Twcapabcedta

9

CURRENTCONCEPTS

Scapholunate Instability: Current Concepts in

Diagnosis andManagement

Christina E. Kuo, MD, Scott W.Wolfe, MD

Injuries to the scapholunate joint are the most frequent cause of carpal instability and accountfor a considerable degree of wrist dysfunction, lost time from work, and interference withactivities. The complex arrangement and kinematics of the 2 rows of carpal bones allows foran enormous degree of physiologic motion, and a hierarchy of primary and secondaryligaments serves to balance an inherently unstable structure. Although insufficient to causeabnormal carpal posture or collapse on static radiographs, an isolated injury to the scapholu-nate interosseous ligament may be the harbinger of a relentless progression to abnormal jointmechanics, cartilage wear, and degenerative change. Intervention for scapholunate instabilityis aimed at arresting the degenerative process by restoring ligament continuity and normal-izing carpal kinematics. In this review, we discuss the anatomy, kinematics, and biome-chanical properties of the scapholunate articulation and provide a foundation for understand-ing the spectrum of scapholunate ligament instability. We propose an algorithm for treatmentbased on the stage of injury, degree of secondary ligamentous damage, and arthritic change.(J Hand Surg 2008;33A:998–1013. Copyright © 2008 by the American Society for Surgeryof the Hand. All rights reserved.)

Key words Scapholunate advanced collapse, scapholunate dissociation, scapholunate instability.

raaccmialfja

ATpagchic

HE HUMAN CARPUS IS A product of millions ofyears of evolutionary adaptation and isuniquely designed to position the hand any-

here within its nearly hemispherical arc of motion. Toall the wrist a joint is actually a misnomer; it is in factcollection of several joints and, from a kinematic

erspective, arguably one of the most complex sets ofrticulations in the body. Traditionally, the wrist haseen conceptually simplified into a dual linkage systemomposed of proximal and distal carpal rows, whereinach bone in a given row moves in the same directionuring wrist motion. The ligamentous connections be-ween each bone in each row, however, allow for subtlelterations in kinematic behavior depending on the di-

From the Hand and Upper Extremity Service, The Hospital for Special Surgery, New York, NY; and WeillMedical College of Cornell University, New York, NY.

Received for publication March 20, 2008; accepted in revised form April 24, 2008.

No benefits in any form have been received or will be received related directly or indirectly to thesubject of this article.

Corresponding author: Scott W. Wolfe, MD, The Hospital for Special Surgery, Hand and UpperExtremity Service, 523 E. 72nd Street, New York, NY 10021; e-mail: wolfes@hss.edu.

0363-5023/08/33A06-0033$34.00/0

rdoi:10.1016/j.jhsa.2008.04.027

98 � © ASSH � Published by Elsevier, Inc. All rights reserved.

ection and degree of hand position required.1 Thisrrangement is potentially unstable and delicately bal-nced; the motion of each bone is dependent on me-hanical signals from its neighbors and restrained by aomplex set of intrinsic and extrinsic ligaments. Liga-entous or bony injury to the wrist has the potential to

rreversibly disrupt the balance and to set the stage forn inexorable progression to abnormal motion, jointoading, and degenerative change. This review willocus on the critical importance of the scapholunateoint to carpal function and emphasize timely diagnosisnd management of these difficult injuries.

NATOMYhe clustering of the 8 small carpal bones intoroximal and distal carpal rows has been widelyccepted, based on their kinematic behavior duringlobal wrist motion. The 4 bones of the distalarpal row (trapezium, trapezoid, capitate, andamate) are tightly bound to one another via stoutntercarpal ligaments, and motion between theman be considered negligible. Similarly, the nearly

igid ligamentous connection of the trapezium and

SCAPHOLUNATE INSTABILITY 999

capitate to the index and middle metacarpals andlack of motion between these bones allows us toconsider the distal row functionally as part of afixed hand unit that moves in response to themusculotendinous forces of the forearm. Thescaphoid, lunate, and triquetrum can be describedas an intercalated segment because no tendonsinsert upon them and their motion is entirely de-pendent on mechanical signals from their sur-rounding articulations.2,3 The motions of thesebones are checked by an intricate system of intrin-sic, or interosseous, and extrinsic carpal ligaments.

The most frequently injured of these intercarpal re-lationships is the scapholunate joint. When viewedthrough an arthroscope or at arthrotomy (Fig. 1), thenormal scaphoid and lunate appear nearly seamless,bound together by a tough scapholunate interosseousligament (SLIL). The SLIL is C-shaped and attachesexclusively along the dorsal, proximal, and volar mar-gins of the articulating surfaces, leaving a crevice be-tween the bones distally. The 3 subregions of the liga-ment have been demonstrated to have different materialand anatomic properties, and the dorsal component isnow regarded as the thickest, strongest, and most crit-ical of the scapholunate stabilizers.4,5 It is a true liga-ment, with transversely oriented collagen fibers, and isa primary restraint not only to distraction but also totorsional and translational moments as well. The palmarcomponent, though considerably thinner, is also a typ-ical ligament and has important contributions to rota-tional stability of the scapholunate joint. The proximal,or membranous, portion of the SLIL appears histolog-ically as a fibrocartilaginous structure and, in isolation,contributes little to no restraint to abnormal motion of

FIGURE 1: The scapholunate interosseous ligament (blackarrow) creates a seamless transition between the articularsurfaces of the scaphoid and lunate.

the scapholunate joint.

