476 THE JOURNAL OF BONE AND JOINT SURGERY

Carpal Instability*

BY LEONARD K. RUBY, M.D.t. BOSTON. MASSACHUSETTS

An Instructional Course Lecture, The American Academy ofOnthopaedic Surgeons

Although the anatomy and function of the wrist

have been studied since medieval times, the current em-

phasis on this subject dates from the classic 1972 study

by Linscheid et al.’9, which increased interest in trau-

matic instability of the wrist and its pathomechanics.

That study was based on the works of several authors,

including Destot5, Navarro24, Gifford et al.9, and Fisk7.

The present lecture describes the recent advances in the

understanding of the structure and function of the wrist

and summarizes the current thinking regarding the di-

agnosis and treatment of the clinically important carpal

instabilities.

Bones

Anatomy

The carpus includes four sets of joints: the distal

radio-ulnar joint, the radiocarpal joint. the mid-canpal

joint, and the carpometacarpal joints. In this lecture,

I will limit my discussion to the radiocarpal and mid-

carpal joints. The bones of the carpus can be thought of

as lying in two rows. The proximal row consists of the

scaphoid, the lunate, and the tniquctrum. The pisiform is

a sesamoid bone in the tendon of the flexor carpi ulnanis

and, as such, is not a functional part of the proximal row.

The distal row is composed of the trapezium, the trape-

zoid, the capitate, and the hamate. The mid-carpal joint

is the confluent articulation between the proximal and

distal carpal rows. The scaphoid occupies a unique posi-

tion, as it spans the mid-carpal joint and forms an osse-

ous link between the proximal and distal rows’7.

Ligaments

Each bone is relatively tightly and securely bound

to its neighbors by strong interosseous ligaments. The

interosseous ligaments of the distal row seldom fail din-

ically. The interosseous ligaments of the proximal row

include the ligament between the scaphoid and the lu-

nate (the scapholunate interosseous ligament) and the

*printed with permission of The American Academy of Ortho-

paedic Surgeons. This article will appear in Instructional Course

Lectures, Volume 45, The American Academy of Orthopaedic Sur-

geons, Rosemont. Illinois, March 1996.tNew England Medical Center, 750 Washington Street. Boston,

Massachusetts 02111.

ligament between the tniquetrum and the lunate (the

tniquetrolunate interosseous ligament). These ligaments

are c-shaped: they are attached to the dorsal, palmar,

and proximal edges of each of the three bones of the

proximal row. They are open distally into the mid-carpal

joint, so that an anthrogram of a normal mid-canpal joint

shows contrast medium between the three bones. The

ligaments are thickened dorsally and palmarly and have

a relatively thin membranous portion centrally (Figs. 1

and 2). Recent studies have shown that the central por-

tions are not nearly as strong as the dorsal and palmar

portions and, therefore, may not be as important me-

chanically. Mayfield et al.2’ and Logan et al.’9 measured

the failure strength’ and stress-strain behavionis �f these

ligaments in cadavenic specimens and reported that the

scapholunate interosseous ligament failed at 232.6 ±

10.9 newtons (52.3 ± 2.5 pounds) and the tniquetro-

lunate interosseous ligament, at 353.7 ± 69.2 newtons

(79.5 ± 15.6 pounds). Furthermore, both of these liga-

ments elongated by as much as 50 to 100 per cent of

their original length before failure.

In addition to the interosseous ligaments, the wrist

contains the dorsal and palmar capsular ligaments,

which are thickenings of the wrist capsule. These liga-

ments also have been well described by several authors,

including Taleisnik32, Mayfield et al.si, and Berger and

Landsmeeni. The dorsal capsular ligaments include the

dorsal radiocanpal ligament and the dorsal intercarpal

ligament (Fig. 3); the former may be especially impor-

tant as an accessory stabilizer of the tniquetrolunate and

radiocarpaljoints37.Taleisnik32 described the palmar cap-

sular ligaments as consisting of the nadioscaphocapitate,

the radiolunate, the radioscapholunate, the ulnolunate,

and the ulnotriquetral ligaments. In addition, he de-

scnibed the radioscaphocapitate and tniquetrocapitate

ligaments as crossing the mid-carpal joint and, together,

forming the so-called V. deltoid, or arcuate ligaments.

