Scapholunate instability

SCAPHOLUNATE INSTABILITY BY SCOTT W. WOLFE, MD

Injuries to the scapholunate joint are the most frequent cause of carpal instability and account for a considerable degree of wrist dysfunction and lost time from work and activities. The complex arrangement and kinematics of the 2 rows of carpal bones allows for an enormous degree of physiologic motion, and a hierarchy of primary and secondary ligaments serve to balance an inherently unstable structure. Although insufficient to cause abnormal carpal posture or collapse on static radiographs, an isolated injury to the scapholunate interosseous ligament may be the harbinger of a relentless progression to abnormal joint mechanics, cartilage wear, and degenerative change. Once disrupted, ligament repair methods and reconstructive options seldom serve to restore this delicately balanced design. Treatment options are predicated on the stage of injury, degree of secondary ligamentous damage, and arthritic change. Copyright © 2001 by the American Society for Surgery of the Hand he human carpus is a product of millions of years of evolutionary adaptation, and it is uniquely designed to position the hand anywhere within its nearly hemispherical arc of motion. To call the wrist a joint is actually a misnomer; it is in fact a collection of several joints and, from a kinematic perspective, is arguably one of the most complex set of articulations in the body. Traditionally, the wrist has been conceptually simplified into a dual linkage system comprising proximal and distal carpal rows, wherein each bone in a given row moves in the same direction during wrist motion. The ligamentous connections between each bone in each row, however, allow for subtle alterations in kinematic behavior de-

T

pending on the direction and degree of hand position required.1 This arrangement is potentially unstable and delicately balanced; the motion of each bone depends on mechanical signals from its neighbors and is restrained by a complex set of intrinsic and extrinsic ligaments. Ligamentous or bony injury to the wrist has the potential to irreversibly disrupt the balance and to set the stage for an inexorable progression to abnormal motion, joint loading, and degenerative change. This article focuses on the critical importance of the scapholunate joint to carpal function and emphasizes timely diagnosis and management of these difficult injuries.

ANATOMY From the Vilar Center for Research of the Hand and Upper Extremity, The Hospital for Special Surgery, Cornell University School of Medicine, New York, NY. Address reprint requests to Scott W. Wolfe, MD, The Hospital for Special Surgery, 535 E. 70th St, New York, NY 10021. Copyright © 2001 by the American Society for Surgery of the Hand 1531-0914/01/0101-0004$35.00/0 doi:10.1053/jssh.2001.21779

he clustering of the 8 small carpal bones into proximal and distal carpal rows has been widely accepted based on the kinematic behavior of these bones during global wrist motion. The 4 bones of the distal carpal row (trapezium, trapezoid, capitate, and hamate) are tightly bound to one another via stout intercarpal ligaments, and motion between them can

T

JOURNAL OF THE AMERICAN SOCIETY FOR SURGERY OF THE HAND 䡠 VOL. 1, NO. 1, FEBRUARY 2001

45

46

SCAPHOLUNATE INSTABILITY 䡠 WOLFE

also a typical ligament, and it contributes to rotational stability of the scapholunate joint. The proximal, or membranous, portion of the SLIL appears histologically as a fibrocartilaginous structure that, in isolation, contributes little to no restraint to abnormal motion of the scapholunate joint.

WRIST MECHANICS s the anterior cruciate ligament is considered the primary stabilizer of the knee, so too can the SLIL be considered the primary stabilizer of the scapholunate joint. It is surrounded in turn by several secondary stabilizers, each insufficient to cause instability after isolated disruption but each important in the maintenance of normal scapholunate kinematics and vulnerable to attritional wear after complete disruption of the SLIL. On the volar-radial side are the stout extrinsic ligaments, the radioscaphocapitate, the long and short radiolunate ligaments, and the radioscapholunate ligament (ligament of Testut) (Fig 2). The relative importance of each of these ligaments to scapholunate stability has not been definitively established, but the radioscapholunate ligament, once thought to be a critical stabilizer of this joint, is now

A FIGURE 1. The SLIL creates a seamless transition between the articular surfaces of the scaphoid and lunate.

be considered negligible. Similarly, the nearly rigid ligamentous connection of the trapezium and capitate to the index and middle metacarpals and lack of motion between these bones allows us to consider the distal row functionally as part of a fixed hand unit that moves in response to the musculotendinous forces of the forearm. The scaphoid, lunate, and triquetrum can be described as an intercalated segment,2 because no tendons insert upon them and because their motion is entirely dependent on mechanical signals from their surrounding articulations. The motions of these bones are checked by an intricate system of intrinsic, or interosseous, and extrinsic carpal ligaments. The most frequently injured of these intercarpal relationships is the scapholunate joint. When viewed through an arthroscope or at arthrotomy (Fig 1), the normal scaphoid and lunate appear nearly seamless, bound together by a tough scapholunate interosseous ligament (SLIL). The SLIL is C-shaped, and it attaches exclusively along the dorsal, proximal, and volar margins of the articulating surfaces, leaving a crevice between the bones distally. The 3 subregions of the ligament have been shown to have different material and anatomic properties, and the dorsal component is now regarded as the thickest, strongest, and most critical of the scapholunate stabilizers.3 It is a true ligament with transversely oriented collagen fibers, and it is a primary restraint not only to distraction but to torsional and translational moments as well. The palmar component, although considerably thinner, is

FIGURE 2. The stout extrinsic volar ligaments serve as secondary stabilizers of the scapholunate joint. LRL, long radiolunate ligament; SRL, short radiolunate ligament; RSC, radioscaphocapitate ligament; RSL, radioscapholunate ligament; ST, scaphotrapezial ligaments. (Reprinted with permission.29)

