pathological anatomy and dynamic effect of the displaced plantar plate and the importance of the

Ann R Coll Surg Engl 1997; 79: 58-68

Pathological anatomy and dynamic effect of

the displaced plantar plate and theimportance of the integrity of the plantarplate-deep transverse metatarsal ligamenttie-bar

G D Stainsby FRCSConsultant Orthopaedic Surgeon

Royal Victoria Infirmary and Freeman Hospital Trusts*, and Nuffield Hospital, Newcastle upon Tyne

Key words: Foot deformities; Hallux valgus; Toes; Metatarsophalangeal joint

Normal and deformed forefeet have been investigatedby cadaver anatomical dissections and experiments,by radiographs, CT and MRI scanning, and by clinicalstudies.Evidence is presented to show that the skeleton of

the foot rests on and is controlled by a multi-segmental ligamentous and fascial tie-bar system.Transversely across the plantar aspect of the forefoot,the plantar plates and the deep transverse metatarsalligaments form a strong ligamentous structure whichprevents undue splaying of the forefoot. Longitudin-ally, the five digital processes of the deeper layer of theplantar fascia are inserted into the plantar plates andcontrol the longitudinal arch of the foot.

It is suggested that many forefoot deformities resultfrom the failure of parts of the tie-bar system and thedynamic effect of displacement of the plantar plates.Understanding this allows a more logical approach totheir treatment.

SECTION ONEThe multisegmental tie-bar system and thenormal foot

The transverse tie-bar

Anatomical studies

A sagittal section through the metatarsophalangeaI jointof a lesser toe of a normal cadaver foot shows that belowthe metatarsal head the capsule is thickened to form the'plantar plate'. It is firmly attached to the base of theproximal phalanx. Below and anterior to this is thethickened subcutaneous tissue adapted for weight-bearingwhich is the plantar pad (Fig. la).The plantar plates of the metatarsophalangeal joints

and the intervening deep transverse metatarsal ligamentsform a continuous band of strong ligamentous tissueacross the forefoot (Fig. lb), and on transverse section eachplantar plate is seen to be anchored to its metatarsal headby the collateral ligaments (Fig. lc).

*Retired from National Health Service appointnents on 1 July1993

Based on a Hunterian Lecture given at the Meeting of the BritishOrthopaedic Association in Nottingham on 16 September 1994

Correspondence to: Mr G D Stainsby, 9 Meadow Court, DarrasHall, Ponteland, Newcastle upon Tyne NE20 9RB

Radiological studies

Radiological studies on normal living feet demonstratedthat weight-bearing increases the width across theforefoot. Measurements were made from the medialborder of the first metatarsal to the outer border of the

Displaced plantar plate 59

(a)

(b)

(c)

Figure 1. (a) Sagittal section through lesserMTP joint of anormal foot showing the thickened plantar capsule (plate)beneath the metatarsal head. (b) The transverse tie-bar(altemate plantar plates and deep transverse metatarsalligaments). (c) Transverse section through normal fore-foot at metatarsal head level showing the plantar platesand the collateral ligaments.

fifth, the average increase in 20 female feet was 3 mm, and5 mm in the feet of 10 males.

Cadaver studies with division of the deep transversemetatarsal ligaments

Lateral traction was applied to the metatarsals of threedissected cadaver forefeet before and after division of thedeep transverse metatarsal ligaments. It was found thatafter division of the ligaments the first metatarsal moved

more medially, and the fourth and fifth metatarsals morelaterally away from the second and third metatarsals.

It was seen that the plantar plates and the deeptransverse metatarsal ligaments form a segmental 'tie-bar' across the forefoot which controls the splay betweenneighbouring metatarsals as well as between the first andthe fifth.

The longitudinal tie-bar mechanism

Hicks (1,2) described the mechanisms supporting thelongitudinal arch of the foot; the 'beam' mechanism whichoperates when the ends of the arch are not fixed, and the'truss (or tie-bar)' mechanism (Fig. 2). Everyoneremembers his explanation of the windlass mechanismcontrolling the plantar fascia, and that the longitudinalarch of the foot rises as a result of dorsiflexion of the bigtoe (Fig. 3a), but Hicks also pointed out that thismechanism is present in all the toes, and that thewindlass works in reverse when the flat foot is submittedto a weight-bearing strain (Fig. 3b).