The palmar ligaments recently were described again

by Bergen and Landsmeen’, who suggested that the

nadioscaphocapitate ligament inserts strongly into the

scaphoid and weakly into the capitate. They renamed

the radiolunate ligament, calling it the long nadiolu-

nate ligament in order to distinguish it from the short

nadiolunate ligament, which originates from the palman

Fio. 1

CARI’AL INSTABILITY 477

VOL. 77-A. NO. 3. MAR(’ll 1995

Cross-section of the proximal carpal row of a cadaveric wrist. C = capitate. R = radius. P = pisiform. S = scaphoid. L = lunate. T = triquetrum.SLI = scapholunate interosseous ligament. LTI = triquetrolunate interosseous ligament. LRL = long radiolunate ligament. and is =

interligamentous sulcus. (Reprinted. with permission. from: Berger. R. A.. and Landsmeer. J. M. E.: The palmar radiocarpal ligaments: a study

ofadultand fetal human wristjoints.J. Hand Surg.. 1SA:851. 1990.)

edge of the distal part of the radius at its lunate facet

and inserts into the palmar pole of the lunate (Fig. 4).

The short radiolunate ligament had not been described

previously. and it should not be confused with the

radioscapholunate ligament described by Talcisnik’-3.

The space of Poirier, a mechanically weak area of the

palmar wrist capsule between the proximal and distal

carpal rows. is continuous with the ligamentous sul-

cus between the radioscaphocapitate ligament and the

long radiolunate ligament. Stress-strain testing of pal-

mar radiocarpal ligaments in cadavera showed that the

radioscaphocapitate ligament failed at 151 ± 30 new-

tons (33.9 ± 6.7 pounds) and that the long radiolunate

ligament failed at 107.2 ± 14.8 newtons (24.1 ± 3.3

pounds); the ligaments elongated approximately 30 per

cent before failure”. Therefore. as indicated previously,

the interosseous ligaments of the proximal row are

stronger and more elastic than any of the capsular liga-

mcnts that have been tested.

Tetidons

The musculotendinous units that move the hand and

wrist originate at the elbow and insert on the metacar-

pals. No muscles attach to the proximal carpal row.

The primary tiexors are the flexor carpi radialis and

the flexor carpi ulnanis. The primary cxtensons are the

extensor carpi radialis longus and the extensor carpi

radialis brevis. The primary radial deviator is the abduc-

tor pollicis longus. and the primary ulnar deviator is the

extensor carpi ulnanis. Because all of these tendons in-

sent on the metacarpals and because the carpomctacan-

pal joints and the articulations of the distal row are

relatively immobile. as is the distal row, the entire prox-

imal row functions as an intercalated segment. In addi-

tion, the motors of the wrist arc located peripherally. as

far from the center of motion of the wrist (that is, the

Fi;. 2

Drawing showing the dorsal view of the carpal interosseous liga-

ments. SL = scapholunate ligament. LT = triquetrolunate ligament.

-F-F = trapeziotrapezoid ligament. CT = capitotrapezoid ligament. and

CH = capitohamate ligament. ( Reprinted. with permission. from: An.

K-N.: Berger. R. A.: and Cooney. W. P.. Ill: Biomechanics of the Wrist

Joint. p. 13. New York. Springer. 1991.)

47�; I.. K. RUBY

I’HE Jt)URNAL OF BONE �\NI) JOINT SURGERY

Ft(. 3

I)rawitig (if the dorsal capsular liganients. 1) R(’ = dorsal radiocar-

PZLl ligiiiient. E)l(’ = dorsal intercarpal liganient. C = capitate. S =

scaphoid. 1 = triquetrum. R = radius. and 1.1 = ulna. (Reprinted. with

pernlission. from: i\ii, K-N.: Berger, R. A.: and Cooney. W. P., III:

Biomeehanies of the Wrist Joint, p. 10. New York. Springer. 1991.)

head of the capitate) as possible. which maximizes their

effect on wrist niotion. Conversely. the digital mo-

tors are located more centrally (that is, closer to the

head of the capitate). which diminishes their effect on

wrist motion.

Kinematics

Over the last seventy years. two theories - the row

theory and the column theory - have been used to

explain the kinematics of the wrist. According to the

row theory. as described earlier. the hones of the wrist

can he thought of as lying in two rows. the proximal row

and the distal row. According to the column theory. as

originally stated by Navarro4, the wrist is composed of

three columns: the radial column (including the scaph-

oid. the trapezium. and the trapezoid), the central col-

umn (including the lunate and the capitate). and the

ulnar column (including the triquetrum and the ha-

mate). Recent studies have shown that the row theory

more clearly accounts for the function of the wrist.