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WRIST MECHANICSAs the anterior cruciate ligament is considered the pri-mary stabilizer of the knee, so too can the SLIL beconsidered the primary stabilizer of the scapholunatejoint, if not the entire carpus. It is surrounded in turn byseveral secondary stabilizers, each insufficient to causeinstability after isolated disruption, but each importantin the maintenance of normal scapholunate kinematics,and vulnerable to attritional wear after complete disrup-tion of the SLIL. On the volar-radial side are the stoutextrinsic ligaments, the radioscaphocapitate, the longand short radiolunate ligaments, and the radioscapholu-nate ligament (of Testut) (Fig. 2). The relative impor-tance of each of these ligaments to scapholunate stabil-ity has not been definitively established, but theradioscapholunate ligament, once thought to be a criti-cal stabilizer of this joint, is now regarded primarily asa neurovascular conduit with little mechanical integrity.The volar-ulnar extrinsic ligaments include the ulnolu-nate and ulnotriquetral ligaments, predominately in-volved in stabilizing the triquetrolunate joint. Distally,the scaphotrapezial ligamentous complex has beenidentified as an important secondary stabilizer of thescaphoid in biomechanical studies.6–8

The dorsal ligamentous structures have been the fo-cus of several recent investigations and are importantsecondary stabilizers of the scapholunate joint. Both thedorsal radiotriquetral (DRC) and dorsal intercarpal

FIGURE 2: The stout extrinsic volar ligaments serve assecondary stabilizers of the scapholunate joint. LRL, longradiolunate ligament; SRL, short radiolunate ligament;RSC, radioscaphocapitate ligament; RSL, radioscapholunateligament; UT, ulnotriquetral ligament; UL, ulnolunateligament. (From Wolfe SW, McLarney E. Carpal fracturesand dislocations. In: Craig E, ed. Clinical orthopedics.Philadelphia: Lippincott, 1999:30. Reprinted with permissionof Lippincott, Williams & Wilkins.)

(DIC) ligaments have attachments to the lunate (Fig. 3).

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1000 SCAPHOLUNATE INSTABILITY

The thickest portion of the DIC inserts on the dorsalgroove of the scaphoid, and a thinner arm of the liga-ment inserts onto the dorsal trapezium and proximaltrapezoid. Cadaver studies have shown that the uniqueV-arrangement of the DIC and DRC ligaments confersimportant secondary stability to the scapholunate com-plex during repetitive wrist motion.9

Thus, normal kinematics of the scapholunate jointare tightly governed by a tough intrinsic ligament thatbinds the scaphoid to the lunate proximally and by anenvelope of surrounding extrinsic ligaments, orientedobliquely to the primary axis of wrist motion (flexion-extension). The scaphoid, lunate, and triquetrum rotatecollectively in flexion or extension depending on thedirection of hand motion. As the hand flexes or turnsinto radial deviation, mechanical forces from the distalcarpal row drive the distal scaphoid into flexion, and thelunate follows passively into flexion through the strongSLIL. As the hand ulnarly deviates, the unique helicoi-dal articular surface of the hamate engages the concor-dant surface of the triquetrum and, via a screw-likeengagement, directs it into a dorsally tilted and palmarlytranslated position (Fig. 4).10 The lunate and scaphoidrotate into extension through a combined effect of theirunyielding interosseous ligaments and the coupled ro-tation of the distal row into a dorsally translated posi-tion. Dorsal translation of the distal row effectivelytensions the radioscaphocapitate and scaphotrapezialligaments and hoists the scaphoid into extension. Dur-ing hand/wrist extension, the intercalated segment ro-

FIGURE 3: The dorsal extrinsic ligaments also serve asimportant secondary stabilizers of the scapholunate joint. DIC,dorsal intercarpal ligament; RT, dorsal radiotriquetral ligament.(From Wolfe SW, McLarney E. Carpal fractures and dislocations.In: Craig E, ed. Clinical orthopedics. Philadelphia: Lippincott,Williams & Wilkins, 1999:30. Reprinted with permission ofLippincott, Williams & Wilkins.)

tates as a unit, as tension in the extrinsic ligaments locks

JHS �Vol A, July

the scaphoid, lunate, and triquetrum to the capitate inconjoined extension.1 This phenomenon was explainedby MacConnail, who cited the critical role of the DICligament in producing a unified motion of the bones ofthe proximal and distal carpal rows by a “screw-clamp”mechanism that captures the capitate between thescaphoid and triquetrum as the ligament tightens.11

Whereas the scaphoid, lunate, and triquetrum allrotate in the same primary direction during hand posi-tioning, it must be recognized that there is considerablemultiplanar motion that occurs between each bone atthe interosseous joints, and this is attributable to theunique design and character of the interosseous liga-ments. During a 120° arc of flexion and extension, forexample, scaphoid flexion–extension exceeds lunateflexion-extension by approximately 35°. Scaphoid pro-nation is approximately 3 times that of lunate pronationduring wrist flexion, and lunate ulnar deviation exceedsscaphoid deviation considerably.1 Interestingly, duringwrist and hand extension, both the primary and out-of-plane rotations of the scaphoid and lunate are moretightly coupled, and this may be due in part to theinfluence of the dorsal extrinsic ligaments mentionedabove.

The literature is rife with controversy concerning therelative contribution of different carpal bones to globalwrist motion and whether or not the scaphoid can beconsidered kinematically part of the proximal carpalrow or rather an independent coupling link between theproximal and distal rows.12–14 Recent studies have fo-cused attention on “coupled motion” of the wrist; thatis, combination motions of flexion–extension and ra-dioulnar deviation, such as the dart-thrower’s motion ofradial-extension to ulnar-flexion.15–19 This oblique pathof motion has been postulated to be uniquely human19

and is widely used in occupational activities such ashammering or pouring from a pitcher,20 as well as insports and recreational activities.17 Kinematic studiesduring this functional arc of motion have demonstrateda remarkable degree of consistency between subjectsand between investigators and show that the scaphoidand lunate demonstrate minimal motion relative to eachother or to the radius during the dart thrower’s mo-tion.15,16,18 The implications of these findings are broadand include the potential to develop rehabilitation pro-grams after wrist injury or repair that incorporate thedart thrower’s motion and reduce strains on thescapholunate interosseous ligament during wrist mo-tion.

