extensor apparatus - aofas (dalmau-pastor)

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Foot & Ankle International®

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DOI: 10.1177/1071100714546189fai.sagepub.com

Topical Review

Introduction

Lesser toe deformities are a common condition faced by the

orthopedic foot and ankle surgeon, with a reported inci-

dence that ranges from 2% to 20%.12,17 These deformities

are more frequent in females, and their incidence increaseswith age.

11,27,44 The causes of lesser toe deformities include

anatomic factors, neuromuscular disease, connective tissue

disorders, congenital anomalies, trauma, constricting foot-

wear, or poor foot biomechanics.25,27,29

These can result in

an imbalance between the extensor and flexor muscles of

the toes, which leads to lesser toe deformities.5,9 Lesser toe

deformities are complex and involve the interphalangeal

joints, metatarsophalangeal joints, and associated tendons

and ligaments.29

Depending on the joints affected, the

deformity is classified as claw toe, hammer toe, and mallet

toe, all of which can appear as flexible or fixed deformi-

ties.27

Once the cause of the deformity is determined, the

surgeon can decide which deforming force has to be neu-tralized so that the appropriate procedure can be chosen.29

Lesser toe deformities can be corrected using techniques

applied to both soft tissue and bone.11,25,27,29

The extensor apparatus of the toes is an important struc-

ture in the etiology of lesser toe deformities and therefore

the object of the surgical procedures used to correct the

deformity.27

Anatomy is the basis of orthopedic surgery,43

and knowledge of the morphologic and functional anatomy

of the extensor apparatus of the toes is necessary before

performing surgical procedures to correct lesser toe

deformities.10,21,26,27,29,32

However, despite the importance of a sound knowledge

of these structures, classic anatomy textbooks and chapters

on lesser toe deformities in surgery textbooks reveal a lack

of detail, inaccuracies, or even errors in the descriptions ofthe extensor apparatus.

The objective of this article was to present an anatomi-

cal description of the components of the extensor appara-

tus of the lesser toes based on a thorough literature review

and the dissections performed in our dissecting room. The

fifth toe has been excluded from this study because the

extensor brevis muscle does not reach it, the fact that it has

proper intrinsic muscles, and that with high frequency it is

a biphalangic toe. We present the anatomical features of

these complex structures and examine their role in clinical

and surgical practice in order to enhance the orthopedic

foot and ankle surgeon’s knowledge and understanding oflesser toe deformities. Finally, the lack of high-quality

189 FAIXXX10.1177/1071100714546189Foot & AnkleInternationalDalmau-Pastor etal.

1University of Barcelona, Barcelona, Spain2Private practice, Balearic Islands, Spain3Unit of Foot and Ankle Surgery, Hospital Quirón, Barcelona, Spain4University of Pittsburgh, Pittsburgh, PA, USA

Corresponding Author:

Jordi Vega, MD, Unit of Foot and Ankle Surgery, Hospital Quirón,

Barcelona, Spain. Plaza Alfonso Comín 5, 08023 Barcelona, Spain.

Email: [email protected]

Extensor Apparatus of the LesserToes: Anatomy With ClinicalImplications—Topical Review

Miquel Dalmau-Pastor 1, Betlem Fargues1, Enric Alcolea1, Nerea Martínez-Franco1,

Patricia Ruiz-Escobar 2, Jordi Vega3, and Pau Golanó1,4

Abstract

Lesser toe deformities are one of the most common conditions faced by orthopedic surgeons. Knowledge of the anatomy

of the lesser toes is important for ensuring correct diagnosis and treatment of deformities, which are caused by factorssuch as muscle imbalance between the extensor apparatus and flexor tendons. However, this apparatus has not received

sufficient attention in the literature. In addition, the large number of inaccurate and erroneous descriptions means that

gaining an understanding of these structures is problematic. The objective of the present article is to clarify the anatomy

of the extensor apparatus by means of a pictorial essay, in which the structures involved will be grouped and discussed indetail. The most relevant clinical implications will be addressed.

Level of Evidence: Level V, expert opinion.

Keywords: anatomy, extensor apparatus, orthopedic surgery, lesser toe deformities.

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2 Foot & Ankle International

images of the extensor apparatus of the foot led us to pres-

ent this article as a pictorial essay that will provide readers

with an up-to-date visual portrayal of the anatomy of this

structure.

Extensor Apparatus

Current knowledge of the anatomy and function of the

extensor apparatus of the lesser toes is limited. Most stud-

ies focus on the extensor apparatus of the hand, with lessattention being paid to that of the foot. In their description

of the extensor apparatus of the lesser toes, most anatomy

textbooks refer us to the extensor apparatus of the

fingers.

A search of the literature on the extensor apparatus of the

lesser toes reveals only 2 articles that provide an overview

of its anatomy.15,38

The 1969 work by Sarrafian and

Topouzian38 provides the most complete description of the

components of the extensor apparatus and will be used as a

reference in our description. Given the lack of a specific

nomenclature for this structure in the International

Anatomical Terminology of the Federative InternationalCommittee on Anatomical Terminology16 and the indis-

criminate use of various terminologies, we will use the

nomenclature proposed by Sarrafian and Topouzian.38

Extension of the toes is the result of the combined action

of the extensor digitorum longus, extensor digitorum bre-

vis, interossei muscles, and lumbrical muscles, all of which

converge to form a tendinofibroaponeurotic structure

known as the extensor apparatus (Figure 1).

