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SLAC & SNAC WRIST
1. P R E S E N T E D B Y :
D R . N . B E N T H U N G O T U N G O E
P . G , M S ( O R T H O P E D I C S )
C E N T R A L I N S T I T U T E O F O R T H O P E D I C S
V M M C & S A F D A R J U N G H O S P I T A L
N E W D E L H I
SNAC & SLAC WRIST
2. INTRODUCTION
Scapholunate advanced collapse (SLAC) and
scaphoid nonunion advanced collapse (SNAC) are
the two most common patterns of post-traumatic
wrist arthritis.
4. SCAPHO LUNATE LIGAMENTOUS COMPLEX
The scapholunate ligament complex is a U-
shaped ligamentous complex joining thelunate and
the scaphoid.
It is divided into dorsal, volar and intermediate
components with surrounding secondary stabilisers.
5. Dorsal component
blends with joint capsule, scaphotriquetral and intercarpal
ligaments
strongest portion of the complex
controls flexion/extension
Volar component
oblique collagen fibres
blends with extrinsic volar radioscapholunate ligament
controls rotational motion
major proprioceptive role
6. Intermediate/interosseous component
located proximally and centrally and therefore may be
referred to as the central or proximal component
fibrocartilage
weakest portion of the complex
extends a few millimeters into the joint, akin to a
meniscus
Secondary stabilisers
scapho-trapezial-trapezoidal ligament
radio-scapho-capitiate ligament
7. RADIOGRAPHIC FEATURES
The pattern is that of a progressive osteoarthritis
affecting initially the articulation between the radial
styloid and the scaphoid. In later stages of the disease,
osteoarthritis affects the whole radioscaphoid
articulation, then the articulation
between lunate and capitate. Finally it may involve other
intercarpal joints. In addition there is widening of the
space between scaphoid and lunate as well as proximal
migration of the scaphoid and the capitate
CT FINDINGS: angulations of the scaphoid and lunate
bones (increased scapholunate angle and dorsal or volar
intercalated segment instability deformity),
radioscaphoid incongruity, cartilage loss, and
subchondral bone degenerative changes.
10. Watson staging (often used by hand surgeons)
I: osteoarthritis of the articulation between the radial styloid
and the scaphoid
II: osteoarthritis involving the whole radioscaphoid
articulation
III: osteoarthritis of the radioscaphoid and capitolunate
articulations
IV: osteoarthritis of the radiocarpal and intercarpal
articulations +/- distal radioulnar joint (DRUJ)
NOTE: Note that the radiolunate joint is almost preserved
until very last stages of the disease. It is also worth noting that
the scaphoid fossa in the radius may be deep / preserved in
cases of CPPD in contrast to post-traumatic SLAC wris
12. SNAC(scaphoid non union advcance collapse)
In a SNAC wrist, the proximal scaphoid fragment
usually remains attached to the lunate (which rotate
together during extension), while the distal scaphoid
fragment rotates into flexion. This results in
abnormal contact in the radioscaphoid
compartment, characterised by early styloid
osteoarthritis between the distal scaphoid fragment
and the radial styloid process
13.
14. Jupiter et al classification of non union
based on the extent of arthosis:
1. nonunions without arthrosis,
2. nonunions with radiocarpal arthrosis,
3. nonunions with advanced radiocarpal and
intercarpal arthrosis
15. Radiographic findings of SNAC
radioscaphoid narrowing,
capitolunate narrowing,
cyst formation,
pronounced dorsal intercalated segment
instability(DISI)
Note: The radiolunate joint usually is spared in early
stages but may show degenerative changes as the
arthritis becomes more diffuse.
16.
17. Effect of SLAC & SNAC ON JOINT
KINEMATICS:
Both of these processes lead to abnormal joint
kinematics, since the lunate is unrestrained by the
distal scaphoid and, therefore, assumes an extended
posture.
Over time, this may result in a dorsal intercalated
segment instability (DISI) deformity, which
invariably progresses to degenerative arthritis at the
radioscaphoid articulation, followed by carpal
collapse and midcarpal arthritis
19. Radiographic features
On an AP view the normal trapezoidal configuration
of the scaphoid may be lost and it may appear
triangular.
On lateral plain film typically shows a dorsal tilt of
the lunate:
scapholunate angle > 60º: sign of scapholunate
ligament dissociation
capitolunate angle > 30º: the capitate is displaced
posteriorly compared to the distal radius