Re: 펌글. Repair & Grafting of Skeletal Muscle

[문형철]

Chap 16. Repair & Grafting of Skeletal Muscle

� 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(자세유지근)

               ⒜ mitochondria, myoglobin↑ ("red")

               ⒝ metabolize ketones & fatty acid aerobically

           ⓑ Type II fiber(속근)

               ⒜ phosphorylase↑

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

               ⒞ fast contracting

               ⒟ 1^o 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