Title: Type II Lunate

Imaging findings:
Figure Normally the lunate articulates with the capitate distally (arrows). This is referred as to as a Type I lunate.

Figure Type II lunate (1) shows a dual facet lunate articulating with the capitate and hamate(arrows).

Clinical:
Can present with ulnar sided wrist pain and nonspecific symptoms of osteoarthrosis. This variant is found in approximately 50% of the population.

Etiology:
Unknown etiology felt likely to represent a variation in carpal ossification (2). Average accessory facet size is 4.6mm. Propensity toward the development of associated arthritis appears to be related to the amount of apposition with the hamate (3).

References:
1. Viegas SF, Wagner K, Patterson RM, Peterson P. The medial (hamate) facet of the lunate. J Hand Surg 1990; 15A:564-571.
2. Burgess RC. Anatomic variations of the midcarpal joint. J Hand Surg 1990; 15A:129-131.
3. Malik AM, Schweitzer ME, Culp RW, Osterman LA, Manton G. MR imaging of the type II lunate bone: frequency, extent, and associated findings. American Journal of Roentgenology 1999; 173:335-338.