Anatomy of the juncturae tendinum of the hand

Three distinct morphologic types of juncturae tendinum of the extensor tendons were identifiedin the dissection of 40 cadaver hands. Type 1 juncturae consists of filamentous regions withinthe intertendinous fascia that attached to the extensor tendons on either side of the intermeta­carpal space in a transverse or oblique direction. The second type, consists of much thicker andwell-defined connecting bands. Type 3 juncturae consist of tendon slips from the extensor tendonsand were subclassified into "y" or "r" subtypes depending on shape. Type 1 juncturae werepresent in 88% of the second intermetacarpal spaces and in 28% of the third intermetacarpalspaces. Type 2 juncturae were present in 40% of the third intermetacarpal spaces and in 23%of the fourth intermetacarpal spaces. Type 3 juncturae were present in 33% of the third Inter­metacarpal spaces and in 80% of the fourth intermetacarpal spaces. Juncturae were absent inall of the first intermetacarpal spaces and in 12% of the second intermetacarpal spaces; theywere present in all other spaces. The extensor indicis proprius did not receive a juncturalconnection, whereas extensor digiti quinti tendons did receive junctural connections. Interten­dinous fascia was present between all extensor digitorum communis tendons regardless of pres­ence of juncturae. (J HAND SURG 1990j15A:595·602.)

Herbert P. von Schroeder, MD, Michael 1. Batte, MD, and Harris Gellman, MD,San Diego, Calif.

The juncturae tendinum consist of narrowconnective tissue bands extending between the extensordigitorum communis (EDC) tendons and the extensordigiti quinti (EDQ) tendons. They are frequently de­scribed as variable':" and are often unmentioned in clin­ical and anatomic studies. 4·8 Various functional roleshave been attributed to the juncturae tendinum, includ­ing: spacing of the EDC tendons.?: 10 force redistribu­tion," coordination of extension," and stabilization ofthe metacarpophalangeal (MP) joints.P They pre­vent independent extension of the digits!': 13 and areclinically important since they may bridge and hencemask tendon lacerations. 14. 15 The juncturae tendinum

From the Division of Orthopaedic Surgery, University of California,San Diego, School of Medicine.

Presented in part at the American Society for Surgery of the Hand,Annual meeting, Baltimore, Maryland, September 1988.

Received for publication April 13, 1989; accepted in revised formSept. 1, 1989,

No benefits in any form have been received or will be received froma commercial party related directly or indirectly to the subject ofthis article.

Reprint requests: Michael J. Botte, MD, University of California,San Diego, Division of Orthopaedic Surgery, UCSD Medical Cen­ter, 225 Dickinson St. H-894, San Diego, CA 92103-1190.

3/1/16876

are also surgically useful for the proper identificationof the tendons of the hand" and have been used in therepair of the dorsal aponeurosis. 17 Complete transectionof a juncturae and the intertendinous fascia may leadto subluxation of the EDC tendon over a flexed MP. 18

In 1963, KaneffS proposed a classification for the junc­turae; however, his study, as well as others.v " 19 didnot fully examine and define the variability of the junc­turae tendinum. This study was undertaken to describeand define in more detail the juncturae tendinum of thehand.

Materials and methods

Forty randomly selected fresh-frozen postmortemadult upper extremities (19 right, 21 left) were thawedfor dissection. After removal of the skin and carefuldissection of the superficial fascia on the back of eachhand, the extensor retinaculum was divided longitudi­nally to fully expose the tendons, intertendinous fascia,and juncturae tendinum. The juncturae were examinedfor gross appearance, size, shape, thickness, location,and distribution with the hand in neutral position. Thelength of the juncturae was a measurement of the in­tertendinous distance along the middle of the juncturaetendinum (IT); the width was measured as the averagedistance of the JT perpendicular to the length. Mea­surements for the morphologically different types of

THE JOURNAL OF HAND SURGERY 595

596 Von Schroeder, Botte, and GellmanThe Journal of

HAND SURGERY

Fig. 1. Juncturae tendinum and intermetacarpal (IMC) spaces. Variations of the juncturae areapparent; second (a), third (b), and fourth (c) IMC spaces are labeled respectively. Tendons fromleft to right are: EDC and EIP to the index finger, EDC to the long finger, a double EDC to thering finger, which coalesces into one tendon of insertion, and a triple EDQ tendon to the smallfinger.

