CHAPTER I3 TFIE PTANTAR SKIN AND SOFT TISSUE,S: Private Surgical Anatomy Review
Tlcom,as F. Smitb, DPM
Plantar surgical approaches are feared clue to a specialized aspects of the subcutaneous tissues or concern for symptomatic scarring. There should be fat pzrds will be reviewed with emphasis on a respect for the plantar skin and associated exposure and visualization. subcutaneous tissues, but not fear. To avoid the possibility of a painful scar, it has been THE SKIN recommended that plantar incisions be placed on the non-u.eightbearing areas of the plantar skin. The histology of skin is impoment to review. Skin is Incisions can likewise be piacecl plantarly in areas of composed of tu.o basic layers, the epidermis on the potential non-weightbearing w'here a sesamoicl or surface and the cleeper dermis. The epidermis is metatarsal is to be resectecl. A non-rvei5lht- composed of the stratified squalnous epithelium. bearing xea plantariy is in essence created from a The major ce1l of the epiclermis is the keratinocyte. weightbearing area. A more complete approach to Other cells of the epidermis include melanocl,tes. the plantar scar is to orlent the scar to not only Melanocyes are not nllmerolls in plantar skin and consider the weightbearing status of the skin but little melanin pigment is formed. Plantar skin gets its neuroyasclllar concerns, relaxed skin tension lines, characteristic yel1ow-golden color from the pigment and adequacy of exposure.'l carotene that exists in the subcutaneous fat, not the The plantar skin and soft tissues are very more translucent skin. The pink coloration of the specialized to provide the suppleness and padding plantar foot comes from the oxlrhemoglobin in the neecled for absorbing the forces of weightbearing. highly vascular plantar dermis. Langhans's cells in The plantar soft tissues possess the strength to resist the epidermis play a role in immunologic fr-rnction. ground reactive forces whether walking shod or Merkel's cells present in the plantar epidermis are unshod. Special techniques of surgical approach, thought to sen,e as mechanoreceptors.s repair, zrnd postoperative management are The dermis is primarily made r-rp of collagen urarranted. Plantar approaches are \rery reasonable fibers and a protein matrix network that strengthens to consider, and do not necessarily result in plin or and binds the epidermis to the subcutaneous tissue. problems of scar hypertrophy. Callous formation or Cel1s in this layer are primarily fibroblasts. The outer loss of padding and protectir.e function are not papillary lzryer of the dermis is loosely arranged. The common place following p1'.rntar incisions.'1 ' inner reticuiar layer is composed of denser Nlany surgical procedures require a plantar connective tissue. There is a rich network of approach. Advances in nerve and odrer soft tissue neurovascular and lymph structures within the and osseous techniques related to the foot open dermis, feeding and nourishing the epidermi.s. new vistas for reconstruction, if plantar zrpproaches The dermis has trvo viscoelastic properties that can he utilized with conficlence. Plantar incisions can be utilized surgically to expand coverage of should not be fezrred. but respected zrnd jucliciously defects.' The first is termed creep. Creep r,rtilized. A ful1 understanding of topographical represents the ability of skin stretchecl at a constant and local plantar anatomy is required. Special tension to expand in surface area. Creep can occur understanding of the nenrovascular supply ancl by two mechanisms. Biological creep is not the associated subcutaneous tissues of the plantar foot stretching of skin, but the expansion or grou,th of are importzrnt. The plantar foot anatomy will be additional skin over slow insidior-rs expanding revieu,'ed as an introclr:ction to plantar foot sr-rrgery forces. Biological crecp occurs in pregnancy zrnd in general. Emphasis rvill be placed on the skin and subcutaneous tllmor growth. Mechanical creep of derrnal neurovascul'ar supply as it impacts the clermis is the zrctr:a1 stretching of skin over a plantar incision placement consiclerations. The much shorter time beyond the limits of its ability to CHAPTER 13 69 return to the original surface area, not the additional glands, but not apocrine glands." The excretions to FJrowth of