The redundancy of primary and secondary ligamentstabilizers explains why division or injury to a single

supporting ligament is generally insufficient to cause

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SCAPHOLUNATE INSTABILITY 1001

abnormalities in scaphoid or lunate posture on staticradiographs. Even a complete division of the scapholu-nate ligament may cause no static increase in scapholu-nate gap or change in lateral scapholunate angle. Dra-matic changes in force transmission and kinematics ofthe 2 bones during wrist motion do occur after SLILdivision, however, and likely explain the symptoms ofcatching, popping, and pain seen in dynamic scaphoidinstability.5,8,21 Additional division of 1 or more of thesecondary restraining ligaments is necessary beforestatic changes in scaphoid and lunate posture are seen,and these changes have been documented after transec-tion of the volar extrinsic ligaments, the DIC ligament,and the scaphotrapezial ligaments.6,7,8,9,22,23 Attritionalwear of the secondary restraints is thought to be theetiology of delayed development of dorsal intercalatedsegment instability (DISI) after isolated disruption ofthe SLIL. Recently, it has been postulated that differ-ences in bony anatomy of the radioscaphoid articulationmay affect the scaphoid stability after soft-tissue injuryand help explain why some patients go on to progres-sive instability and others do not.24

SCAPHOLUNATE INSTABILITY

Definition

Classically, the diagnosis of scapholunate instabilitywas predicated on abnormal scaphoid or lunate align-ment as seen on static radiographs (Fig. 5).23 This

FIGURE 4: The unique helicoidal surface of the triquetrohamrotation of the triquetrum into palmar displacement and extenHand 2001;1:16. Reprinted with permission of Elsevier.)

definition, however, was not inclusive enough to ex-

JHS �Vol A, July

plain the often disabling symptoms of pain with me-chanical loading or sudden shifts or “clunks” that werenoted among some injured patients with normal radio-

oint converts ulnar deviation of the hamate into a conjoined. (From Wolfe SW. Scapholunate instability. J Am Soc Surg

FIGURE 5: Previous definitions of scapholunate instability reliedon demonstration of grossly abnormal posture of the carpal boneson static radiographs. Note increased scapholunate interval afterattempted operative stabilization.

ate jsion

graphs. The concept of dynamic scapholunate instabil-

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1002 SCAPHOLUNATE INSTABILITY

ity was proposed to describe abnormal carpal position-ing that required special stress radiographs to bemanifested. It is now recognized that scapholunate in-stability is a spectrum of injury and not an all-or-nonecondition (Table 1).7,25–27 The current definition ofscapholunate instability has been expanded to includethose wrists that exhibit symptomatic dysfunction, areunable to bear loads, and do not demonstrate normalkinematics throughout the complete arc of motion.28

Clinical signs

In the emergency department, a high index of suspicionis necessary to correctly diagnose an acute isolatedscapholunate ligament disruption. Tenderness is usuallypoorly localized about the periscaphoid area, and painwill generally preclude most provocative wrist ligamenttesting. Diffuse swelling may obscure the characteristicwrist effusion, which is indicative of a serious intra-articular injury. Arthrocentesis is helpful when the his-tory is suggestive and radiographs are normal. Vascularor neural compromise is rare, except in extreme liga-ment injuries such as lunate or perilunate disruption.

Patients with subacute injuries (1–6 weeks) oftenpresent with a history of painful popping or clickingwith activities, decreased grip strength, and well-local-ized tenderness about the scaphoid and dorsal scapholu-nate interval. Watson described a provocative maneu-ver known as the scaphoid shift test that can be helpful

TABLE 1. Stages of Scapholunate Instability51

I. Occult II. Dynamic

Injuredligaments

Partial SLIL Incompetent orcomplete SLIL;partial volarextrinsics

X-rays Normal Usually normal

Stress x-rays Normal; abnormalfluoroscopy

Abnormal

Treatment Pinning orcapsulodesis

SLIL repair withcapsulodesis

CL, capitolunate; DJD, degenerative joint disease; RL, radiolunate; R

in the detection of subtle degrees of scaphoid instabil-

JHS �Vol A, July

ity.29 Pressure is applied by the examiner’s thumb to thescaphoid tubercle as the patient’s wrist is brought froma position of ulnar deviation and slight extension toradial deviation and slight flexion (Fig. 6). The scaphoidwill normally flex and pronate during this maneuver,but in scaphoid instability, the maneuver will be pain-ful, and thumb pressure may force the proximal scaph-oid from the scaphoid fossa and onto the dorsal articularlip of the radius. Relief of thumb pressure will allow thescaphoid to spontaneously reduce, often with an audibleor palpable clunk. The test may be falsely positive in upto one third of individuals and is thought to be due toligamentous hyperlaxity that permits capitolunate trans-lation with similar findings.30,31 Patients with an appro-priate history and a positive scaphoid shift test shouldbe considered as having a suspected scapholunate lig-ament disruption and be confirmed with appropriateimaging or arthroscopic evaluation.

Radiographs

High-quality posteroanterior (PA), lateral, navicular,and anteroposterior (AP) grip radiographs should beobtained, and contralateral wrist radiographs are helpfulfor comparison.3 Lateral radiographs should be care-fully evaluated for adequate technique and should berepeated if the radius, capitate, and third metacarpal arenot roughly collinear in the sagittal plane. Yang et al.

Stage

capholunatessociation IV. DISI V. SLAC

lete SLIL,lar or dorsalrinsics

Complete SLILvolar extrinsics;secondary changesin RL, ST, DICligaments

As in stage IV

p �3 mm;angle �60°

SL angle �70°SL gap �3 mmRL �15°CL �15°

I. Styloid DJDII. RS DJDIII. CL DJDIV. Pancarpal DJD

ly abnormal Unnecessary Unnecessary

repair withsulodesistriligamentonstruction

Reducible:triligamentreconstruction

Fixed: intercarpalfusion

Intercarpal fusionor proximal rowcarpectomy

ioscaphoid; SL, scapholunate; ST, scaphotrapezoid.

