Specialised Flaps



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Specialised Flaps

 Sensory neurovascular,

 Osseo-cutaneous,

 En bloc (composite) flaps

 Venous flaps

 Reverse flow flaps

 Pre-fabricated flaps

1. SENSATE FLAPS


  • Littler’s neurovascular island flap (1960) from the ulnar aspect of the MF to resurface the distal pulp of the thumb was the first example. Sensation was often restored to the Th, but thought to arise from theMF! (Localisation was poor).


Principles of neurovascular free flaps (Daniel, Terzis and Midgley, 1976)

 Vascular distribution and sensory innervation must overlap

 It must be possible to isolate the flap on an anastomosable vascular pedicle

 The nerve supplying the flap must be identifiable and anastomosable

 The quality of sensation must be appropriate for the defect

 The donor site morbidity must be acceptable.




  • The dorsalis pedis flap showed that re-innervation did occur and that localisation was possible.

  • Wrap-around flap from the big toe to the thumb provides good 2 point discrimination, durable coverage and the option of incorporating a nail.

  • Radial forearm flap can provide sensation via the lateral cutaneous n of the forearm.

  • Intercostal flaps (a single intercostal n/v bundle can support a flap 5 intercostal spaces wide) can be used to provide sensate flaps for sacral sore coverage in plegics.



 OSSEOCUTANEOUS FLAPS

Used first by Blair (1912) when he incorporated clavicle in a cervical flap.

Taylor (1982): free fibula flap, osseocutaneous groin flap (deep circumflex iliac).
Vascularised bone has the following advantages over non-vascularised bone graft:


  1. higher rate of union,

  2. hypertrophies earlier,

  3. has greater mechanical strength,

  4. has a lower rate of infection (and thus non-union.)


 COMPOSITE FLAPS

The old school: For a complex facial defect (eg, post GSW), multiple flaps and grafts would be used: local flap for oral lining, rib graft for bone, delto-pectoral flap for skin. Infection and necrosis were the common result.
The modern school (Daniel, 1978; Taylor, 1982; Swartz, 1986): Single en bloc composite free tissue transfer. Advantages are better blood supply with resultant better healing and better cosmetic results.

 VENOUS FLAPS

  • A flap based exclusively on a venous pedicle that is anastomosed to either a vein or an artery (arterialised). There may be no outflow or an exiting vein may be anastomosed to an artery or a vein.


Types (Nakayama, 1981)




Type


Inflow


Pedicle


Outflow




VO

venous

venous

none

Single pedicle venous flap

2.

VV

venous

venous

venous

Flow through venous flap

3.

AV

arterial


venous

venous

Arterialised venous flap


4.

AA

arterial


venous

arterial

Arterialised venous flap






  • Type 1 may be subdivided into proximally or distally based.

  • Type 2 may be divided up into free flaps, unipedicled flaps or bipedicled (sliding) flaps.

  • Types 1 and 2 rely on venous perfusion and are said to survive as a graft!

  • Types 3 and 4 are arterialised venous flaps. Inflow and outflow may be orthograde or retrograde further subdividing the group (o/o, o/r, r/o, r/r). Higher pressures lead to greater survival.


Classification (Thatte and Thatte)

Type 1 – supplied by a single venous pedicle

Type 2 – venous flow-thru flap (V-V-V)

Type 3 – arterialized venous flaps

A-V-A

A-V-V



Theories


  1. Reverse Shunting

    1. With denervation, AV Anastomoses allow retrograde flow from the veins to the arterioles and then antegrade flow through the nutrient capillary beds and out through the veins.

  2. Reverse Flow

    1. retrograde flow from the veins through the nutrient capillary bed into the arterioles and then antegrade flow back out the veins via A-V shunts or other capillary beds.

  3. Capillary Bypass

    1. normal tissue can extract up to 50% of the oxygen content of blood prior to it reaching the capillary beds

    2. flaps like the VFTF survive on the lower oxygen content supplied by antegrade flow through the venous plexus.

  4. As a composite graft: plasmatic imbibition and neovascularisation.

    1. Rapid arterialisation aided by the presence of draining vein


VFTFs designed with a central venous plexus with two or more efferent veins have a survival pattern similar to that of conventional flaps which have an inflow artery and outflow vein.


Potential VFTF donor sites:

  1. Distal Volar Forearm

  2. Proximal Volar Forearm

  3. Dorsum Digit/Hand

  4. Dorsal Foot

  5. Medial Thigh/Leg

  6. Upper Arm


Advantages

  1. Revascularized and resurface

  2. Single stage procedure

  3. Thin/pliable tissue

  4. Low donor morbidity

  5. Spares donor artery

  6. Constant long pedicle

  7. Good cosmetic result

  8. Can include composite tissue



Disadvantages

  1. Germann showed poor O2 consumption, early thrombosis and no flap survival.

  2. Small size, variable rate of tissue necrosis, formation of AVF (haemodynamic effects).



Clinical Experience

  • Most venous flaps are based on the prominent veins of the limbs: cephalic or saphenous.

