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Purpose: This study continued our previous investigations of the ligaments stabilizing the scaphoid and lunate in which we examined the scapholunate interosseous ligament, the radioscaphocapitate, and the scaphotrapezial ligament. In this current study, we examined the effects of sectioning the dorsal radiocarpal ligament, dorsal intercarpal ligament, scapholunate interosseous ligament, radioscaphocapitate, and scaphotrapezial ligaments. In the current study, the scapholunate interosseous ligament, radioscaphocapitate, and scaphotrapezial ligaments were sectioned in a different order than performed previously.Methods: Three sets of 8 cadaver wrists were tested in a wrist joint motion simulator. In each set of wrists, only 3 of the 5 ligaments were cut in specific sequences. Each wrist was moved in continuous cycles of flexion-extension and radial-ulnar deviation. Kinematic data for the scaphoid and lunate were recorded for each wrist in the intact state, after the 3 ligaments were sectioned in various sequences and after the wrist was moved through 1,000 cycles of motion.Results: Dividing the dorsal intercarpal or scaphotrapezial ligaments did not alter the motion of the scaphoid or lunate. Dividing the dorsal radiocarpal ligament alone caused a slight statistical increase in lunate radial deviation. Dividing the scapholunate interosseous ligament after first dividing the dorsal intercarpal, dorsal radiocarpal, or scaphotrapezial ligaments caused large increases in scaphoid flexion and lunate extension. Conclusions:Based on these findings, we concluded that the scapholunate interosseous ligament is the primary stabilizer and that the other ligaments are secondary stabilizers of the scapholunate articulation. Dividing the dorsal radiocarpal, dorsal intercarpal, or scaphotrapezial ligaments after cutting the scapholunate interosseous ligament produces further changes in scapholunate instability or results in changes in the kinematics for a larger portion of the wrist motion cycle. KeywordsScapholunate instability; wrist; biomechanics Treatment of soft tissue injuries of the wrist is clinically frustrating. The diagnosis of which specific ligaments are injured is difficult. The most common instability problem occurs at the scapholunate (SL) joint. Many surgical procedures have been advocated, but the long-term outcomes of these procedures are undetermined. One of the primary difficulties in understanding this problem is that the specific function of the carpal ligaments is not known. It is important to define the function and relative importance of these structures to develop better surgical treatments for the injured SL joint. This biomechanical study is one of a series of experiments that evaluates the importance of ligaments that attach to the scaphoid or lunate. 1,2 According to previous anatomical studies 3-9 there are 7 ligaments that crossover or attach to the scaphoid or lunate. These are the scapholunate interosseous ligament (SLIL), the radioscaphocapitate ligament (RSC), the long radiolunate liga...