In a normal wrist, the total arc of motion averages

l5() degrees: 70 degrees of extension and 80 degrees of

flexion. Approximately one-half of this total arc of mo-

tion occurs at the mid-carpal joint and the other half

occurs at the radiocarpal joint. From neutral to full cx-

tension. approximately 66 per cent of the motion occurs

at the radiocarpal joint and 33 per cent occurs at the

mid-carpal joint. From neutral to full tiexion. 60 per cent

01 the motion occurs at the mid-carpal joint and 40 per

cent occurs at the radiocarpal joint�. The total amount

of nadio-ulnan deviation is 50 degrees. of which 20 de-

grees is radial deviation and 30 degrees is ulnar devia-

tion; 60 per cent of this motion occurs at the mid-carpal

joint. and 40 per cent occurs at the radiocarpal joint29.

Not only do the mid-carpal and radiocarpal joints

contribute different amounts of motion to the total arc,

but they also allow movement in different directions

when the wrist is moving between radial and ulnar de-

viation. As the wrist moves from radial to ulnar devia-

tion, the entire proximal row rotates from a position of

flexion to one of extension: as the wrist moves from

ulnar to radial deviation, the entire proximal row rotates

from extension back into flexion (Figs. 5-A and 5-B).

Although the mechanism by which this occurs is not

completely understood, most authors have agreed that

it is a combination of the geometry of the carpal hones,

their ligamentous restraints. and the wrist motors acting

through the distal carpal row that causes this conjoined

synchronous motion of the proximal carpal row. Lin-

scheid and Dobyns’7 suggested that, in radial deviation,

pressure on the distal pole of the scaphoid by the trape-

zium and trapezoid causes the scaphoid to flex. This

flexion force is transmitted through the scapholunate

interosseous ligament to the lunate and through the

tniquetrolunate interosseous ligament to the tniquetrum,

thereby causing the entire proximal row to flex. The

Fu;. 4

Drawing of the palmar capsular ligaiiients. RSC = radio-scaphocapitate ligament. LRL = long radiolunate ligament. SRL =

short radiolunate ligament. UL = ulnolunate ligament. UT = ulno-

triquetral ligament. C = capitate. L = lunate, and S = scaphoid.

(Reprinted. with permission. from: An. K-N.: Berger. R. A.: and

Cooney. W. P.. III: Biomechanics of the Wrist Joint, p. 6. New York.

Springer. 1991.)

Fit;. 5-A FRi. 5-B

CARI’AL INSTABILITY 479

�‘OI.. 77-A. NO. 3. NIARCII 1995

Figs. 5-A and 5-B: Lateral radiographs of the wrist of the author. C = capitate. L = lunate. and R = radius.

Fig. 5-A: Radiograph made with the wrist in radial deviation. Note the flexion of the proximal row (the lunate and scaphoid).

Fig. 5-B: Radiograph made with the wrist in ulnar deviation. Note the extension ofthe proximal row (the lunate and scaphoid) and the dorsal

translation of the distal row (the capitate) (black arrow). The white arrows signify the direction of rotation-extension of the lunate.

reverse occurs in ulnar deviation, with the scaphoid be-

ing extended through tension on the scaphotrapezial

ligament. Alternatively. Weher4 proposed that the heli-

coidal shape of the triquetrohamate articulation causes

the distal �OW to translate dorsally during ulnar devia-

tion. therehy putting pressure on the dorsal aspect of the

proximal �OW and causing it to extend. In radial devia-

tion. the distal row translates palmarly, thereby putting

pressure on the palmar aspect of the proximal row and

causing it to flex.

Whatever the exact mechanism. there normally is a

predictable amount of smooth, synchronous motion be-

tween and within the two carpal rows. There is less than

9 degrees of motion between the capitate. the trapezoid.

and the hamate in all arcs of motion of the wrist. There

is 10 ± 3 degrees of motion between the scaphoid and

the lunate and 14 ± 6 degrees of motion between the

tniquetrum and the lunate as the wrist moves from full

radial deviation to full ulnar deviation. There is 25 ± 15

degrees of motion between the scaphoid and the lunate

and l� ± 2 degrees of motion between the triquetrum

and the lunate as the wrist moves from full flexion to

full extension. These data were derived from cadaveric

studies, and it is possible that the actual values in vivo

are greater (Figs. 6-A and 6-B). Partly on the basis of

these cadavenic studies, we agree with Destot� that the

proximal carpal row functions as an intercalated seg-

mcnt with variable geometry between the distal row and

the radius-triangular fibrocartilage complex’.