skin. the sole are more watery than oily in character. The second viscoelastic propefiy of the clermis The sweat function is controlled by the sympathetic is stress relaxation. Stress relaxation represents the nelvous system as is plantar skin lvrinkling in propefiy that as skin is stretched, the amount of response to water exposllre. tension required to maintain the stretch is decreased Numerous creases ancl line systems have been ()vcr a f,actor ol timc. clescribed within the skin. Dermographic patterns The skin of the sole of the foot is thickened fbr are finger and foot prints unique to each individual. a protective function. It is thickest at the heel and Foot or finger prints have no surgical significance. lateral plantar margin of the fbot. The plantar pedal Flexion skin creases or folds in plantar skin are skin is tighter and more fkecl than the clorsal pedal nllmerous (Figure 1) Flexion creases plantzrrly skin that is more mobile. Surgical exposllre represent the flxed and resilient natLrre of this skin, plantarly may require longer or more varied shapes as well as the aclaptable and mobile qualities of the of incisions to provide a similar degree of exposure plantar foot needecl to permit joint motion. Flexion as shofier linear dorsal foot incisions. Accuracy of creases can hicle scars u,'hen placed within theil placement for specific areas of visualization on the depths. This technique is most commonly exploited plantzrr aspect of the fbot is more critical and leaves on the face not the plantar foot. Iess room for error. The plantar skin is much more Cleavage lines, as described Lry Cox, la1n resistant to abrasion. Plantar skin has a higher' longitudinally in a proximal ancl distal orientation on pain threshold to altrasion when compared with the plantar foot.'' There is a slight convex clifl/ature thigh skin. These two characteristics of elevatecl pain on the fibuiar side and a circumferential orientation threshold and abrasion resistance attest to the ability about the posterior plantar heel area (Figure 2). of the plantar skin to avoid pain and injury in Cleavage lines were based on studies originally barefoot u.alking.''' done by Langer. Cleavage lines were determinecl The dermis contains numerolts appenclages by skin hole orientation following awl pLrnctures that may have their origin in tl-ie subcutaneous tissue in fresh cadaver skin. Langer's lines generally tencl just beneath the dermis. The plantar skin does not to follow in the direction of muscle pr-rl1 throughout contain hair follicles. Sebaceous gland function and the body, cleavage lines do not.'3 Cox's and Langer's excretions do not exist without hair follicles. Sweat lines vary in orientation on the foot dorsally, but function does exist on the plantzrr skin as eccline not plantarly.
Figure 1. Flexion creases on the plantar aspect of Figurc 2. Clcar.age lines on the plantar aspect of tlie lirot. the foot. 70 CHAPTER 13
Relaxed skin tension lines (RSTL) were subcutaneous padding and be problematic, yet not described by Borges and Alexander.'a They be considered hypetrophic. Pefiaps this tendency determined the tension on the skin with respect to of plantar scars not to hypertrophy is a function of elasticity of the skin, stretch of the skin as related to the rigid nature of the plantar skin that splints and muscle pull, and 1oca1 anatomy considerations. protects the scaq as well as the pressure of weight These lines have proven to be more effective in bearing that is therapeutic in adding compression determining orientation of scars to prevent forces to the plantar scar. hypertrophy. Incisions parallel to RSTL do not gap as much as those perpendicular to RSTL. Incisions BLOOD SUPPLY paral1el to RSTL have much less tension on them after closure. The tension demonstrated by RSTL is As a general rule, one thinks of afierial outflow constant, whether the wound is dressed, placed in a and venoLrs retlrrn in a proximal and distal cast, of suppoted by suture. Scars are much less orientation (Figure ,t). This is accurate in most areas likely to hypertrophy when parallel to RSTL due of the body. The deep arterial flow to the plantar to the lessened degree of tension on the wound. aspect of the foot follorvs this orientation from the RSTL run transversely across the plantar aspect of posterior tibial