Anatomical studies

Dissections of cadaver feet have confirmed the findings ofPoirier (3) and Bojsen-M0ller and Flagstad (4) that in thedistal part of the sole of the foot, at about the level of thenecks of the metatarsals, the plantar fascia divides intosuperficial and deep layers. The deeper layer of theplantar fascia is thick and strong and divides into fiveprocesses. Each process goes towards its correspondingtoe, and close to the metatarsal head divides into twostrong slips, between which the flexor tendons emerge tocome to lie on the plantar aspect of the plantar plate.These two slips pass dorsally around the flexor tendons

and are inserted into the medial and lateral sides of theplantar plates of the metatarsophalangeal joints (and thesesamoids under the first metatarsal head). Fibres fromthese plantar fascial slips were found to sweep mediallyand laterally into the proximal edges and substance of theintervening deep transverse metatarsal ligaments, and indoing this fibres from neighbouring medial and lateralslips interdigitated (Fig. 4).The effect of tightening the deeper part of the plantar

fascia in a normal cadaveric foot with intact metatarso-phalangeal joints was studied. When the plantar fascia wasrelaxed the toes could be dorsiflexed at the metatarso-phalangeal joints. When weight-bearing was simulatedwith pressure under the metatarsal heads, the longitudinalarch flattened, the plantar fascia tightened, the toes flexeddown, and it was then found that the proximal phalangesof the toes could not be dorsiflexed from this position.

Clinical investigation

The reversed windlass mechanism can be observed in thenormal living foot when standing with the toes over theedge of a footstool or table. When weight-bearing on themetatarsal heads the toes flex down and the proximal

60 G D Stainsby

Figure 2. The 'beam' and the 'truss (or tie-bar)' mechanisms as described by Hicks.

phalanges resist being pushed up into dorsiflexion. Theinterphalangeal joints remain mobile, indicating that thelong flexor and extensor tendons are not responsible, andthat the flexion of the proximal phalanges is due to thetight plantar fascia tethering the plantar plates.This has been called the 'footstool edge weight-bearing

test'. Normally all the toes (or to be more correct theproximal phalanges) come down to the same level and arein slight plantarflexion (Fig. 3c,d). This test can be used toassess the integrity and performance of the windlassmechanism of the plantar fascial process to each toe.

The windlass effect is greatest in the big toe and is seenin gradually lessening degrees in the second, third, andfourth rays and is almost absent in the fifth. This can berelated to the size of the metatarsal head, which is thepulley, and the length of the lever, which is the toe (or itsproximal phalanx).

Discussion

The transverse tie-bar (plantar plates and deep transversemetatarsal ligaments) controls the splay of the forefoot.

Figure 3. (a) Dorsiflexion of the big toe and the windlass effect of the plantar fascia asdescribed by Hicks. (b) The 'reversed' windlass mechanism (with weight-bearing thelongitudinal arch flattens, the foot lengthens, the plantar fascia tightens, the proximalphalanx becomes plantarflexed and the mechanism comes to a stop when the proximalphalanx presses against the ground). (c) and (d) The 'footstool edge weight-bearing test'.


lnterdigitatng fibres l

|J ... .............. --

Figr4. Digamai ilutrto of th pate of........::

ineto of th plnafasc*ials prcse intthelstrnves Xtie|-bar. _ _|

Figure 5. Diagrammatic illustration of the multisegmentalfascial and ligamentous tie-bar system of the foot.

The five longitudinal processes of the deeper layer of theplantar fascia form a longitudinal tie-bar system. They areinserted into the whole of the transverse tie-bar and theyare very strong.The longitudinal tie-bar system (the deeper layer of the

plantar fascia) controls the longitudinal arch of the footwhen the normal foot is weight-bearing. Both tie-bars arecentred on the plantar plates and are activated by weight-bearing pressure on the metatarsal heads. If two or moremetatarsal heads are submitted to upward pressure fromweight-bearing they will tend to splay apart and thecorresponding metatarsal rays will flatten. For example,when weight-bearing on only the medial three metatarsalheads the medial part of the tie-bar system will be activeand tighten. The proximal phalanges of the medial threetoes are then held down in flexion but the lateral two toesremain mobile.The foot skeleton therefore rests on and is controlled by