In order to better understand the extensor apparatus, and

following the structure established by Sarrafian and

Topouzian,38 we identified 3 basic components: the extrinsic

contribution, which is formed by the extensor digitorum lon-

gus; the intrinsic contribution, which is formed by the exten-

sor digitorum brevis, lumbrical muscles, and interossei

muscles; and a third component, which we term the stabiliz-

ing ligaments, comprising the extensor sling, extensor wing,

and triangular lamina. As their names indicate, the main

function of these ligaments is to ensure that the extrinsic andintrinsic contributions remain in their appropriate anatomic

location (Figure 2 and 3).

Extrinsic Contribution

Extensor Digitorum Longus

The extensor digitorum longus is a muscle of the anterior

compartment of the leg. It provides 4 tendons for the sec-

ond to fifth toes. These tendons reach their respective

metatarsophalangeal joints, where they meet the extensor

apparatus and thus form their main axis. At the level of themetatarsophalangeal joints, the extensor tendons are

attached to the digital axis using a fibroaponeurotic struc-

ture known as the extensor sling, which is a stabilizing

ligament. At this level, the extensor digitorum longus ten-

don divides into 3 tendinous components known as slips:

a middle or central slip and 2 lateral slips, medial or lateral

depending on their anatomic location (Figure 4).38

The

middle slip inserts into the dorsal area of the base of the

Figure 1. Anatomical dissection of the dorsum of the foot showing the main components of the extensor apparatus. Neurovascularstructures were removed. (A) Dorsal view. (B) Lateral view. (1) Extensor digitorum longus tendons. (2) Middle or central slip. (3)Lateral slips. (4) Terminal tendon. (5) Extensor digitorum brevis tendons. (6) Extensor sling. (7) Triangular lamina. (8) First dorsalinterosseous. (9) Extensor hallucis longus tendon. (10) Peroneus tertius tendon. (11) Abductor digiti minimi tendon.


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Dalmau-Pastor et al. 3

Figure 2. Main drawing of the extensor apparatus and its components based on the drawings of Sarrafian and Topouzian.35 (A)Dorsal view. (B) Lateral view. (C) Medial view. (1) Extensor digitorum longus tendons. (2) Middle or central slip. (3) Lateral slips. (4)Terminal tendon. (5) Extensor digitorum brevis tendons. (6) Lumbrical muscle and tendon. (7) Interosseous muscles. (8) Extensorsling. (9) Extensor wing. (10) Triangular lamina. (11) Deep transverse metatarsal ligament. (12) Flexor digitorum longus tendon. (13)Flexor digitorum brevis.

Figure 3. Extension of the toes is the result of the combined action of the extensor digitorum longus, extensor digitorum brevis,interossei muscles, and lumbrical muscles. All of which converge to form a tendinobroaponeurotic structure known as the extensorapparatus.




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middle phalanx and into the capsule of the proximal inter-

phalangeal joint. After receiving contributions from the

intrinsic muscles, the 2 lateral slips run distally over the

dorsum of the middle phalanx before gradually inserting

into the dorsum of the distal phalanx via a single tendon

known as the terminal tendon. The triangular space between both lateral slips is occupied by an aponeurotic

structure known as the triangular lamina (Figure 4 and

5).37 When the proximal interphalangeal joint is flexed,

the middle slip is compressed against the head of the prox-

imal phalanx, which acts as a pulley. For this pulley mech-

anism to function, the middle slip has a sesamoid

fibrocartilage at its plantar side at the level of the proximal

interphalangeal joint, just proximal to the insertion of the

central slip into the middle phalanx.30

Although most authors6,8,20,21,27,29,31,34-36,41 agree with the

description by Sarrafian and Topouzian,38

a review of the

literature reveals divergence in many aspects. For example,

there are several versions of the location of the trifurcation

of the tendon of the extensor digitorum longus muscle, as

well as of the nomenclature used to describe its compo-

nents, or slips. Sarrafian and Topouzian state that this divi-

sion occurs at the level of the metatarsophalangeal joint,

whereas other authors have reported this division to occur

at the level of the diaphysis of the proximal pha-

lanx.6,21,27,29,31,36,41 Gosling,20 however, makes no mention

of where this trifurcation is formed, and some authors even

refer us to the section on anatomical descriptions of the

extensor apparatus of the hand.35

The trifurcation of the extensor digitorum longus has

received several names, which, while morphologically refer-

ring to the same structure, cause confusion in the study of

the extensor apparatus. Although we find the terms “parts”35

and “bands,”31

“slips” is the most widely used,6,8,27,

29,34,36,38,39,41,44 and thus, the nomenclature that is used in this

review.

