Chapter 9.

Principles & Physiology of Skin Flap Surgery

PRINCIPLES OF FLAP SURGERY

Classification

Method of movement

Blood supply

Composition

Soft Tissue Coverage

Macrocirculation

Embryology

Anatomy

Types of Flaps

Random cutaneous flaps

Arterial cutaneous flaps

Fasciocutaneous flaps

Myocutaneous flaps

Muscle flaps

Specialized flaps

Complications

FLAP PHYSIOLOGY

Microcirculation

Anatomy

Physiology

Pathophysiologic Changes

Anatomic changes

Hemodynamic changes

Metabolic changes

Pharmacology

Axon blockers

Receptor blockers

Direct smooth muscle relaxants

Altering rheology of blood

Increasing tolerance ot ischemia

Miscellaneous agents

Tests of Skin Flap Circulation/Monitors

PRINCIPLES OF FLAP SURGERY

Skin flap : recipient bed에서의 생존이 functioning intravascular circulation에 의함

cf) skin graft : plasmatic imbibition에 의존

□ Surviving length를 연장시키기 위해서 flap 폭을 크게 잡는 것은 효과가 없으며 incorporated blood supply에 의존(Daniel,1973)

□ length-to-width ratio(275)

: face - 5:1, lower extremity - 1:1

Classification

1. Method of Movement 에 따른 분류(Table 9-1, Fig 9-1)

2. Blood Supply

□ blood supply to covering tissue

① segmental

② perforator

③ cutaneous : MC, SC

□ Blood supply에 따른 분류(fig 9-2)

□ musculocutaneous artery : major vessel로부터 분지되어 나와 muscle에 분포하고 상부 dermal plexus로 이어지는 artery

□ septocutaneous artery : segmental 또는 muscular artery에서 분지되어 fascial septa(근육사이)를 지나기전 enveloping fascia와 상부 skin에 분포하는 artery

참조) 발생학적으로 cutaneous carpillary plexus와 하부의 segmental artery는 동시에 발생하는데 이를 연결해주는 혈관이 muscular septa에서 발견, 이의 이름을 septocutaneous artery로 함

3. Composition에 따른 분류(fig 9-3)

① compound flap : cutaneous, fasciocutaneous, myocutaneous, skin graft and muslce flap

② composite flap : osseocutaneous flap

③ specialized flap : sensory flap

Soft Ttissue coverage

□ soft tissue coverage에 대한 multiple factor

① recipient site requirement

② donor site morbidity

③ operative complexity

④ patient factors : occupation, advocation, mobility or immobility, age

□ hierarchy of closure technique(table 9-2, fig 9-4)

Macrocirculation

1. Embryology

⑴ 3 level in major embryologic change of macrocirculation

① deep distribution system of primary vessel : aorta의 연장, final definitive configuration지님

② intervening muscle mass : 많은 recombination, migration 거침

③ various plexus of cutaneous vasculature : external factor에 영향 받음

□ "longitudinal annexation" : femoropopliteal-posterior tibial system의 발생

- femoral artry의 stem과 distal 쪽의 femoral artery사이에 primitive sciatic artery가 첨가(annexation)되어 femorolpopliteal- posterior tibial system을 형성

⑵ vascular anatomy in 5mm human embryo(fig 9-5)

⑶ Schafer : fascial vascular network의 분화는 태생기 후반부에 시작 final pathway는 출생후에 일어남

⑷ 어떤 organ의 vascularity를 지배하는 4 factors(in embryonic view)

① vessel lumen의 size는 blood flow rate에 의해 결정

② vessel length는 longitudinal tension에 의함

③ vessel wall 두께: BP에 의함

④ capillary pressure가 높아지면 new capillary formation 발생

2. Anatomy

□ body의 blood supply는 3 level에서 일어남

① internal system

② muscular system

③ cutaneous system

□ 5 distinct plexus of cutaneous system(fig 9-6)

ⓐ subepidermal

ⓑ dermal

ⓒ subdermal(cutaneous)

ⓓ subcutaneous

ⓔ fascial(prefascial, postfascial)

⑴ internal vascular system(fig 9-7)

□ intercostal flap

⑵ Muscular system (fig 9-8)

□ Mathes & Nahai Classificaiton

① type I	: one vascular pedicle(TFL)

② type II	: dominant pedicle and minor pedicle(s)(gracilis)

③ type III	: two dominant pedicles(gluteus max)

④ type IV	: segmental pedicle(sartorius)

⑤ type V	: dominant pedicle and 2o segmental pedicle(LD)

□ muscle의 embryologic formation의 6 pattern

① migration : latissimus dorsi

② fusion : rectus abdominis

③ longitudinal splitting : trapezius

④ tangential splitting : transversus abdominis

⑤ change in direction

⑥ degeneration

⑶ Cutaneous System (fig 9-9)

