closure or cyanoacrylate if minimal tension

SPF – Types (classified by how skin is moved)

  • Advancement – move skin forward without rotation

  • Rotation – pivots a flap that has a curvilinear configuration

  • Transposition – pivots with a linear axis

  • Interpolation – pivots with a linear axis, but the pedicle must pass over/under intervening tissue

  • Plasty – alteration of tissue shape; essentially advancement and rotation depending on the design letter

  • Distant – flap from a region not adjacent to the wound (rare in veterinary medicine; “pouch” or hinge flap)

  • Classification basis: how the skin is moved or stretched

Pivotal Flaps (Single Pedicle SPF)

  • Advancement, Rotation, Transposition and Interpolation flaps may be used with a single pedicle (pivotal flaps)

  • Pantographic expansion: divergent arms with back cut to gain extra length and relieve tension

  • Single vs. bipedicle configurations depend on wound geometry and donor site

Advancement Flaps

  • Characteristics: single pedicle or bipedicle designs

  • Examples:

    • H-plasty

    • V-Y Plasty

  • Single Pedicle Advancement Flap

  • Pantographic expansion concept: divergent arms & back cut to gain extra length and relieve tension

  • Practical note: maintain robust vascular supply while achieving advancement

Rotation Flaps

  • The effective length of a pivotal flap moving through an arc of 180° is reduced by about 40%

  • Formula: if the design length is L, the effective length after 180° rotation is L_effective = 0.6 times L

  • Burow’s triangle: dog-ear excision used to optimize inset and reduce tissue bunching

  • Design considerations: flap length must accommodate arc without excessive tension; account for length reduction during planning

Rotation Flaps – Visual/Anatomical Insights

  • Figures illustrate rotational movement and how to manage tissue tension and contour; images courtesy of clinical contributors

Transposition Flaps

  • Elbow fold flap (forelimb)

  • Flank fold flap

  • Z-plasty (and modified transposition designs, e.g., TP modification)

  • Flank Fold details:

    • Incisions: U-shaped over the inguinal flank fold on the cranial aspect of the thigh

    • Flap base position can be distal (for distal pelvic limb wounds) or proximal (for ventral abdomen/lateral thigh wounds)

  • Immediate postoperative (PO) and 2 weeks PO examples shown in illustrative figures

Transposition Flaps – Flank Fold (Detailed)

  • Flank Fold flap deployment for ventral abdominal or thigh defects

  • Base location and direction tailored to defect geometry

Interpolation Flaps

  • Requires division at a later date via a second surgery

  • Pedicle must pass over or under intervening tissue

  • Used when direct adjacency is not possible but flap can still recruit robust perfusion via the pedicle path

Distant Flaps (Pouch Flap)

  • Pouch flap is a distant flap type; conceptually remote donor site contributes to wound bed

  • In veterinary medicine, distant flaps are infrequently utilized but exist as a theoretical option when local flaps are insufficient

SPF – Complications

  • Infection: ensure recipient bed has healthy granulation tissue; use sound aseptic technique; delay flap until bed is clean

  • Seroma: more common with flaps from lateral flank & thorax due to large dead space; consider closed suction drain placement or compressive bandage

  • Desensitization & self-trauma: monitor for neuropathic changes; implement protective measures as needed

  • Skin edge dehiscence: caused by excessive tension, infection, seroma, or pre-existing disease (e.g., diabetes mellitus, Cushing’s, prior radiation)

  • Global flap necrosis: due to compromised blood supply; etiologies include iatrogenic insults, thrombosis, or self-trauma

  • Most complications are detected within 2–3 days postoperatively; if devitalized tissue is present, debridement should not be delayed – allow tissue to declare initially but intervene promptly for nonviable tissue

Practical/Strategic Takeaways

  • SPF relies on robust subdermal plexus perfusion and surrounding collateral networks; plan around the vascular reliability of the SDP

  • Preoperative optimization of patient health improves flap viability

  • Plan flap length and width with explicit ratios (e.g., L is greater than or equal to 1.5 times W and L over W is less than or equal to 3 for safe advancement and rotation designs)

  • Use Halsted’s principles: staged elevation, minimal undermining of critical vascular networks, layered closure, and protection of the donor site

  • Be prepared to convert to alternative flap designs if vascular adequacy is compromised or defect geometry changes

Axial Pattern Flaps (APF) – Note

  • Axial pattern flaps (APF) are also referenced in objectives as commonly utilized for wound reconstruction

  • Specific APF indications, designs, risks, and comparisons to SPF are not detailed in this material; review dedicated APF resources for comprehensive coverage

Ethical, Philosophical, and Practical Implications

  • Selection of flap type should balance maximal tissue viability with minimal donor-site morbidity

  • Consider long-term functional and aesthetic outcomes (e.g., limb function, contour, scar visibility)

  • Ensure informed consent includes discussion of potential complications, need for additional surgeries, and reconstruction timelines

Key Formulas and Ratios (Plain Text)

  • Flap length to wound width ratio (3:1 Rule):

    L over W is less than or equal to 3

  • Ideal flap length relative to width:

    L is greater than or equal to 1.5 times W

  • Rotation flap effective length after 180° arc:

    L_effective = 0.6 times L

References and Illustrations

  • Practical design principles referenced from clinical resources (e.g., clinicalgate) for flap classification and design

  • Images and figures accompany sections on Rotation Flaps, Transposition Flaps (including flank fold and Z-plasty variants) in the original slide deck

Summary of Scope

  • This set focuses on Subdermal Plexus Flaps (SPF): anatomy, basic guidelines, flap types, pivotal flaps, and common complications

  • Axial Pattern Flaps (APF) are acknowledged but not elaborated within these slides; consult APF-focused materials for detailed coverage