a multisegmental ligamentous transverse and longitudinaltie-bar system. This system is capable of automaticallyresponding to the weight-bearing surface and adjusting theposture of the foot skeleton, and of altering the alignmentof the mid-foot and hind-foot when the forefoot only isweight-bearing and the toes are dorsiflexed during 'heelelevation'. Differing tensions in the medial and lateral partsofthe longitudinal system can be adjusted by movement ofthe os calcis as occurs with inversion and eversion of theheel (Fig. 5).

SECTION TWO

Deformities of the foot and defects in themultisegmental tie-bar system

Further studies have shown that defects in the tie-barsystem can explain why common forefoot deformitiesdevelop.

Hallux valgusIn the normal first metatarsophalangeal joint, thesesamoid bones articulate with grooves on either side ofa longitudinal ridge (the crista) on the plantar aspect ofthe metatarsal head. A V-shaped pulley is thereforeformed (Fig. 6a).

Anatomical and CAT scan studies have been carriedout on eight cadaver feet with hallux valgus and theseconfirm Haines and McDougall's (5) findings that ashallux valgus develops the crista is gradually eroded awayby the medial sesamoid (Fig. 6b), and that the metatarsalhead then drifts medial to the sesamoid bones as themedial capsule becomes stretched. In severe hallux valgusthe lateral sesamoid groove of the metatarsal head comesto articulate with the medial sesamoid and the lateralsesamoid migrates to the lateral side of the metatarsal(Fig. 6c).

62 G D Stainsby

(a)

(b)

Figure 6. Transverse CT scans offorefeet. (a) The normal first MTPjoint with the sesamoid bonesstraddled over the crista. (b) Moder-ate hallux valgus with erosion of thecrista by the medial sesamoid. (c)Medial displacement of the first MThead and medial sesamoid articulat-ing with the lateral groove under themetatarsal head.

(C)


When the big toe is normal and unconstrained, and thefoot is weight-bearing, the equal tension in the twoplantar fascial slips to the sesamoids, straddled over theprominence of the crista, will keep the toe straight (Fig.7a). However, if the toe is pushed laterally into valgus bythe tightness or shape of a shoe, the plantar fascia willtend to bow-string across the lateral side of themetatarsophalangeal joint. The medial sesamoid mustthen impinge with increased pressure against the medialside of the crista of the metatarsal head. If the cristabecomes eroded the stability of the sesamoid articulationand its ability to resist lateral displacement is lost (Fig.7b,c). Once the first metatarsal head moves medially, thebow-string effect of the plantar fascia, which is tightthroughout the weight-bearing period, will be establishedand will inevitably cause progressive valgus angulation ofthe big toe. It is therefore suggested that the wearing ofnarrow and pointed-toed shoes is a potent cause of halluxvalgus.

Patients with hallux valgus have been assessed by the'footstool edge weight-bearing test' and it was found thatthe ability of the plantar fascia to keep the proximalphalanx of the big toe plantarflexed became progressivelyless as the valgus deformity increased. Indeed, when thedeformity was severe the test failed to produce anyresponse and the toe remained dorsiflexed and rotated.This can be explained by the realisation that, as the valgusdeformity develops, the plantar plate and sesamoid bonesfall off their pulley (the metatarsal head), so theeffectiveness of the windlass mechanism of the plantarfascia of the big toe gets less and less as the metatarsalhead moves medially. The resulting slackening of thelongitudinal fascial tie-bar on the medial side of the footexplains the loss of height of the medial longitudinal archof the foot which is usually seen in feet with hallux valgus.Hicks showed that the excursion of the sesamoids

around the first metatarsal head of the normal foot whenthe big toe is dorsiflexed is only about 1 cm (2). Ourstudies have confirmed this. Therefore, only a slightdefect in its plantar fascial windlass mechanism will have aprofound weakening effect.

Figure 7. (a) Normal alignment of the plantar fascialprocess to the big toe. (b) With the big toe pushed intovalgus the medial sesamoid impinges against the crista. (c)The bow-string effect of the plantar fascia when the cristais eroded.