III. SDi

Compvoext

SL gaRS

Gross

SLILcapvs.rec

S, rad

recommend that the scaphoid tubercle and pisiform be

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° sca

SCAPHOLUNATE INSTABILITY 1003

maximally superimposed to ensure a true lateral radio-graph of the wrist.32

Measurement of intercarpal angles on staticfilms is difficult and subject to a great degree ofvariability between examiners. To precisely andreproducibly determine the position of a bisectingline in each irregularly shaped small carpal bone isnearly impossible. Approximation of intercarpalangles using tangents to the external contour ofeach bone is an easier and perhaps more reliable

FIGURE 6: A During the performance of the scaphoid shift tewhile the subject’s hand is moved from ulnar deviation and slview of a positive scaphoid shift test, demonstrating subluxatioof the distal radius.

FIGURE 7: Reproducible measurement of intercarpal angles isthe lunate axis is perpendicular to the lunate tangent line. B (aradiograph shows a 20° DISI posture of the lunate and a (d) 90

technique. The examiner draws a tangent to the

JHS �Vol A, July

palmar cortex of the scaphoid proximal and distalpoles and a second tangent to the distal articularsurface of the lunate palmar and dorsal lips(Fig. 7). A perpendicular is drawn from the lunatetangent to determine lunate posture in the sagittalplane. Deviation of this line from the longitudinalaxis of the radius (the radiolunate angle) by morethan 15° in the dorsal direction on a true lateralfilm is indicative of DISI. Though unusual in in-juries of the scapholunate ligament, a radiolunate

e examiner’s thumb applies pressure to the scaphoid tuberclextension to radial deviation and slight flexion. B Fluoroscopicthe proximal scaphoid (white arrow) from the scaphoid fossa

itated by drawing tangents to the carpal contours. A Note thatnate tangent, (b) lunate axis, (c) scaphoid tangent. This lateralpholunate angle.51,96

st, thight en of

facil) Lu

angle of more than 15° in the volar direction is

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1004 SCAPHOLUNATE INSTABILITY

indicative of volar intercalated segment instability(VISI). Scapholunate angle is measured betweenthe scaphoid tangent and the perpendicular to thelunate tangent and normally measures 46° (rangeof 30° to 60°). A unilateral scapholunate angle ofgreater than 70° is considered highly suggestive ofincreased flexion, or rotatory subluxation of thescaphoid.26 Capitate posture can be approximatedby a tangent to the dorsal cortex of the thirdmetacarpal, and a flexed capitolunate joint in ex-cess of 15° signifies collapse of the midcarpal jointand is confirmatory of a DISI deformity.

Other radiographic signs of advanced stages ofscapholunate instability include scapholunate diastasis,a positive ring sign, and foreshortening of the scaphoidon the PA film. A PA static film or AP grip stress filmdemonstrating unilateral widening of the scapholunatejoint in excess of the width of other intercarpal joints(2–3 mm) is considered suspicious, but not diagnosticof scapholunate dissociation.33 There is considerablenormal variability in scapholunate joint configuration,and differences in radiographic technique and wristposture account for a high degree of variance in thesemeasurements.34 The scaphoid ring sign is visible on a

FIGURE 8: Radiographic evaluation of scapholunate instabilitywaist in a PA radiograph when the scaphoid is abnormally flexstress view shows abnormal scaphoid subluxation dorsally withfrom the SLIL dorsal insertion site on the scaphoid can be idwidening of the scapholunate interval.

PA film when the distal scaphoid tubercle is superim-

JHS �Vol A, July

posed on the scaphoid waist (Fig. 8). When the scaph-oid is flexed more than 70°, it appears foreshortened onthe PA film when compared with films of the uninjuredwrist.

Stress radiographs

Stress radiographs are obtained when carpal instabilityis suspected clinically but static radiographs are normal.The most frequently used stress radiograph is the APgrip film, which profiles the scapholunate joint anddemonstrates pathologic scapholunate widening underaxial loaded conditions. Care should be taken to posi-tion the wrist in neutral flexion–extension. Lateral fullflexion and full extension radiographs can be examinedfor subtle differences in intercarpal motion and are mostuseful when compared with similar films from the un-injured wrist. A full-flexion lateral will on occasiondemonstrate frank subluxation of the scaphoid proximalpole onto the dorsal rim of the radius (Fig. 8B). Fullulnar and full radial deviation PA radiographs completethe sequence and may demonstrate abnormal wideningof the scapholunate joint (Fig. 8C). Lastly, the so-called“carpal stress test,” a PA film with the thumb and indexfingers under traction, can also aid in diagnosis espe-

The scaphoid tubercle becomes superimposed on the scaphoidreating the so-called “ring sign” (white arrow). B A full flexionimal conjoined flexion of the lunate. A fleck of avulsed bone

ed (white arrow). C An ulnar deviation view shows abnormal

. Aed, c

minentifi

cially if it demonstrates a stepoff at the scapholunate

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Dep

SCAPHOLUNATE INSTABILITY 1005

joint.35 Normal static and stress films in the acute situ-ation do not always rule out serious injury, and patientswith suspected acute SLIL injury should be placed in athumb spica cast and referred for early diagnostic eval-uation.