artery to the medial and lateral the foot (Figure 3). plantar arteries dista1ly. The medial and lateral RSTL vary fiom cleavage lines plantarly by plantar afieries continue distally within the central 90 clegrees. RSTL run lransversely whereas cleavage compaftment of the sole of the foot deep to the lines mn longitudinally on the plantar aspect ol plantar fascia to the cligits. the foot. Incisions, however, in either line system The blood flow through the plantar skin within of the plantar foot are said to show little tendency the subdermal plexus follows a different orientation. to hypertrophy. The arterial flow to the skin and related soft tissues The incidence of hypertrophic scars or keloids of the sole of the foot is rich and plentiful. The on the plantar skin is minimal, whether RSTL or vessels reach the skin through a perforating system cleavage lines are followed. Scars in either direction from principally the larger lateral piantar artery and on the plantar skin whether transverse or the smaller medial plantar afiery deep in the central longitudinal in orientation show 1ittle signs of compafiment of the foot. The vessels must perforate hypertrophy.a Plantar scars can still be sensitive, the deep fascia towards the plantar skin (Figure 5). have keratotic thickening, or have atrophy of the This perforating system occurs along either side of
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FOREFOOT
MIDFOOT
Figr-rre J, ITSTL on the plantar aspect of the lbot Figure 4. Arterral blood flow to the plantar aspect of the fbot. CHAPTER 13 71 the strong central portion of the plantar fascia clorsal skin attests to the abundance of the plantar through the medial and lateral plantar su1ci.'' skin blood supply. Lacerations or incisions in this Curtin has shown through infrarecl photo- marginal skin may require substantial hemostasis. graphy that the distribution of vessels in the plantar These superficial veins then drain dorsally into the skin follou,'s a more transverse orientation, not large saphenous system medially, and the small longitudinal.'6 The flow originates laterally and saphenous system latera1ly. medially and proceeds toward the plantar central aspect of the sole of the foot. This is a critical I\I-ERYES concern n'hen designing plantar surgical approaches or assessing the viability of plantar skin after lacera- The nerves to the plantar skin zlnd related soft tions. Parallel plantar incisions or longitudinally- tissues reach the sole of the foot in the midfoot oriented lacerations could result in a compromise to region much in the same manner as the arterial the tissue between them (Figure 6). Parallel incisions system. The major plantar nelves of the midfbot and transversely oriented would not be as prone to forefoot are the large meclial plantar nerve and avascularity. Large medially or laterally based skin smaller lateral plantar nen'e. These nerves course flaps that cross into and transect the blood flon, from deep to the plantar fascia within the central the opposite direction can result in significant tip compartment of the foot. The clltaneous nen/e necrosis (Figure 7). Skin flap and plastic surgical extensions pierce the deep fascia along the meclizrl techniques on the plantar skin must respect the and laterai margins of the planlar fascia w-ithin the deep and superficial variations in ar-terial blood flow. medial ancl lateral sulci in the midfoot region."'The Viability of the skin would outweigh concerns clrtaneous nerves branch ttansversely w'ithin the of scarring, given the choice of surgical wound neurovascular arcade to inneruate the skin. orientation options. The plantar heel skin nen e supply originrtes The deep venous flow runs from distal to from two sources. The sural nerve innelates the proximal through the posterior tibial veins (Figure lateral heel area plantarly. The medial heel is inner- B). The subdermal nelwork of veins frorn the skin vated by the medial calcaneal nefl/e as a branch of and related soft tissues flows olttward from the the tibial nerve. The cutaneous perfbrating branches central plantar foot in a meclial and lateral direction. to the plantar heel are variable in presentation, and The multitude of superficial veins about the difficult to rrisualize and identifv. periphery of the foot where the plantar skin joins the
