The Possibility Of The Sensory Reconstruction Of The Distally Based/Reverse Sural Flap By The Nerve Anastomosing:Clinical Anatomical Study

1.IntroductionThe resurface of soft tissue defects in distal lower limbs,ankle,heel and foot,due to limited availability of the soft tissue in this region,have been a difficult problem,even a challenge to the surgeons of the orthopaedic trauma,podiatry,plastic surgery et al.The soft tissue defects in these place had been repaired by the skin grafting,cross-leg flaps,local random flap,local pedicle flap or composite flap,and free flaps transfer,which sacrificed the main artery,long term immobilization,the risk of operation failure to the patients.The sural fasciocutaneous flap(Abbreviation in this text:sural flap)was first introduced by Donski et al.in 1983,and the sural neuroskin flap was illustrated in details from multi-cutaneous nerve study by Masquelet in 1992,it provided a versatile choice in the repairing of soft tissue defects in lower limbs.With its modified types,the sural flap technology ushered in the era which the distally based sural neurovascular/or fasciocurtaneous flap were wide used in the worldAfter 1998,more and more literatures published in the fields of anatomy and clinical researches,the anatomy study mainly focus on the blood supply,blood supply’s characteristics and protection,in order to improve the survival rate of sural flap and enlarge the donor sites range to repair more distal and more larger defects.Many reports about the sural flap various modifications and advance,such as:the lesser saphenous vein ligated in distal pedicle or anastomosed in proximal edge,lobulated sural flap,delayed technics,by combining the VSD and sural flap,free perforators sural flap repairing the wounds and soft tissue defects in upper limbs(forearm,wrist,hand),oral cavity reconstruction.The sural flaps were used mainly in Orthopaedics Trauma,Podiatric Surgery(after cancer ablation,osteomyelitis),Hand Surgery,Burn,and Plastic Surgery et al.The sural flap were widely adopted for its advantages which the author summarized:sensory reconstruction by reinnervation;no recurrent ulcer after footwear;versatility,flexible design and harvest in the size;long pedicle with flexible arc of rotation;not sacrificed the main artery;one-stage,quick dissect;no need microsurgery and saving time.Many related literatures consented the viewpoint that the transferred flaps in heel and plantar should get reinnervation,it is helpful to the flap stability,enabled early walk,in case of frozen injury and recurrent ulcer caused by shoe wearing.The neurotized sural flap meet the demand.Nowadays,some specialists recommend it to be the first choice in Trauma,Orthopedics,and Plastic Surgery.Many authors have tended to confirm that patients could get satisfied sensory reconstruction in sural flap so long as by the sural nerve in the neurovascular axis coapted to the nerve in recipient sites.So far,the reliability and possibility acquired by the sural nerve anastomosed in sural flap haven’t been proved by a thorough anatomical study.The author raised the question about the clinical effects of the neurotized sural flap,based on the clinical experience in many years operation.The conclusion of the research,although could be used to evaluate the previous reports retrospectively,we more wish the conclusion can provide the reference to surgeons in related speciality.2.Objectives2.1 By observing the forming branches of the SN(MSCN and PCB)and the branch of the common peroneal nerve(LSCN)supplying in posterior lower leg,to discuss their correlation with the sensory reconstruction of sural flap.The author wish to provide a basis for the related surgeons during the operation.2.2 By the statistical analysis of the anatomical results to above cutaneous nerve branches,to evaluate the influence of aforementioned cutaneous nerve branches occurrence rate to the clinical efficacy of the sensory reconstruction in the sural flap.2.3 By analysing the level(location)of the supplying points distributing of the cutaneous nerve branches which related to the sural flap in middle and proximal section of the posterior lower leg,to discuss the relationship between the upper margin location of the sural flap and the clinical effects to the neurotized sural flap,aim to provide prospective reference to mapping a sensate sural flap for the related surgeons.2.4 By observing the saphenous nerve in every leg specimen,and post femoral cutaneous nerve(PFCN)in some lower limbs,to discuss its role to the sensory reconstruction of the sural flap.3.Subjects Data were collected by dissecting 40 lower legs in 30 Chinese adult cadavers,.None of the specimens showed evidence of deformity,texture is abnormal,and previous wounds in lower legs.4.Methods4.1 Incision designing According to the largest size sural flap descripted in previous