Table I. Number of intertendinous connections in the interrnetacarpai spaces

lntermetacarpal spacePrimary

I Iconnection Side Second Third Fourth Subtotals Totals

Fascia alone R 2 2L 3 3

5

IT type 1 R 17 4 21L 18 7 25

46

IT type 2 R 7 4 11L 9 5* 14 25

IT type 3 R 8 15 23L 5 17* 22

45

*One case with two juncturae in the fourth space.IT, Juncturae tendinum; R, right; L, left.

juncturae were recorded to the nearest 0.01 mm andwere statistically analyzed using Student's t test. Theextensor tendons were inspected from their muscle bellyof origin to their insertion; the presence Dr absence ofEDC to the small finger was noted, and, when presentwas differentiated from the EDQ tendon by identifyingtheir separate muscle bellies and their separate coursethrough their respective osseofibrous tunnels deep tothe extensor retinaculum. The sites of juncturae attach­ment to the tendons were noted and the locations of thejuncturae were defined with respect to the adjacent ten­dons of origin and insertion, the distance from the ra-

diocarpaljoint, and by the intermetacarpal (IMC) space.The first IMC space was defined as the space betweenthe metacarpals to the thumb and index fingers, andsecond, third and fourth spaces were between the indexand long, long and ring, ring and small fingers, re­spectively (Fig. 1). Diagrams were drawn of each dis­section and representative photographs taken.

Results

The JT were classified into three types on the basisof their distinct appearances and dimensions (Fig. 1).

JT type 1. These juncturae consisted of filamentous

Vol. 15A, No.4July 1990

B

Anatomy of juncturae tendinum of hand 597

Fig. 2. A-B, Juncturae tendinum (JT) type 1. A, The thin filamentous type 1 JT. B, Correspondingdrawing of JT type 1 between EDC tendons of the long (EDC m) and index (EDe i) fingers;juncturae did not connect to the Erp tendon. The numbers on the right indicate the incidence oftype 1 juncturae in the second and third fMC spaces, respectively. There were no type 1 juncturaepresent in any of the other spaces.

Table II. Characteristics of the juncturae tendinum

Angle of Angle ofiT Length Width Thickness origin insertion

type n (mm} (mm) (mm) (degrees) (degrees)

Type IType 2Type 3

462545

6.4 ± 0.3*8.6 ± 0.79.8 ± 0.6

10.7 ± 0.58.7 ± 0.74.0 ± 0.5

0.12 ± 0.010.55 ± 0.051.00 ± 0.04

105 ± 2131 ± 4138 ± 3

66 ± 241 ± 440 ± 3

•All values ± standard error.

regions within the intertendinous fascia that containedtiny bands of connective tissue (Fig. 2). These bandsattached to the EDC tendons on either side of the IMCspace but did not connect to the EIP tendons, nor didthey attach to aberrant EIP tendons to the long fingeror extensor medius proprius (EMP) tendons when thesewere present. Type 1 juncturae were the only type pres­ent in the second IMC space where they were observedin 88% of cases. They represented 28% of the juncturaein the third IMC space and they were never present inthe fourth space (Table I). They were square, rhom­boidal, or triangular and had either a transverse or, morecorrunonly, an oblique orientation. Since the obliqueorientation was proximal on the EDC tendon to the longfinger in the second IMC space, and proximal on theEDC tendon to the ring finger in the third IMC space,

these tendons were defined as the tendons of origin.The angulation varied to some degree with independentmovement of the digits from the neutral position. Thelength, width, and thickness of the type 1 juncturae(Table II) were significantly different (p -s 0.01)from type 2 or 3 juncturae. The dimensions of thetype 1 juncturae did not differ between the second ver­sus the third IMC space (6.5 X 11.0 X 0.12 versus6.1 x 9.9 x 0.14 mm). The Locations of the type 1juncturae were also more proximal than the other typesof juncturae; two thirds of type 1 juncturae originatedover the third quarter of the underlying metacarpal(MC) (Table III). Type 1 juncturae were slightly morecommon on the left hand in the second IMC space thanon the right (Table I); however, there were no othersignificiant right/left tendencies. In one case a JT re-

598 Von Schroeder. Batte. and Gellman

The Journal ofHAND SURGERY

Fig. 3. A-B, Juncturae tendinum type 2. A, The thicker type 2 juncturae. B, Corresponding drawingof JT type 2 between EDC tendons of the ring (EDC r) and long (EDC m) fingers. The incidencesof type 2 juncturae in the third and fourth !MC spaces are shown on the right; they were not presentin any of the other spaces.