Figure 5. Topographical idcntitlcetion of the Figure 6. Sl The ball of the foot anc'l cligits are suppliecl peripheral nelves. Careful study ancl memorization primarily by the mecli:Ll, and to a lesser degree. the of these dermzrtomal maps is required. Some lateral plantar nen/e. These t\vo neta,es overlap at variability exists and the distribution patterns are not the third intermetatarsal space where both sencl a zrbsolr-rte. Complicating rhe situation is the finding brzrnch that sr-rpplies the lateral aspect of the third that texts ancl afticles represent these clermatom:1l toe and medial aspect of the fourth toe, ancl is distribution maps differently. Representative involr.ed in the classic Morton,s neuroma. These c1ermatomal maps zrre proviclecl here for rer,,iew, mzrjor plantar nel1.es are axon extensions of cells study, ancl comparison (Figures 9-11). whose ce11 b Shori l-cng Saphenous Saphenous Vein Vein Syslem @*@ System Figurc Skin 7. riect-osis at the clistal tip of the skin Figru'e B. Venoris blood f'lor,,. fron the pl:rntar flap that ertcndecl ir-rto ancl tr:rnscctecl bloocl flou. aspect of thc fbot. fioni the opposite sicle of t1-re firot. CHAPTER 13 73 Saphenous Nerua Figr,rre !. Largc peripheral ner-ve innervation to Figure 10. Small peripheral nefl/e inneruation to the plantar foot. the plantar fbot, other bodily fatty tissues. The increased unsaturated fatty acid rutio may decrease triglyceride viscosity and enhance biomechanical efficiency. No difference in this fatty acid ratio is found when comparing normal or atrophic heel fat pads.re The thickness of the subcutaneolrs tissue of the heel can be 2 cm. Fibrous septa are oriented in a spiral fashion through the subcutaneous tissue to hold the heel fat about the calcaneus in chambers plantarly.'n The septa form a precise system of chambers that retains the adipose tissue (Figure 72). The hydrodynamics of these chambers provide for the effective absorption and distribution of body weight through the weight-bearing process. The most plantar and superficial spiral septal system originates medially on the calcaneus. The septa spiral posterior and lateral.. A second more proximal spiraling system of septa, originates on the laterai calcaneus. These septa spiml posteriorly, but end more medial-ward in the subcutaneous tissues. A Figure 11. Spinal nerve root inneruation to the plantar lbot. third converging septal system runs from the anterior calcaneus and curves lateral and forward. The more anterior septa on the l-reel run anterior towards the plantar skin. The more posterior septa run relatively posterior as they course towards the plantar skin. A complex of multiple smaller chzlmbers is created, which gives the strength to the overall system to 74 CHAPTER 13 t*.i .l \ .-..1 tt : I t| l. 9,:'-. ,. t /t.:,.,1!- ,t ..*-. li ,.i.. l,a1 t: ':l I t tt l, 1 { 1' 1,- l t! i tll ' , t 1i.,.-, t\- ,t it .,...... -, ::# t 1-..& la I r, ,{ a& I \*,"Jliv\ I il .,:, @^&I gil **8 ':1 ttt ,,/ Figure 12A. Diagrenmtatic reprcsentation of the Figure 12ts. Thc seconclan'spiral septal svstem prim2rr\. fibrolrs sepral svsrem of thc heel originates ntore lateral ancl spir:rls posterior end sllllcut:lneolls tissr-Le layer that odginatcs mecliall,v encls n'rore rneclial. on thc c:rlc:rneLls end spirals postcriot :1nai lateral. pro\ride resiliency and shock absorption. It is clifficult whether the plantar heel incision is transverse or longituc'linal, not to violate this septal system. A rather large subcalcaneal bursa is present just beneath the w.eighr-bearing calcaneus to provicle additional paclding. The non-weight$earing arch sltbcutaneous tissue varies little from other areas of the body. Linear vefiical bands bind the fat 1oose1y. The stlarcture is not nearly as formal as the heel or ball lrea of the plantar foot (Figure 1, Tl-re subcutaneolis tissr'te in the 21rch area ol the plantar foot is r.ery thin. Scarring from the skin can readily firrm adhesions to the deeper plantar fascia. plastic surgical techniques that involve fr_r11-thickness transf-er of skin and subcutaneous tissue from the arch area to the weight-bearing areas may not provide adeqlrate padcling against weight bearing. The plantar subcutaneous tissue of the ball of the fbot is retained and maintained by a complex Figure 12C. C:rclaveric r.ieu. of thc