Intrinsic Contribution

Extensor Digitorum Brevis

The extensor digitorum brevis muscle, which is the only

muscle of the dorsum of the foot, arises on the anterior

superior process of the calcaneus and runs obliquely to the

medial and anterior area before dividing into 4 fleshy fas-

cicles, each of which finishes in a flattened tendon. The

tendons of the extensor digitorum brevis are generally

Figure 4. (A) Dorsal view of the anatomical dissection showingthe trifurcation of the tendon of the extensor digitorum longus

muscle. (B) Main drawing of the extensor apparatus in dorsal viewin which the contribution of extensor digitorum brevis muscle ishighlighted. (1) Extensor digitorum longus tendons. (2) Middle orcentral slip. (3) Lateral slips. (4) Terminal tendon. (5) Extensorsling. (6) Triangular lamina. (7) Extensor digitorum brevis.

Figure 5. Sagittal section of the third toe. (1) Extensordigitorum longus tendon. (2) Middle or central slip. (3) Lateralslip. (4) Terminal tendon. (5) Metatarsal head. (6) Proximalphalanx. (7) Middle phalanx. (8) Distal phalanx. (9) Flexor

digitorum tendon. (10) Flexor digitorum longus tendon. (11)Plantar plate.




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thinner than those of the extensor digitorum longus, deeper

and more oblique in direction. These tendons reach the

metatarsophalangeal joint and contribute to the extensor

apparatus from the first to the fourth toe.

Most descriptions of the incorporation of these 4 exten-

sor tendons into the extensor apparatus state that they are

incorporated on the lateral aspect of the extensor digito-rum longus,6,29,34-36,38,39,41 thus countering the oblique

direction of the tendons of the long extensor of the toes.

Therefore, from a functional viewpoint, the action of both

muscles is considered a single action.29,41 This description

is corroborated by Sarrafian and Toupouzian,38 although the

authors state that the extensor digitorum brevis sometimes

runs independently, without joining the extensor digitorum

longus, and thus forms the lateral slip by itself. Our dissec-

tions generally confirm this description. The lateral slip is

formed exclusively by the extensor digitorum brevis, and

this is more apparent the more lateral the toe under study is,

except for the fifth toe, which does not have extensor brevis

tendon (Figure 6). We consider this anatomic detail to be

crucial for our understanding and treatment of lesser toe

deformities. We stress the importance of this structure, since

the extensor digitorum brevis muscle is omitted or poorly

addressed in the description of the extensor apparatus inchapters on lesser toe deformities in surgery textbooks7,8,44

and in common anatomy textbooks.31

Lumbrical Muscles

The lumbrical muscles, which are numbered 1 to 4 medial

to lateral, are found at the bifurcation of the tendons of the

flexor digitorum longus muscle and arise from the neigh-

boring tendons, except for the first lumbrical, which arises

from the flexor tendon of the second toe (Figure 7). From

Figure 6. (A) Dorsolateral view of the extensor tendons ofthe toes on the dorsum of the foot. The image shows howthe lateral slip is formed exclusively by the extensor digitorumbrevis and is more apparent the more lateral the toe is (black

arrows). (B) Lateral view of the main drawing in which thecontribution of extensor digitorum brevis muscle of theextensor apparatus is highlighted. (1) Extensor digitorum brevistendons. (2) Extensor digitorum longus tendons. (3) Middle orcentral slip. (4) Medial slip. (5) Lateral slip. (6) Terminal tendon.(7) Extensor sling. (8) Triangular lamina.

Figure 7. Plantar view of the lumbrical muscles andsurrounding structures. (1) Flexor digitorum longus tendon.

(2) Tendon to the second toe. (3) Tendon to the third toe.(4) Tendon to the fourth toe. (5) Tendon to the fifth toe. (6)First lumbrical muscle. (7) Second lumbrical muscle. (8) Thirdlumbrical muscle. (9) Fourth lumbrical muscle. (10) Flexorhallucis longus. (11) Chiasma plantare. (12) Quadratus plantaemuscle.




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their point of origin, the lumbrical muscles run distally and

diverge slightly to reach the medial side of the metatarso-

phalangeal joints of the second to fifth toes. At this point,

they are already in the form of their insertion tendon and run

plantar to the deep transverse metatarsal ligament, thus

forming part of the extensor apparatus.

Sarrafian and Topouzian38

and other authors6,29,33,36

state

that the lumbrical muscles insert into the extensor apparatus

(medial and middle slip) via a triangular structure formed by

oblique fibers known as the extensor wing (Figure 8). Some

authors report that the lumbrical muscles can also insert via

tendinous fibers on the phalangeal tuberosity, at the base of

the proximal phalanx.29,37,38 Our dissections occasionally

show that the lumbrical muscle itself forms the medial slip of

the extensor apparatus (Figure 9). However, the terminology

used in many chapters on lesser toe deformities and anatomy

textbooks is often confusing, thus making it difficult to

understand the insertion of the lumbrical muscles.8,29,31,41

Given their plantar location with respect to the axis of

rotation of the metatarsophalangeal joint, these muscles actas flexors of the metatarsophalangeal joint by countering

the extensor action of the extensor digitorum longus mus-

cle. They act on the extensor apparatus by means of their

expansion, or extensor wing, thus contributing to the exten-

sion of the interphalangeal joints.21,23,31

Interossei Muscles

The 7 interossei muscles (3 plantar and 4 dorsal) arise on

the metatarsal aspects that delimit the corresponding inter-

metatarsal spaces. The plantar muscles are found in the

second, third, and fourth intermetatarsal spaces and arise

on the medial aspect of the delimiting metatarsal bones inits inferior segment. The dorsal muscles, which are larger

than the plantar muscles, are found in all the intermetatar-

sal spaces (Figure 10).