When the big toe windlass mechanism fails, thencontrol and support of the longitudinal arch of the footwill depend increasingly on the tie-bar mechanism of theplantar fascial processes to the lateral four toes,particularly the second and third.

Digitus minimus varus

Haines and McDougall (5) suggested that this deformitycan be regarded as a 'mirror-image' to hallux valgus.Cadaver dissections, and CAT and MRI scans haveconfirmed this and demonstrated that the lateral capsuleof the fifth metatarsophalangeal joint stretches allowingthe metatarsal head to drift laterally away from the plantarplate and the proximal phalanx. The plantar fascialprocess to the little toe then becomes a deforming forceas it bow-strings across the medial side of the metatarso-phalangeal joint.

Claw toes

Cadaver dissections and MRI scan studies have shownthat as clawing of a lesser toe develops, and the metatarso-phalangeal joint becomes dorsiflexed when the foot isweight-bearing, the plantar plate and the plantar pad arepulled distally and follow the proximal phalanx aroundthe metatarsal head (Fig. 8a). When the claw deformitybecomes severe and the metatarsophalangeal jointdislocated, the plantar plate is then displaced on to thedorsal aspect of the metatarsal head. The head is theninvariably prominent on the plantar aspect of the forefootwith very little tissue cover (Fig. 8b).When a lesser toe is clawed the proximal phalanx is no

longer held down into flexion by its plantar fascial processwhen the foot is weight-bearing and so the flexor andextensor tendons can cause the typical deformity. For thisto happen the windlass mechanism of the plantar fascia tothe toe must be defective.The middle of the plantar plate of lesser toes is thinner

where it is grooved for the flexor tendons. Dissections ofcadaver feet with clawed toes have shown that as themetatarsophalangeal joint of a lesser toe becomes dorsallysubluxed the proximal part of the plantar plate stretchesand even ruptures in the grooved area. This confirms theprevious reports of Fitton and Swinburne (6) andJohnston et al. (7). This defect allows the distal part ofthe plantar plate to move to the dorsal aspect of themetatarsal head with the base of the proximal phalanx andthe plantar fascial slips to slide dorsally around the sidesof the metatarsal head (Fig. 9a,b). They are therefore nolonger around the circumference of the metatarsal headand become ineffective. Indeed, when the slips havemoved dorsal to the axis of rotation of the metatarso-phalangeal joints, they will depress the metatarsal head asthey tighten.

It has been shown experimentally that when the plantarplate is displaced dorsally it is tethered by the deeptransverse metatarsal ligaments and this causes depressionof the metatarsal head by a 'plunger' effect (Fig. 9a). It isconsidered that this 'plunger' mechanism and the

Hammer toe

Hammer toe deformity is seen frequently in second toeswhich are longer than the big toe. Typically, when thefoot is weight-bearing the metatarsophalangeal joint isdorsiflexed, the proximal interphalangeal joint flexed andthe distal interphalangeal joint extended. For themetatarsophalangeal joint to be dorsiflexed whenweight-bearing (and when the footstool edge weight-bearing test is performed) the longitudinal tie-bar to thattoe must be defective, and the central part of the plantarplate stretched, allowing the plantar fascial slips to slideoffthe greatest diameter of the metatarsal head. A possibleexplanation is the wearing of shoes that are too short socausing the long toe to 'buckle'.

(b)

Figure 8. Sagittal sections through lesser MTP joints ofcadaver feet. (a) Moderate clawing with distal movementof the plantar plate and pad. (b) Severe clawing. Plantarplate now on dorsal aspect of the MT head, and very littletissue remains under its plantar surface as the plantar padhas also moved distally and dorsally.

malalignment of the plantar fascial slips are the causes ofmetatarsal head depression seen in the severely clawedlesser toe. The 'plunger' effect has been clearly observedmany times at operation, and corrected by replacing theplantar plate under the metatarsal head.

Discussion

It is therefore concluded that defects in the ligamentoustie-bar systems of the foot allow deformities of theforefoot to develop. Failure of the medial capsularligaments of the first metatarsophalangeal joint (aftererosion of the crista of the metatarsal head) results inhallux valgus; stretching of the lateral capsular ligamentsof the fifth metatarsophalangeal joint is present in digitusminimus varus.

