ABSTRACT
Scapholunate advanced collapse (SLAC) is a progressive
pattern of arthritis that develops in the setting of a chronic
scapholunate ligament tear. This ligamentous injury leads to
abnormal carpal alignment, altered force transmission, and
increased focal joint contact (1-3). Scapholunate instability is
characterized radiographically by scapholunate joint widening,
extension of the lunate, palmarflexion of the scaphoid, and
capitate proximal and dorsal translation (4-6). In the normal
wrist, pressure or load across the carpus is unevenly distributed
and dependent on both the position of the wrist and on the
direction of motion (7). One study demonstrated that with
progressive scapholunate instability, contact area and pressure
is concentrated at the radioscaphoid rather than the radiolunate
joint (1,2). However, others found that with scapholunate
ligament sectioning, the radiocarpal pressure shifts from the
radioscaphoid to the radiolunate fossa (8). Additionally,
scaphoid palmarflexion causes a decreased radioscaphoid
contact area and changes contact to the dorsal lip of the
radius (9). The greatest carpal shear forces lie between the
distal radius and scaphoid and between the proximal capitate
and the distal lunate. The above changes in carpal bone rotation
and translation, force concentration, and contact area explain
the radioscaphoid and lunocapitate arthritis (5,10,11).