① 3 anatomic level

ⓐ fascia

ⓑ subcutaneous fat

ⓒ skin

② 5 type plexsus

③ 2 type of cutaneous artery

ⓐ musculocutaneous

ⓑ septocutaneous

□ vessel orientation에 영향주는 factor : amount of fat(by Timmons)

① fat이 많을수록 more perpendicular and separated → fascial vessel

② thin skin : richer vascular network

□ 5 types of plexus

① Fascial Plexus :

ⓐ subfascial plexus는 minor - 예외) tensor fascia lata

ⓑ prefascial plexus가 dominant distribution system

□ fascial polexus의 blood supply(91,93)

ⓐ septocutaneous artery

ⓑ adjacent musculocutaneous arteries

ⓒ retrograde flow from the overlying subcutaneous plexus

② Subcutaneous plexus

ⓐ superficial fascia level에 위치하는 horizontal linear plexus로 sububcutaneous fat을 superficial & deep 2 부분으로 나눔

□ superficial fascia는 panniculus carnosus의 상동기관으로 사람에게는 platysma, scarpa's fascia로 관찰

ⓑ dermal plexus와 reciprocal relationship을 지님

③ Subdermal plexus(=cutaneous plexus)

ⓐ 1o blood supply to skin

ⓑ skin flap edge의 dermal bleeding의 source

ⓒ deep reticular dermis와 subcutaneous fat사이에 위치(by Moretti)

④ Dermal & Subepidermal Plexuses - true skin circulation

□ Function & Characteristics of Plexuses(fig 9-12)

① subdermal(artery) p : have continuous arterial muscular wall

--> 1o distribution function

② dermal(arteriole) p : having isolated musculature

--> 1o thermoregulation

③ subepidermal(capillary) p : no muscle coverage

--> 1o nutritive function

□ □external vascular belt" - dermal & subepidermal plexus

- 70% 의 blood가 thermoregulation 에 쓰인다.

□ skin : 150/mm2, 4.5% of total blood

--> 1/20%만이 nutrition(나머지는 pressure & temperature regulation)

muscle : 2,000/mm2, 13.2 % of total blood

Types of Flaps

1. Random Cutaneous Flaps

□ advantages & disadvantages

2. Arterial Cutaneous Flaps

□ arterial flap의 vascular pattern

3. Fasciocutaneous Flaps

□ Ponten(1981)의 super-flap : lower extremity와 several upper arm flap에서 intermuscular septum을 따라 나오는 multiple perforator를 base로 하는 flap

□ Fasciocutaneous flap이 vascularity가 클수록 septocutaneous a.에 근간을 둔 arterial flap의 형식이 됨.

ex) parascapular flap : arterial cutaneous & FC flap 모두 가능

□ Forearm의 4 principle region(Cormack & Lamberty)

① radial a with its inf. cubital a

+ prox. 1/3의 brachioradialis와 pronator teres사이의 SC a.

+ distal 2/3의 brachioradialis와 FCR사이의 br.es

② ulnar a.

③ post. interosseous a.

④ antero-osseous a.

□ Septocutaneous branches of radial artery : 3 group(Timmon)

① proximal protion off the radial recurrent artery

② branches off the proximal artery

③ distal half로 부터의 branches

□ reversed forearm flap(distally based radial forearm flap)의 시행시 artery의 retrograde flow는 가능하나 vein은 ?

① venae comitantes는 valve가 없다? : dissection 결과 valve가 있다.

② "crossover pattern" of communicating br. between the 2 venae comitantes

③ "bypass pattern" of collateral br. on each vein

→ 그래도 가능하려면 3 가지 조건이 필요

ⓐ denervation

ⓑ valve의 prox.과 distal에 blood가 있고

ⓒ valve의 prox.의 venous BP가 distal보다 높아야함

□ Facial & fascio-fat flap

① example

ⓐ temporal fascia

ⓑ posterior calf fascial free flap

② 장점

ⓐ fat을 포함하여 deep str. exposure를 cover → 후의 재건을 가능케

ⓑ skin이 포함되지 않아 donor site morbidity ↓

③ 단점

ⓐ fascia는 muscle처럼 infection에 저항이 없음

ⓑ flap monitoring이 어려움

4. Myocutaneous Flaps

□ Same prepectoral skin에서 만들 수 있는 3 flaps

□ Medial gastrocnemius MC flap의 3 방법

5. Muscle flaps

□ muscle flap으로 사용가능한 group : type I, III, V

□ muscle flap selection시의 technical criteria

□ sternal dehiscence의 closure시 pectoralis majorm. flap의 3 application

ⓐ advancement flap(based on the thoracoacromial blood supply)