Force Transmission

Several recent studies have dealt with the subject of

quantitative assessment of force transmission through

the carpus�’4��. For technical reasons, force transmis-

sion has been and continues to be a difficult area to

study. Nevertheless, with use of load-cells, pressure-

sensitive film. and cadaveric specimens. data have been

generated that describe the magnitude and location of

forces at the radiocarpal joint in normal cadavera and

in simulated abnormal conditions. Palmer and Werner29

showed that. in an intact cadaveric wrist in the neutral

position, 82 per cent of the total load is carried by the

radius and 18 per cent. by the ulna. If the ulnar head is

resected or the triangular fibrocartilage complex is re-

moved, the axial load that is borne by the ulna is re-

duced to 0 or 5 per cent, respectively. These findings

were confirmed by Trumble et aI.#{176}.who found that. in

intact specimens, 83 per cent of the load was borne by

the radius and 17 per cent, by the ulna. Viegas et al.9’.

who studied the contact areas of the radius-triangular

fibrocantilage complex in axial-loaded cadaveric wrists,

found that with a light load of twenty-three pounds

(ten kilograms). only 20 per cent of the available antic-

ular surface of the radius was in contact with the bones

of the proximal now. With a heavier load of forty-six

pounds (twenty-one kilograms) or more. this area in-

creased to a maximum of 40 per cent and did not

increase further even if the load was doubled. They

concluded that there normally is a great deal of incon-

gruity at the radiocarpal joint. They also found that 60

per cent of the radial load normally is borne by the

scaphoid facet and 40 per cent, by the lunate facet’�.

Honii et al.’ and Viegas et al.5 calculated the load

distribution at the mid-carpal joint. Honii et al. reported

that 31 per cent of the total axial load was transmit-

ted through the scaphoid-trapezium-trapezoid joint; 19

per cent, through the scapholunate joint; 29 per cent.

through the capitolunate joint: and 21 per cent. through

the tniquetrohamate joint. Viegas Ct al. reported similar

data. The areas that transmitted the higher loads come-

lated well with the reported distribution of osteoarthro-

sis at the radiocarpal and mid-carpal levels”.

Carpal Instability

Carpal instability is defined as carpal malalign-

ment. Therefore, all wrist dislocations. such as a perilu-

Radial deviation #{247}

Fi;. 6-A

4k”) I.. K. RUBY

IHE JOURNAL OF BONE ANt) JOINT SURGERY

nate dislocation, and all wrist subluxations, such as a

scapholunate dissociation. are examples of carpal insta-

hility. Carpal instability is not always synonymous with

increased joint laxity, as a malaligned wrist may he very

stiff. It also is important to realize that not all unstable

wrists are painful. The present discussion will be limited

to the diagnosis and treatment of some of the more

common and suhtle intercarpal instabilities (that is.

subluxations).

Classification

There is no universally accepted classification of

wrist instability. In my opinion. the system that is based

Ofl the row theory of wrist motion is the most logical and

best fits the known clinically important instabilities. Ac-

cording to Linscheid et al.’5, most instabilities can be

thought of as mid-carpal malalignments. These mid-

carpal malalignments can he classified either as dorsal

intercalated-segment instability (commonly known as

DISI) or as volar intercalated-segment instability (com-

monly known as VlSI). In dorsal intercalated-segment

instability. the proximal row (as defined by the long axis

of the lunate) is extended with respect to the radius on

lateral radiographs. In volar intercalated-segment insta-

hility. the proximal row is flexed with respect to the

radius on lateral radiographs. These patterns can be sub-

divided further into non-dissociative and dissociative

carpal instability4”. In non-dissociative canpal instability,

the proximal row is intact: in dissociative carpal instabil-

ity. as occurs in association with a fracture of the scaph-

oid, the proximal row is not intact. Thus, there are four

basic patterns of carpal instability that can he seen on

posteroanterior and lateral radiographs of the wrist: non-

dissociative and dissociative dorsal intercalated-segment

instability. and non-dissociative and dissociative volar

intercalated-segment instability.

This system of classification can he expanded to in-

elude radiocarpal and axial malalignment as well. hut

these patterns are less common and are beyond the

scope of the present discussion. Additional subdivision

based on the time since the injury (that is. as acute or

chronic) is possible. Dynamic instabilities that, by defi-

nition, are produced only by evocative or stress maneu-

vers4’ can he added to expand further the system of

classification. The clinical importance of dynamic in-

stabilities is controversial and will not be considered

here.