The tendons from both the plantar and dorsal interossei

muscles course distally before running dorsal to the deep

transverse metatarsal ligament—in contrast with the lumbri-

cal muscles, which do so plantarly—to reach the metatarso-

phalangeal joint and insert in the plantar area of the proximal

phalanx and plantar plate.8,15,27,31,33,36,38,39 At their insertion,

they are covered by the extensor sling (Figure 11).37,38

According to the description of the extensor apparatus pro-

posed by Sarrafian and Topouzian,

38

the tendons of the inter-ossei muscles are closely associated with the capsule, into

which some fibers insert. The remaining fibers extend distally

and insert into the base of the proximal phalanx. Some of

these fibers insert into the deep side of the extensor sling and

occasionally extend until they reach the extensor wing.

The vast majority of authors report that the interossei

muscles insert at the phalangeal tuberosity on the base of

the proximal phalanx.8,15,27,31,33,36,41

The area of greatest

Figure 8. (A) Medial view of the anatomical dissection of thesecond toe showing the anatomical relationships of the firstlumbrical muscle. (B) Same anatomical image in which the extensorwing (black arrows) and the extensor sling (white arrows) have

been identified by software (Adobe PhotoShop). (C) Medial viewof the main drawing showing the anatomy of the lumbrical muscle.(1) First lumbrical muscle. (2) Lumbrical tendon. (3) Extensorwing. (4) Flexor digitorum longus tendon. (5) Medial slip. (6) Deeptransverse metatarsal ligament and plantar plate (cut). (7) Extensordigitorum longus tendon (cut). (8) Extensor sling. (9) First dorsalinterosseous muscle. (10) Second dorsal interosseus muscle.(11) Vertical septum of plantar fascia. (12) Shaft of the secondmetatarsal bone. (13) Annular pulley of the fibrous sheath of theflexor tendons. (14) Toenail. (15) Nail matrix.




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confusion is the direct contribution of the tendons of the

interossei muscles to the extensor apparatus. Some authors

describe this contribution without specifying how it is pro-

duced.6,8,27,36,41 Other authors state that the interossei mus-

cles make no contribution to the extensor apparatus and

only insert into the base of the proximal phalanx.15,31,33

Consistent with Fahrer and Chapius,15 our dissections

show that the interossei muscles only insert at the base of

the proximal phalanx. We are unable to establish the

existence of fibers that extend distally to this insertion point and contribute to the formation of the extensor

apparatus, thus corroborating the findings of previous

studies (Figure 12).3,15,23

Given their location plantar to the axis of rotation of the

metatarsophalangeal joint, the interossei muscles flex the

joint by countering the extensor function and stabilizing

the extensor apparatus.8 Given the lack of insertion at the

level of the extensor apparatus, the interossei muscles have

no function at the level of the interphalangeal joints.

Therefore, the lumbrical muscles and the extensor

Figure 9. Dorsal view of the anatomical dissection of theextensor apparatus of the second toe showing a case in whichthe lumbrical muscle itself forms the medial slip of the extensor

apparatus. (1) First lumbrical muscle. (2) Extensor digitorum longustendon. (3) Middle slip. (4) Lateral slip. (5) Medial slip. (6) Extensorwing. (7) Extensor sling. (8) Extensor digitorum brevis tendon.(9) First dorsal interosseous muscle. (10) Medial terminal branch(sensitive) of the deep peroneal nerve. Figure reproduced withkind permission from De Prado et al.13

Figure 10. Schematic drawing of the anatomical disposition ofthe interosseous muscles (D, dorsal; P, plantar) at the level of theintermetatarsal spaces.

Figure 11. Anterior-dorsal view of the anatomical dissection ofthe second intermetatarsal space. (1) Second dorsal interosseousmuscle. (2) First plantar interosseous muscle. (3) Deep transversemetatarsal ligament. (4) Second lumbrical tendon. (5) Extensordigitorum longus tendon. (6) Extensor digitorum brevis tendon.(7) Middle slip. (8) Medial slip. (9) Extensor sling. (10) First dorsalinterosseous muscle.




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digitorum brevis are the only intrinsic muscles with an

extensor function at the level of the interphalangeal joints.23

The second toe is anatomically unique because it has 2

dorsal interossei muscles and no plantar interossei muscles.

Consequently, it could be more prone to dorsomedial dislo-

cation,10,22 thus explaining why the second toe is dislocatedmore often than the others.1,2,18,19,37,45

Stabilizing Ligaments

Extensor Sling

The tendons of the extensor apparatus are anchored on the

dorsum of the metatarsophalangeal joint and on the proxi-

mal phalanx by a fibroaponeurotic structure known as the

extensor sling.6,36,38,39,41

This aponeurosis is formed by

transversely oriented fibers at the level of the metatarso-

phalangeal joint and covers the extensor digitorum brevis

and extensor digitorum longus tendons. From this point, it

runs in a plantar direction and covers the insertion tendons

of the interossei muscles, before reaching the plantar plate,

deep transverse metatarsal ligament, and the fibrous syno-

vial sheath of the flexor digitorum longus and flexor digi-

torum brevis tendons. This reinforcement extends distally

to the base of the proximal phalanx. In our dissections, we

constantly observed this structure at the level of the meta-

tarsophalangeal joint, although it was somewhat difficult to

clearly identify its insertions in the plantar region (Figure

13 and 14).