ⓑ turn-over flap(based on the int. mammary perforator)

: transposition이 더 쉽고 더 큰 size 이용 가능

ⓒ split mammary system(split & turn-over) : distal defect coverage 위해

□ prociple for the management of chronic osteomyelitis(Gordina)

ⓐ extensive resection of scarred surrounding soft tissue

ⓑ radical debridement of necrotic bone

ⓒ coverage with well vascularized muscle

ⓓ end to side vascular anastmosis

□ muscle flap & skin graft의 long term result : atrophy 25 ~ 50%

□ myocutaneous flap이 muscle flap 보다 더 유용한 경우

① esthetic skin match

② 상당량의 soft tissue가 필요한 경우

--> breast reconstruction

cf) lower extremity에 경우 myocutaneous flap이 muscle only flap보다 더 큰 size를 얻을 수 있으나 donor site problem이 크므로 muscle flap + skin graft가 더 유용

6. Specialized Flaps

⑴ Sensate flaps

① neurovascular free flap의 principle(Daniel)

ⓐ vascular distribution과 sensory innervation이 overlap되어야

ⓑ anastomosable vascular pedicle을 가진 flap을 isolation할 수 있어야

ⓒ flap에 supply하는 nerve를 찾아 이을 수 있어야

ⓓ sensation의 quality가 defect에 적합해야

ⓔ donor site morbidity가 acceptable해야

② sensate flap 종류

ⓐ neurovascular flaps of the digit(digital n.)

ⓑ (free) dorsalis pedis flap(SPN, DPN)

ⓒ wrap-around flap of the great toe(deep, superficial peroneal n.)

잇점

㉠ low two point disrimination : 6 ~ 8mm

㉡ durable soft tissue coverage

㉢ optimal finger nail

ⓓ radial forearm flap(lateral antecubital cut. n.)

ⓔ intercostal neurovascular free flap

ⓕ post. thigh flap

ⓖ tensor fascia lata neurovacular free flap

□ single intercostal NV bundle --> can support a flap 5 interspaces wide

□ sensate flap은 young child에서 spina bifida로 인해 lumbar kyphosis상부에 pressure sore가 발생한 경우 특히 유용

⑵ Osseocutaneous Flaps

□ vascularized bone graft의 잇점

① higher rate of union

② earlier evidence of bony hypertrophy

③ greater mechanical strength

④ lowest rate of infection & nonunion

⑶ Composite flaps

□ composite flap으로서의 scapular flap의 장점

① multiple skin paddle of varying thickness

② additional soft tissue 포함가능(LD)

③ complementary bone architecture

Complications

□ Flap complication의 원인(Table 9-3)

FLAP PHYSIOLOGY

Microcirculation

1. Anatomy

□ microcirculation : nutrition, blood flow의 local regulation에 관여

- arterioles, capillaries, venules, arteriovenous anastomosis

□ sympathetic innervation이 직접되어 있는 곳

① arterioles

② precapillary sphincter

③ a-v anastomoses

□ arteriolar network이 조직혈류의 1o regulator

□ skin의 total blood flow : 20 ml/min/100gm

--> heating or acute sympathetic block 시 AV anastomosis 통해 증가

2. Physiology

* cutaneous microcirculation에 작용하는 physiologic factor

		Vasoconstriction	Vasodilatation
Systemic control	1. nervous(mi)	□-adrenergic serotonergic	□-adrenergic cholinergic
	2. humoral	epinephrine(□-adr) serotonin PGE2, PGF2□ thromboxane A2	histamine bradykinin PGE1, PGI2 Leukotrienes LTC4, LTD4
Local control	3. metabolic	hypoxia acidosis hypercapnia interstitial K+
	4. physical	viscosity(ischemia등) hypothermia myogenic distention	hyperthermia

Pathophysicologic Changes

□ flap elevation시 initial stage의 primary importance

① sympathetic innervation의 functional loss

② insult of ischemia

□ 이러한 flap이 생존하기 위해 8 ~ 12시간이내에 적절한 circulation이 유지되어야 함

1. Anatomic Change

□ skin flap elevation 후 early anatomic change

① subdermal plexus의 small a.의 수, size ↑

② longitudinal reorientation

③ dermal venous channel의 size ↑

④ flap base의 vessel number ↑

□ 이들 vessel은 toneless dilated, local change에 반응 못함

□ Changes in autonomic innervation of flap

① catecholamine (실험)

ⓐ acute □rat" flap : unipedicled flap

㉠ 18hr에 사라지기 시작 → 30hr에 completed(6-24 hr)