SCAPHOLUNATE INSTABILITY 䡠 WOLFE

regarded primarily as a neurovascular conduit with little mechanical integrity. The volar-ulnar extrinsic ligaments include the ulnolunate and ulnotriquetral ligaments, which are predominantly involved in stabilizing the triquetrolunate joint. Distally, the scaphotrapezial ligamentous complex has been identified as an important secondary stabilizer of the scaphoid in biomechanical studies.4,5 The dorsal ligamentous structures have been the focus of several recent investigations and are important secondary stabilizers of the scapholunate joint. Both the dorsal radiotriquetral and dorsal intercarpal ligaments (DIC) have attachments to the lunate (Fig 3). The thickest portion of the DIC inserts on the dorsal groove of the scaphoid, and a thinner arm of the ligament inserts onto the dorsal trapezium and proximal trapezoid. It has been postulated that the unique V arrangement of the DIC and dorsal radiotriquetral confer important dorsal stability to the scapholunate complex during the extremes of wrist motion that could not be permitted by independent dorsal radioscaphoid and radiolunate ligaments.6 Thus, normal kinematics of the scapholunate joint are tightly governed both by a tough intrinsic ligament that binds the scaphoid to the lunate proximally and by an envelope of surrounding extrinsic ligaments, oriented obliquely to the primary axis of wrist

FIGURE 3. The dorsal extrinsic ligaments also serve as important secondary stabilizers of the scapholunate joint. DIC, dorsal intercarpal ligament; DRT, dorsal radiotriquetral ligament. (Reprinted with permission.29)

47

motion (flexion-extension). The scaphoid, lunate, and triquetrum rotate collectively in flexion or extension depending on the direction of hand motion. As the hand flexes or turns into radial deviation, mechanical forces from the distal carpal row drive the distal scaphoid into flexion, and the lunate follows passively into flexion through the strong SLIL. As the hand ulnarly deviates, the unique helicoidal articular surface of the hamate7 engages the concordant surface of the triquetrum and, via a screw-like engagement, directs it into a dorsally tilted and palmarly translated position (Fig 4). The lunate and scaphoid rotate into dorsiflexion (extension) through a combined effect of their unyielding interosseous ligaments, and the coupled rotation of the distal row into a dorsally translated position. Dorsal translation of the distal row effectively tensions the radioscaphocapitate and scaphotrapezial ligaments and hoists the scaphoid into extension. During hand/wrist extension, the intercalated segment rotates as a unit while tension in the extrinsic ligaments locks the scaphoid, lunate, and triquetrum to the capitate in conjoined extension.1 This phenomenon was explained by MacConnail,8 who cited the critical role of the dorsal intercarpal ligament in producing a unified motion of the bones of the proximal and distal carpal rows via a “screwclamp” mechanism that captures the capitate between the scaphoid and triquetrum as the ligament tightens. Although the scaphoid, lunate, and triquetrum all rotate in the same primary direction during hand positioning, it must be recognized that considerable multiplanar motion occurs between each bone at the interosseous joints; this is attributable to the unique design and character of the interosseous ligaments. During a 120° arc of flexion and extension, for example, scaphoid flexion-extension exceeds lunate flexion-extension by approximately 35°. Scaphoid pronation is approximately 3 times that of lunate pronation during wrist flexion, and lunate ulnar deviation exceeds scaphoid deviation considerably.1 Interestingly, during wrist and hand extension, both the primary and out-of-plane rotations of the scaphoid and lunate are more tightly coupled, and this may be due in part to the influence of the dorsal extrinsic ligaments mentioned above. The redundancy of primary and secondary ligament stabilizers explains why division or injury to a single supporting ligament is generally insufficient to cause abnormalities in scaphoid or lunate posture on static

48

SCAPHOLUNATE INSTABILITY 䡠 WOLFE

FIGURE 4. The unique helicoidal surface of the triquetrohamate joint converts ulnar deviation of the hamate into a conjoined rotation of the triquetrum into palmar displacement and dorsiflexion.

radiographs. Even a complete division of the scapholunate ligament may cause no static increase in scapholunate gap or change in lateral scapholunate angle.9 Dramatic changes in force transmission and kinematics3,4,10 of the 2 bones during wrist motion do occur after SLIL division, however, and likely explain the symptoms of catching, popping, and pain seen in dynamic scaphoid instability (see below). Additional division of one or more of the secondary restraining ligaments is necessary before static changes in scaphoid and lunate posture are seen, and these changes have been documented after transection of the volar extrinsic ligaments, the dorsal intercarpal ligament, and the scaphotrapezial ligaments.2,4,5,9 Attritional wear of the secondary restraints is thought to be the cause of delayed development of dorsal intercalated segment instability (DISI) after isolated disruption of the SLIL.

STAGES

OF

SCAPHOLUNATE INSTABILITY

lassically, the diagnosis of scapholunate instability was predicated on abnormal scaphoid or lunate alignment as seen on static radiographs2 (Fig 5).

C

This definition, however, was not inclusive enough to explain the often disabling symptoms of pain with mechanical loading or sudden shifts or “clunks” that were noted among some injured patients with normal radiographs. The concept of dynamic scapholunate instability was proposed to describe abnormal carpal positioning that was observed on special stress radiographs.11 It is now recognized that scapholunate instability is a spectrum of injury and not an all-or-none condition12,13 (Table 1).The current definition of scapholunate instability has been expanded to include those wrists that exhibit symptomatic dysfunction, are unable to bear loads, and do not demonstrate normal kinematics throughout the complete arc of motion.14 The mildest form of scapholunate instability, occult instability,13 is usually initiated by a fall on the outstretched hand that may only cause a tear or attenuation of a portion of the SLIL, with or without a disruption of the ligament of Testut. Patients with this injury may not seek treatment initially, have no abnormalities of scaphoid or lunate posture on static or stress radiographs, and have wrist pain or dysfunction with mechanical loading. Watson has termed this

SCAPHOLUNATE INSTABILITY 䡠 WOLFE

FIGURE 5. Previous definitions of scapholunate instability relied on appearance of grossly abnormal posture of the carpal bones on static radiographs. Note the wide scapholunate diastasis after a previous attempt at operative stabilization.

