This document summarizes recent advances in understanding the structure and function of the wrist. It describes the anatomy of carpal bones and ligaments. The proximal row includes the scaphoid, lunate, and triquetrum bones connected by strong interosseous ligaments. The distal row includes the trapezium, trapezoid, capitate, and hamate bones. Motion occurs at both the mid-carpal joint between rows and the radiocarpal joint. The row theory, not column theory, best explains wrist kinematics. Ligament strength testing showed interosseous ligaments are stronger than capsular ligaments.

1. 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

2. 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.)

3. 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: iii, 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.)

4. 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-

5. 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

6. FIG. 6-B
Relative motion as the wrist moves from flexion to extension.
FIG. 7-A Fo. 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.

7. 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.

8. 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

9. A 5.
,/
I
1
C
I
1
.. F
N
,,,t.T )
E
1.’
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.)

10. 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

11. 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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Vol.. 77-A. NO. 3. MARCEl 995