literatures.The skin incision began from the popliteal crease in all legs,investigated the LSCN superficially;investigated the MSCN and PCB subfacially,traced the SN to the lateral malleolus,in some cases to the lateral heel and foot;explored the saphenous nerve,and the PFCN in 8 leg specimen in the popliteal fossa.4.2 Observing,measure and recording the existing,origin,course,layer,pierce point,union,distribution of sensory branches in lateral lower limbs,and variations of the PCB,MSCN,SN,LSCN,the saphenous nerve,and the PFCN;Pay attention to the location of the supply point(Abbreviation:SP)of the cutaneous nerve which the diameter was bigger than 0.5 mm in every specimen.4.3 Building a coordinate system in every posterolateral lower leg;Located,labelled and measured the SP of the LSCN,the PCB and MSCN et al.in a coordinate system in every lower leg;acquired measure value.(detail content see the text)4.4 Making the percentage unit distribution figure of all the SP in lower limbs of this group(Fig.9A-9C).The distributed coordinates figure of all the SP in every leg by percentage unit of X-axis compressed formed(Fig.9C).Fig.9C and Fig.9D was overlapped in equal percentile point,the percentage distributing graph of all the SP in posterolateral lower limbs of this group was finally got(Fig.9E).The course is as follow:4.4.1 Transforming the coordinate value of every measured SP(±X,Y)in every leg into SP(±X,y)with percentage unit,and marked in the percentage unit coordinate system Fig.9A.4.4.2 Fig.9A was coordinates figure of the X:y=1:1 percentage unit,it could not be overlapped to the model coordinates figure with percentage unit of the right lower leg in this group,the percentage unit of X-axis in Fig.9A need compressed according to the ratio[OM:ML=(average maximal length of sural flap):(average maximal 1/2 width of sural flap)= 5.17:1],then could be overlapped.The distributed coordinates figure of all the SP in every leg by percentage unit of X-axis compressed formed(Fig.9B,Fig.9C).4.4.3 Building a percentage unit model coordinates figure of the right lower leg(Fig.9D).Building of the percentage unit model coordinates figure of the right lower leg,it must conform to following standard:O(0,0%),M(0,100%);(Unit of y-axis):(Unit of x-axis)=OM:ML=5.17:1[in this group,OM:ML=(average maximal length of sural flap):(average maximal 1/2 width of sural flap)].4.4.4 The distributed coordinates figure of all the SP by the percentage unit of X-axis compressed(Fig.9C),and the percentage unit model coordinates figure of the right lower leg(Fig.D),was overlapped in equal percentile point,the percentage distributing graph of all the SP in posterolateral lower limbs of this group was finally got(Fig.9E).[Note:The reason why the author used the above data treatment method in Section 4.4.1--4.4.4,is because the SP value acquired in every lower limbs of this group in section 4.3 was absolute value,it would cause obviously distortion if the SP absolute value marked on the model coordinates figure of the right lower leg.While the SP coordinate value in every legs transformed to percentage value,then marked all the SP in the figure with the percentage unit coordinates system,and unit in X-axis compressed to the unit of x-axis in the ratio of OM:ML in this group,the compressed coordinates figure was overlapped to a percentage model coordinates figure of the right lower leg,by percentage point equal overlapping,in that way every SP relative distributing location in lower limbs of this group was truly reflected.Avoiding the figure’s distortion by means of absolute value marking of every SP].4.5 Equipment:Conventional surgical instruments,vernier caliper,steel measure tape,Sony a550 camera,Nikon D800 camera.The photo drawing and label was by Photoshop 6.4.6 The measure Unit:The external diameter measure unit(mm);length and width measure unit(cm);because the nerve from the latent course to migrating course into the supplying point is difficult to measure accurately,measure unit(0.5cm);Some of the non-key indicators such as irregular distribution range and distance measure unit,record the numerical range or average number;occurrence rate of the LSCN,PCB and MSCN etc.,used the "x%".5.Results and statistic analyses5.1 LSCN LSCN was present in 77.5%(31/40)cases.The LSCN and the PCB branched off the common peroneal nerve(PN)in 18 legs,they coursed down and penetrated deep fascia behind the fibular head to suprafascial plane.Its cutaneous branch ramified several sensory sub-branches and terminated in the upper and middle posterolateral surface of the lower limbs.LSCN was deficient in 22.5%(9/40)cases.The way of LSCN supplying and location.The author categorized it into two patterns:1.branch-terminal pattern:percentage 25%(10/40).The single or double branch of the LSCN coursed between deep and suprafascial plane,when the LSCN pierced