49

predynamic instability,12 but this term implies progression toward static instability, and this may not be a certainty for all patients in this category. Higherenergy trauma may cause a subtotal or complete tear of the scapholunate ligament, including its critical dorsal portion, and untreated injuries will predictably lead to abnormal kinematics and load transfer, with pain during activities. This is the first stage of Mayfield’s classic description of progressive perilunate instability,15 and it may present even weeks or months after injury with radiographs that appear relatively normal. Abnormal stress radiographs or motion studies are necessary in this stage to confirm the diagnosis of dynamic scaphoid instability. An additional tear or attrition of one or more secondary ligament restraints will allow the scaphoid to rotate into increased flexion, with concomitant increase in the scapholunate interval. In this stage, known as scapholunate dissociation, rotation of the lunate becomes independent of the scaphoid, and the lunate tends to assume an abnormally extended posture during motion or mechanical load under the dorsally-directed compressive forces of the capitate. With the passage of time, a fixed DISI deformity develops, characterized by flexion of the scaphoid, extension of the lunate and triquetrum, and dorsal and proximal translation of the capitate and distal carpal row. This is an irreversible condition that is associated with secondary changes in most or all of the supporting ligamentous structures. Abnormal articular loading presages a relentless progression of degenerative change known as the SLAC (scapholu-

TABLE 1 Stages of Scapholunate Instability Occult (I)

Dynamic (II)

Scapholunate Dissociation (III)

Injured ligaments

Partial SLIL

Incompetent or torn Complete SLIL, volar or SLIL; partial palmar dorsal extrinsics extrinsics

Radiographs

Normal

Usually normal

Stress Normal; abn Abnormal radiographs fluoroscopy

DISI (IV)

SLAC16 (V)

Complete SLIL, volar extrinsic; secondary changes: RL, ST, DIC

As in stage IV

SL gap ⱖ 3 mm ⫾ SL angle ⱖ 70°

SL angle ⱖ 70° SL gap ⱖ 3 mm RL angle ⱖ 15° CL angle ⱕ ⫺15°

I. Styloid DJD II. RS DJD III. CL DJD IV. Pancarpal

Grossly abnormal

Unnecessary

Unnecessary

Abbreviations: abn, abnormal; CL, capitolunate; DIC, dorsal intercarpal ligament; DJD, degenerative joint disease; RL, radiolunate; RS, radioschaphoid; SL, scapholunate; SLIL, scapholunate interosseous ligament; ST, scaphotrapezoid.

50

SCAPHOLUNATE INSTABILITY 䡠 WOLFE

nate advanced collapse) wrist, first noted along the scaphoid facet of the distal radius, next within the radial midcarpal joint, and finally involving the entire carpus.16

DIAGNOSIS high index of suspicion is necessary to correctly diagnose an acute isolated scapholunate ligament disruption in the emergency department. Tenderness is usually poorly localized about the periscaphoid area, and pain will generally preclude most provocative wrist ligament testing. Diffuse swelling may obscure the characteristic wrist effusion, which is indicative of a serious intra-articular injury. Arthrocentesis is helpful when the history is suggestive and radiographs are normal. Vascular or neural compromise is rare, except in extreme ligament injuries such as lunate or perilunate disruptions.

A

Radiographs High quality posteroanterior (PA), lateral, navicular and anteroposterior (AP) grip radiographs should be obtained, and contralateral wrist radiographs are helpful for comparison. Lateral radiographs should be carefully evaluated for adequate technique and should be repeated if the radius, capitate, and third metacarpal are not roughly colinear in the sagittal plane. Yang et al17 recommend that the scaphoid tubercle and pisiform be maximally superimposed to assure a true lateral radiograph of the wrist. Measurement of intercarpal angles on static films is difficult and subject to a great degree of variability between examiners. It is nearly impossible to precisely and reproducibly determine the position of a bisecting line in each irregularly shaped small carpal bone. Approximation of intercarpal angles by using tangents to the external contour of each bone is an easier and perhaps more reliable technique. The examiner draws a tangent to the palmar cortex of the scaphoid proximal and distal poles and a second tangent to the distal articular surface of the lunate palmar and dorsal lips (Fig 6). A perpendicular is drawn from the lunate tangent to determine lunate posture in the sagittal plane. Deviation of this line from the longitudinal axis of the radius (the radiolunate angle) by more than 15° in the dorsal direction on a true lateral film is indicative of DISI. Although unusual in injuries of the scapholunate ligament, a radiolunate angle of more