As mentioned previously, the extensor digitorum longus

does not insert into the proximal phalanx. The proximal

phalanx extends via the pull exerted by the extensor digito-

rum longus on the extensor sling, which Sarrafian and

Topouzian37

described as a “sling mechanism” (Figure 15).Furthermore, this extensor sling prevents the extensor ten-

don excursion from being used exclusively in metatarso-

phalangeal extension, and in so doing enables extension of

the interphalangeal joints. Injury to this structure and others

allows the extensor digitorum longus to exert its entire

excursion on the metatarsophalangeal joint, thus favoring

hyperextension. Extensor action on the interphalangeal

joints disappears, and the flexor force predominates, lead-

ing to lesser toe deformity.

Figure 12. (A) Lateral view of the anatomical dissection ofthe second toe, showing the insertion of the second dorsalinterosseous muscle in the phalanx tubercle. (B) Main drawingshowing the anatomy of the interosseous muscle, which has beenhighlighted in the drawing. (1) Second dorsal interosseous muscleand tendon. (2) Phalanx tubercle. (3) Vertical septum of the plantarfascia, plantar plate, and deep transverse metatarsal ligament (cut).(4) Extensor sling. (5) Extensor digitorum longus tendon. (6)Extensor digitorum brevis tendon. (7) Middle slip. (8) Lateral slip.(9) Flexor digitorum brevis tendon. (10) Flexor digitorum longustendon. (11) Shaft of the second metatarsal bone.

Figure 13. Lateral view of the anatomical dissection of thesecond toe showing the extensor sling and its anatomicalrelationships. (1) Extensor sling. (2) Extensor digitorum longustendon. (3) Extensor digitorum brevis tendon. (4) Deeptransverse metatarsal ligament (cut). (5) Plantar plate. (6) Second

dorsal interosseous muscle. (7) Phalanx tubercle. (8) Verticalseptum of the plantar fascia (cut) inserted into the plantar plate.(9) Flexor digitorum longus tendon. (10) Flexor digitorum brevistendon. (11) Annular pulley of the fibrous sheath of the flexortendons. (12) Metatarsal tubercle.




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Extensor Wing The extensor wing, or extensor hood, is an aponeurosis situ-

ated distal to the extensor sling. It is composed of obliquely

oriented fibers and is triangular in shape.6,27,36,38,39

The

extensor wing unites the tendinous fibers of the intrinsic

muscles with the 3 slips of the extensor digitorum longus

(Figure 16).38 According to Sarrafian and Topouzian,38 the

extensor wing is situated on both sides of each toe. The

superior border of each triangle inserts into each of the lat-

eral slips corresponding to the trifurcation of the extensor

digitorum longus muscle. Some fibers extend toward the

dorsum of the proximal interphalangeal joint and join the

middle slip. The proximal border is continuous with the dis-

tal margin of the extensor sling, and the inferior border runs

obliquely, distally, and dorsally. Observed in a medial view,

the tendon of the lumbrical muscle—after passing plantar to

the deep transverse metatarsal ligament—runs dorsally to

form the oblique border of the extensor wing.6,29,33,36,38,39

Although most of the authors who discuss the extensor

wing29,36

agree with the description proposed by Sarrafian and

Topouzian,37

our dissections confirm that on the medial side,

the extensor wing is evident, owing to the presence of the lum-

brical muscle. However, we did not observe a structure

comparable to the extensor wing on the lateral side of the lesser

toes. Therefore, our illustration differs in this detail from the

original drawing by Sarrafian and Topouzian (Figure 17).

Triangular Lamina

The triangular lamina occupies the space between the lateral

slip and the medial slip at the dorsum of the middle phalanx.37

This structure comprises a fine, almost transparent lamina of

tissue that is pearl in color and extends until it becomes the

terminal extensor tendon. The triangular lamina was a con-

stant finding in our dissections (Figure 18). Although we do

not discuss its function, we think that the triangular lamina

helps to maintain the lateral and medial slips in their originalanatomic position, thus avoiding their plantar displacement.

If this happens, the slips function as flexors rather than exten-

sors of the proximal interphalangeal joint.

Clinical Implications of the Extensor

Apparatus

The extensor apparatus of the lesser toes is a basic struc-

ture that must be addressed in order to correct lesser toe

Figure 14. (A) Drawing of the extensor apparatus in proximal-superior view showing the anatomical relationship of the extensorsling based on the drawings of Oukouchi et al.30 (B) Lateral view of the main drawing showing the highlighted extensor sling. Medialview of the main drawing showing the highlighted extensor sling. (1) Extensor sling. (2) Extensor digitorum longus tendon. (3) Middleslip. (4) Lateral slips. (5) Terminal tendon. (6) Entensor digitorum brevis tendon. (7) First lumbrical muscle. (8) Extensor wing. (9) Firstdorsal interosseous muscle. (10) Second interosseous muscle. (11) Triangular lamina. (12) Deep transverse metatarsal ligament.(13) Flexor tendons. (14) Metatarsal bone (cut).




