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 forearmflap 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.
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:
higher rate of union,
has greater mechanical strength,
has a lower rate of infection (and thus non-union.)
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.
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)
Single pedicle venous flap
Flow through venous flap
Arterialised venous flap
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.
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.
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.