than 15° in the volar direction is indicative of volar intercalated segment instability. Scapholunate angle is measured between the scaphoid tangent and the perpendicular to the lunate tangent, and it normally measures 46° (range, 30° to 60°). A unilateral scapholunate angle of greater than 70° is considered highly suggestive of rotatory subluxation of the scaphoid. Capitate posture can be approximated by a tangent to the dorsal cortex of the third metacarpal, and a flexed capitolunate joint in excess of 15° signifies collapse of the midcarpal joint and is confirmatory of a DISI deformity. Other radiographic signs of advanced stages of scapholunate instability include scapholunate diastasis, a positive ring sign, and foreshortening of the scaphoid on the PA film. A PA static film or AP grip stress film showing unilateral widening of the scapholunate joint in excess of the width of other intercarpal joints (2 to 3 mm) is considered suspicious but not diagnostic of scapholunate dissociation. There is considerable normal variability in scapholunate joint configuration, and differences in radiographic technique and wrist posture account for a high degree of variance in these measurements. The scaphoid ring sign is visible on a PA film when the distal scaphoid tubercle is superimposed on the scaphoid waist (Fig 7). When the scaphoid is flexed more than 70°, it appears foreshortened on the PA film when compared with films of the uninjured wrist. Stress radiographs are obtained when carpal instability is suspected clinically but static radiographs are normal. The most frequently used stress radiograph is the AP grip film, which profiles the scapholunate joint and shows pathologic scapholunate widening under axial-loaded conditions. Care should be taken to position the wrist in neutral flexion/extension. Lateral full flexion and full extension radiographs can be examined for subtle differences in intercarpal motion and are most useful when compared with similar films from the uninjured wrist. Full ulnar and full radial deviation PA radiographs complete the sequence, and these may show abnormal widening of the scapholunate joint. Normal static and stress films do not always rule out serious injury, and patients with suspected SLIL injury should be placed in a thumb spica cast and referred for early diagnostic evaluation. Patients with subacute injuries (1 to 6 weeks) often present with a history of painful popping or clicking

SCAPHOLUNATE INSTABILITY 䡠 WOLFE

FIGURE 6. Reproducible measurement of intercarpal angles is facilitated by drawing tangents to the carpal contours. This lateral radiograph shows a 20° DISI posture of the lunate and a 90° scapholunate angle. (Adapted with permission.30)

51

52

SCAPHOLUNATE INSTABILITY 䡠 WOLFE

FIGURE 7. Radiographic evaluation of scapholunate instability. (A) The scaphoid tubercle becomes superimposed on the scaphoid waist in a PA radiograph when the scaphoid is abnormally flexed, creating the so-called ring sign. (B) A full flexion stress view shows abnormal scaphoid subluxation dorsally with minimal conjoined flexion of the lunate. (C) An ulnar deviation view shows abnormal widening of the scapholunate interval.

SCAPHOLUNATE INSTABILITY 䡠 WOLFE

with activities and well-localized tenderness about the scaphoid and dorsal scapholunate interval. Watson described a provocative maneuver known as the scaphoid shift test that can be helpful in the detection of subtle degrees of scaphoid instability. Pressure is applied by the examiner’s thumb to the scaphoid tubercle as the patient’s wrist is brought from a position of ulnar deviation and slight extension to radial deviation and slight flexion (Fig 8). The scaphoid will normally flex and pronate during this maneuver, but in scaphoid instability the maneuver will be painful, and thumb pressure may force the proximal scaphoid from the scaphoid fossa and onto the dorsal articular lip of the radius. Relief of thumb pressure will allow the scaphoid to spontaneously reduce, often with an audible or palpable clunk. The test may be falsely positive in up to one third of individuals, and this is thought to be due to ligamentous hyperlaxity that permits capitolunate translation with similar findings. Patients with an appropriate history and a positive scaphoid shift test should be considered as having a suspected scapholunate ligament disruption; the diagnosis should be confirmed with fluoroscopic and/or arthroscopic examination under anesthesia. Ancillary imaging studies may be helpful to confirm a suspected diagnosis of scapholunate ligament injury but should not be used in isolation because of a relatively high rate of falsely positive results. Several authors have shown a high rate of bilaterally positive

53

wrist arthrograms in patients with unilateral symptoms and/or unilateral injury. Arthrography is most sensitive if the radiocarpal, midcarpal, and radio-ulnar compartments are injected separately (3-compartment arthrography). Magnetic resonance imaging (MRI) examination, when combined with gadolinium injection, has been reported to be up to 90% accurate for perforations in the SLIL, but high normal variability in scapholunate morphology has been reported as well. It should be noted that both arthrography and MRI yield only anatomic evaluations of the wrist ligaments and give no information concerning their functional integrity. Cineradiography or cinearthrography can be helpful to show abnormal kinematics of the scaphoid or lunate during wrist motion, especially with ulnarto-radial deviation and with wrist flexion/extension. Traction films showing a stepoff at the scapholunate joint may signify a serious injury to intercarpal ligaments. Wrist arthroscopy is widely considered the gold standard for both anatomic and functional evaluation of the interosseous and extrinsic ligaments of the wrist, and it can be combined with fluoroscopic evaluation under anesthesia for additional kinematic information.18 The ability to pass the arthroscope from the radiocarpal joint into the midcarpal joint through the scapholunate interval (drive-through sign) indicates complete incompetency of this ligament and laxity or disruption of its secondary stabilizers. It cannot be overemphasized, however, that ancillary imaging studies or arthroscopy should be used only to confirm a clinical diagnosis of scapholunate injury, and treatment must be predicated by the patient’s symptoms and clinical examination.

TREATMENT

FIGURE 8. (B) Fluoroscopic view of a positive scaphoid shift test showing subluxation of the proximal scaphoid from the scaphoid fossa of the distal radius.

Occult Scapholunate Instability Partial tears of the scapholunate ligament may be effectively treated by thumb spica cast immobilization if diagnosed acutely, but they are usually diagnosed weeks or months after an acute traumatic episode. Patients classically present with mechanical symptoms of clicking or pain with heavy loads or extremes of wrist motion. The wrist may be able to tolerate short periods of exercise or loading but characteristically aches after use and may exhibit swelling in the periscaphoid region. The scaphoid shift test may show increased scaphoid mobility and usually generates