Clawing of the lesser toes is often seen to develop in feetwith hallux valgus. It is suggested that in feet with a

significant deformity of the big toe the powerful windlassmechanism of its plantar fascial process is defective andthat the longitudinal tie-bar function of the plantar fascia,controlling the medial arch of the foot (particularly for the'push-off' phase of the walking cycle), will fall upon thefascial processes to the lateral four toes. They are not as

strong as the fascial process to the big toe, theirmechanical advantage is not as good as they are more

closely placed to the axis ofmovement of the subtalar jointcomplex, and their windlass mechanisms are not as

powerful, as the diameters of the metatarsal heads andthe proximal phalanges of the lesser toes are smaller thanthose of the big toe. Perhaps, therefore, it is not surprising

that the plantar plates of the central lesser toes then giveway where they are stretched over the metatarsal heads.

Figure 9. (a) When a lesser toe is severely clawed the plantar plate becomes dorsallydisplaced; tethered by the deep transverse metatarsal ligaments it causes MT headdepression by the 'plunger' effect. (b) The plantar fascial slips slide around the MThead as the central part of the plate stretches. If they now tighten the MT head will bedepressed.

64 G D Stainsby

(a)


Stretching of the central part of the plantar plate of alesser toe allows displacement of the slips of the plantarfascia from offthe greatest circumference of the metatarsalhead, making the windlass mechanism of the plantar fasciaineffective. Dorsiflexion deformity can then develop at themetatarsophalangeal joint when the foot is weight-bearing, and this can progress to dorsal dislocation ofthe joint and dorsal displacement of the plantar plate. The'plunger' effect of the displaced plantar plate, andmalalignment of the plantar fascial slips, then causedepression of the metatarsal head and metatarsalgia.

SECTION THREE

The multisegmental tie-bar ligamentoussystem of the foot and the principles ofsurgical treatment of forefoot deformities

When it is realised that the skeleton of the foot is to a greatextent controlled by a ligamentous tie-bar system, andthat defects in this system result in deformities of the fore-foot and toes, it is surely logical to try to repair thesedefects when the deformities are corrected surgically.

Hallux valgus

Many surgical procedures have been described for thecorrection of hallux valgus-soft tissue operations,osteotomies of the first metatarsal and the proximalphalanx of the big toe, and arthroplasties of themetatarsophalangeal joint of the excision and replace-ment type. The results of these operations have usuallybeen assessed with regard to patient satisfaction, cosmeticappearance and alignment of the big toe, and thereduction in the angle between the first and secondmetatarsals has been measured on radiographs. Thepostoperative position of the first metatarsal head relativeto the sesamoid bones has rarely been recorded, and thefunction of the big toe with regard to the restoration of itsplantar fascial windlass mechanism does not appear tohave been assessed.Our studies indicate that one of the most important

functions of the big toe during the weight-bearing phaseof walking is to activate the windlass mechanism of themost medial process of the plantar fascia. It is thestrongest part of the longitudinal tie-bar system whichelevates the arch of the foot, and realigns the bones of thefoot skeleton so that the direct weight-bearing thrust fromthe ankle is transferred down the medial side of the footwhen the heel is elevated. To restore this function, if it ispossible, must surely be one of the main aims of surgery

for hallux valgus. The stretched medial capsule of the firstmetatarsophalangeal joint also requires tightening so thatthe medial splay of the first metatarsal is controlled.

It is suggested that if, when surgery for hallux valgus iscarried out, the first metatarsophalangeal joint can be

preserved, the medial capsule should be tightened and thefirst metatarsal head replaced over the sesamoid bones.The effectiveness of the windlass mechanism of theplantar fascia will only be fully restored if the firstmetatarsal head is correctly positioned above the sesamoidbones. Should an osteotomy of the first metatarsal berequired (if there is restricted movement at, or malalign-ment of, the first tarsometatarsal joint) then shortening ofthe first metatarsal needs to be avoided as this will weakenthe windlass mechanism. If a lateral release procedure iscarried out to the first metatarsophalangeal joint, thendivision of the deep transverse metatarsal ligamentbetween the first and second metatarsals should beavoided, and the integrity of the lateral slip of theplantar fascia and its lateral sesamoid attachment needsto be preserved as otherwise a varus deformity of the bigtoe may result from the unbalanced pull of the medialplantar fascial slip.When the first metatarsophalangeal joint is degenerate

and cannot be retained, then, if an excisional arthroplastyis carried out, it is suggested that the medial capsuleshould still be tightened to restore the integrity of thetransverse tie-bar, and so prevent splaying of the firstmetatarsal postoperatively.