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deformities. Release of the extensor digitorum longus,

extensor digitorum brevis, metatarsophalangeal joint cap-

sule or lengthening of the extensor digitorum longus ten-

don are common procedures aimed at eliminating the pull

of the extensor apparatus, thus avoiding hyperextension of

the proximal phalanx.5,13,25,27,29 A tenotomy decreases the

radiographic sagittal angulation of the toe.14 The correction

of these deformities is most effective if the deformity is

completely flexible and less effective if it is rigid.42

These

procedures, although described for correction of lesser

toes deformities, have not been documented in the litera-

ture as effective as isolated procedures. They can, how-

ever, be useful as adjunctive procedures in lesser toes

deformities.39,40 A detailed knowledge of the extensor

apparatus is key to an appropriate performance of these

procedures.

Most authors agree that both the extensor digitorum lon-

gus tendon and extensor digitorum brevis tendon should be

released.13,25,27

Joint capsule release, on the other hand,

depends on how fixed the deformity is. Additional release

of the lumbrical tendons has been suggested.24 Tendon

release at the level of the metatarsophalangeal joint pre-

vents proximal displacement of the tendon ends, owing to

the attachment of the extensor sling. It is also possible to

perform dorsal release of the metatarsophalangeal joint

capsule through the same incision. Lengthening of the

extensor digitorum longus tendon could be performed

proximal to the extensor sling, since no proximal excursion

Figure 15. Anatomical images showing the “sling mechanism”of the extensor sling. (A) Without action of the extensordigitorum longus. (B) With action of the extensor digitorumlongus (black arrow). In this case, the extensor sling preventsthe extensor tendon excursion (its fibers in tension), allowingthe extensor digitorum longus extend all the toe joints. (1)Extensor digitorum longus tendon. (2) Extensor sling. (Figurereproduced with kind permission from De Prado M, Ripoll PL,Golanó P. Minimally Invasive Foot Surgery . Barcelona: About YourHealth; 2009: 221-38).13

Figure 16. (A) Medial view of the anatomical dissection ofthe second toe in which the anatomy of the extensor wing andthe limits are underlined by software (Adobe PhotoShop). (B)

Medial view of the main drawing showing the extensor wing. (1)Extensor wing. (2) First lumbrical tendon (tensioned-arrow). (3)Extensor digitorum longus tendon. (4) Middle slip. (5) Medialslip. (6) Extensor sling. (7) Extensor digitorum brevis tendon.(8) Phalanx tubercle. (9) First dorsal interosseous muscle. (10).Plantar plate and deep transverse metatarsal ligament (cut). (11)Shaft of the second metatarsal bone. (12) Metatarsal tubercle.




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of the tendon is observed. There is no connection between

the extensor digitorum longus tendon and extensor digito-

rum brevis tendon at the metatarsophalangeal joint.

Consequently, when a lesser toe deformity is identified, theextensor digitorum brevis tendon is displaced laterally and

plantar to the extensor digitorum longus. The surgeon has

to be aware of this fact, as both tendons should be cut.

Cutting only the extensor digitorum longus could lead to

incomplete correction of the deformity.

Lesser toe deformities can be caused by other patho-

logical entities, such as spastic equinovarus deformity,

paralytic foot, or compartment syndrome (when affect-

ing the lateral, deep posterior, or superficial posterior

compartments of the leg28

). Release of the lumbrical ten-dons has been suggested when addressing lesser toe