54

SCAPHOLUNATE INSTABILITY 䡠 WOLFE

pain at the dorsal scapholunate joint. Static and stress radiographs are generally normal, and an arthrogram or MRI may or may not show a break in the continuity of the SLIL. If a concerted effort at splinting, activity modification, and anti-inflammatory medications are ineffective, arthroscopic and fluoroscopic confirmation of the injury may be necessary. Because the pathoanatomy of this condition may vary, so too should its treatment. Simple arthroscopic debridement for partial membranous scapholunate ligament injuries without gross fluoroscopic abnormalities of carpal motion have been associated with satisfactory results in the majority of cases. Frank scaphoid subluxation out of the radial fossa during the scaphoid shift test under fluoroscopy (Fig 8b) indicates increased mechanical scaphoid instability that may not be amenable to simple debridement. Wintman et al achieved highly satisfactory results in 15 of 17 patients with a Blatt dorsal capsulodesis procedure for patients with incapacitating pain and a positive scaphoid shift test13,19 (Fig 9). Technique of Dorsal Capsulodesis A 4- to 5-cm oblique incision is centered over the proximal pole of the scaphoid, incorporating the 3-4 arthroscopic portal. The third dorsal compartment is partially opened, and the extensor pollicis longus and wrist extensor tendons are reflected, while the dorsal sensory nerve branches are carefully protected. A 1.5cm–wide by 2- to 3-cm–long flap of dorsal capsuloligamentous tissue is created with a scalpel, based just radial to Lister’s tubercle. Careful exposure of the distal scaphoid is performed, and a transverse trough is created with a curette or rongeur in the distal third,

FIGURE 9. The Blatt capsulodesis procedure creates a passive dorsal restraint to abnormal flexion of the scaphoid. (Reprinted with permission.31)

well past the scaphoid waist. A joystick in the scaphoid may be helpful at this stage to assure anatomic scaphoid reduction in its fossa, and an approximate 45° angle to the longitudinal axis of the radius. Two .045-inch K-wires are directed across the scaphoid and into the capitate to maintain this position. Two Keith needles are passed dorsal to volar through the bony trough, exiting through the scaphoid tubercle and thenar skin. Monofilament sutures are then woven through the capsular flap, and the flap is advanced into the trough by passing the sutures through the drill holes via the Keith needles. The sutures are secured over a button or cotton bolster. The dorsal capsular tissues are imbricated to the capsular flap during closure, and the wrist immobilized in pronation in a long arm thumb spica cast for 8 weeks. The wires and button are removed at that time, and wrist motion begun gradually. Full loading of the wrist is delayed for 4 to 6 months. Dynamic Instability Patients in this category have sustained a range of severe injuries to the SLIL and supporting extrinsic ligaments. The injury to the SLIL may be partial or complete, and usually includes disruption or severe attenuation of the important dorsal component. Dynamic instability presents with normal static radiographs and is defined by appearance of abnormal scaphoid and/or lunate posture on stress films.11 AP clenched fist radiographs in supination or ulnar deviation PA views will usually show widening of the scapholunate interval. Similarly, full flexion lateral views may show a pathologic increase in scaphoid flexion or a decrease in lunate flexion, and should be compared with the opposite wrist. Depending on the duration since injury and the degree of SLIL incompetence, nonoperative treatment of dynamic instability includes casting, splinting, antiinflammatory medication, and activity modification and may have a role in diminishing symptoms. The kinematic abnormalities shown on stress radiographs, however, may continue to produce abnormal shear stresses across the wrist cartilaginous surfaces, and pain with sports or heavy mechanical loads may be incapacitating. Nonoperative treatment of acute, complete scapholunate ligament disruptions is generally unsuccessful and should be reserved for the inactive, elderly, or infirm. Casting or splinting is insufficient to control the high forces transmitted across the

SCAPHOLUNATE INSTABILITY 䡠 WOLFE

scaphoid and scapholunate interval, and the process will predictably progress. On occasion, nonoperative treatment is selected because of a missed or unconfirmed diagnosis, and a delay in diagnosis can make direct ligament repair more difficult or impossible. Operative stabilization of the dynamically unstable scaphoid is advocated for intractable symptoms and, like occult scaphoid instability, must be tailored to suit the pathology. Fluoroscopic examination under anesthesia and arthroscopic inspection of the interosseous and extrinsic ligaments provides useful information to guide operative intervention. Fluoroscopy may show dynamic subluxation of the proximal scaphoid pole over the dorsal lip of the radius during wrist flexion, with a dramatic and sometimes audible reduction in neutral. The scaphoid shift test under anesthesia is confirmatory if positive, and fluoroscopy should be used simultaneously to confirm the site of abnormal mobility. Arthroscopy will confirm partial or complete disruption of some or all components of the SLIL; extrinsic ligaments are generally normal in acute or subacute cases. In cases of dynamic scaphoid instability without complete SLIL disruption, dorsal capsulodesis is generally effective. For complete SLIL disruptions, closed reduction and pinning under arthroscopy have not been shown to be universally effective, especially in subacute or chronic injuries. SLIL reduction and pinning is occasionally performed when a complete SLIL tear occurs in association with an unstable fracture of the distal radius that requires operative stabilization. Direct open ligament repair is indicated in acute or

55

subacute cases when satisfactory ligament tissue remains on the lunate, and it is usually augmented with a dorsal capsulodesis to the distal pole of the scaphoid20 (Fig 10). Technique of SLIL Ligament Repair The scapholunate joint is exposed through a 4 to 5 cm oblique dorsal incision as is used in the dorsal capsulodesis procedure. The membranous portion of the ligament is identified on the lunate and repaired to a trough on the interosseous border of the scaphoid using 3-0 braided polyester transosseous sutures. The important dorsal component of the ligament is directly repaired to its insertion site with through-bone sutures or a bone anchor. The scaphoid is anatomically reduced to the lunate with a reduction forceps, and 2 divergent wires are passed percutaneously from the waist of the scaphoid into the lunate. The distal pole of the scaphoid is similarly fixed to the capitate with a third wire for additional stability. A 1.5-cm dorsal capsular flap is fashioned based on the radius and is advanced distally to a transverse trough in the distal third of the scaphoid and fixed with through-bone pullout sutures or a bone anchor. Immobilization in a long-arm thumb spica cast in pronation is maintained for 8 weeks, at which time the wires are removed and gradual resumption of wrist motion permitted. Scapholunate Dissociation Patients with static postural changes of the scaphoid and/or lunate have additional injuries to the secondary ligamentous stabilizers that will influence the