Table m. Locations of the points of origin and insertion of the juncturae tendinum with respect toradiocarpal* joint and metacarpalt

Origin over one fourtn ofMet Insertion over one fourth of(No. of cases) Met (No. of cases)

IT Origin" Insertion"

I I I IType n (em) (em) 2nd 3rd 4th 2nd 3rd 4th

123

462545

5.5 ± 0.16.0 ± 0.26.1 ± 0.1

5.7 ± 0.16.7 ± 0.26.8 ± 0.1

1121

321832

35

12

5oo

281212

131333

*Dislance from radiocarpal (Re) joint. Note: average distance from RC joint to third Mep joint of all specimens was 8.25 ± 0.12 em.tMC (metacarpal) corresponding to tendon of origin or insertion.

ceived an independent EDC tendon that inserted intoits center; in another case, a JT received a tendon slipfrom an EDC tendon to the ring finger.

JT type 2. The type 2 juncturae (Fig. 3), primarilyrhomboidal, were thicker than type I juncturae, yetthinner than type 3 (p ::5 0.001; Table Il). They werefrequently thin proximally and thicker distally, and al­though they were slightly wider and shorter in the thirdIMC space than in the fourth, the mean thickness wasthe same in both locations.

Type 2 juncturae accounted for 40% of the juncturaein the third IMC space and in 23% of the juncturae inthe fourth space; they were never found in the secondspace (Fig. 3). Of the nine cases in which a type 2 JToccurred in the fourth IMC space, eight were observedin the presence of an EDC tendon to the small finger(Table IV). (EDC to the small finger was present in 19of 40 cases.) In all of these cases, the juncturae passedfrom the EDC tendon of the small finger to the tendon

of the ring finger. The juncturae also incorporated thelateral slip of the EDQ tendon in one specimen. In onlyone case was there a type 2 JT present in the fourthspace in the absence of an EDC tendon to the smallfinger; it connected the EDQ tendon (lateral slip) to theEDC tendon to the ring finger.

The type 2 juncturae were more distally located thanthe type I juncturae (Table III). They occurred in theright hand in 44% of cases and in the left in 56% andhad an oblique orientation with the exception of twocases, which were transverse.

The juncturae themselves received a tendon slip fromadjacent tendons in five cases. They formed a webbetween type 3 juncturae and the tendon in four cases.These four, highly variable connections were consid­ered secondary connections and were not quantitatedtogether with the other type 2 JTs.

JT type 3. The type 3 juncturae were the longest,most narrow, and thickest of the three types (Table II),

Vol. 15A, No.4July 1990 Anatomy ofjuncturae tendinum of hand 599

Fig. 4. A-B, Juncturae tendinum type 3, subtype y. A, The y-shaped tendon and juncturae whichappears as a split tendon inserting into two adjacent digits . B, Corresponding drawing of JT type3y between EDC tendons of the ring (EDC r) and long (EDC m) fingers. The incidences of type3y juncturae in the third and fourth IMC spaces are shown on the right; they were not present inany of the other spaces.

Table IV. Number of juncturae tendinum in the fourth intennetacarpal space with respect to the presenceor absence of an EDC tendon to the small finger

Presence of EDC10 small finger

PresentAbsent

JT type 2

81

JT type 3y

71

IT type 3 r

419

Towl type 3

1120

and accounted for 33% of the juncturae in the thirdIMC space and 80% of the juncturae in the fourth space(Table 1, Figs. 4 and 5).

Type 3 JTs were subclassified into "y" and "r" sub­types depending on shape . In cases in which a tendonsplit into two equal halves that inserted into the twotendons of adjacent digits, one slip was defined as they-juncturae, the other as a continuation of the basetendon (Fig. 4). The base tendon was defined by themuscle belly from which it originated . An r-subtypewas a more oblique juncturae stemming from a basetendon (Fig. 5).

In all of the third IMC spaces in which the type 3juncturae were present (13 cases), they ran from theEDC tendon of the ring finger to the tendon of the longfinger. Twelve of these were of the r-subtype and onewas a y-subtype.

In the fourth IMC space the juncturae were assessedwith respect to the presence of an EDC tendon to the

small finger (Table IV). This tendon was present in 19of 40 hands and in 11 of these 19cases, it was associatedwith a type 3 juncturae. In 8 of those 11 cases, thejuncturae ran from the EDC tendon of the small fingerto the tendon of the ring finger. In these cases, the EDCtendon to the ring finger tended to bepresent as a singletendon. In the remaining 3 of 11 cases, the juncturaeran from the EDC tendon of the ring finger to the tendonof the small finger, and in these cases the EDC of thesmall finger was present only as a very narrow band.In one case the EDC tendon to the small finger wasconnected not only to the ring finger by a type 2 JT,but there was also a type 3-r connection from the lateralband of the EDQ tendon.