Clinical Diagnosis

Symptoms of wrist instability include pain, weak-

ness, giving-way, and a so-called clunk, snap, or click

during use. Physical examination may reveal tenderness

in an area in which synovitis has developed in response

to the overloading of articular surfaces. In the acute

situation. the torn ligaments may be discretely tender:

however. wrist pain often is difficult for the patient and

physician to localize. There are several provocative ma-

Figs. 6-A and 6-B: Diagrams showing the relative motion of se-

lected carpal hones with respect to one another and to the radius. The

numbers indicate degrees of motion.

Fig. 6-A: Relative motion as the wrist moves from radial to ulnar

deviation. Note the minimum amount of motion between the bones

of the proximal row.

neuvers that can be helpful. Watson et al.5 described a

maneuver for the detection of scapholunate dissociation

in which the examiner moves the wrist of the patient

from ulnar to radial deviation while maintaining don-

sally directed pressure over the scaphoid tubercle to

prevent flexion of the scaphoid and to cause the proxi-

mal pole of the scaphoid to subluxate over the dorsal

edge of the radius. A positive result was defined as a

characteristic painful clunk on reduction of the proxi-

mal pole of the scaphoid into its radial facet as the

examiner moves the wrist of the patient back into ulnar

deviation. Reagan et al.7 used a ballottement test for the

detection of tniquetrolunate dissociation; a positive re-

sult was defined as the ability to displace the tniquetrum

in a dorsal-to-volar direction with respect to the lunate.

Non-dissociative volar intercalated-segment instability’�

is considered to be present if a characteristic clunk. sig-

nifying sudden extension or flexion of the proximal row,

occurs as the examiner moves the wrist of the patient

from radial to ulnar deviation and hack while placing

axial compression on the hand.

Plain radiographs can be used to screen for carpal

instability. Routine studies should include a true lateral

radiograph as well as posteroantenior radiographs made

with the wrist in neutral, in radial deviation, and in ulnar

deviation. Radiographs of the contralateral wrist can be

FIG. 6-B

Relative motion as the wrist moves from flexion to extension.

FIG. 7-A F�o. 7-B

CARPAL INSTABILITY 481

VOL. 77.A, NO. 3. MARCH 1995

made for comparison. In scapholunate dissociation (dis-

sociative dorsal intercalated-segment instability), the

lateral radiograph shows an increased scapholunate an-

gle of more than 60 degrees, dorsal angulation of the

lunate and the tniquetrum, and an increased capitolu-

nate angle of more than 15 degrees. The postenoantenior

radiognaphs made with the wrist in neutral and in ulnar

deviation show an increase in the scapholunate interval

of more than four millimeters compared with the non-

mal side; a so-called ring sign; and an increased overlap

of the lunate and the capitate, with the blunt volan pole

of the lunate projecting through the head of the capitate

(Figs. 7-A and 7-B). The ring sign is a radiographic phe-

nomenon in which the distal half of the scaphoid is seen

end-on because of the abnormally vertical position of

the bone. In this condition, there also is decreased carpal

height as determined by the fixed ratio between the

length of the third metacarpal and the length of a line

drawn from the base of the third metacarpal to the distal

pant of the radius on the posteroantenion radiograph

made with the wrist in the neutral position; the normal

ratio2#{176}is 0.54 ± 0.02.

When a patient has tniquetrolunate instability (dis-

sociative volar intercalated-segment instability), the

posteroantenion radiograph shows a flexed scaphoid

(that is, a positive ring sign) and a flexed lunate, with

the sharp dorsal pole of the lunate overlapping the

capitate (Fig. 8-A). In addition, there is a step-off at

the tniquetrolunate joint, with the triquetrum proxi-

mal to the lunate in ulnan deviation and distal to it in

radial deviation. The lateral radiograph shows a de-

creased scapholunate angle of less than 30 degrees and

volar flexion of the lunate and the scaphoid (Fig. 8-B).

In non-dissociative volan intercalated-segment insta-

bility, the postenoantenion radiograph shows flexion of

the entire proximal row (as evidenced by the sharp

dorsal pole of the lunate overlapping the capitate) but

no scapholunate gap on triquetrolunate step-off (Fig.

9-A). The lateral radiograph shows a reduced or non-

mal scapholunate angle, flexion of the lunate, and a

decreased capitolunate angle of less than 15 degrees

(Fig. 9-B).