FIGURE 10. Direct repair of the SLIL is augmented by a dorsal capsulodesis, as described by Lavernia et al.19

56

SCAPHOLUNATE INSTABILITY 䡠 WOLFE

choice of treatment. Acute injuries presenting with unilateral scapholunate diastasis and increased scaphoid flexion (rotatory subluxation of the scaphoid) have sustained injuries to the volar or dorsal extrinsic ligaments, scaphotrapezial ligaments, or a combination of these. Patients with chronic injuries may have fixed deformities not amenable to reduction and repair. Although arguably more effective when performed acutely, scapholunate ligament repair should not necessarily be abandoned in patients with divergent scapholunate joints or in those with injuries more than 4 to 6 weeks old. Although delayed repair is considered somewhat controversial, Lavernia et al20 showed satisfactory results in patients up to 3 years after injury using the combination of transosseous ligament repair and dorsal capsulodesis outlined above. Requirements for open reduction and ligament repair include (1) satisfactory remaining SLIL ligament tissue (2) an easily reducible scaphoid, and (3) absence of degenerative changes. In my experience, selected patients in the subacute category treated in this fashion have some degree of recurrent widening of the scapholunate interval, but symptoms can remain tolerable and activity level high. In those subacute or chronically injured patients without a repairable ligament but with a reducible scaphoid and no degenerative changes, many procedures designed to re-establish the critical scapholunate linkage have been reported. Several reconstructive procedures including ligament reconstruction with tendon grafts, creation of a pseudoarthrosis using a Herbert screw, and various intercarpal fusions have all been attempted with variable results. Hom and Ruby21 reported success in only 1 of 7 patients with attempted scapholunate fusion, and this procedure has been abandoned. Although a number of tendon graft reconstructions have been designed to reunite the scaphoid and lunate and to limit abnormal scaphoid flexion, their relative complexity has restricted their widespread use. A tendon graft used to replace this complex mechanical structure must have sufficient tensile strength to oppose the tremendous axial forces that drive the scaphoid and lunate apart, as well as the elasticity to permit a high degree of multiplanar rotation between the 2 bones.1 The inability of a tendon graft to simulate the mechanical profile of a ligament has limited the effectiveness of these procedures to some extent. Early experience with the

Brunelli flexor carpi radialis FCR tendon graft reconstruction, intended to simultaneously addresses the scaphotrapezial and scapholunate ligament deficiencies, appears promising (Fig 11). Recently, several bone-ligament-bone complexes have been designed and tested biomechanically and clinically for use in reconstruction of scapholunate dissociation.22 Weiss reported the successful use of an autogenous bone-retinaculum-bone preparation harvested from the third dorsal compartment in 14 patients with dynamic instability and less predictable results in 5 patients with static scapholunate dissociation.22 Biomechanical studies of tarsal bone-ligament-bone autogenous grafts show similar biomechanical profiles to the SLIL, and early clinical reports of the use of the medial cuneonavicular ligament preparation appear promising (Culp RW, Osterman AL: personal communication, Oct 5, 2000). Another approach to the reducible scapholunate dissociation is to stabilize the malrotated scaphoid with intercarpal arthrodesis. Scaphotrapezial-trapezoid fusion has gained popularity since first reported in 1967 by Peterson and Lipscomb.24 Satisfactory results for both dynamic and static instabilities have been reported by several authors, but concern lingers over abnormal load transmission to the distal radius and a high rate of complications in some series.25 Scaphocapitate fusion has also been advocated to stabilize the scaphoid, but by spanning the midcarpal joint, this leads to an obligate 50% reduction in wrist motion. To prevent degenerative changes between the less mobile scaphoid and the remaining styloid after either type of fusion, most authors advocate avoidance of over-reduction of the scaphoid and perform a limited radial styloidectomy. Technique of Scaphocapitate Fusion The scaphoid and capitate are readily exposed through a short dorsal longitudinal or transverse incision. Decortication of the apposing facets is performed, preserving the most volar cortical margin to maintain proper intercarpal spacing. Through a 2-cm transverse incision at the radial styloid, a 1-cm radial styloidectomy is performed, with care taken to preserve the radioscaphocapitate ligament origin. Abundant cancellous bone graft may be obtained directly through the styloidectomy site, and the cap of styloid removed is reversed and impacted as a plug into the defect so created. The scaphoid is reduced by using

SCAPHOLUNATE INSTABILITY 䡠 WOLFE

57

FIGURE 11. The Brunelli tendon graft reconstruction, which incorporates an flexor carpi radialis hemitendon to reconstruct both the scaphotrapezial and the scapholunate ligaments.21

joysticks to an intermediate position of 50° to 60° degrees of radioscaphoid flexion and is provisionally fixed with Kirschner wires after packing the fusion site with cancellous graft. The wires may be exchanged for cannulated screws, and the wrist is immobilized in a short-arm thumb spica cast until fusion occurs at approximately 6 weeks (Fig 12). DISI Massive ligament disruption at the time of injury, as may occur in perilunate or lunate dislocations, or gradual attrition of the secondary extrinsic stabilizers leads to abnormal extension of the lunate and carpal collapse after scapholunate dissociation. The combined effects of an extension moment transmitted through the intact triquetrolunate ligament and coupled dorsal translation of the capitate force the lunate into extension and exacerbate the abnormal posture of the scapholunate joint. Capsular contracture may serve to fix the deformity and dictate the limited treatment options. Nonoperative treatment is likely to result in a slow, relentless progression to degenerative arthritis, beginning first at the radial styloid, progressing proximally to involve the entire scaphoid facet, and finally involv-

FIGURE 12. Scaphocapitate fusion fixed with 2 cannulated screws.

