Chap 16.

Repair & Grafting of Skeletal Muscle

INNERVATION

TENOTOMY

BLOOD SUPPLY

MUSCLE INJURY

MUSCLE GRAFTS

MICRONEUROVASCULAR MUSCLE TRANSFERS

□ muscle grafting시 적절한 생존과 기능을 위해 필수적인 요소

① blood supply

② balance of physiologic tension between points of origin & insertion

③ innervation

□ striated muscle의 특징

① Striated muscle : 30-40% of body weight

② Motor unit : group of fibers innervate by a single alpha motor neuron

③ Neural innervation : metabolic activity, enzyme content, histochemical pattern of the muscle을 결정

④ Full contraction : shorten 40% of length

⑤ muscle with shorter fiber	: greater tension production

muscle with long fiber	: greater velocity

⑥ 2 basic fiber systems

ⓐ Type I fiber

□ mitochondria, myoglobin↑ ("red")

□ metabolize ketones & fatty acid aerobically

ⓑ Type II fiber

□ phosphorylase↑

□ oxidative enzyme, mitochondria, myoglobin↓("white")

□ fast contracting

□ 1o energy source: glycogen

cf) soleus m.: 대부분 type I fiber 지님

INNERVATION

□ Motor nerve disconnection : muscle atrophy --> 섬유조직으로 대치

□ Innervation

: continuing synthesis of acetylcholinesterase at motor end plate

: muscle의 enzyme composition은 innervation되는 nerve에 의해 결정

□ Neural influence on muscle : histochemical profile(=enzymatic composition of fiber)을 결정

- fast(anaerobic) muscle로 가는 신경을 slow muscle로 transfer시 contractile, histochemical staining 특성이 fast muscle로 변화

□ 일반적인 mosaic pattern에서 같은 histochemical type("type grouping")을 보이는 근섬유들의 군집(cluster)이 나타나면 axonal regeneration이나 neural innervation의 reestablishment를 나타냄

□ Denervated muscle이나 muscle graft에서 reinnervation되는 기전

- reinnervation : 근 재생과정에서 가장 중요한 과정

① surgical neurorrhaphy

② implantation of nerve directly into the muscle

③ muscular neurotization	: sprouting of nerve from adjacent normal muscle	--> 위의 두 방법에 비해 효과↓

□ Fascia - barrier to reinnervation between muscles

□ face와 anus의 m은 fascial coverage가 없어 free muscle graft후 결과가 좋다

□ Denervation → motor end plate degeneration → reformation by axonal growth

① choline acetyltransferase level이 reinnervation의 정도와 일치

② biopsy가 불가능할 경우 유용한 방법

ⓐ grip manometer

ⓑ EMG

Electromyography - EMG(fig 16-4)

① normal muscle : electrically silent at rest

② denervated muscle : fibrillation pattern, positive sharp waves

③ reinnervation : large polyphasic units <-- 하나의 신경에 의해 여러 개의 motor end plate가 지배

TENOTOMY

□ Reduction of resting length of muscle : atrophy, fibrosis, loss of normal	elasticity ( injury 수주내 )

□ Insufficient resting tension

① cross sectional area↓

② length↓

③ limiting motor function and strength

□ Increasing length & excessive stretch시 섬유화와 수축력을 상실

□ Tenotomy(division of the origin and insertion)

--> nerve나 blood supply를 단절시킨 후 즉시 microscopic repair를 시행한 경우보다 더 심한 손상을 초래

□ Donor site에서 recipient site로 muscle transfer시 resting tension을 맞추어서 길이를 정하는 것이 중요하다.

BLOOD SUPPLY

□ muscle : anoxia에 민감(time-limiting tissue) <-- high metabolic demand

→ 1 시간 이상의 normothermic ischemia면 muscle damage

□ Metabolic effect of ischemia - 300 mmHg 2Hr torniquet후 관찰

① capillary permeability to protein & fluid↑

→ pO2↓

→ edema formation

② increased blood flow with significant AV shunt

□ ①,② → fluid collection within the muscle

→ pressure↑

→ focal area of necrosis

□ Oxygen deprivation

① metabolism : glycolysis → produce ATP

② lactic acid accumulation

③ muscle metabolites & tissue gas tension

: tourniquet제거 후 1.5hr후 정상으로 돌아옴 (300mmHg, 2hr 후)

