chapter  31
10 Pages

Minimally Invasive Treatment of Arthritis Associated with Scapholunate and Scaphoid Nonunion Advanced Collapse

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).