Digitus minimus varus

It has been demonstrated that in this deformity the lateralcapsule of the fifth metatarsophalangeal joint becomesstretched. It would seem logical, therefore, that when this iscorrected the surgical procedure should include tighteningof the lateral capsule so that the fifth metatarsal head ismoved medially and replaced over its plantar plate.

Claw toes

For the early deformity, where the metatarsophalangealjoint is still stable and the capsular ligaments intact,procedures such as fusion of the proximal interphalangealjoint and flexor-extensor transfer have produced satisfac-tory results. Both these procedures aid plantarflexioncontrol of the proximal phalanx and may be sufficient toprevent progression of the dorsiflexion at the metatarso-phalangeal joint.Treatment of the severe claw deformity is notoriously

difficult. Metatarsalgia has often persisted after excision ofthe base of the proximal phalanx, and the previouslyreported good results from various types of metatarsalosteotomy (8-10) have recently been questioned.The investigations and studies reported here show

that in severe claw deformity of a lesser toe the plantarplate becomes displaced onto the dorsal aspect of themetatarsal head. This results in depression of themetatarsal head owing to the 'plunger effect'. To correctthis, and relieve the metatarsalgia, it is thereforenecessary to replace the plantar plate to its normalposition beneath the metatarsal head and to preserve thelength of the metatarsal. Shortening of the metatarsalwill cause slackening of the plantar fascia and loss of

66 G D Stainsby

Figure 10. Diagrammatic illustration of the 'modifiedKeller's procedure' for severely clawed lesser toes. (a) V-shaped incision to avoid longitudinal skin contracture. (b)Extensor tendon divided at the level of the MT neck andreflected distally. (c) Proximal phalanx sectioned throughthe neck and the shaft and base removed preserving theplantar plate. (d) and (e) Plantar plate replaced beneaththe MT head using a periosteal elevator which is takenunder the MT neck. (t) Stabilise toe in correct alignmentwith an intramedullary wire, suture the extensor tendonto the flexor tendons without tension, and excise anyexcess extensor tendon. Close wound with small sutures.

the windlass mechanism, and the weight-bearing struc-tures (the plantar plates and pads) are left distal tothe metatarsal head. Osteotomy of the distal shaft ofthe metatarsal without replacement of the plantar platecan result in uncontrolled displacement of the headfragment by the 'plunger mechanism'.

Since 1976, the author has corrected severe clawing oflesser toes by a procedure which preserves the metatarsalhead and replaces the plantar plate. The principal steps ofthe procedure are shown in Fig 10.The results of this operation in 74 feet with a single

severely clawed toe were reviewed independently in 1990(11). The average length of follow-up was 3.5 years. In85% the results were considered to be excellent or goodwith satisfactory cosmetic appearance, and relief of painand metatarsalgia.

Hammer toe

Provided the metatarsophalangeal joint is not subluxed ordislocated, fusion of the proximal interphalangeal jointusually corrects the deformity and the proximal phalanxcomes down against the ground when the foot is weight-

bearing. The added power of the short flexor tendon, nowacting to plantarflex the proximal phalanx, assists theweakened windlass mechanism of the plantar fascia andhelps to prevent dorsiflexion at the metatarsophalangealjoint when the foot is weight-bearing.

The rheumatoid forefoot

Severe deformity of the toes can occur in patients withrheumatoid arthritis. Gross hallux valgus and markedclawing of the lesser toes with prominence of themetatarsal heads in the sole of the foot is commonly seen.