Anthrognaphy has been the traditional next step af-

ten stress radiography in the diagnosis of carpal insta-

bility because it is technically straightforward and only

minimally invasive and because it can demonstrate de-

Figs. 7-A and 7-B: Radiographs of a wrist in which there is a scapholunate dissociation.

Fig. 7-A: Posteroanterior radiograph showing a scapholunate gap of more than four millimeters, a palmar flexed scaphoid (S) (the ring sign),

and an extended lunate (L) and triquetrum (T). H = hamate and R = radius.

Fig. 7-B: Lateral radiograph showing the palmar flexed scaphoid with dorsal subluxation of the proximal pole of the scaphoid and the

extended lunate and triquetrum.

Ft.. 8-A Fia. 8-B

482 L. K. RUBY

THE JOURNAL OF BONE ANI) JOINT SURGERY

Figs. 8-A and 8-B: Radiographs of a wrist in which there is a triquetrolunate dissociation. (‘= capitate. II = hamate. 1. = lunate. R = radius,

S = scaphoid. and T = triquetrurn.

Fig. 8-A: Posteroanterior radiograph showing a flexed scaphoid (the ring sign) and a flexed lunate. with the sharp dorsal pole of the lunate

overlapping the capitate. There is a step-off at the triquetrolunate joint. with the triquetrum proximal to the lunate.

Fig. 8-B: Lateral radiograph showing a decreased scapholunate angle and volar flexion of the lunate and the scaphoid.

fects of the scapholunate interosseous ligament. the

tniquetrolunate interosseous ligament. and the tniangu-

lam fibrocartilage complex reasonably welP’. Greater

sensitivity (that is. a lower false-negative rate) can be

achieved by injection of the contrast medium into the

mid-carpal joint�’. However, arthrography does not reli-

ably demonstrate the degree or the exact location of

interosseous-ligament damage. subtle ligamentous lax-

ity, the condition of the articulan surfaces, or small de-

grees of synovitis22.

Other non-invasive modalities that I occasionally

find useful include cineradiography. stress radiography.

bone-scanning. and magnetic resonance imaging. Al-

though magnetic resonance imaging is an excellent tech-

nique for the detection of avascular necrosis, it currently

is not cost-effective for the detection of partial tears of

the ligaments of the wrist3.

Because of the limitations of arthrography and

other non-invasive diagnostic modalities, arthroscopy is

becoming more popular for the evaluation of patients

suspected of having carpal instability94. In my experi-

ence, anthroscopy often has led to a definitive diagno-

sis and arthroscopically guided treatment often has

been successful. With arthroscopy, the extent and exact

location of ligamentous injuries; the condition of the

articulan surface: the presence and location of synovitis;

and, in some instances, the degree of carpal displace-

ment can be ascertained. The disadvantages of this tech-

Figs. 9-A and 9-B: Radiographs of a wrist in whtch there is non-dissociative volar intercalated-segment instability. C = capitate. H = hamate.

L = lunate. R = radius. S = scaphoid. and T = triquetrum.

Fig. 9-A: Posteroanterior radiograph showing flexion of the entire proximal row. Note the lack of any triquetrolunate step-off or

scapholunate gap.

Fig. 9-B: Lateral radiograph showing the decreased scapholunate angle. The appearance is the same as that of dissociative volar

intercalated-segment instability because the triquetrum is difficult to visualize.

FI1. 10

CARPAL INSTABILITY 483

VOL. 77.A, NO. 3. MARCH 1995

nique include a steep learning curve, an increased risk

of nerve and tendon damage, and increased expense.

Treatment of Selected Carpal Instabilities

Dissociative Dorsal Intercalated-Segment Instability:

Scapholunate Dissociation

A patient who has an acute complete scapholunate

dissociation often has a history of a donsiflexion injury

after a fall with immediate pain and tenderness at the

scapholunate interval. Plain radiographs show the char-

actenistic changes noted previously: a scapholunate gap

of more than four millimeters, palmam flexion of the

scaphoid with dorsal subluxation of the proximal pole,

and an extended lunate and tniquetrum (Figs. 7-A and

7-B). If there still is uncertainty as to the diagnosis,

arthrography or arthroscopy, on both, can be performed.