Of the 11 cases in which a type 3 juncturae waspresent with an EDC tendon to the small finger, 7 ofthe juncturae were of the y-subtype and 4 were of ther-subtype. In contrast , in the absence of an EDC tendonto the small finger (21 cases) 19 were associated with

600 Von Schroeder, Botte, and Gellman

The Journal ofHAND SURGERY

Fig. 5. A·B, Juncturae tendinum type 3, subtype r. A, The more oblique r-shaped juncturae betweenthe EDC to the ring finger and the most radial of three EDQ tendons to the small finger. B,Corresponding drawing of JT type 3r between EDC tendon of the ring (EDe r) finger the and EDQtendon. The most frequent orientation and the incidences of type 3r juncturae in the third and fourthIMC spaces are shown on the right; they were not present in any of the other spaces.

a r-subtype and all were directed from the EDC tendonof the ring finger to the fifth finger where they coalescedwith the most lateral slip of the EDQ tendon or dorsalextensor hood adjacent to the insertion of the EDQtendon. Only one y-subtype was seen in the absence ofthe EDC tendon to the small finger, and the remainingcase was a type 2 juncturae (Table IV). EDQ was pres­ent as a single, double, triple, and quadruple tendon atmidsubstance in 2%, 84%, 7%, and 7% of cases, re­spectively, and tendon multiplicity of the EDQ tendonwas unrelated to the type of JT present in the fourth!Me space.

The orientation of the type 3 juncturae was obliquein 41 of the 45 cases in which they were present. Inthe remaining four cases, they were either transverse(2 cases), or arcuate (2 cases) in orientation.

Absence of juncturae tendinum. Juncturae wereabsent in all cases between the extensor tendons of thethumb and the extensor tendons of the index finger inthe first intermetacarpal space. Juncturae were absentin only 5 (12.5%) of 40 cases in the second interme­tacarpal space (Table I). They were never absent in anyof the other spaces.

Intertendinous fascia. The intertendinous fascia, afilmy transparent layer, was present between all EDCtendons regardless of whether or not a juncturae waspresent. This layer also connected to the EIP, but it didnot connect to the EDQ; it occasionally extended dis-

tally beyond type 1 and type 2 juncturae, but neverbeyond type 3. The fascia maintained tendons in a lat­eral position with respect to each other but did not affectextension of adjacent digits; that is, a tendon could becut distally and pulled through its tendon sheath andparatenon proximally (or vice versa) without affectingthe movement of the adjacent digit. If however a junc­turae was present between the tendons of adjacent dig­its, the cut tendon could be pulled through its tendonsheath but would remain attached to the adjacent tendonby the juncturae through which it would extend theadjacent digit maximally at the metacarpophalangeal(MP) joint.

Discussion

We have classified the juncturae tendinum into threetypes on the basis of their respective unique morpho­logic features. Thin filamentous juncturae were clas­sified as type I and were found primarily between EDCtendons to the index andlong fingers and between thetendons to the long and ring fingers. Type 2 juncturaewere thicker and well defined and were present betweenEDe tendons to the long and ring fingers and betweenthe tendons to the ring and small fingers. Type 3 junc­turae consisted of tendon slips between the extensortendons to the long and ring fingers and between thetendons to the ring and small fingers. The type of junc­turae in the fourth IMC space was related on the pres-

Vol. l5A, No.4July 1990

ence of an EDC tendon to the small finger: in the ab­sence of EDC to the small finger, 90% of cases wereobserved to have a type 3r junctural connection. Thetype 3 juncturae were subdivided into y and r subtypesbecause of their morphologic differences and becauseof the apparent function of the 3r subtype to substitutefor an absent EDC to the small finger . The intertendi­nous fascia was not defined as a junctural connectionsince it attached to the paratenon and tendon sheath andnot to the tendons, and was present between all EDCtendons regardless of whether or not a juncturae ten­dinum was present and also connected to the EIP.

In 1963 Kaneff" recognized two types of juncturae.His "type 1" included the intertendinous fascia and allfascial connections that had small connective filaments;the latter were defined as types I and 2 in this studyon the basis of their distinct features. Kaneff, as wellas Leslie;" recognized that "type 1" juncturae in thethird IMC space were often thicker than in the secondspace, and our data demonstrated that these juncturae(type 2) had significantly different dimensions and amore distal location than the juncturae typical to thefirst IMC space (type 1) . Kaneff's "type 2" were thesame as the type 3 presented here. Leslie" noted thatthe juncturae became progressively thicker from theradial to the ulnar IMC space, and Moore andassociates" recognized that the juncturae in the first!MC space were unique and provided a photographshowing three types of juncturae, but these were notfurther differentiated by the authors.