deformities in patients with spastic equinovarus defor-

mity.24

Release of the flexor digitorum longus and brevis

tendons alone can result in flexion deformity of the meta-

tarsophalangeal joint because of the effect of the lumbri-

cals tendons. Also in cases of paralytic foot, the paralysis

of the plantar intrinsic musculature of the foot leads to

claw toes and moreover causes a shift in distal direction

of the plantar fat pad below the metatarsophalangeal

joint, exposing the thinner part of the skin to pressure.4

Secondary toe deformities can develop in cases of pero-

neal nerve palsy, especially when tibialis anterior muscle

is affected, which can result in secondary recruitment

and overactivity of the extrinsic toe extensors to assist

ankle dorsiflexion.28

Conclusion

The extensor apparatus of the lesser toes is an important

set of structures for the biomechanics of the toes that

involve an extrinsic contribution (extensor digitorum lon-

gus), an intrinsic contribution (extensor digitorum brevis,

lumbrical muscles, and interossei muscles), and stabiliz-

ing ligaments (extensor sling, extensor wing, and triangu-

lar lamina).The action of the extensor and flexor muscles of the

lesser toes produce hyperextension of the metatarsophalan-

geal joint and plantarflexion of the proximal and distal

interphalangeal joint. Traction of the interossei muscles

flexes and stabilizes the metatarsophalangeal joint. The

lumbrical muscles plantarflex the metatarsophalangeal joint

and extend both of the interphalangeal joints. Thereby,

complete extension of the lesser toes is the result of the

combined forces between the extensor digitorum longus

Figure 17. Medial and lateral view of the anatomical dissectionof the extensor apparatus of the second toe intending todemonstrate the absence of a structure comparable to theextensor wing on the lateral side of the lesser toes. (A) Medialview. (B) Lateral view. (1) Extensor wing. (2) First lumbricaltendon. (3) Medial slip. (4) Flexor digitorum longus tendon.(5) Extensor digitorum longus tendon. (6) Extensor digitorumbrevis tendon. (7) Extensor sling. (8) Phalanx tubercle. (9) Flexordigitorum brevis tendon. (10) First dorsal interosseous muscle.(11) Second dorsal interosseous muscle. (12) Vertical septum ofthe plantar fascia (cut). (13) Shaft of the second metatarsal bone.(14) Collateral ligaments of the proximal interphalangeal joint.

Figure 18. Anterior view of the anatomical dissection of thedorsal aspect of the middle phalanx showing the triangularlamina anatomy (white arrows). (1) Triangular lamina. (2) Middleslip. (3) Medial slip. (4) Lateral slip. (5) Terminal tendon.




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muscle and the intrinsic muscles, all of which converge to

form the extensor apparatus. The imbalance between the

extensor apparatus and the flexors of the toes leads to lesser

toe deformities. These deformities can often be corrected by

soft tissue procedures. Knowledge of these structures can

have great importance when performing these surgical pro-

cedures and in avoiding recurrence.

Acknowledgments

We thank Roser Torres for her valuable help with the drawings

presented in this paper. The authors are grateful to Thomas O’Boyle

for editorial assistance. We thank Dr Cristina Manzanares for her

institutional support at the University of Barcelona.

Editor’s Note

This article is published in memory of Pau Golano, MD, who died

unexpectedly during the production phase of this outstanding sci-

entific contribution.

Declaration of Conflicting Interests

The author(s) declared no potential conflicts of interest with

respect to the research, authorship, and/or publication of this

article.

Funding

The author(s) received no financial support for the research,

authorship, and/or publication of this article.

References

1. Bade H, Tsikaras P, Koebke J. Pathomorphology of the ham-

mer toe. Foot Ankle Surg . 1998;4:139-143. 2. Blitz NM, Ford LA, Christensen JC. Second metatarsopha-

langeal joint arthrography: a cadaveric correlation study. Foot

Ankle Surg . 2004;43(4):231-240.

3. Bojsen-Møoller F. Anatomy of the forefoot, normal and

pathologic. Clin Orthop Relat Res. 1979;(142):10-18.

4. Brand PW. The insensitive foot (including leprosy). In: Jahss

MH, ed. Disorders of the Foot . Philadelphia: W. B. Saunders

Company; 1982:1266-1286.

5. Chadwick C, Saxby TS. Hammertoes/clawtoes: meta-

tarsophalangeal joint correction. Foot Ankle Clin N Am.

2011;16(4):559-571.

6. Chan R. Anatomy of the digits. Clin Podiatr Med Surg .

1986;3(1):3-9.

7. Cooper PS. Disorders and deformities of the lesser toes. In:Myerson MS, ed. Foot and Ankle Disorders. Philadelphia:

W.B. Saunders Company; 2000:308-358.

8. Coughlin MJ. Lesser toe deformities. In: Coughlin MJ, Mann

R, Saltzman CL, eds. Surgery of the Foot and Ankle. 8th ed.

Philadelphia: Mosby; 2007:363-464.

9. Coughlin MJ. Lesser-toe abnormalities. J Bone Joint Surg

Am. 2002;84(8):1446-1469.

10. Coughlin MJ. Subluxation and dislocation of the sec-

ond metatarsophalangeal joint. Orthop Clin North Am.

1989;20(4):535-551.

11. Coughlin MJ, Dorris J, Polk E. Operative repair of the fixed

hammertoe deformity. Foot Ankle Int . 2000;21(2):94-104.

12. Cyphers SM, Feiwell E. Review of the Girdlestone-Taylor

procedure for clawtoes in myelodysplasia. Foot Ankle Int .

1988;8(5):229-323.

13. De Prado M, Ripoll PL, Golanó P. Minimally Invasive Foot

Surgery. Barcelona: About Your Health; 2009:221-238.

14. Espinosa N, Myerson MS. Current concept review: metatar-salgia. Foot Ankle Int . 2008;29(8):871-879.

15. Fahrer M, Chapius PH. Proceedings: the functional anatomy

of the extensor apparatus of the second, third and fourth toes.

J Anat . 1973;116(3):478.

16. Federative Committee on Anatomical Terminology.

International Anatomical Terminology. Stuttgart: Thieme; 1998.

17. Femino JE, Mueller K. Complications of lesser toe surgery.

Clin Orthop Relat Res. 2001;391:72-88.

18. Ford LA, Collins KB, Christensen JC. Stabilization of the

subluxed second metatarsophalangeal joint: flexor tendon

transfer versus primary repair of the plantar plate. Foot Ankle

Surg . 1998;37(3):217-222.