58

SCAPHOLUNATE INSTABILITY 䡠 WOLFE

ing the midcarpal joint.16 Depending on the chronicity of the injury and the relative activity level of the patient, the option of activity modification and splint wear may be reasonable and may forestall a motionlimiting salvage procedure. Tendon graft reconstructions and soft-tissue procedures have not been able to satisfactorily address the multiplicity of bony and ligamentous alterations. If the scaphoid and lunate are reducible and no degenerative changes have occurred at the radiocarpal joint, arthrodesis of the scaphoid, capitate, and lunate is an option that enjoys a high rate of fusion and a relatively low complication rate. Kinetic studies have shown a more normal distribution of load to the scaphoid and lunate facets of the radius after scaphoid-capitatelunate fusion than after other partial arthrodesis procedures.26 Motion is predictably reduced by 50%, and as in other intercarpal arthrodesis procedures, a radial styloidectomy is recommended to reduce styloid impingement. If the scaphoid is fixed in palmar flexion, efforts to free capsular adhesions and restore scaphoid kinematics will generally be unsuccessful. Most investigators advocate excision of the fixed scaphoid and salvage via a proximal row carpectomy or partial or complete wrist fusion. Technique of Proximal Row Carpectomy Through a 4-cm dorsal transverse or longitudinal incision, the capsule of the wrist is opened in an inverted-T fashion to expose the bones of the proximal carpal row. The scaphoid, lunate, and capitate are subsequently excised, and the insertion of a threaded external fixation pin or Steinman pin into each bone greatly facilitates the process. Extreme care is taken to preserve the volar extrinsic ligaments in continuity. A limited radial styloidectomy is preferred to avoid subsequent impingement with the trapezium. The wrist capsule is closed after hemostasis, and the wrist immobilized for 1 to 2 weeks to encourage soft tissue stability, followed by a removable wrist orthosis for 4 to 6 weeks (Fig 13). Scapholunate Advanced Collapse In the earliest stage of the SLAC wrist deformity, degenerative changes are limited to an area of abnormal contact between the abnormally rotated scaphoid and the radial styloid. Radial styloidectomy will not alter the progression of the degenerative process at

FIGURE 13. A successful proximal row carpectomy is predicated on preservation of the volar extrinsic ligaments to prevent ulnar translation of the remaining distal carpal row.

this stage, and any degree of pain relief is generally regarded as temporary. The scaphoid remains rotated into palmar flexion, and its contact area with the radius is reduced and shifted dorsally. Persistent abnormal load transfer and shear across the cartilaginous surfaces lead to degeneration of the proximal scaphoid facet in stage II of SLAC wrist deformity. With time, the dorsally translated capitate migrates proximally into the widened scapholunate interval, and degenerative changes at this joint herald stage III. The relative congruency of the radiolunate joint in all positions of lunate rotation preserves this articulation until late in the disease process. If the extent of degenerative disease is not clearly delineated on routine radiographs, computed tomography is an excellent means to individually assess changes at the midcarpal and radiocarpal articulations. A mobile and reducible scaphoid can be stabilized by scaphoid-trapezium-trapezoid, scaphoid-capitate, or scaphoid-lunate-capitate fusion, provided the proximal radiocarpal joint is free of degenerative change. A fixed scaphoid or degeneration in the proximal scaphoid facet is best treated by excision of the scaphoid, with additional surgery that is predicated by the status of the capitolunate joint. Extensive degenerative changes at the midcarpal joint, with preservation of the radiolunate joint, is best treated with capitatelunate-hamate-triquetral (4-corner) fusion. If this joint is relatively well preserved, proximal row car-

SCAPHOLUNATE INSTABILITY 䡠 WOLFE

59

pectomy is an option, and has compared favorably to 4-corner fusion in terms of range of motion and grip strength.27,28 Neither procedure is without the potential for complications such as including nonunion, progression of arthritis, and persistent pain, and patients should be advised that these procedures are collectively referred to as “salvage” procedures for a wrist that otherwise be a candidate for complete wrist fusion. Technique of 4-Corner Fusion The procedure is performed through a similar exposure as is used in proximal row carpectomy. The scaphoid is excised piecemeal or en bloc, and palmar extrinsic ligaments are carefully left intact. The apposing surfaces of the capitate, hamate, triquetrum, and lunate are decorticated to bleeding cancellous bone, leaving the volar osteoarticular contact intact for proper intercarpal spacing. The intercarpal spaces are packed with autogenous cancellous bone graft, and the capitate is reduced with dorsal digital pressure until the lunate is restored to a neutral position on both the PA and lateral radiographs. Preliminary or final fixation is attained with multiple Kirschner wires; cannulated screws or other internal fixation devices may enable earlier postoperative range of motion. Immobilization in a thumb spica cast is tailored to the stability of fixation, but generally requires 6 to 8 weeks for union (Fig 14). Wrist arthrodesis is a dependable procedure, with fusion rates approaching 100% when newer implants are used. The loss of motion from a fused wrist is considerable, however, but for some patients the dependable, pain-free, and durable option of an arthrodesis is preferable to an occasionally painful wrist with retained mobility.

FIGURE 14. Four-corner arthrodesis is designed to restore stability while maintaining motion of the radiocarpal joint.

SUMMARY The SLIL is the critical stabilizer of a delicately balanced system of joints. Carpal alignment may be maintained after isolated disruption of this ligament because of a complex array of secondary stabilizers. Disruption of this important ligament may be the first stage of a slow and steady progression toward wrist dysfunction and degenerative disease. Early diagnosis of abnormal carpal mechanics is critical before extrinsic ligaments are secondarily affected. Treatment must be individualized based on the degree of anatomic and kinematic alteration.