Accounting for the differences in classification, theincidence of junctural types was very similar betweenthis study and those reported by Kaneff for fetal andadult hands. 5 Our results confirm Kaneff' s observationthat the juncturae in the second IMC space are primarilytransverse, whereas those in the third space are virtuallyalways oblique. This oblique orientation was from theEDC tendon of the ring to the EDC of the long finger,which is opposite to the description by Kaplan." Mest­dagh et a1. 2 and Kaneff noted type 3 juncturae in thesecond IMC space with a frequency of less than 1%;the incidence in our series was zero.

Kaneff recognized that there were variations of thetype 3 juncturae in the fourth IMC space but did notfurther categorize them." He noted that if the EDC ten­don to the small finger was separate, the juncturae usu­ally passed from the small finger to the ring finger, ifhowever the EDC tendon to the small finger was inclose proximity to the tendon of the ring finger, thejuncturae passed from the ring finger to the small fingertendon. Our findings support these observations.Schenck" found type 3 juncturae present in 93.8% of

Anatomy of juncturae tendinum of hand 601

cases in which EDC to the small finger was absent,similar to our result of 95.2%; type 2 juncturae ac­counted for the remainder which was not recognizedby Schenck. The high incidence of type 3 juncturae inthe fourth IMC space, which was also associated witha higher incidence of type 3 ' s in the third space, wouldindicate that the juncturae substitute for, or are a rem­nant of the absent tendon. The radial insertion of thejuncturae, or EDC tendon to the small finger whenpresent, into the aponeurosis of the small finger or radialslip of EDQ, may prevent ulnar deviation of the smallfinger. This radial insertion would however not interferewith harvesting of the ulnar slip of the EDQ tendonsince, even when the EDQ slips coalesce at the dorsalaponeurosis, this occurs distal to the MP joint. IIi thepresence of an EDC tendon to the small finger, thejunctural connection was between the EDC tendons ofthe ring and small fingers and a junctural connectionfrom the EDC tendon of the small finger to the EDQwas see in only one case.

Juncturae tendinum allow the extensors to functionas a unit, to such a degree that independent extensionof the digits is impaired. 11. 13 This is disputed by Ka­plan,"? who stated that independence is lost because ofunified EDC tendons and a common muscle belly.Moore and colleagues" claimed that extracapsular con­straints further limit independent extension of the fin­gers. The ring finger is the least independent and typ­ically has oblique juncturae originating from its EDCtendon that run in a direction opposite to the pull of theEDC tendon and therefore inhibits extension of the ringfinger if the adjacent tendons are flexed. The acuteangles of insertion of the juncturae into the extensortendons of the long and small fingers allow for greatermobility of these digits since the direction of insertionis in the same direction as the pull of the tendon. Theindex finger is the most mobile for two reasons. First,it receives an ElP tendon, which does not have a june­tural connection. Second, the juncturae to the EDCtendon of the index finger may be absent, and whenpresent (type 1), is quite thin and usually transverse oracute to the tendon, thus allowing for greater laxity andmobility yet allowing for the various functions attrib­uted to the juncturae.":"

Junctural or tendinous connections between EDC ten­don to the index finger and extensor pollicis lon­gus,22.24 which can limit mobility, were not seen in ourseries . Juncturae between EDQ tendon and adjacenttendons were frequently noted in this series, as well asothers," s, 21 dispelling the notion that EDQ is not in­volved in such connections. 16 These junctural connec­tions must be considered when EDQ tendon transfer or

602 Von Schroeder, Botte, and Gellman

harvesting is employed. An appreciation of the tendonsand junctural connections can occasionally be gainedby observing and palpating the tendons while activelyor passively flexing individual fingers with all otherfingers maximally extended. However, physical ex­amination is often unreliable because of subcutaneoustissue, and variability and laxity of the tendons andjuncturae.

In conclusion, three distinct types of juncturae ten­dinum are present on the dorsum of the hand. A com­plete knowledge of their anatomy, location, and rela­tionship to the extensor tendons is important in assess­ing injuries and subluxations of the tendons on thedorsum of the hand, in assessing tendons for surgicaltransfer, and when considering the potential reconstruc­tive uses of the juncturae.

We thank William Collins for his assistance in the prep­aration of anatomical specimens.

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