  • Arterialised perfusion better than pure venous.

  • Wolff examined 3 types of venous flaps with respect to perfusion and long term survival:

 arterialised venous flaps: 93%

 flow through venous flaps: 63%

venous island flaps: 31%

 REVERSE FLOW FLAPS


  • By virtue of their design (eg distally based flaps), some flaps exhibit reversed vascular flow, ie, retrograde flow.

  • Since the arterial system does not contain valves, reversal of flow is not problematic.

  • The venous system has valves - how does flow reverse?

  • Two systems of venous arcades facilitate the reversal of flow:

    1. Macro-venous connections

      1. Valveless oscillating veins

        • Inter-connecting veins, devoid of valves, 1-3 mm in diameter which skip the valves of the venae comitantes (like a ladder).

        • allow venous flow in any direction under pressure

        • connects between larger valved superficial veins

        • Crossover and bypass patterns (reverse radial artery flap – Lin 1984)

          1. Crossover branches between the two venae comitantes

          2. Bypass branches within each vein

      1. Incompetent valve (radial artery - Nakajima 1997)

        • Effect of pressure and denervation

        • Veins with relatively weak valve resistance became the drainage pathway.

    1. Micro-venous connections

      1. Plexus of tiny veins, also free of valves, which surround the artery as the venae arteriosa.

      2. Although these are sufficient, they are small and require a relatively high pressure and time to dilate and allow blood flow.

      3. Venous congestion will therefore occur for the 1st 12-24 hours while these veins dilate



 PRE-FABRICATED FLAPS

  • Introduced by Orticochea and Washio (1971).

  • Termed prelamination by Pribaz and Fine.

  • Allows the creation of an unlimited array of composite flaps. Can create what is needed.

  • Can be combined with expansion and delay to increase versatility still further.

  • Facilitated by the reliability of free flap transfers: uniformly > 95%, usually 99%.


Methods

Based on 1 or more of the following principles:

 Delay or expansion

 Grafting (skin, cartilage, etc)

 Vascular induction (staged flap transfer)

 Experimental: Tissue transformation from one type to another


 Delay and Expansion

  • A powerful tool to increase the safety of flaps. Extends the limits of perfusion.

  • Expansion of a flap may allow primary closure to the donor site or a much larger flap to be created to cover a large defect.

  • Can allow expansion to be done in a safe area rather than an unsafe area, eg, a scapula flap can be expanded prior to transfer to the lower leg where expansion would be hazardous.


 Pre-transfer Grafting

  • Necessary when

 complete graft take is mandatory to the success of reconstruction

 when post-transfer grafting is not feasible or practical



  • Can be done for pedicled and free flaps.

  • Pedicled flaps: Para-median forehead flap can be grafted with skin and cartilage prior to transfer for nasal reconstruction. Temporo-parietal flap can be pre-grafted with skin to close palatal defect or nasal defect (can be used free too).

  • Free flaps: Creation of a urethra in a RFF.


 Vascular Induction (true prefabrication)

  • Any selected block of tissue, regardless of its native vascular anatomy can become a transferable flap by inducing a vascular carrier to perfuse it. Based on the well established principle of staged flap transfer (eg, using the wrist as a carrier).

  • The vascular carrier can be a small flap of muscle, fascia, intestine, omentum, or even an arteriovenous bundle or fistula. This is implanted beneath the tissue that one wants to transfer and by a process of neovascularisation the two become incorporated after a relatively short period of time.

  • Orticochea transferred STA into retroauricular concha and then transferred conchal skin and cartilage to the nose for reconstruction.

  • Shen implanted the descending branch of the lateral femoral circumflex artery subcutaneously in the thigh (vascular induction stage) and then after 6 weeks transferred it as a free flap to resurface a burn contracture of the neck.

  • Omentum has been placed in the lower abdominal fat which has then been used for breast reconstruction.

  • The radial artery has been placed subcutaneous in the abd and then the abd skin transferred to the head as a free flap based on the radial artery.

  • Temporo-parietal free flap, hitched to dorsalis pedis artery and wrapped around the 2nd toe PIPJ as a 1st stage. 2nd stage is harvest of the composite temporo-parietal flap and toe PIPJ which can be transferred to the hand.

  • Veins have also been placed beneath a future flap for transfer.

  • Revascularisation can be hastened by the application of angiogenic growth factors (TGF, FGF, PDGF).


 Flap Tissue Transformation

  • Regulating gene expression and cell biology are now making this a reality.

  • Involves the use of bone morphogenic proteins which can allow the conversion of a simple muscle flap into an adequate piece of vascularised bone of the required shape and size. Silicone moulds are used into which is placed the muscle flap and BMP.


Advantages

 Allows more tissue to be transferred.

 Allows any tissue to be transferred.

 Allows specialised tissue to be transferred.

 Can reduce donor site morbidity.

 Allows elegant transfer of an already functional unit and can reduce the number of stages required.


But requires a lot of investment into a flap.


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