Ancillary imaging studies

Ancillary imaging studies may be helpful to con-firm a suspected diagnosis of scapholunate liga-ment injury but should not be used in isolationbecause of a relatively high rate of falsely positiveresults.30,36 Several authors have demonstrated ahigh rate of bilaterally positive wrist arthrogramsin patients with unilateral symptoms and/or unilat-eral injury.37,38 Arthrography is most sensitive ifthe radiocarpal, midcarpal, and radioulnar com-partments are injected separately (3-compartmentarthrography) but has been all but supplanted bymagnetic resonance imaging (MRI) or computedtomography (CT) arthrography. CT arthrographyhas been reported as having a 95% sensitivity and86% specificity for detecting SLIL tears whencompared with arthroscopy.39 MRI examination,with or without gadolinium injection, has beenreported to have an average of 71% sensitivity(38% to 88%), 88% specificity (46% to 100%), and84% accuracy (53% to 100%) in detectingscapholunate ligament tears, although high vari-ability in normal morphology and poor interob-server reliability have also been reported.40 – 46 Re-liable and accurate magnetic resonance–aideddiagnosis at this time may depend on multiple

FIGURE 9: High-resolution coronal gradient echo MR imagi(white arrowhead). B Midportion of scapholunate tear (white a(MRI images courtesy of the Hospital for Special Surgery MRI

factors such as the imaging protocol, the radiolo-

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gist’s experience, and whether the tear is completeor incomplete. At our institution, we rely on high-resolution, noncontrast MRI of the wrist read bymusculoskeletal magnetic resonance radiologistswith a reported 88% sensitivity and 100% speci-ficity when compared with arthroscopy (Fig. 9).47

It should be noted that both arthrography and MRIyield only anatomic evaluations of the wrist ligamentsand give limited information concerning their func-tional status. A perforation or partial tear in thescapholunate ligament, although yielding leakage ofdye into a neighboring compartment, is not synony-mous with complete scapholunate ligament disruption.Cineradiography or simple fluoroscopy can be a helpfulancillary study to demonstrate abnormal kinematics ofthe scaphoid or lunate during wrist motion, especiallywith ulnar to radial deviation and with wrist flexion–extension.48

Wrist arthroscopy is widely considered the goldstandard for both anatomic and functional evalua-tion of the interosseous and extrinsic ligaments ofthe wrist and can be combined with fluoroscopicevaluation under anesthesia for valuable kinematicinformation.31,49 The ability to pass the arthro-scope from the radiocarpal joint into the midcarpaljoint through the scapholunate interval (drive-through sign) indicates complete incompetence ofthis ligament and laxity or disruption of its sec-ondary stabilizers.50 It cannot be overemphasized,however, that ancillary imaging studies or arthro-scopy should be used only to confirm a clinicaldiagnosis of scapholunate injury, and treatmentmust be predicated by the patient’s symptoms and

f a scapholunate tear. A Dorsal portion of scapholunate tearead). C Volar portion of scapholunate tear (white arrowhead).

artment.)

ng orrowh

clinical examination.

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1006 SCAPHOLUNATE INSTABILITY

CLASSIFICATION (TABLE 1)51

The mildest form of scapholunate instability, or occultinstability, is usually initiated by a fall on the out-stretched hand that may only cause a tear or attenuationof a portion of the scapholunate interosseous ligament,with or without a disruption of the ligament of Testut.27

Patients with this injury may not seek treatment ini-tially, have no abnormalities of scaphoid or lunate pos-ture on static or stress radiographs, and have wrist painor dysfunction with mechanical loading. Fluoroscopicexamination of occult injuries may be normal or abnor-mal. Watson has termed this pre–dynamic instability,but this term implies progression toward static instabil-ity, and this may not be a certainty for all patients in thiscategory.26 Higher-energy trauma may cause a subtotalor complete tear of the scapholunate ligament, includ-ing its critical dorsal portion, with a partial extrinsicligament injury. Untreated, these more involved injurieswill predictably lead to abnormal kinematics and loadtransfer, with pain during activities characterized asdynamic scaphoid instability.5,21 This is the first stageof Mayfield’s classic description of progressive perilu-nate instability and may present even weeks or monthsafter injury with relatively normal appearing static ra-diographs.52 Abnormal stress radiographs or motionstudies are necessary in this stage to confirm the diag-nosis of dynamic scaphoid instability.

A complete tear of the scapholunate interosseousligament with an additional tear or attrition of one ormore secondary ligament restraints will allow thescaphoid to rotate into increased flexion, with concom-itant increase in the scapholunate interval.6,22 In thisstage, known as scapholunate dissociation, rotation ofthe lunate becomes independent of the scaphoid, andthe lunate tends to assume an abnormally extendedposture during motion or mechanical load, under thedorsally directed compressive forces of the capitate.From this point on, patients will present with abnormalstatic radiographs. With the passage of time, a DISIdeformity develops, characterized by flexion of thescaphoid, extension of the lunate and triquetrum, anddorsal and proximal translation of the capitate and distalcarpal row.3 In time, the postural changes of the scaph-oid, capitate, and lunate become irreversible because ofsecondary changes in most or all of the supportingligamentous structures and are uncorrectable with softtissue reconstructive procedures alone. The resultingaltered kinematics lead to abnormal articular loadingand eventually to predictable progressive degenerativechanges known as scapholunate advanced collapse

(SLAC). Arthritis first develops along the scaphoid

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facet of the distal radius, next within the radial midcar-pal joint, finally involving the entire carpus.53

Principles of management

Garcia-Elias et al. developed a set of 5 questions thatprovide a useful framework for development of a treat-ment algorithm for the various stages of scapholunateinstability.7

1. Is the dorsal scapholunate ligament intact?2. Does the dorsal scapholunate ligament have suf-

ficient tissue to be repaired?3. Is the scaphoid posture normal?4. Is any carpal malalignment reducible?5. Is the cartilage on radiocarpal and midcarpal sur-

faces normal?

Based on the responses to these questions, scapholu-nate injuries can be grouped into 6 stages, with corre-sponding treatment based on each stage. Although ourclassification differs from that of Garcia-Elias et al. inthe number of categories, they are conceptually similar.The main distinction is that our scheme places all DISIdeformities under a single heading, whereas the 6-stagescheme separates the reducible and fixed DISI deformi-ties into 2 groups. Our recommendations for treatmentare also based on the principles laid out by the 5questions listed above with the addition of 1 key con-cept: that the abnormal scapholunate relationship in-volves 2 distinct planes of deformity.