㉡ reaccumulation : 4-8주에 시작(re-innervation signal 보일때)

ⓑ delayed "pig" flap : bipedicled flap

㉠ 2hr부터 감소시작 → 10일 되면 정상으로 환원

□ acute situation에서 profound effect 보임

2. Hemodynamic Changes

□ delay procedure

① Reinisch의 연구(1980년대 까지의 가장 popular concept)

delay procedure란 : dilated AV shunt가 spontaneous constriction될 때 까지 적절한 nutrient & non-nutrient flow를 유지시키는 작업

→ acute flap의 distal portion은 AV shunt를 통한 부적절한 non-nutritive flow의 때문에 necrosis

② Pearl의 □unifying theory" of delay phenomenon

: sympathectomy 직후 vasoconstricting neurotransmitter의 배출

→ hyperadrenergic state

→ vasoconstriction

- delay flap은 이러한 vasoconstriction의 early stage를 견디나 acute flap은 그렇지 못함

③ Kerrigan의 data

- acute elevated flap에서 a. insufficiency가 distal flap failure의 1o cause

- distal에서 AV shunt flow의 흔적이 없음 → die

3. Metabolic Changes

□ acute flap에서 anaerobic metabolism에 의해

① O2, glucose, ATP↓

② CO2, lactate ↑

□ ischemic distal but viable flap을 check 할 경우

① glucose 소비 : 3일 까지 max → 7일에 recover

② lactate생산 ↑, tissue glycogen, glucose content ↓↓

③ cyclic AMP

ⓐ acute stage시 ↓

ⓑ viable portion은 12시간 후 ↑↑

□ toxic superoxide radical(by-product of xanthine metabolism)

□ SOD(superoxide dismutase) free radical에 대항

ⓐ delayed flap에서는 normal level 유지

ⓑ acute flap의 distal portion에서 감소

□ metabolic change에 따른 rheologic properties

① viscosity↓ → flap blood flow↑

② anemia, protein depletion → flap survival length ↑

□ fibrinolysis 변화 : ischemic skin flap의 reperfusion 24hr후 fibrinolytic activity ↓

□ PLT aggregation과 arachidonic acidpathway의 변화

① acute flap : thromboxane↑↑

② delayed flap : prostacyclin↑↑ - 7th day에 max.

Pharmacology

1. Axon Blockers : ganglion이나 axon자체를 block

① reserpine	② dopamine

③ guanethidine

2. Receptor Blockers : skin에는 □가 중요 muscle에는 □가 중요

① □-blocker

ⓐ phenoxybenzamine	ⓑ phentolamine

ⓒ tolazoline	ⓓ thymoxzmine

② □-blocker

ⓐ epinephrine	ⓑ isoproterenol

ⓒ metaproterenol	ⓓ terbutaline

ⓔ isoxsuprine	ⓕpropranolol

3. Direct smooth muscle relaxant

① hydralazine	② nitroglycrine

③ dimethyl sulfoxide(DMSO)	④ Ca++ channel blocker

⑤ diazoxide	⑥ PG inhibitor

□ Prostaglandin blockers -  Arachidonic acid metabolism 방해하는 agent

① indomethacin	② imidazole

③ ibuprofen

4. Altering rheology(유동성) of blood

① pentoxifylline : smooth m. relax,	RBC의 flexibility 회복, PLT deaggregation

② Anemia

③ 그외 drugs :

ⓐ ancrod	ⓑ xanthiol

ⓒ niacinate(Complamin)	ⓓ low M.w. dextran

ⓔ dicumoral	ⓕ dipyridamol

ⓖ heparin	ⓗ hyaluronidase

□ streptokinase

5. Increasing tolerance to ischemia

① steroid

② superoxide radical scavenger or blocker

ⓐ allopurinol : xanthine oxidase inhibitor

ⓑ superoxide dismutase(SOD) :

ⓒ deferoxamine : iron chelating agent, free radical scavenger

③ hyperbaric oxygen

Tests of Skin Flap Circulation/Monitors(Table 9-4)

□ flap perfusion의 monitors

① stab wound bleeding : useful subject measure(특히 free flap)

② Laser doppler : most promising test currently available for clinical use

③ surface temperature ; free flap에 가장 많이 사용하는 test

④ differential thermometry : burried tissue transfer시 standard

(차이가 3oC 이상이면 유의해야)

⑤ fluorescein : intrinsic failure에 best test

⑥ radioactive microsphere : Golden standard for lab.

□ 2 most widely needed clinical applications

① free tissue transfer

ⓐ skin flap : surface temperature

ⓑ burried tissue : differential thermometry with thermocouple prove

② acute skin flap for a distal zone of ischemia : fluorescein dye test