For an acute injury (one that occurred less than six

weeks previously) with a partial tear of the scapholu-

nate interosseous ligament, closed reduction and an-

throscopically and radiographically guided pinning can

be performed. Closed reduction is performed with the

patient under axillary block or general anesthesia by

first translating the capitate (and distal row) volanly

with respect to the lunate and stabilizing the capitolu-

nate joint with a smooth 0.062-inch (0.157-centimeter)

Kirschner wire. The scapholunate gap then is closed

by direct volarly directed thumb pressure on the proxi-

mal pole of the scaphoid and stabilized either with

multiple 0.045-inch (0.1 14-centimeter) Kirschner wires

across the scapholunate interval or with one 0.062-inch

(0.157-centimeter) wire placed across the scapholunate

joint and another across the scaphocapitate joint (Fig.

10). The wires are cut off under the skin and left in place

for eight to ten weeks while the hand and wrist are

supported in a below-the-elbow cast that extends from

the metacarpophalangeal joints to distal to the elbow.

After removal of the wires, range-of-motion and wrist-

strengthening exercises are begun, and the wrist is

protected with a removable splint until three to four

months after the operation.

For complete injuries of the scapholunate intenos-

seous ligament or more chronic conditions, open reduc-

tion and formal ligamentous repair, reconstruction, or

even anthrodesis usually is necessary because reduction

and adequate fixation cannot be achieved with closed

means9’5. A dorsal approach is used for visualization of

the tear of the scapholunate interosseous ligament, the

displaced proximal pole of the scaphoid, the extended

lunate, and the dorsally displaced proximal head of the

capitate (Fig. 11. A). Kirschner wires are placed in the

scaphoid and lunate and used as joysticks to aid in me-

duction. The lunate facet of the scaphoid is cleared of

scar tissue, and a trough is created. Drill-holes are

placed in this trough, and heavy non-absorbable sutures

are placed in the ligamentous remnant that is attached

to the lunate (Fig. 1 1 . B and C). The sutures are passed

through the drill-holes in the scaphoid (Fig. 11, D).The

Posteroanterior radiograph made after open reduction and in-

ternal fixation of a scapholunate dissociation (dorsal intercalated-

segment instability). The capitolunate wire was placed first. and then

the scapholunate and scaphocapitate wires were placed.

dissociation is reduced and stabilized with 0.062-inch

(0.157-centimeter) Kirschner wires as described pre-

viously, and the sutures are tied (Fig. 11, E and F). The

adjacent dorsal capsule of the wrist can be imbnicated

to reinforce the primary repair. The postoperative care

is the same as that for the acute injury.

If the dissociation is irreducible, osteoarthrosis al-

ready has occurred, or soft-tissue repair has failed, I

prefer to perform a total mid-carpal or a complete wrist

arthrodesis. This is a controversial area, and many au-

thors have recommended a more limited arthrodesis,

such as a scaphoid-trapezium-trapezoid anthrodesis for

chronic instability without osteoarthrosis or a capitate-

hamate-tniquetnum-lunate (four-corner) arthnodesis and

scaphoid excision if osteoarthrosis is present43. Scapholu-

nate, capitolunate, and scaphocapitate anthrodeses and

capitate-hamate-tniquetrum-lunate arthrodeses without

excision of the scaphoid also have been used for the

treatment of chronic instability”39. My experience and a

careful review of the literature both have demonstrated

high rates of complications and unpredictable results

after all of these partial arthrodeses.

Dissociative Volar Intercalated-Segment Instability:

Triquetrolunate Dissociation

A patient who has an acute tniquetnolunate dissocia-

tion often has a history of a notational injury of the wrist,

commonly as the result of holding a power drill when the

drill bit has jammed. The patient has pain in the wrist on

A5.

,/I

��1

C

I

1�

.�\. FN

,,,t.T� )

E1.�’F N.

FIG. 11

THE JOURNAL OF BONE ANI) JOINT SURGERY

484 I.. K. RUBY

B

Drawings showing the repair of a scapholunate interosseous ligament with adjunct capsular repair. A, The tear in the scapholunate

interosseous ligament (SLIL) is visualized through a dorsal approach (L = lunate. R = radius. and S = scaphoid). B. Horizontal mattress

sutures of 0 non-absorbable material are placed in the ligament. C. A trough is created along the lunate facet of the scaphoid. and drill-holes

are placed from the scaphoid waist to the trough. D. Keith needles are used to pass the sutures through the drill-holes. E and F,The scaphoid.

lunate, and capitate are reduced and pinned. after which the sutures are tied. (Modified, with permission. from: Lavernia. C. J.; Cohen, M. S.;

and liileisnik.J.:Treatment ofscapholunate dissociation by ligamentous repair and capsulodesis.J. Hand Surg.. 17A: 355. 1992.)