REFERENCES 1. Wolfe SW, Neu CP, Crisco JJ III. In vivo scaphoid, lunate and capitate kinematics in wrist flexion and extension. J Hand Surg [Am] 2000;25A:860-869. 2. Linscheid RL, Dobyns JH, Beabout JW, Bryan RS. Traumatic instability of the wrist. J Bone Joint Surg Am 1972; 54A:1262-1267. 3. Berger RA, Imeada T, Berglund L, An KN. Constraint and material properties of the subregions of the scapholunate interosseous ligament. J Hand Surg [Am] 1999;24A:953-962. 4. Blevens AD, Light TR, Jablonsky WS, et al. Radiocarpal articular contact characteristics with scaphoid instability. J Hand Surg [Am] 1989;14:781-790.

5. Drewniany JJ, Palmer AK, Flatt AE. The scaphotrapezial ligament complex: an anatomic and biomechanical study. J Hand Surg [Am] 1985;10:492-498. 6. Viegas SF, Yamaguchi S, Boyd NL, Patterson RM. The dorsal ligaments of the wrist: anatomy, mechanical properties, and function. J Hand Surg [Am] 1999;24A:456-468. 7. Weber ER. Concepts governing the rotational shift of the intercalated segment of the carpus. Orthop Clin North Am 1984;15:193-207. 8. MacConaill MA. The mechanical anatomy of the carpus and its bearings on some surgical problems. J Anat 1941;74:166176.

60

SCAPHOLUNATE INSTABILITY 䡠 WOLFE

9. Meade TD, Schneider LH, Cherry K. Radiographic analysis of selective ligament sectioning at the carpal scaphoid: a cadaver study. J Hand Surg [Am] 1990;15:855-862. 10. Short WH, Werner FW, Fortino MD, Palmer AK, Mann KA. A dynamic biomechanical study of scapholunate ligament sectioning. J Hand Surg [Am] 1995;20:986-999. 11. Taleisnik J. Post-traumatic carpal instability. Clin Orthop 1980;149:73-82. 12. Watson H, Ottoni L, Pitts EC, Handal AG. Rotary subluxation of the scaphoid: a spectrum of instability. J Hand Surg [Br] 1993;18:62-64. 13. Nathan R, Blatt G. Rotatory subluxation of the scaphoid revisited. Hand Clin 2000;16:417-431. 14. Garcia-Elias M, Berger RA, Horii E, et al. Definition of carpal instability. J Hand Surg [Am] 1999;24A:866-867. 15. Mayfield JK, Johnson RP, Kilcoyne RK. Carpal dislocations: pathomechanics and progressive perilunar instability. J Hand Surg [Am] 1980;5:226-241. 16. Watson H, Ballet FL. The SLAC wrist: scapholunate advanced collapse pattern of degenerative arthritis. J Hand Surg 1984;9A:358-365. 17. Yang Z, Mann FA, Gilula LA, Haerr C, Larsen CF. Scaphocapitate alignment: criterion to establish a neutral lateral view of the wrist. Radiology 1997;205:865-869. 18. Wolfe SW, Gupta A, Crisco JJ III. Kinematics of the scaphoid shift test. J Hand Surg [Am] 1997;22:801-806. 19. Wintman BI, Gelberman RH, Katz JN. Dynamic scapholunate instability: results of operative treatment with dorsal capsulodesis. J Hand Surg [Am] 1995;20A: 971-979. 20. Lavernia CJ, Cohen MS, Taleisnik J. Treatment of scapholunate dissociation by ligamentous repair and capsulodesis. J Hand Surg [Am] 1992;17A:354-359. 21. Hom S, Ruby LK. Attempted scapholunate arthrodesis for

22. 23. 24. 25.

26.

27.

28. 29. 30.

31.

chronic scapholunate dissociation. J Hand Surg [Am] 1991; 16:334-339. Brunelli GA, Brunelli GR. A new technique to correct carpal instability with scaphoid rotary subluxation: a preliminary report. J Hand Surg [Am] 1995(suppl);20:S82-S85. Weiss AP. Scapholunate ligament reconstruction using a bone-retinaculum-bone autograft. J Hand Surg [Am] 1998; 23A:205-215. Peterson HA, Lipscomb PR. Intercarpal arthrodesis. Arch Surg 1967;95:127-134. Kleinman WB, Carroll C IV. Scapho-trapezio-trapezoid arthrodesis for treatment of chronic static and dynamic scapholunate instability: a 10-year perspective on pitfalls and complications. J Hand Surg [Am] 1990;15:408-414. Viegas SF, Patterson RM, Peterson PD, et al. Evaluation of the biomechanical efficacy of limited intercarpal fusions for the treatment of scapho-lunate dissociation. J Hand Surg [Am] 1990;15:120-128. Wyrick JD, Stern PJ, Kiefhaber TR. Motion-preserving procedures in the treatment of scapholunate advanced collapse wrist: proximal row carpectomy versus four-corner arthrodesis. J Hand Surg [Am] 1995;20A:965-970. Krakauer JD, Bishop AT, Cooney WP. Surgical treatment of scapholunate advanced collapse. J Hand Surg [Am] 1994; 19A:751-759. Wolfe SW, McLarney E. Carpal fractures and dislocations. In: Craig E, ed. Clinical Orthopedics. Philadelphia: Lippincott, 1999:30. Larsen C, Stigsby B, Lindequist S, Bellstrom T, Mathiesen F, Ipsen T. Observer variability in measurements of carpal bone angles on lateral wrist radiographs. J Hand Surg [Am] 1991; 16(A):893-898. Galberman RH, ed. The Wrist. New York: Raven Press, 1984.