Scapholunate dissociation describes a condition withaltered kinematics in both the coronal plane and thesagittal plane.54 Dynamic or static widening of thescapholunate interval indicates coronal plane instabilityand is best addressed by repair or reconstruction of theinterosseous ligament. Rotary subluxation of the scaph-oid, on the other hand, represents sagittal plane insta-bility that results from additional injury or attenuationof the secondary ligamentous stabilizers and is bestaddressed with the addition of a dorsal capsulodesis. Itis important to understand that both components mustbe addressed in order to achieve successful outcomes;correcting either in isolation will predictably lead tofailure.33,55

Treatment by stage

Occult instability: Diagnosed acutely, occult instabil-ity may benefit from conservative treatment suchas casting, splinting, nonsteroidal anti-inflamma-tory drugs, and therapy. Arthroscopic debridementhas also been reported with success. After arthro-scopic debridement of partial scapholunate tears,Weiss et al. reported satisfactory improvement in

11 of 13 patients and Ruch and Poehling reported

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SCAPHOLUNATE INSTABILITY 1007

satisfactory improvement in 7 of 7 patients with noprogression to instability in the short term.56,57

This procedure is best for those who have partialtears without clinical or intraoperative findings ofinstability. In 1 series, debridement alone for com-plete tears fared less well, with only 10 of 15patients reporting satisfactory improvement.56 Pa-tients in this category may also benefit from tem-porary scapholunate pinning; clinical experienceof the senior author reveals satisfactory outcomesat 2 years after surgery.

Dynamic instability and scapholunate dissociation with a repairableSLIL: Those with dynamic instability have a completescapholunate tear and demonstrate instability in 1 orboth planes under stress examination. Again, each com-ponent of instability should be addressed separately,including a direct scapholunate repair for the coronalplane and a dorsal capsulodesis for instability in thesagittal plane.27,51,58,59 Patients with scapholunate dis-sociation present with static postural changes of thescaphoid and/or lunate with additional injuries to thesecondary ligamentous stabilizers that will influence thechoice of treatment. Acute injuries presenting with re-ducible scapholunate diastasis and rotatory subluxationof the scaphoid have sustained injuries to the volar ordorsal extrinsic ligaments, scaphotrapezial ligaments, ora combination injury and are best treated by open re-duction, scapholunate repair, and a dorsal capsulodesis.Repairs are temporarily supplemented by 2 divergentscapholunate K-wires across the scapholunate joint anda single scaphocapitate wire to support the capsulode-sis, all inserted percutaneously just distal to the radialstyloid.60

Although arguably more effective when performedacutely, scapholunate ligament repair should not neces-sarily be abandoned in patients with divergentscapholunate joints or in those with injuries more than4 to 6 weeks old. Requirements for open reduction andligament repair include (1) satisfactory remaining SLILligament tissue, (2) an easily reducible scaphoid, and(3) absence of degenerative changes. Although delayedrepair is considered somewhat controversial, Laverniaet al. demonstrated satisfactory results in patients up to3 years after injury using the combination of transosse-ous ligament repair and dorsal capsulodesis.61

There are 2 techniques for dorsal capsulodesis: thetraditional Blatt technique, which tethers the scaphoidto the distal radius and predictably leads to limitationsin wrist flexion; and a modified DIC ligament tech-nique, which eliminates the tether to the radius andinstead tethers the scaphoid to the triquetrum.27,58,6–64

As an isolated procedure, the Blatt capsulodesis can

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lead to satisfaction rates as high as 15 of 17 patients,with the knowledge that most patients are limited some-what in flexion and are not completely pain-free (Fig.10).33,55,65 With time, however, the scapholunate gapand rotatory subluxation reliably recurs with a percent-age of patients going on to radiographic but mostlyasymptomatic evidence of degenerative changes. A re-cent follow-up of the isolated DIC capsulodesis at anaverage of 7 years after procedure reported findingssimilar to the Blatt technique.64 Patients demonstratedsome decreases in wrist flexion when compared with2-year follow-up, though on the same magnitude as theBlatt technique, with outcome measures revealing a58% satisfaction rate. The authors also reported failureto maintain correction of scapholunate angle and gap at7 years after procedure with half of the patients dem-onstrating radiographic evidence of progressive degen-erative arthritis, although none had needed further treat-ment. Level of demand may also have an impact onoutcomes after repair and capsulodesis. At an averagefollow-up of 5 years, 1 study found that those withstrenuous jobs had significantly increased pain andpoorer subjective outcome scores than did those withnonstrenous jobs (p � .05).66

FIGURE 10: The Blatt capsulodesis procedure creates apassive dorsal restraint to abnormal flexion of the scaphoid.(From Blatt G. Capsulodesis in reconstructive hand surgery.Dorsal capsulodesis for the unstable scaphoid and volarcapsulodesis following excision of the distal ulna. Hand Clin1987;3:9. Reprinted with permission of Elsevier.)

The author’s preferred option for a patient who pre-

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sents with instability and a stout, repairable ligament isscapholunate repair and combined Blatt-type dorsalcapsulodesis. The vector of the Blatt procedure is bestaligned to counteract scaphoid malrotation in the sagit-tal plane. Although not a perfect solution, selected pa-tients in the subacute category treated in this fashionmay have some degree of recurrent widening of thescapholunate interval, but symptoms remain tolerableand activity level high. For those who place a highdemand on their wrists on a daily basis, the proceduremay still be viewed as the best option to restore morenormal anatomy and delay the progression to debilitat-ing wrist arthritis. However, not entirely happy with therigidity of smooth pin fixation of scapholunate repair insubacute and chronic cases of scapholunate diastasis,the senior author has moved to augmenting the repairand capsulodesis with a temporary scapholunate screwin select populations such as high-demand athletes (Fig.11). In these patients, a scaphocapitate pin is still usedto protect the capsulodesis, and a temporary scapholu-nate screw is added to protect the scapholunate repair.This is not a new concept, although previous authorshave recommended that the screw be left in place per-

FIGURE 11: A 32-year-old male athlete treated with scapholunradiograph 3 months after surgery demonstrating reduction oflateral radiographs 6 months after surgery demonstrating intervreduction.

manently.67 Concerns for screw loosening and/or

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breakage underlie our preference for temporary screwfixation. The screw provides more rigid fixation than doK-wires when the soft tissue repairs are healing, as wellas the possibility of earlier motion. We begin dart-thrower’s motion of the midcarpal joint at 2 monthsafter surgery, after removal of the scaphocapitate pin,and remove the scapholunate screw at 4 monthspostoperatively.