* 1 hr ischemia 후의 histologic findings

① 3 day : inflammatory cell infiltration

② 1 week : proliferation of interstitial CT & myonuclei proliferation

③ 2 week

ⓐ irregular m. fiber shape

ⓑ intermyofibrillar space vacuolization

④ 2개월 : return to normal cross striation pattern

□ EM findings

① 1 week : mitochondria atrophy, sarcoplasmic reticulum destruction

② 4, 5 week : evidences of repair

ⓐ glycogen granule & mitochondria↑

ⓑ fibrous tissue↓

□ Maximal time of induration for anoxia

① 6 hrs of normothermic ischemia

② 8 hrs if cooled

MUSCLE INJURY

□ functional recovery of muscle

① complete laceration(transection)

ⓐ 50% of tension production

ⓑ 80% of normal contraction

② partial laceration

ⓐ 60% of tension production

ⓑ normal shortening

□ transection의 distal muscle portion

① microscopic denervation atrophy

ⓐ small, irregular-shaped muscle cells

ⓑ central positioning of nuclei

ⓒ increased amount of fibrous tissue

② denervated segment는 fibrous tissue의 양이 증가하여 contraction시 stretch하지 않음

□ Healing : by scar formation

□ innervation은 regeneration process나 repair에 아주 중요하며 nerve supply가 없는 경우 regenerative activity가 일어나나 계속되지는 못함

MUSCLE GRAFTS

□ Concept of preoperative denervation :

--> graft 초기의 anoxic period에 좀더 잘 적응할 수 있도록 □근대사□를 변화

--> induce a "plastic state" of regenerative activity within the muscle

⑴ muscle내의 변화

① enlargement and division of nuclei

② amitotic division of nuclei

③ growth of sarcoplasm masses

④ formation of myofibrils

⑵ predenervation의 효과

① metabolic demand ↓

② satellite cell(myogenic activity를 가진 dormant cell)을 자극

③ reduce muscle bulk

④ capillary circulation ↑

□ Watson's concept : methods for clinical success of free muscle graft

① preoperative denervation - 3주전 (Thompson concept)

② transplantation of entire muscle belly length : damage를 줄임

<-- live muscle cell이 regenerative activity보다 더 중요

③ restoration of physiologic tension

④ removal of all fascia <-- neurotization을 도움

□ Effective use of free muscle graft

① facial palsy

② anal sphincter reconstruction

--> 이 두 곳은 muscle이 fascia에 싸여있지 않은 곳이며, 정상 muscle위에 이식하여 muscular neurotization을 통한 neural innervation이 용이

□ most common muscle : palmaris longus

Histology of Free Muscle Grafts

□ 동뮬실험 : 4gm 이하의 muscle free graft시

1. Within hours after grafting : graft periphery의 thin rim of cell(전체의 5% 미만)을 제외한 나머지 muscle fiber는 ischemic necrosis됨

<-- by diffusion of fluid from recipient site

2. within 2 days

① vascular ingrowth begin to penetrate the graft

② leukocytes and macrophages : remove the dead sarcoplasm

③ basal lamina는 intact

3. 3일째 : 새로운 근육의 재생을 처음으로 관찰

□ Cross section of free muscle graft(3 distinct circular zone)

① peripheral rim of surviving muscle fiber

② ring of muscle regeneration

③ core of necrotic fibers

□ Size of the graft(radius of the graft) : graft의 complete survival을 결정하는 가장 중요한 인자

<-- graft 중심부에 위치한 residual myogenic cell의 영양공급을 위한 centripetal vascular penetration에 필요한 시간에 의존

□ Satellite cell - myogenic potential 가진 resting cell

① source of regeneration : activation of dormant stem cell

② location : beneath the basement membrane of muscle fiber

③ EM으로만 감별가능

- observed throughout muscle, 총 nuclei의 2 - 35%(age에 따라 다름)

④ denervation 후 숫자가 증가한다. <-- regeneration과 관련성을 시사

⑤ resistance to ischemia : low metabolic rate

이유	ⓐ small amount of cytoplasm

ⓑ survived by plasmic circulation

MICRONEUROVASCULAR MUSCLE TRANSFERS

1. technical aspect of procedure(reinnervation potential을 극대화 하고자 할 때)

① selection of donor muscle with a single artery and nerve

<-- residual functional disability를 최소화 할 수 있음

② reduction of the length of ischemia time

③ proximal neural repair

2. muscle이 완전히 생존하고, reinnervation(8-9개월 소요)된 후에도 function은 정상 maximal work capacity의 25%(Terzis의 경우, But Frey 55%)에 불과하다

□ functional test : fatigue rate, tetanic tension

3. 3 variables affecting muscle function

① blood supply

② innervation

③ tension

□ Muscle function was more adversely altered by tenotomy alone than by

microneurovascular repair