superficial system of intersecting ligaments and fascial laver of the l'reel subcutancous tissues just belon- the clermis. The scptal s_vstem lies deep to this bands. The plantar fascia forms bands that are srrrface. longitudinally oriented. The more transverse bands are cal1ed transverse fhsciculi proximal to the metatarsal heacls, and natatory ligaments more distal1y. These longitudinal and transverse filtrous structures clefine adipose deposits tenned fat bodies CI-IAPTER 13 75 that protect and cushion the neurovascular REFERENCES structures betn'een the metatarsals. The sub- Stapp \fD. I)lantal shin incisions: an clt'en.ict'. In \rickels \S. metatarsai heads is termecl cutaneous fat benezrth the ecliicrr. necon-strtLctiue Su.rgetl' (t tlJe Foot ctrtcl Leg tipLl.tle '96 the submetatarsal cushion (Figure 74). The I.r.kc-'L, \,: l'nd...lr\ ln.litr tr: 1O'rli. p. lrrr-ll. col'rsicler:rtions. Il'r submetatzrrsal cushion is confined medially ancl ,\{:Lhan K'I . Plantar flbrclnalosis: srLrgic:rl XIcGlamry ED. eclitor. Recotlstructiue Surgery- of'the Ft)ot .111.1 Le!. laterally betn,een trv-o longitr-rdinal fascial bancls 1986. TLrcl ktue r Ex I tt:nt it.y 7t).c) 6 : 3 : 2 3 L -6. CONCLUSION 9. Armstrong DG. Sotcr-ison .[C. RrLshtran T1l; lixpkriting thc: liscoelasric Propefiies of pecial skjn \\.ith lhe surt' closttrc skin stretching tletice. J l'rtot Ankle 5L;.rg 199i:31:217 i3. of thc Plzrntar incisions are a safe methocl of zrccessing the 10. Robbins S. Goul'GJ. NlcClarar-i.1. cI:11. Protective sensation plantxr aspect of the foot. Foat Ankle 7t)t)3a11317-1f ' foot for surgical procedures. The speciahzecl 11. B:rtes IJ. A gulcle to Ph\:sice1 ExaminiLtion ancl History T:rkrng in Fitih ec1. Philadelphi:r (1'A): JR Lippincottrl99l. p. l'i0. piantar soft tissue and skin anzltomy aicls L) 12.. Cor H'I . The cle:lr'agc lines of the skin. Brllrs'i./Si'//q [qxs:r):1t y31 providing strength to resist t'eight bearing, 1i. l-angel K. tieber clie Spaltbelkcit cier Cutis. SitzrLnopll'd, K cushioning for *'eight-bearing 1oac1s. The plantar Akaci.cl.N('issensch. trlath n:LttLny CL 'i3:23, 1861. Cited b1' 1(raissl 'fhe of apl)roprirte liues for elcctive sr-rlgical and soft tissue reaclill' senies this function' Clr sclectlon skin incisions. Pl.ts/ Re c o nsrr Szriig 1!5 1 :,3: 1 -28. Surgerl througl-r this area requires :Ln undet- 11. Borges AF, AleranclerJE. Relared skin tcnsion 1ines. z-plasties or.r ercisiol'r of lcsions Br.l Plttst stancling of anatomy ancl function to yield the best scar.s ancl firsifolm '\trrg 7962:15:21)-i1. results u.ith the fell'est cornplications. Figure li. A. Surgical exposllre o1' thc pl:rnter thscil in the arch area [-ith the subcutaneous tissne l:r1'er rcteined to thc clemris fbr vascltlar presefl':lticln o1'the skin f1aps. F-igurc 1JB. Cad:rvelic r ies' of the sltpcrficilll lar.er of the arch slLllcutlneous tisslles jtlst lrc,rl Llrc tlr'ttnis. I lre 'l.l \ lllirn(uL' l:\\llr'' 'lle fairlr.' contiguous throughout in the erch arer of fhe frxrt. 76 CHAPTER 13 Figr-rre 1,1A. Diagramntatic representltion of the Figure f.iB. Scgtnentecl look in the fr-ontal pl:rne subcutaneous tissues of the plantal' foreioot l-r thc transve rse plane. Notc the scgmented vari:rtion in tissuc character frorl beneath the met.Ltersal hcacls ancl the fat pacl or sLlbmetatal-sal cushion to between the metatarsal heads ancl the fat bodies. 15. Curtin J\(/. Fibromatosis Of the plantar fascia. Bone Surg ,)()i;t-: J /oint / i, I lU{ ri d. philaclelphia: 16. Sarrafian SK: ArtoLtomy cl' tbe Foot and Ankle JB Lippincon;1 !83. 17. Jahss MH, Kurrmer F, Michelson JD. Invcstigations into thc fat pads of the sole of ti're fbot: heel pressure sttdtes. l.'oot Ankle 1992:73:22732. 1,3. Buschmann \VR, Jahss MtI. Kummer F, et al. Histologl. ancl histonorphometric analysis of the norm:rl ancl atrophic heel lat pad. Foctt Ankle 191)i;76:251-8. 19. Buschrnann IflR, Hudgins LC, Kummer F, et al. Fatty acicl composit:ion of normal and atrophicd heel fat pad. Ictctt Ankle 7993:74:389-91. 20. tslechschmidt E. Die Alchitecktur cles Fcrsenpolsters. In Gegenbaurs Morphologisches Jahrbuch, Leipzig, Akacl Vcrlag MBH, 1933. p. 65-6 Figure 14C. NIore anatomic look in the liontal plane r,-ith the deeper fat body in the intermetatarsal spaces and the more superticial fat pad beneath t1're mctltarsal herrls.