An alternative to soft tissue reconstruction for thosewith dynamic instability with or without a repairablescapholunate ligament is the bone–ligament–bone re-construction.68–71 Several bone–ligament–bone com-plexes have been designed and tested biomechanicallyand clinically for use in reconstruction of scapholunatedissociation. Weiss reported the successful use of anautogenous bone–retinaculum–bone preparation har-vested from the third dorsal compartment in 14 patientswith dynamic instability and less predictable results in 5patients with static scapholunate dissociation.68 Biome-chanical studies of tarsal bone–ligament–bone autoge-nous grafts demonstrate more similar biomechanicalprofiles to the SLIL, such as the medial cuneonavicularligament.69,70 Similar testing has been done on hand-

epair, dorsal capsulodesis, and temporary screw fixation. A APholunate interval with temporary screw fixation. B, C AP andmoval of scapholunate screw and maintenance of scapholunate

ate rscapal re

based bone–ligament–bone such as the trapezoid–sec-

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ond metacarpal or capitate–hamate articulations.71–74

Clinical results with any of these bone–ligament–bonereconstructions are limited. However, as an isolatedprocedure, they should be restricted to those with dy-namic instability, because isolated reconstruction of thedorsal scapholunate ligament cannot be expected toeffectively address the scaphoid malrotation in the sag-ittal plane.

Scapholunate dissociation without a repairable SLIL: In those sub-acute or chronically injured patients without a repair-able ligament but with a reducible scaphoid and nodegenerative changes, many procedures designed toreestablish the critical scapholunate linkage have beenreported. Several reconstructive procedures includingligament reconstruction with tendon grafts, creation of apseudarthrosis using a Herbert screw, and various in-tercarpal fusions have all been attempted with variableresults. Hom and Ruby reported success in only 1 of 7patients with attempted scapholunate fusion, and thisprocedure has been abandoned.75 Rosenwasser et al.presented early and encouraging results of the conceptof a scapholunate pseudarthrosis supplemented by apermanent screw, called the RASL (reduction and as-sociation of the scaphoid and lunate) procedure.76 Re-cently, other authors have described an arthroscopicallyassisted RASL where preparation of the bony surfaces

FIGURE 12: The triligament tenodesis tendon graft reconstrucvolar scaphoid tuberosity to the dorsal ridge to reconstruct thlunate, passed through a slit in the dorsal radiotriquetral ligligament. (From Garcia-Elias M, Lluch AL, Stanley JK. Threeindications and surgical technique. J Hand Surg 2006;31A:125–

and reduction of the scapholunate articulation are per-

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formed under direct arthroscopic visualization prior toplacing the Herbert screw; clinical results of this tech-nique are not yet available.77 Conceptually, a perma-nent rigid construct linking the scaphoid and lu-nate cannot reliably reproduce the complexities ofnormal scapholunate kinematics, as there is not afixed axis of rotation for all planes of scapholunatemotion. Innovative devices have been introducedto allow scapholunate rotation around a permanentscrew implant, but clinical results are not yet avail-able. Similarly, any tendon graft used to bridge thetwo dissociated carpal bones must have sufficienttensile strength to oppose the tremendous axialforces that drive the scaphoid and lunate apart, aswell as the elasticity to permit a high degree ofmultiplanar rotation between the 2 bones.1 Theinability of a tendon graft to simulate the mechan-ical profile of a ligament has limited the effective-ness of these procedures to some extent.23

Brunelli and Brunelli proposed a flexor carpi radialistendon graft reconstruction, intended to simultaneouslyaddress the scaphotrapezial and scapholunate ligamentdeficiencies, which appeared promising.78 This tech-nique was subsequently modified to eliminate the tetherto the radius and reconstruct not only the scaphotrape-zial and scapholunate ligaments but the dorsal radiotri-

A A strip of flexor carpi radialis tendon is passed from theaphotrapezial ligament. B The tendon is fixed dorsally to thent, and sutured back on itself to re-create the scapholunatement tenodesis for the treatment of scapholunate dissociation:Reprinted with permission of Elsevier.)

tion.e scame-liga

quetral ligament as well, thereby addressing both the

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coronal and sagittal plane abnormalities and intrinsicand extrinsic ligament pathology (Fig. 12).7,79–81 Four-to 5-year follow-up of this triligament tenodesis re-vealed on average a 30% loss of flexion extension arc,maintenance of 65% to 80% of contralateral gripstrength, and subjective pain relief in a majority ofpatients with 1 series reporting a satisfaction rate of79%.7,72 In another series, 26 of 38 patients maintainedcorrection of the rotational deformity at latest follow-up. Similar to other soft tissue procedures, some pa-tients (24%) developed radiographic evidence of degen-erative arthritis, although no patient had gone on torequire further management.

DORSAL INTERCALATED SEGMENTINSTABILITYMassive ligament disruption at the time of injury, asmay occur in perilunate or lunate dislocations, or grad-ual attrition of the secondary extrinsic stabilizers leadsto abnormal extension of the lunate and carpal collapseafter scapholunate dissociation. The combined effectsof an extension moment transmitted through the intacttriquetrolunate ligament and coupled dorsal translationof the capitate force the lunate into extension and ex-acerbate the abnormal posture of the scapholunate joint.Capsular contracture may serve to fix the deformity anddictate the limited treatment options.