In 1912, HofEman (12) recommended excision of themetatarsal heads for the severely deformed rheumatoidforefoot. A number of modifications to this procedurehave been described (13-15). So, for over 80 years,excision arthroplasty with removal of the metatarsal headshas been the usual procedure for this condition. Althoughsome good results have been reported it is accepted thatthe foot is inevitably shortened, that there can besubsequent problems with exostoses developing on thestumps of the metatarsals, that plantar callosities recur(16), and that postoperatively many patients need surgicalshoes (17).When it is accepted that the metatarsal heads control

the multisegmental tie-bar system of the foot, it followsthat excision of the metatarsal heads must completelydestroy the ligamentous tie-bar support to the foot.

Since 1976 the author has carried out a forefootreconstruction procedure preserving the metatarsal heads(Fig. 11). In this operation the valgus deformity of the bigtoe is corrected by a Keller's procedure with division ofboth long and short extensor tendons and tightening ofthe medial capsule. The severe clawing of lesser toes iscorrected by the procedure previously described for thetreatment of the single severely clawed toe. Themetatarsal heads are preserved and an attempt is madeto reconstruct the ligamentous tie-bar system as far as ispossible. The plantar plates are replaced to their correctposition and the transverse tie-bar tightened. The plantarpad also returns to its weight-bearing position beneath themetatarsal heads and any plantar skin callosities moveproximally and subsequently separate spontaneously.The results of this forefoot reconstruction on 42 feet

were reviewed independently (11). The mean follow-upwas 5 years (range 2 years to 11 years 7 months). Atreview, 34 feet (81%) were considered excellent and 5(12%) good (example shown at Fig. 12). Many patientswere able to dispense with surgical shoes, the length of thefeet was preserved, 39 (93%) had no pain, only three hadplantar callosities and 14 patients were able to walkcomfortably on the forefoot alone.

Conclusion

The foot skeleton is supported and controlled by a multi-segmental ligamentous and fascial tie-bar system centredon the plantar plates of the metatarsophalangeal joints.The integrity and correct positioning of the compo-


Figure 11. (a) Incisions for forefoot reconstruction. (b) Diagrammatic illustration ofcorrection of displaced plantar plates and repair of the medial and lateral ends of thetransverse tie-bar.

(a) (b)

nents of the multisegmental longitudinal and transversetie-bars are necessary for the normal function of the foot.The longitudinal tie-bar system (the deeper layer of the

plantar fascia) is controlled by the windlass mechanism asdescribed by John Hicks.The function of the longitudinal tie-bar system can be

assessed by the 'footstool edge weight-bearing test'.Defects in the ligamentous tie-bar system and

malalignment of the plantar plates allow and causedeformities of the forefoot and toes to develop.When deformities of the forefoot and toes are corrected

surgically, an attempt should be made to reconstruct thetie-bar system, and so restore normal foot anatomy andfunction as far as is possible.When there is severe clawing of a lesser toe the

'plunger' effect of the dorsally displaced plantar platecauses depression of the metatarsal head. When treatedsurgically it is important to replace the dorsally displacedplantar plate to its correct position under the metatarsalhead.When the severely deformed rheumatoid forefoot is

treated surgically, it is recommended that the metatarsalheads be preserved as they are an essential part of theweight-bearing structure of the forefoot and they controlthe tie-bar systems.

(C) (d)Figure 12. (a) and (b) Severely deformed rheumatoidforefoot before surgery. (c) and (d) One year after forefootreconstruction.

The anatomical studies would not have been possible without thehelp and guidance of Professor Simon Miller, and I amparticularly grateful to Mrs Christine Harkness who kindlycarried out the cadaver dissections in the School of Anatomy ofthe University of Newcastle upon Tyne.The co-operation, generosity and enthusiasm of the staff ofthe

X-ray Department and the Alliance Medical MRI Unit at theNuffield Hospital, Newcastle upon Tyne, and the RadiologyDepartment and CT Unit at the Royal Victoria Infirmary, aregratefully acknowledged.

68 G D Stainsby

The author also wishes to thank Mr John Bulmer, Mr PeterBriggs, Professor Garth Johnson and, in particular, ProfessorLeslie Klenerman, for their help, advice, and encouragement.

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aponeurosis and the arch. J Anat 1954; 88: 25-30.3 Poirier P. Traite d'Anatomie Humaine. Vol 2, Paris: L

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Received 29 July 1996