deep fascia into the superficial plane,it produced supplying point SPA,or SPA and SPB,before LSCN ramified terminals(diameter less than 0.5mm)to the skin;2.branch-subbranch-terminal pattern:percentage 52.5%(21/40),before the LSCN went into the superficial plane,the LSCN split and gave off several thick subbranches and produced several supplying points SPA-SPE.etc.The subbranches ramified sensory terminals to the skin of the calf.Datum of the every SP(±X,Y)of the LSCN and the PCB,ML and OM in the group,transformed percentage value of SP(±x,y),see Table 1.Data of "column y" in Table 1.revealed that average value of the SP was 73.2%in the maximal length of sural flap in theory(roughly the length of the cadaveric lower leg);located on the ML in 25.5%lateral to the y-axis.Compressed coordinates graph of the every SP was overlapped to a model coordinates figure of the right lower leg(Fig.9E),the morphometric graph revealed that the SP distributed in the middle and upper posterolateral part of the lower legs,concentrated relatively on a little bit below the junction of the proximal 1/4 parts and distal 3/4 parts of the posterolateral lower leg,dispersed up and down;about 1/4 of the half width of flap laterally,and dispersed right and left.There was scarcely SP lower than junction of the upper 1/2 and lower 1/2 sections of the lower leg.5.2 PCB PCB was present in 75%(30/40)legs.The PCB and the LSCN came from the common trunk or the multi-branches from common trunk above the level of popliteal crease in 45%(18/40)legs;derived independently from the common peroneal nerve in 30%(12/40)legs.There are 2 cases--the PCB send the sensory branches to the middle part skin of the posterolateral calf;The PCB hadn’t sent sensory branch to the posterior and lateral skin of the upper and middle calf in other 28 cases(the PCB coursed down subfascially in 26 cases).The coordinate system of the supply point of the PCB,referred to the section 5.1.5.3 MSCN MSCN was present in 34/40(85%)specimens.MSCN originated above the popliteal crease from the tibial nerve and descended between the surface of two gastrocnemius heads or under the gastrocnemius aponeurosis,normally the MSCN joined with the PCB formed the SN under the lower edge of the middle 1/3 sections of the calf.The SN ramified 5-8 branches to surface of the lateral distal 1/4 section of the leg,Achilles tender,the lateral malleolus,heel and foot.Above the MSCN-PCB union point,we found no sensory sub-branches split from the MSCN.5.4 Post femoral cutaneous nerve(PFCN)The sensory terminals of the post femoral cutaneous nerve were dissected in 8 cases in the post proximal limb,occurred in all the cases,went around the saphenous vein in the middle of popliteal fossa in subfascial layer,constant union and bifurcating with 1-2 branches,the diameter less than 0.5mm,supply the post and up part fascia and skin beneath the popliteal crease.5.5 Saphenous nerve The thick saphenous nerve was detected in only 1 case out of the 40 cases,the diameter was 1.5mm,supplied the posterior inner skin of the proximal calf.There was no obviously saphenous nerve in the other posterior lower legs.6.Conclusions6.1 LSCN is the nerve of choice and the key branch to reinnervate the sural flap,it is in suprafascial plane(in superficial fascia).6.2 The occurrence rate of the LSCN was about 65%--77.5%in human legs,if the LSCN was anastomosed to recipient nerve,at most about 65%--75%of the sural flaps could get neurotization.6.3 The clinical effects of the neurotized sural flap is anatomically decided by the top edge of the flap elevated level in posterior leg,i.e.by the level of the lowest supplying point of the LSCN.When the surgeons map a sensate sural flap,the upper edge had better close to or above the junction of the proximal 1/4 parts and distal 3/4 parts of the posterolateral lower leg.6.4 The PCB offered very low possibility in sensory reconstruction—provided 5%chance to the reinnervated sural flap by anastomosing.The PCB is basically under deep fascia in the sural flap donor site.6.5 The MSCN had no sensory sub-branch to the upper and middle posterolateral surface of the calf.Anastomosing the MSCN has no role to neurotize the sural flap.The MSCN was mostly termed as the SN and got anastomosed with the recipient nerve in previous literatures.The MSCN is basically under deep fascia in the sural flap donor area.6.6 The branch of the saphenous nerve was not visiable for coapting,except 1 variational case with the occurring rate of 2.5%could get anastomosed when indicated.6.7 The diameter of PFCN was too thin to be coapted,and the supplying territory was limited to proximal part of the posterior lower leg,the author don’t advise to dissect the nerve in the operation.6.8 The nerve selecting of the sensate sural flap(anastomosing ladder):LSCN→PCB→the saphenous nerve,from good effect to poor effect.