Nonoperative treatment is likely to result in a slow,relentless progression to degenerative arthritis, begin-ning first at the radial styloid and progressing proxi-mally to involve the entire scaphoid facet and finally themidcarpal joint.53 Depending on the chronicity of theinjury and the relative activity level of the patient, theoption of activity modification and splint wear may bereasonable and may forestall a motion-limiting salvageprocedure. The goals of surgery for this stage are torestore alignment, improve load distribution, and slowor arrest the onset of degenerative changes.

If the scaphoid and lunate are reducible and nodegenerative changes have occurred at the radiocarpaljoint, triligament tenodesis as described in the previoussection may be attempted. Alternatively, these patientsmay benefit from stabilization of the malrotated scaph-oid using intercarpal arthrodesis. For the chronic, irre-ducible DISI deformity without marked arthritis, thebest option is intercarpal arthrodesis. Scaphotrapezio-trapezoidal joint arthrodesis has gained popularity sincefirst reported in 1967 by Peterson and Lipscomb.82

Satisfactory results for both dynamic and static insta-bilities have been reported by several authors, but con-cern lingers over abnormal load transmission to the

distal radius and a high rate of complications in some

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series.83–86 Scaphocapitate arthrodesis has also beenadvocated to stabilize the scaphoid, but by spanning themidcarpal joint, it leads to an obligate 50% reduction inwrist motion.87 Alternatively, arthrodesis of the scaph-oid, capitate, and lunate is an option that enjoys a highrate of fusion and relatively low complication rate.88

Kinetic studies have demonstrated a more normal dis-tribution of load to the scaphoid and lunate facets of theradius after scaphocapitolunate arthrodesis than withother partial arthrodesis procedures, although motion isalso predictably reduced by 50%.83 To prevent degen-erative changes between the less mobile scaphoid andthe remaining styloid after any of the intercarpal fu-sions, most authors advocate avoidance of over-reduction of the scaphoid and inclusion of a limitedradial styloidectomy. The indications for these proce-dures are limited, as radiocarpal degenerative changefrequently accompanies symptomatic DISI deformity.Very few clinical studies are available to support wide-spread use of scaphoid-retaining intercarpal fusion pro-cedures.

SCAPHOLUNATE ADVANCED COLLAPSE WRISTIn the earliest stage of the SLAC wrist deformity, de-generative changes are limited to an area of abnormalcontact between the abnormally rotated scaphoid andthe radial styloid. Radial styloidectomy will not alter theprogression of the degenerative process at this stage,and any degree of pain relief is generally regarded astemporary. The scaphoid remains rotated into palmarflexion and its contact area with the radius remainsreduced and shifted dorsally. Persistent abnormal load

FIGURE 13: Four-corner arthrodesis is designed to restorestability while maintaining motion of the radiocarpal joint.

transfer and shear across the cartilaginous surfaces

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leads to degeneration of the proximal scaphoid facet instage II. With time, the dorsally translated capitatemigrates proximally into the widened scapholunate in-terval, and degenerative changes at this joint heraldstage III. The relative congruency of the radiolunatejoint in all positions of lunate rotation preserves thisarticulation until late in the disease process. If the extentof degenerative disease is not clearly delineated onroutine radiographs, CT is an excellent means to indi-vidually assess changes at the midcarpal and radiocar-pal articulations.

A fixed scaphoid or degeneration in the proximalscaphoid facet is best treated by excision of the scaph-oid, with additional surgery that is dictated by the statusof the capitolunate joint. Extensive degenerativechanges at the midcarpal joint, with preservation of theradiolunate joint, is best treated with capitate-lunate-hamate-triquetral (4-corner) arthrodesis (Fig. 13). If thisjoint is relatively well preserved, proximal row carpec-tomy is an option and has compared favorably with4-corner fusion in terms of range of motion and gripstrength (Fig. 14).63,89–93 Neither procedure is withoutthe potential for complication, including nonunion, pro-gression of arthritis, and persistent pain, and patientsshould be advised that these procedures are collectivelyreferred to as “salvage” procedures for a wrist thatotherwise is a candidate for complete wrist fusion. Wereserve the proximal row carpectomy for older, lower-demand patients with stage I to II SLAC disease andintact volar extrinsic ligaments. With the promisingfusion rate of headless screws, some authors are return-ing to the idea of a 2-bone fusion between the capitateand lunate combined with excision of both the scaphoidand triquetrum. Although outcomes of these procedures

FIGURE 14: A successful proximal row carpectomy ispredicated on preservation of the volar extrinsic ligaments(represented in black) to prevent ulnar translation of theremaining distal carpal row.

are as yet limited, it may be a promising choice for

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younger, higher-demand patients who require a midcar-pal arthrodesis but could benefit from increased rangeof motion.94,95 Newer designs of total wrist arthro-plasty, though a potentially attractive option for patientswith severely degenerative wrists, lack sufficient fol-low-up data to advocate their use at present in thisgroup.

The scapholunate interosseous ligament is the criti-cal stabilizer of a delicately balanced system of joints.Carpal alignment may be maintained after isolated dis-ruption of this ligament because of a complex array ofsecondary stabilizers. Disruption of this important lig-ament may be the first stage of a slow and steadyprogression toward wrist dysfunction and degenerativedisease. It is therefore important to understandscapholunate instability as a spectrum of injury. Ourclassification scheme divides this disorder into 5 stagesbased on an appreciation of the key concepts: staticversus dynamic instability, repairable versus irreparableligament, reducible versus irreducible deformity, andcombined coronal and sagittal plane pathology. Treat-ment is then tailored to the stage of injury and isindividualized to address the degree of anatomic andkinematic alteration.

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