19. Fortin PT, Myerson MS. Second metatarsphalangeal joint

instability. Foot Ankle Int . 1995;16(5):306-313. 20. Gosling JA. Human Anatomy. Color Atlas and Textbook . 4th

ed. Philadelphia: Mosby; 2008.

21. Green DR, Brekke M. Anatomy, biomechanics, and pathome-

chanics of lesser digital deformities. Clin Podiatr Med Surg .

1996;13(2):179-200.

22. Holinka J, Schuh R, Hofstaetter JG, Wanivenhaus AH.

Temporary Kirschner wire transfixation versus strapping

dressing after second MTP joint realignment surgery: a

comparative study with ten-year follow-up. Foot Ankle Int .

2013;34(7):984-989.

23. Jarrett BA, Manzi JA, Green DR. Interossei and lumbricales

muscles of the foot: an anatomical and functional study. J Am

Podiatry Assoc. 1980;70(1):1-13.

24. Keenan MA, Gorai AP, Smith CW, Garland DE. Intrinsic toe

flexion deformity following correction of spastic equinovarus

deformity in adults. Foot Ankle. 1987;7(6):333-337.

25. Kitaoka HB, Richardson EG. Realignment of lesser toe

deformities. In: Kitaoka HB, ed. The Foot and Ankle. 2nd ed.

Philadelphia: Lippincott Williams & Wilkins; 2002:147-168.

26. Knecht JG. Pathomechanical deformities of the lesser toes. J

Am Podiatr Assoc. 1974;64(12):941-954.

27. Mann RA, Coughlin MJ. Lesser-toe deformities. In: Jahss

MH, ed. Disorders of the Foot and Ankle. Medical and

Surgical Management . 2nd ed. Philadelphia: Saunders

Company; 1991:1205-1228.

28. Matuszak SA, Baker EA, Fortin PT. The adult paralytic foot.

J Am Acad Orthop Surg . 2013;21(5):276-285. 29. McGlamry ED, Jimenez AL, Green DR. Lesser ray defor-

mities. In: McGlamry ED, Banks AS, Downey MS, eds.

Comprehensive Textbook of Foot Surgery. 2nd ed. Baltimore:

Williams & Wilkins; 1992:51-102.

30. Milz S1, Putz R, Ralphs JR, Benjamin M. Fibrocartilage

in the extensor tendons of the human metacarpophalangeal

joints. Anat Rec. 1999;256(2):139-145.

31. Moore KL, Dalley AF. Clinically Oriented Anatomy.

6th ed. Philadelphia: Lippincott Williams&Wilkins;

2010:509-669.




13/13


32. Myerson MS, Shereff MJ. The pathological anat-

omy of claw and hammer toes. J Bone Joint Surg Am.

1989;71(1):45-49.

33. Oukouchi H, Murakami T, Kikuta A. Insertions of the lum-

brical and interosseus muscles in the human foot. Okijamas

Folia Anat Jpn. 1992;69(2-3):77-83.

34. Resch S. Functional anatomy and topography of the foot

and ankle. In: Myerson MS, ed. Foot and Ankle Disorders.Philadelphia: W.B. Saunders Company; 2000:25-49.

35. Romanes GR. Cunningham’s Manual of Practical Anatomy.

15th ed. Oxford: Oxford University press; 1986.

36. Samojla BG. Normal anatomy of the forefoot. In: Hetherington

VJ, ed. Hallux Valgus and Forefoot Surgery. New York:

Churchill Livingstone; 1994:7-37.

37. Sarrafian SK, Kelikian AS. Myology. In: Kelikian AS, ed.

Sarrafian’s Anatomy of the Foot and Ankle: Descriptive,

Topographic, Functional . 3rd ed. Philadelphia: Williams &

Wilkins; 2011:223-301.

38. Sarrafian SK, Topouzian LK. Anatomy and physiology

of the extensor paratus of the toes. J Bone Joint Surg Am.

1969;51(4):669-679.

39. Schuberth JM. Hammer toe syndrome. Foot Ankle Int .

1999;38(2):166-178.

40. Solan MC, Davies MS. Revision surgery of the lesser toes.

Foot Ankle Clin N Am. 2011;16:621-645.

41. Standring S, Borley NR. Gray’s Anatomy: The Anatomical

Basis of Clinical Practice. 40th ed. Philadelphia: Churchill

Livingstone; 2008.

42. Tamir E, Vigler M, Avisar E, Finestone AS. Percutaneoustenotomy for the treatment of diabetic toe ulcers. Foot Ankle

Int . 2013;34(10):1-6.

43. Van Eck CF, Schreiber VM, Liu TT, Fu FH. The anatomic

approach to primary, revision and augmentation anterior cru-

ciate ligament reconstruction. Knee Surg Sports Traumatol

Arthrosc. 2010;18(9):1154-1163.

44. Watson AD, Anderson RB, Davis WH. Lesser toes deformi-

ties. In: Kelikian AS, ed. Operative Treatment of the Foot

and Ankle. New York: Appleton & Lange; 1999:99-116.

45. Yu GV, Judge MS, Hudson JR, Seidelmann FE. Predislocation

syndrome. Progressive subluxation/dislocation of the

lesser metatarsophalangeal joint. J Am Podiatr Med Assoc.

2002;92(4):182-199.

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