FIG. 12-A FIG. 12-B

Figs. 12-A and 12-B: Radiographs of a malunited fracture of the distal part of the radius with secondary non-dissociative dorsal

intercalated-segment instability.

Fig. I 2-A: Posteroanterior radiograph. Note the dorsiflexed position of the entire proximal row.

Fig. 12-B: Lateral radiograph.

CARPAL INSTABILITY 485

\‘OI.. 77-A. NO. 3. MARCh 1995

the ulnar side. especially at the tniquetrolunate joint.

The examiner must he careful to distinguish this

injury from injuries of the triangular fibrocartilage com-

plex. which usually cause tenderness in the interval be-

tween the extensor carpi ulnanis and the flexor carpi

ulnanis just distal to the ulnar head. The result of a

hallottement test may be positive. as described pre-

viously. The diagnosis is confirmed by the presence of a

step-off at the tniquetrolunate interval on the postero-

anterior radiograph. Arthroscopic confirmation of the

tear may he necessary. If there is no volar instability

(indicating only a partial tear), percutaneous pinning

guided by arthroscopy or radiography, or both, is recom-

mended. If volar instability has developed or the de-

formity is chronic hut still reducible, open repair of the

triquetrolunate ligament combined with dorsal capsulo-

desis can he performed in a manner similar to that de-

scnihed for dorsal instability. It is important to realize

that. in this instance, the goal of capsulodesis is to pre-

vent excessive flexion of the proximal row, particularly

by imbnication of the dorsal radiotniquetral ligament. It

also may he helpful to imbricate the space of Poinier on

the palmar side to reinforce the dorsal repair’4. I reduce

and pin the capitolunate joint before tying the capsular

sutures: the use of suture anchors can facilitate this me-

pair. I prefer to make the dorsal exposure first, place the

sutures, and reduce and pin the wrist. I then perform the

anterior approach and close the space of Poirier.

If soft-tissue repair has failed or osteoanthrosis

is present. mid-carpal anthrodesis is the treatment of

choice. Although tniquetrolunate arthrodesis seems log-

ical. high rates of failure and of complications have been

reported’4. and I no longer recommend this procedure.

It also has been noted4 that symptomatic tniquetrolu-

nate instability often is accompanied by ulnar-head

abutment. Therefore. ulnar recession osteotomy often

is indicated. If there is no volar intercalated-segment

instability. I prefer to treat chronic. complete. symptom-

atic, irreducible tniquetrolunate teams with ulnar meces-

sion osteotomy alone, especially if there is positive or

neutral ulnar variance.

Non-Dissociative Volar Intercalated-Segment Instability

This condition is almost always a chronic problem

that begins insidiously; usually. it is associated with gen-

emalized ligamentous laxity. It is diagnosed on the basis

of a characteristic clunk on axial compression of the

wrist in radial and ulnam deviation and on the basis of

the signs on plain radiogmaphs described previously.

Anthrogmaphy and arthnoscopy typically reveal normal

findings. As osteoarthrosis has not been shown to de-

velop as a result of this instability, and because the con-

dition may represent a systemic problem, non-operative

treatment consisting of forearm-strengthening exercises

and intermittent splinting should be tried first’�. If this

treatment fails, anterior and posterior capsular imbnica-

tion and temporary mid-carpal pinning can be per-

formed in a manner similar to the technique used for

tniquetrolunate dissociation. If this procedure fails to

relieve symptoms. mid-carpal anthrodesis is an option.

Secondary Non-Dissociative Dorsal

Intercalated-Segment Instability

This pattern of instability has been recognized with

increasing frequency since it was first described by

Taleisnik and Watson� in 1984. It is not a primary disor-

den of the wrist; rather, it is an adaptive posture of

proximal-now extension secondary to dorsal angulation

of a malunited fracture of the distal pant of the radius

(Figs. 12-A and 12-B). If the instability is symptomatic,

dorsal opening-wedge connective osteotomy of the ma-

dius should be curative.

Summary

A great deal of progress has been made in recent

years with respect to understanding the normal and

486 L. K. RUBY

THE JOURNAL. OF BONE AND JOINT SURGERY

pathological anatomy of the wrist. Nonetheless. our with a critical review of the standard radiographs. sup-

knowledge is incomplete. so theme still is room for di- plemented by additional studies as indicated, allow the

vemsity of opinion regarding the diagnosis and treatment astute clinician to identify specific patterns of instability

of most of the presently recognized wrist instabilities. and to formulate an effective treatment program for the

A careful history and physical examination combined patient.

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