Review Question - QID 217829

This patient has evidence of an acute scapholunate dissociation. The dorsal component of the scapholunate interosseous ligament provides the greatest constraint to translation between the scaphoid and lunate bones.

Scapholunate instability frequently develops as a consequence of blunt trauma to the wrist and is associated with significant clinical morbidity. The stability of the scapholunate joint relies on the integrity of the scapholunate interosseous ligament (SLIL). The SLIL has three components, dorsal, proximal, and volar. It is C-shaped, and the dorsal component is the thickest/strongest. The dorsal component attaches the proximal pole of the scaphoid to the dorsal aspect of the lunate. The proximal component has variable thickness and is composed largely of fibrocartilage. The volar component averages only 1 mm in thickness (vs. the dorsal component which is 3mm). Disruption of the SLIL leads to scapholunate dissociation, which causes the scaphoid to flex volarly and the lunate to extend [described as dorsal intercalated segment instability (DISI)]. If left untreated, a DISI deformity can progress into a SLAC wrist.

Short et al. in part II of their investigation of the ligaments stabilizing the scaphoid and lunate, evaluated the effects of sectioning the scapholunate interosseous ligament (SLIL), radioscaphocapitate ligament (RSC), and scaphotrapezial ligament (STL) in 3 sequences. They reported that sectioning only the ST or the RSC resulted in minimal angular changes to the motion of the scaphoid and lunate, and that sectioning of the SLIL significantly altered scaphoid and lunate kinematics comparatively.

Short et al. in part III of their investigation examined the effects of sectioning the SLIL, RSC, and STL ligaments in a different order than performed previously. They reported that dividing the dorsal intercarpal ligament or STL did not alter the motion of the scaphoid or lunate. Dividing the dorsal radiocarpal (DRC) ligament alone caused a slight statistical increase in lunate radial deviation. They concluded that the SLIL is the primary stabilizer and that the other ligaments are secondary stabilizers of the scapholunate articulation.

Rajan and Day provide a review of the SLIL anatomy and biomechanics. They report on scapholunate anatomy and morphology, and the role of the scapholunate articulations in the kinetics and pathomechanics of wrist instability. They further review the current literature on the biomechanical properties of the scapholunate ligament and its subcomponents. They conclude that a sound understanding of the anatomy and biomechanics of the scapholunate ligament can clarify its instability and may better orient current reconstructive procedures or pioneer better future techniques.

Incorrect Answers:
Answer 1: The RSC ligament runs from the radial styloid to the scaphoid fossa. Sectioning the RSC and ST ligaments with an intact SLIL does not significantly alter scaphoid or lunate kinematics with respect to motion in the flexion-extension and radial-ulnar planes.
Answer 3: The DRC ligament originates from the dorsal distal radius and inserts onto the dorsum of the lunate, triquetrum, and lunotriquetral interosseous ligament, and is not as important as the dorsal SLIL for SL stability.
Answer 4: The dorsal intercarpal ligament (DIC) attaches to the dorsum of the triquetrum and extends radially, past the lunate, to insert into the dorsal distal pole of the scaphoid. Again, the DIC is not as important as the dorsal SLIL for SL stability.
Answer 5: The volar SLIL is much thinner and less robust in comparison to the dorsal SLIL and does not portend as much stability comparatively.